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101 Ways to Grow Arabidopsis - Details

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 101 Ways to Grow Arabidopsis - Details

 
Note: Click the "Photos" link next to each entry to see photographs of the experimental results.  

Should a greenhouse, light shelf or growth chamber be used?[Photos]

Short Answer

Growth chamber if temperature is limiting factor

Results

We conducted experiments in both spring season greenhouse lighting (May-June), considered ideal by Arabidopsis researchers at our facility, and winter greenhouse lighting (Nov-Jan), and compared to plants grown in growth chambers with the same environmental setpoints. In the winter study, we also compared with plants grown on light shelves. Light shelves are defined here as shelves in an environmentally-controlled room with fluorescent light suspended above the plants. Results of this study indicate that, given that temperature is not limiting, greenhouse tables and light shelves grew plants of equal or greater quality 'Columbia' plants than growth chambers. This is in agreement with Ernst et al (5), though they were using 'Landsberg' Arabidopsis. Early in the production cycle of our winter study, plants grown on light shelves were equal in quality to other plants. This is significant to note because the cost of this equipment, installation and its maintenance of these units was a tiny fraction of the other two environments. At flowering, light shelf plants were a few days behind the other two environments, shorter, but of excellent quality. In spring season, plants grown under natural days in greenhouse (no supplementation with metal halide lamps) were indistinguishable from plants grown in a growth chamber under 16 hour photoperiod. In the winter study, plants grown under natural days did not flower but produced excellent vegetative growth. Plants grown with 16-hour photoperiods were again indistinguishable from plants grown in a growth chamber under same photoperiod.

Discussion

Commercially manufactured growth chambers are the "easiest" answer to this question, as success is more likely across many mutant lines and the conditions controlled uniformly all year long. Our pest scouting records indicate growth chambers also tend to have fewer insect pests than other environments (data not shown). Given the expense of these machines, however, other environments definitely have value in Arabdiopsis production. Arabidopsis 'Columbia' will grow in any of these growth environments as long as temperature is can be kept lower than 26C and the plants receive at least 80 µmol/m2/s illumination from sunlight, metal halide lamps, high pressure sodium lamps, fluorescent lamps, a combination of any of the above, or a combination of fluorescent and incandescent lamps. Limiting factors of using light shelves could more accurately be described as the limiting factors of the room they are placed in. Obviously, the room needs access to water and drains, have electrical circuits enough to power the number of fixtures used, and should be suitably ventilated for restricted-use pesticide application if that is part of pest management program. Other technical concerns are the heat produced by the fixtures and humidity control of the room. Fluorescent fixtures that utilize thin T8-style lamps and electronic ballasts produce less heat. We strongly recommend researchers work with their physical facilities personnel to confirm utilities, and help find cooling solutions such as Koldwave units that utilize water to transfer heat out of the room rather than using refrigerant. Refrigerant “air-conditioners” such as used for offices dry the air, often to the detriment of plant growth. It is interesting that some researchers viewing results of our formal study were surprised that Arabidopsis can be grown in a greenhouse; no doubt part of the "lablore" surrounding this plant. From our experience and as reported by others (2), the only limiting factor for Arabidopsis production in greenhouses is excessive heat during summer months, and daylength in winter months. Greenhouses in many regions of the United States cannot be cooled to 25C in the hottest part of the summer due to the limitations of evaporative cooling in humid environments, and few institutions can afford to air-condition their greenhouses. Above 25C, we've seen some mutant lines die and wild-type plants exhibit wispy, stress-induced flowering that often does not produce large amounts of seed. Other researchers have reported the maximum temperature for Arabidopsis as 28C (10), 30C for older plants (1), and even 34C (2) given adequate moisture. Purdue produces over 6,000 square feet Arabidopsis year-round in greenhouses, using evaporative cooling in summer and photoperiod extension to 16 hours using metal halide lamp supplementation in winter. Greenhouse light intensity can be as high as 1500 µmol/m2/s during summer months. This does not kill plants absent of temperatures exceeding 25C, but could possibly contribute to the stress-related early flowering response.

What pot size worked the best in this study? [Photos]

Short Answer

3" square (7cm wide x 7cm deep x 7cm high)

Results

Our images show clearly that plants in the 72-cell trays and 201 "half flats" have more chlorosis and often die when irrigation trays are kept full of fertilizer solution compared to plants in 3" square pots or 4" square pots. Likewise, more purpling and stress-related flowering resulted in the trays kept full of clear water. Plants died in the middle of the 72-cell tray kept full of fertilizer solution, while surviving near the tray edges; a pattern we have observed in our facility before.

