ceac : research : archive : Tomato Heat Tolerance Trial (2000-2001)

A Trial to Test Heat Tolerant Tomato Varieties for Use in Desert Climates

Patricia A. Rorabaugh and Merle H. Jensen
Plant Science Department, University of Arizona

introduction
materials and methods
results
   #1 fruit
   taste test
   average stem length
conclusions
acknowledgments

INTRODUCTION (top)

Most tomato varieties were bred originally for cool climate, high latitude regions (Canada, England, Holland, etc.) and do not do well in high temperature areas. In the past ten years Arizona, as well as other high light, high temperature areas around the world, have gained popularity among hydroponic greenhouse growers. In Arizona the optimum elevation for growing indeterminant hydroponic greenhouse tomatoes is between 4000 and 5000 feet (primarily due to heating/cooling costs). However, the educational programs of the Controlled Environment Agriculture Center (CEAC) must be taught at the University of Arizona's Campus Agriculture Center in Tucson which is at about 2500 feet. At this relatively low elevation optimum temperatures are difficult to maintain especially during the initial phases of growth (July through September) and during the final stages of the crop (April through June). Therefore, this project was performed to test heat tolerant indeterminant tomato varieties for use in desert climates, including Tucson.

MATERIALS AND METHODS (top)

Seven varieties of indeterminant, F1 hybrid, beef type tomatoes were selected: Trust, Blitz and Quest from DeRuiter Seeds (3001 Bethel Rd., Ste.118/Box 20228, Columbus, OH 43220), Rapsodie, RFT 18041 and RFT 18043 from Roger's Seeds (P.O. Box 4188, Boise, ID 83711-4188) and Mariachi 74-56 RZ from Rijk Zwann (Zaadteelt En Zaadhandel B.V., P.O. Box 40.NL-2678 ZG De Lier, The Netherlands). All but Trust were listed as heat tolerant varieties. Trust, which has been used before, was the control.

Seeds were planted into 1 ½" Rockwool cubes on 27 July 2000 and placed on a mist bench in a greenhouse (misting with water for 8 seconds every 8 minutes, day temperature about 26 - 30 C and night temperature about 21 C). Seedlings were transplanted into 2 hole 4 X 6" Rockwool blocks on 10 August. Misting continued with intermittent waterings of 3 times concentrated fertilizer. One month old seedlings were placed onto 3" X 8" X 36" Rockwool slabs in the CEAC greenhouse on 24 August. Each variety was replicated 4 times, 36 plants per replication, in a randomized block design.

The trial was performed in the CEAC sawtooth design greenhouse, consisting of a steel structure with polycarbonate glazing, and 2 bays 24 X 108 feet each . Environmental control was via a Q-Com climate control system. Carbon dioxide enrichment was supplied by a natural gas burner that could increase the CO2 up to about 850 ppm. The heating system consisted of 2 natural gas heaters with 8 horizontal air flow fans to distribute the hot air. Natural ventilation was via roll-up roof vents on each bay of the sawtooth. Active cooling was achieved with 4 fans and an evaporative pad "water wall" at opposite ends of the greenhouse. An interior curtain system could be deployed both for shade during sunny days or for heat retention during cold nights (typical day temp. 21 - 25 C; night temp. 18 - 20 C). An open, top drip fertigation system (Dosmatic) was used with a modified Hoagland's solution supplied via 3 tanks (Tank A: calcium nitrate and chelated iron; Tank B: all other macro and micro nutrients; Tank C: nitric acid for pH control). The nutrient recipe used (pH 6; EC 2.5) was typical for the control variety Trust, though commercial growers of Rapsodie normally use solutions with a higher EC, perhaps 3 - 3.5.

Tomato plants were trained using a single stem and were pruned and maintained using standard commercial techniques. Harvest began the second week of November (2000) and continued through June (2001) for a total of 31 weeks of harvest. Tomatoes were classed into 3 categories: #1's (weight >150g with no defects), #2's (weight <150g or weight >150g with some defects) and culls (weight <150g or substantial defects). Primary defects included blossom end rot (calcium deficiency), cat facing (pollination problem) boat shapes (high/low temperature), scaring and insect damage. A "blind" taste test was performed on 21 November 2000 with 35 participants grading each variety from 0 (lowest taste/quality) to 10 (highest taste/quality). Finally, total plant length was measured on 6 plants from each replication of each variety at the end of the project.

RESULTS (top)

Harvest measurements: There were significant differences between the varieties when harvest parameters were compared (see Table 1). Note that, for the most part, Mariachi and Rapsodie produced more #1 fruit and larger #1 fruit than any other variety. These varieties are already in use in places like Mexico and the warmer climates of Europe. Trust and Quest produced slightly smaller and less #1 fruit in our warm Tucson climate than Mariachi or Rapsodie. Trust, in particular, is not considered a heat tolerant variety and is popular in northern climates or at higher elevations in Arizona. Blitz, 18041 and 18043, all of which were listed as heat tolerant, did not fair as well in this variety trial.

Table 1. Results for #1 (marketable) fruit only for each variety over 31 weeks of harvest (top)

* An analysis of variance (Duncan test) was performed. Results with same suffix showed no statistical difference.

Taste test: (top)
A taste test was performed during an open house of the new CEAC teaching greenhouse on 21 November 2000. Thirty-five people participated, grading each variety in a blind test) on flavor and consistency from 0 to 10 (therefore, the maximum points possible for each variety was 350). The results in table 2 suggest that Trust and Quest were preferred over the other varieties.

Table 2. Results of the taste test.

Growth measurements: (top)
At the end of the variety trial 6 plants from each replication of each variety were measured. Table 3 shows that Mariachi was the fastest growing variety. In fact, novice students working on Mariachi found that is was difficult to keep up with pruning and other plant maintenance.

Table 3. Average stem length in meters for 6 plants
from each of the 4 reps for each variety.

** The number of observations for these two varieties was 23 as opposed to 24 for the other varieties (usually 6 plants from each of the 4 reps.).

CONCLUSIONS (top)

When assessing the results from this variety trial one must take into account how this information is to be used. Commercial growers might be most interested in Mariachi and Rapsodie which produce the largest and most fruit. Rapsodie did not do as well as Trust in the taste test, but then Rapsodie is usually grown under higher salt (EC) conditions. The consumer might prefer Trust or Quest, both of which did well in the taste test. In a class situation, however, Mariachi in particular is not recommended for beginning students since they grow so quickly and are difficult for students to maintain.

ACKNOWLEDGEMENTS (top)
Paper #R-125933-15-01. Supported by CEAC, the Controlled Environment Agricultural Center, College of Agriculture and Life Sciences, University of Arizona, and DeRuiter Seeds, Roger's Seeds and Rijk Zwann seed companies. (heat tolerant tomato var paper 2000-2001.doc)

ceac : research : archive : Tomato Heat Tolerance Trial (2000-2001)