Discussion

With proper care, just about any size container can be used for Arabidopsis. 3" square pots seem an appropriate compromise for ease-of-growing and scalability, with 3-6 plants per pot recommended for growth to maturity. Though not tested in our study, 3601 cellpacks (36 individual cells per tray) are a cheaper alternative to a 3" square pot, and have similar volume and shape. They are not as stable as a pot if separated from the other cells, however. A general rule of thumb: The smaller the container, the better grower you need to be. That is because the smaller the container, the less "forgiving" a root environment is. The same soilless mix, watering and fertilizing can result in drastically different plant growth depending on just the pot size and shape. Small container volumes are more likely to dry out and are less buffered against change in nutrient status or pH. Shallow containers—such as when soilless mix is placed in a planting tray or "flat" without pots or cell packs—have a high perched water table (zone of saturation) relative to same soil mix in a tall container. A high perched water table causes root environment to become anaerobic. Root diseases are more likely under these conditions. Also, certain nutrients such as iron become unavailable, resulting in yellowing of young leaves and flower stems.

What soil mix worked the best in this study? [Photos]

Short Answer

Pro-Mix PGX and MetroMix Redi-earth

Results

After planting our study, it was determined by soil analysis that the Sunshine LA4 soilless mix we used was too low in iron for healthy growth of Arabidopsis, though the brand had been used successfully in the past. Also in our study, MetroMix 360 was hydrophobic; the peat component having dried too much due to being stored too long. So this was not a fair comparison of this brand.

Discussion

It should be noted that there are many suitable commercial soilless mixes that are being used with great success with Arabidopsis. Thus other factors-particularly temperature, watering and fertilizing are a most likely a better determinant of success. It should also be noted that there have been many unsubstantiated reports by greenhouse curators and managers of "bad lots" or "bad bags" of soilless mixes, across all manufacturers. Some universities mix two soilless mixes together to lessen the possibility of a problem with the mix. We examined augmenting the soilless mix with calcined clay granules for this and other reasons.

Can a soilless mix be augmented to improve growth?[Photos]

Short Answer

Yes

Results

In our study, augmenting a commercial soilless media with calcined clay granules (also called porous ceramic) ranging in diameter from 0.2-0.5 cm improved plants growing in constant sub-irrigation, across all brands of soilless mix. Addition of these granules also improved health of plants growing in a soilless media that was hydrophobic due to being stored too long, and in plants from soilless media that initially tested low in iron. Addition of the granules did not improve growth of plants compared to plants grown in Pro-Mix PGX or MetroMix RediEarth as long as the fertilizer was strong enough and the trays were drained following irrigation.

Discussion

We conclude from these observations that this simple augmentation (25% by volume) of calcined clay granules might make any commercial soilless mix more "foolproof" from manufacturing or storage problems. Augmentation of 50% by volume is recommended if the researcher must leave water in the tray for any period of time, such as over weekends or holidays. It is very important to remember that these percentages and the size of calcined clay granules are based on 3" pots, and experimentation will need to be done for different size containers. For example, the smaller granule product (<0.1 cm diameter) made by the same manufacturer resulted in poor plant growth when used to augment soilless mixes in this experiment, even though similar rates of augmentation with these granules improved growth of corn in large 8" diameter pots or 1-gallon nursery containers at our facility. We did not examine the benefits of using rockwool media that is used to great success by several researchers, including the Grant Cramer lab at University of Nevada which has trialed many systems for Arabidopsis production (6).

What root media worked best to cleanly remove roots?[Photos]

Short Answer

Fine-textured calcined clay granules

Discussion

Some researchers need to analyze roots, or want roots free of debris prior to transferring into hydroponic systems. We did not examine this aspect formally, but pulled up some plants at the termination of the study to see if some root systems came out cleaner of debris than other. Plants growing in fine-textured calcined clay granules (<0.1 cm diameter) were easier to extract roots from cleanly. Note that plants growing in this media required fertilizer at each irrigation, rather than alternating with clear water irrigations. Early in the production cycle, plants in this media were far behind plants in all the soilless mixes. We changed the fertilizer frequency to every irrigation and plants were of similar vigor and size by the end of the study. The larger granules have been used successfully at our facility as well (no data), though the containers needed to be nearly completely submerged when irrigated due to low capillarity. Of course, the cleanest method would be to use hydroponic methods (5,6,12).

Does soil need to be pressed down prior to planting?[Photos]

Short Answer

No

Results

This does not improve germination or growth, and if done when the soilless mix is wet, may ruin the soil structure.

Do seeds need to be misted to germinate?[Photos]

Short Answer

No

Discussion

We did not examine germination rate in our study, but have made visual observations between treatments in other studies (no data). Seeds grown under intermittent mist (10 seconds every 8 minutes) appeared to have better germination than plants not under mist. However, a vast majority of our Arabidopsis is not germinated under mist due to limitations of space in this specially-equipped propagation area. Plastic wrap or clear plastic domes designed to fit over planting trays also appear to improve germination, unless used in bright sunlight when temperatures under the dome can exceed 40C. This can be remedied by covering the dome with muslin or cheesecloth, venting the dome or propping the dome up for air circulation. Some researchers, including the first reports on growing this species (8) suggest using muslin kept moist by fine spraying until cotyledon expansion begins. Mist systems are recommended for lines that seed is extremely limited, therefore a benefit be gained from improved germination percentage. Commercial systems can be plumbed in using copper pipes and electronic controller units operating solenoid valves. We've constructed simple mist systems from nozzles, pvc pipe and hose connectors that can be stored when not in use (see image).

Can I leave plants sitting in a tray of water? [Photos]

Short Answer

No, in most circumstances it causes growth problems

Results

Many researchers leave their plants sitting in trays of water to minimize need for watering, or because they believe the plants require a saturated root medium. In our study using varying sizes of pots left in 1.5-2.5 cm of standing water, plants fared poorly compared to those where the tray was drained following irrigation. Left standing in fertilizer solution, plants were chlorotic and stunted; in clear water, plants were purple and stress-related flowering induced. The taller the soil column, the less symptoms produced. Symptoms were hardly visible in 4-inch pots. Augmenting a commercial soilless media with calcined clay granules (0.2-0.5 cm diameter) improved plants growing in constant sub-irrigation, across all brands of soilless mix.

Discussion

It usually takes less than 5 minutes of sub-irrigation for most containers to absorb their full capacity of water. One report noted that water needs of the plant greatly increase during silique filling (1), but it is still our recommendation that trays should be drained a few minutes following irrigation even if watering frequency is increased during this period. Plants left sitting in trays of water grow poorly, with symptoms varying according to solution used. Keeping plants sitting in trays of water can lead to a suitable environment for pests such as fungus gnat and shore fly. Accumulation of fertilizer salts is also possible.

What if water HAS to be left in trays?[Photos]

Short Answer

Add calcined clay granules to soil mix or use a capillary mat for irrigation. Also consider a larger (taller) pot.

Results

The taller the soil column, the less over-watering symptoms produced. Symptoms were hardly visible in 4-inch pots.

In our study, augmenting a commercial soilless media with calcined clay granules (0.2-0.5 cm diameter) improved plants growing in constant sub-irrigation, across all brands of soilless mix.

Also the use of a capillary mat resulted in healthier growth than plants left in trays of water.

Discussion

It is our recommendation that researchers who cannot manage irrigation needs of plants over weekends or holidays keep water in trays, but augment soil mix 1:1 with calcined clay granules. This may also be useful in 24-hour photoperiods, when plants might suffer water stress due to high evapo-transpiration rate under this constant light. A taller pot—even if it contains the same volume of soil mix as a shorter, flatter pot--holds less water. A classic demonstration of this is to saturate a rectangular kitchen sponge while holding it out flat and allowing any excess water to drip out. When it has all dripped out, tip the sponge upright on its end without squeezing it. More water drips out! It holds less water when upright even though nothing else about the sponge has changed. Some open cell inserts such as “601cell packs” or the much-dreaded “201 half-trays” are similar to these sponges laying flat.

Did use of capillary matting for sub-irrigation improve growth?[Photos]

Short Answer

Only as compared to constant sub-irrigation

Results

Plants were healthier on the capillary mat than those constantly sub-irrigated, but not as healthy as plants irrigated and drained. Algae grew on the mat, and shoreflies and fungus gnats were visible on the mat and surface of the soilless media. No data was taken on infestation levels of these pests, but it appeared to be worse than other treatments.

Discussion

A simple capillary tray was designed to sub-irrigate plants without keeping the plants sitting in water (see image). Plants in the 3" square pot absorbed water upward through capillary action from an absorbent mat, the mat kept wet by a reservoir of clear water or fertilizer solution. Water was added every 3-7 days, depending on need, so was as "self-watering" as the practice of leaving the plants sitting directly in water. Our conclusions are that capillary mat is a viable option only relative to leaving plants sub-irrigated continuously, and if measures are in place to control fungus gnat population. Note that The Nottingham Arabidopsis Stock Centre uses capillary mats for irrigation with success (10).

Was fertilizer required? [Photos]

Short Answer

Yes

Results

Good growth of Arabidopsis resulted when plants were sub-irrigated with general-use fertilizer solution alternated with clear water. Constant use of this fertilizer solution resulted in death of some plants late in the growth cycle, most likely due to accumulation of fertilizer salts in the soilless mix.

Discussion

Fertilizer is required for growing Arabidopsis. Without fertilizer, plants purple and stress-related, non-productive flowering occurs.

What frequency of fertilizing worked best in this study?[Photos]

Short Answer

Every other irrigation

Results

Use of our fertilizer solution at every irrigation resulted in death of some plants late in the growth cycle, most likely due to accumulation of fertilizer salts in the soilless mix.

Discussion

At our facility, we use a solution of 15-5-15 general-use fertilizer at a strength of 200 ppm N to accommodate a large number of species. Use of a weaker fertilizer at each irrigation may well be possible, but was not tested.

What fertilizer strength worked best in this study?[Photos]

Short Answer

200 ppm Nitrogen

Results

Use of the same15-5-15 fertilizer at a strength of 50 ppm (alternated with clear water irrigations) resulted in chlorotic plants.

Discussion

At our facility, we use a solution of 15-5-15 general-use fertilizer at a strength of 200 ppm N to accommodate a large number of species. Use of a weaker fertilizer at each irrigation rather than alternating with clear may well be possible, but was not tested.

Did use of slow release fertilizer result in healthy plants?[Photos]

Short Answer

Yes

Results

Use of 14-14-14 slow release fertilizer, incorporated into the root medium prior to planting, resulted in good plant growth. At a rate of 1.4 grams/ 3" square pot (3.6 kg/m3)--2X the recommended rate for low-use plants—the Arabidopsis plants were larger and greener in both early and late stage of vegetative growth. Analysis of soilless mix taken in late stage of vegetative growth indicated that this slow release formulation improved soil pH (6.9) over plants irrigated alternatively with fertilizer solution and clear water (7.6). Clear water at our facility is highly alkaline (250-300 ppm CaCO3) and has pH of 7.5 or above, so this soil pH benefit from slow release fertilizer use may not be realized at facilities with better water quality.

Editor's Update: Though slow release fertilizer was effective in this study, a subsequent study has shown that slow release fertilizer was not effective in a fast-production system using 24-hour light.

Discussion

Effect on flowering and seed production was not studied. However, we observed a 5-7 delay in flowering in one study on plants with slow release incorporated, as compared to plants grown with liquid fertilizer and no slow release fertilizer. This was in a study conducted in the greenhouse during high light season. It begs the question whether some of the wispy, stress-induced flowering of summer greenhouse-grown Arabidopsis can be overcome with differing fertilization product or rate. Further study is needed in this area.

What light intensity worked best in this study?[Photos]

Short Answer

200 µmol/m2/s

Results

In an earlier study using continuous light, we observed damage to plants growing at 300 µmol/m2/s but not 100 µmol/m2/s. We followed this up with a study where we grew plants at 100, 200, 250 and 275 µmol/m2/s using a combination of fluorescent and incandescent lamps in a growth chamber. This time, though, the lights were on a more standard photoperiod of 16 hours. Plants under 200 µmol/m2/s were larger and appeared greener than those at 100 µmol/m2/s. Higher light intensities than 200 resulted in death of some seedlings. It should be noted that in both experiments, no barrier was placed between the lamps and the plants, so the death could have been caused by high temperatures emitted from the lamps.

Discussion

200 µmol/m2/s is a slightly higher intensity than suggested by the Arabidopsis Biological Resource Center at The Ohio State University, which recommends 130-150 µmol/m2/s for 16 hours per day. The Nottingham Arabidopsis Stock Centre which uses 122 µmol/m2/s for 24 hours per day in their greenhouses. We did not investigate intensities between 100-200 µmol/m2/s.

Can high intensity discharge lights be used?[Photos]

Short Answer

Yes

Results

We compared plants grown using a combination fluorescent and incandescent lighting with three other treatments using high-intensity discharge (HID) lamps as sole source of illumination: high pressure sodium at 180 µmol/m2/s; metal halide at 250 µmol/m2/s; and a mix of these two lamp types at both 125 and 200 µmol/m2/s. All produced satisfactory plants. The plants under HIDs appeared to have longer petioles and narrower leaves (data not taken).

Discussion

HID lamps of 400-1000 watts are common in research greenhouses in temperate climates. They are used for lengthening the natural photoperiod or for supplementing sunlight. This study proves that they can be used as sole source of illumination for this species. Warnings that Arabidopsis cannot grow using HIDs may have resulted from damage seen after moving plants from low-light environment of tissue culture rooms without acclimation.

What photoperiod (daylength) worked best in this study?[Photos]

Short Answer

16 hours for flowering

Results

It is well-documented and comes as no surprise that 'Columbia' plants grown under winter photoperiods (<12 hours) did not flower during the duration of this experiment, whereas all plants grown under 16-hour photoperiod flowered. We confirmed that growth was vigorous under both 16-hour and 24-hour photoperiods, and that flowering occurred 8-12 days earlier using 24-hour photoperiods. The 24-hour treatment was promising, but no data was taken comparing seed production.

Discussion

Critical photoperiod to induce flowering has been reported as 8 hours by Corcos (4) and as 12 hours by Tocquin et al (12). Our studies were done with 'Columbia' wild types and will not apply to all A. Thaliana. There may be some occasional research use for large, vegetative plants such as we produced with short photoperiods, but the vast majority of our researchers need seed production. We were intrigued by the use of 24-hour photoperiods used by some researchers at Purdue University and as reported by others (1, 2, 10). We investigated how growth would compare between 16-hour and 24-hour illumination, with an eye toward speeding up production for large-scale, high thru-put mutant screening projects. Conventional wisdom would suggest these the 24-hour illuminated plants may not produce as much seed, having had less time to accumulate carbohydrates by vegetative growth. We found only one report that suggested lower seed yield results from this treatment, and it involved "weak mutants" (7). Also, it was difficult for us to keep the plants irrigated because of the increased water use of continuous-lighted plants, and many plants died of water stress. Researchers who use this technique have to keep their plants sub-irrigated continuously, and one wonders if this may be the origin of the myth of Arabidopsis needing constant sub-irrigation. Nutrition is another concern; often these plants look nutrient-starved, with the light duration being (or mutant genetics) assumed causal. Further study needs to be conducted using 24-hour light with increasing rates of fertilizer to see if these deficiencies can be overcome. Other treatments in our study suggest that 'Columbia' is more responsive to fertilization than often prescribed.

Does growth under 24-hour light hasten production?[Photos]

Short Answer

Yes, except as compared to greenhouse summer production.

Results

In our study, Growth of Arabidopsis seedlings under continuous fluorescent/incandescent lighting, continuous fluorescent/incandescant lighting at 100 µmol/m2/s resulted in a healthy crop with hastened production as compared to results documented in other studies on our website. Note that fertilizer frequency was increased to using fertilizer at each irrigation, and that slow release fertilizer was ineffective. Days until 50% of plants were in flower in our studies:

24 hour light in growth chamber = 19 days

Natural day sunlight in greenhouse, summer = 18 days

Natural day sunlight in greenhouse, spring = 26 days

16 hour light in growth chamber = 26 days

Natural light in greenhouse supplemented to 16 hours, winter = 39 days

Discussion

This study suggests that a growth system can be designed to hasten production of Arabidopsis by 1-3 weeks using 24-hour lighting and increased fertilization. Over the course of a year, this might result in roughly 1 to 1.5 more plant generations produced. However, there are many things that can go wrong, as we will document in detail under other questions on this website. Plants will purple if not fertilized enough, can be damaged if light intensity is above 100 µmol/m2/s, and can quickly become water-stressed due to increased evapo-transpiration. We lost plants on two occasions due to water stress alone. It is our assumption that slow-release fertilizer granules did not result in healthy plants under continuous high lighting (300 µmol/m2/s) because the production period was too fast for the nutrients to be released in sufficient quantities for vigorous growth.

Does 24-hour illumination using fluorescent/incandescent lamps result in high-light damage?[Photos]

Short Answer

No, at 100 µmol/m2/s. Yes, at 300 µmol/m2/s.

Results

Plants under continuous light at 300 µmol/m2/s showed purpling of leaves, leaf margin necrosis, leaf twisting, petiole elongating and more dead plants (data not taken) after 10 days from sowing. However, the plants that survived were further developed; 3 sets of leaves as opposed to the 2 sets of leaves on the plants illuminated by continuous 100 µmol/m2/s, and had increased number of leaf hairs (data not taken). Increased liquid fertilization reduced the purpling somewhat at this 10-day stage. By day 30, all plants under 300 µmol/m2/s had purple leaves with margin necrosis except the plants being sub-irrigated with fertilizer solution. These fertilized plants exhibited yellow leaf tips observed in other 24-hour light experiments late in the production cycle. Even the plants under continuous illumination under 100 µmol/m2/s had some dying seedlings after 10 days. Though data was not taken, we suggest it was less than 5% of the total number of seedlings. Slow-release fertilizer was no more effective at providing nutrients than tap water controls throughout the experiment for the plants under the higher light intensity. For plants under the lower intensity, increasing the rate of slow release fertilizer improved plant vegetative growth, but not as much as constant sub-irrigation of fertilizer solution.

Discussion

We need to confirm that this intensity of illumination from fluorescent/incandescent lighting is damaging at photoperiods more commonly used in plant production, such as 14- or 16-hour. It is interesting that the plants do not exhibit such symptoms at much higher intensities (up to 1500 µmol/m2/s) of sunlight in a greenhouse. The most productive plants were grown under continuous 300 µmol/m2/s and constant sub-irrigation with fertilizer solution. However, we doubt many researchers could afford the risk to plants involved, especially if available seed were limited. We recommend the safer light intensity of 100 µmol/m2/s with constant sub-irrigation using fertilizer solution.

Can plants be transferred from low light environment to high light?[Photos]

Short Answer

Acclimate plants to higher light over 7-10 days

Results

Purpling of leaves is the first symptom of high light damage, usually occuring within 24 hours. We've saw this occur in our winter study. Two-month old plants growing under natural day conditions were exposed to one 24-hour exposure to an additional 200 µmol/m2/s of light provided by a combination of metal halide and high pressure sodium fixtures. However, in our spring study, 14-day old plants moved from a growth chamber of 100 µmol/m2/s to a greenhouse where light intensity was measured in excess of 1000 µmol/m2/s did not show any damage.

Discussion

More study is needed in this area. Either the plants are damaged by a certain light quality or by high light at a certain developmental age or a combination of both. We have grown plants under artificial lighting of all kinds and have not observed a damage we associated with the use of a certain type of high-intensity fixture, except as reported here. However, many of our researchers have reported problems with light higher than 300 µmol/m2/s using fluorescent lamps in growth chambers. Since transferring plants from tissue culture to greenhouses or other higher light environments may be required in Arabidopsis research, it would be prudent to acclimate the plants over 7-10 days by using shading such as muslin or cheesecloth in greenhouses or by slow ramping of light intensity in growth chambers.

Can early, stress-induced flowering and purpling of leaves during long, hot days be avoided?[Photos]

Short Answer

No, but more fertilizer may help.

Results

No single study we performed was thorough enough to determine the interaction of variables that take place in a summer greenhouse on growth and flowering: high temperature, long photoperiod and high light intensity. Taken together, though, our opinion is that early-flowering is a long-day response while purpling of leaves is a nutrient deficiency or a high light intensity stress. We had some success in improving appearance of plants grown under 24-hour artificial illumination by increasing fertilization. Excellent quality plants with less "wispy"--and presumably more productive flower stems--were grown inside an air-conditioned bench (see details elsewhere on this webpage), which lowered both air temperature and light intensity of the environment. But flowering was still early on this A/C bench.

Discussion

We often speak of this species as a “weed” not requiring careful consideration of horticultural inputs. However, we must remember that the wide distribution of Arabidopsis thaliana suggests great adaptability of the species in response to its environment. Seasonal fertilizer recommendations for Arabidopsis may be warranted, just as they are for commercial floriculture crops grown in greenhouses.

Can a table in a greenhouse be modified with air-conditioners?[Photos]

Short Answer

Yes

Results

We built an air-conditioned light shelf for $540 and an air-conditioned table for $470. (For details, see Materials and Methods for Modifying a greenhouse table and greenhouse light-shelf with portable air-conditioners for improved cooling). This cost estimate does not include components we had on hand such as greenhouse table, extension cords, timers and thermometers. Both the shelf and table were located in the same greenhouse, close to the exhaust fans to purge the additional heat created by the a/c units before they added heat load to the greenhouse room. The other advantage of building these in the greenhouse was the presence of drains and the ability to safely apply pesticides. Both grew healthy Arabidopsis crops with no signs of stress through July when greenhouse temperatures reached a maximum of 85F (29.4C) or higher on nine days of the experiment. Temperature on the air-conditioned table was usually less than 70F (21.1C) , and the less than 75F (23.9C) on the shelf.

Discussion

Though the air-conditioned table was cooler, we believe the shelf could have been just as effective with air distribution fans to better mix the air. The lower shelves closest to the a/c units were several degrees cooler. Toward the end of the experiment, on July 19, we added a small fan for vertical distribution. However, this required space on each shelf for air to flow so the potential loss of three trays’ worth of space. The advantages of the a/c table were that it received more light, light was more uniform, and was easier to construct. It’s larger capacity a/c units provided much more flexibility, as well. Those units were turned down from their maximum setting because the day temperature was 60F (15.6C). The advantages of the a/c shelf were that it took up much less floor space and required smaller, less expensive a/c units. Prior testing in summer 2005 (data not shown) had taught us that a critical part of the construction was the insulation of the table top with foam--board insulation and the north side of the shelf with refective insulation “bubble wrap.” Two a/c units were installed in each area for redundancy. They were also plugged in to separate electical circuits to reduce chance of both of them going out at once. Having two a/c units in each area constructed, with each a/c unit on a separate electrical circuit was a critical failsafe; if the a/c unit fails in a system like this, the resulting temperature under the plastic would soar much higher than the greenhouse temperatures. Also critical was the placement of the a/c units near greenhouse exhaust fans so that their heat load would not be added to the room.

Can a shelf unit in a greenhouse be modified with air-conditioners?[Photos]

Short Answer

Yes

Results

We built an air-conditioned light shelf for $540 and an air-conditioned table for $470. (For details, see Materials and Methods for Modifying a greenhouse table and greenhouse light-shelf with portable air-conditioners for improved cooling). This cost estimate does not include components we had on hand such as greenhouse table, extension cords, timers and thermometers. Both the shelf and table were located in the same greenhouse, close to the exhaust fans to purge the additional heat created by the a/c units before they added heat load to the greenhouse room. The other advantage of building these in the greenhouse was the presence of drains and the ability to safely apply pesticides. Both grew healthy Arabidopsis crops with no signs of stress through July when greenhouse temperatures reached a maximum of 85F (29.4C) or higher on nine days of the experiment. Temperature on the air-conditioned table was usually less than 70F (21.1C) , and the less than 75F (23.9C) on the shelf.

Discussion

Though the air-conditioned table was cooler, we believe the shelf could have been just as effective with air distribution fans to better mix the air. The lower shelves closest to the a/c units were several degrees cooler. Toward the end of the experiment, on July 19, we added a small fan for vertical distribution. However, this required space on each shelf for air to flow so the potential loss of four trays’ worth of space. The advantages of the a/c table were that it received more light, light was more uniform, and was easier to construct. It’s larger capacity a/c units provided much more flexibility, as well. Those units were turned down from their maximum setting because the day temperature was 60F (15.6C). The advantages of the a/c shelf were that it took up much less floor space and required smaller, less expensive a/c units. Prior testing in summer 2005 (data not shown) had taught us that a critical part of the construction was the insulation of the table top with foam--board insulation and the north side of the shelf with refective insulation “bubble wrap.” Two a/c units were installed in each area for redundancy. They were also plugged in to separate electical circuits to reduce chance of both of them going out at once. Having two a/c units in each area constructed, with each a/c unit on a separate electrical circuit was a critical failsafe; if the a/c unit fails in a system like this, the resulting temperature under the plastic would soar much higher than the greenhouse temperatures. Also critical was the placement of the a/c units near greenhouse exhaust fans so that their heat load would not be added to the room.

Did any treatments reduce fungus gnat infestation?[Photos]

Short Answer

Beneficial nematodes, Steinernama feltiae

Results

Our first study involving top dressings, beneficial nematodes and different soil mixes showed a statistically significant reduction in fungus gnat larvae captured on soil surface of plants treated with one of the beneficial nematodes treatments. Silica sand at the highest rate significantly increased fungus gnat infestation. A visible layer of green algae formed on the silica sand surface at this rate, which may have explained the attraction. We repeated the nematode treatments in a larger study. 50 untreated pots and 50 treated pots were compared. Fungus gnat larvae per pot of control pots on days 0, 7 and 14 following application were 5.32, 1.54 and 1.48, respectively. Treated pots were 5.92, 1.18 and 0.22. Day 14 results were significantly different at p=.005.

Discussion

Fungus gnats (families Mycetophilidae and Sciaridae), are a common greenhouse pest, prevalent in soilless mix kept too moist. Proper identification is the first step to control. They are easily mistaken for shore flies (family Ephydridae) which, though a nuisance, do not typically damage plants. Both larvae and adult forms of these two species can be distinguished upon close inspection. For your convenience, we've included images of both insects' larval forms in our pictures. Damage from fungus gnat larval feeding on Arabidopsis usually is characterized by skeletonized leaves that are in contact with soil surface. One sound management practice for fungus gnats is to let the soil surface dry completely in between irrigations. This is effective because, as the name implies, fungus gnats feed on the microscopic algae that thrive on soil surfaces where water, sunlight, and nutrients are available. Removing water from the equation keeps the algae from thriving. We've observed reductions in infestations when constant sub-irrigation was ceased, though no controlled studies were performed. Our study also examined the application of top dressings in controlling fungus gnat infestation. The theory is that these thin layers of dressings on the soil surface mechanically damage the fungus gnats as they burrow into the soilless mix to lay eggs. None of the top dressings we used reduced fungus gnat infestation with statistical significance, though we are currently repeating the study with more replicates. Our study of treatments to reduce fungus gnat infestation has shown that beneficial nematodes were very effective. The nematodes were applied to soil of infested pots as a drench and have no REI or mammalian toxicity. Of particular fascination is that the time lapse movie of Arabidopsis plant growth on the TAIR website (11) shows, not only algae forming on the surface of the soilless mix, but what appears to be fungus gnat larvae zipping across the moist surface as well! Note: The original video was provided to TAIR by Dr. Nick Kaplinsky (Swarthmore College, PA).

How much imidacloprid (Marathon 1G) need be applied?[Photos]

Short Answer

If needed, 0.25 teaspoon/3" pot (4.2 kg/m3), the lowest recommended rate

Results

We tested the dose response to this chemical on Arabidopsis, and also the effect of poor mixing, which would result in some pots being over-dosed. Our study showed visible reduction in vegetative growth and delayed flowering at all rates of Marathon 1G higher than the lowest recommended rate, and non-uniform vegetative growth of poorly mixed treatments at all rates. Some inconsequential leaf edge necrosis was photographed even on the lowest rate. It is also interesting that plants with the lowest rate of Marathon 1G flowered several days earlier than control plant that were not treated. However, the treatments were randomized in the irrigation trays (to keep the product from leaching into untreated pots), so early flowering of one treatment could have resulted from watering or fertilizer variation.

Discussion

Marathon 1G is a granular formulation of the chemical imidacloprid, an effective control of the aphid species commonly observed in greenhouses. We do not recommend preventative applications of one chemical class in an environment with continuous cropping such as occurs in Arabidopsis growth areas, lest resistance develop to the chemical. In contrast, we spray a liquid formulation of this active ingredient (or other products) on infested plants at first sign of the aphids. Many institutions have mastered biological control of aphids and other insect pests. However, some researchers still use the granular chemical incorporated into the soil mix prior to planting.

Do any insecticides or fungicides burn foliage?[Photos]

Short Answer

Only a few.

Results

Over the years, we've observed spray damage on Arabidopsis from the following pesticides under certain circumstances:

-Multiple applications of insecticidal soap to the same plants

-Application of insectidal soap or horticultural spray oil to plants in sunny, hot conditions

-PBO synergist

-Nicotine fumigant only when leaves were wet

-Dursban insecticide

-Pipron fungicide at label recommended rate

-Strike fungicide only at 6X label recommended rate

Below is a list (by US trade name) of some of the products we've applied to Arabidopsis without observing damage. This does not mean they are effective in controlling the target pest or to imply an endorsement of the product:

Insectides, Miticides or insect growth regulators:

Akari
Avid
Azatin
Conserve
Distance
Duraguard
Endeavor
Enstar II
Floramite
Garlic extract
Hexygon
Marathon 1G
Marathon II
Mavrik
Mesurol
Orthene
Ovation
Overture
Pepper extract
Pylon
Sanmite
Talstar
Tame
 
Fungicides:

Banrot
Cleary's 3336
Cygnus
Daconil
Strike
Wettable sulfur

Discussion

Arabidopsis is susceptible to most greenhouse pests such as aphids and western flower thrips. On rare occassions it is fed upon by whitefly, spider mites, root aphids and even armyworms! If the planting is small and the insect population low, a spray bottle of ready-to-use pesticide from a garden center may suffice. These consumer-friendly products can be applied without restricting the location. Label directions should be followed and a few test plants should be sprayed and observed for phytoxicity before applying to valuable plants. Spray damage appears in 24-48 hours. Damage from granular formulations added to soil may take up to a week to appear. Do not use any product more than twice on the same Arabidopsis plants. Insecticidal soaps, for example, accumulate on leaves and may lead to damage only after multiple applications. Also keep in mind that mutant plants may be more susceptible to spray damage, particularly those with altered leaf waxes.

I have run out of space in my facility; how can I optimize it?[Photos]

A simple method is to move plants that are beginning to set seed (but before seed pods can shatter) to another room or unlighted shelf so that the valuable growing space can be used for actively growing plants. Rolling benches are a good choice for a greenhouse. Their legs stay in place but tops roll from side to side on rolling bars. You sacrifice permanent aisles for about 20% more usable space. We've also taken a commercial A-frame tiered bench (Hummert International, Inc. St. Louis, MO) and modified if to fit Arabidopsis (and water-proof fluorescent fixtures). Placed upon an existing bench, it doubles greenhouse space. Place upon rolling benches, space utilization of over 100% of floor space can be achieved. Given that the room they are located in is temperature controlled, using light shelves is an excellent way to increase the number of plants per unit area of floor. Units that have rolling shelves on a frame system are available in the storage-specialty industry, especially for hospital storage. These could be modified with fluorescent fixtures for plant growth to greatly improve space utilization of growth rooms, perhaps tripling the useful space more economically than building or adding new utilities to a new room. Of course, the additional cooling and electrical requirements need to be considered.

What is my worst Arabidopsis nightmare?[Photos]

Short Answer

Impatiens Necrotic Spot Virus (INSV)

Discussion

Impatiens Necrotic Spot Virus (INSV) is a viral disease that kills Arabidopsis. It is vectored by western flower thrips, a common greenhouse pest that is attracted to flowering plants. Symptoms include:

-Clearing or yellowing of leaf midrib -Leaf collapse -Wilted or collapsed flower stems -Sudden death of a few plants, followed by death of more plants

INSV can infect more than 600 species, including many commercial floriculture crops and outdoor weeds. Excellent thrips control, rogueing of infected plants and strict quarantine procedures are required to eliminate this disease. We recommend immunostrip test kits should be kept on hand for quick diagnosing. They can be stored in a refrigerator for one year. One commercial source is Agdia of Elkhart, IN.

RESPONDING TO AN INFECTION: Once INSV is discovered in a greenhouse room, there are two practices to choose from, “clearing” or “containment.” For the former, all plants in an infected greenhouse room are discarded. The room is cleaned of all plant material and rubbish that could harbor thrips. The room is left empty for 4-7 days. Only newly seeded plants are allowed back in the room. Of course, clearing a room is often not possible because of irreplaceable plants.

Containment involves discarding any plants showing symptoms and any plants that are easily replaceable even if they don’t exhibit symptoms. The goal is to get the greenhouse empty as soon as possible while collecting seed or other valuable tissue for the research project (the disease is not carried in seed). A date is set that all plants will be removed, allowing enough time for seed maturation. Aggressive pesticide spraying and sanitation is implemented. Dedicated lab coats are kept in the room that all personnel must wear so they don’t carry thrips out into other areas.

PREVENTING AN INFECTION: At Purdue, we have vastly reduced incidence of the disease by implementing a rotating greenhouse room schedule. A room is cleaned and emptied for several days, then newly seeded or cultured plants allowed in the room for two months. At that time, no more plants are allowed in (a new, clean room is made available for new plants) but the plants present in the room are allowed to remain until harvested. Following harvest, the room is cleaned again. Avoiding the continuous culture of plants breaks the thrips life cycle. The theory is simple but the implementation requires multiple rooms and a great deal of communication. It will most likely require pooling many labs into the rotating rooms, rather than allocating each lab their own room.

Is reverse-osmosis purified water required to irrigate plants?

Short Answer

Only if water testing indicates you have very poor water quality

Results

Though we consider our clear water to be of poor quality due to high alkalinity, we saw no visible differences between plants irrigated with reverse-osmosis purified water versus our tap water.

Discussion

Reverse osmosis or other purified water is necessary in laboratory culture or hydroponics, but usually not in crop production in soilless media. We also use it for mixing pesticides, to make them more effective.

What about growth conditions such as light intensity, light quality, cold treatments and hydroponic techniques that this study did not examine?

For your convenience, we've included excellent summaries and reports in our references section on these topics, most of them hyperlinked to the original source. ​