Testing Tomato Hybrids for Heat Tolerance at West Tennessee Experiment Station, 2000 Jim E. Wyatt and Craig H. Canaday Interpretative Summary The highest yielding early tomato hybrid in both spring and fall plantings was Heatmaster. It also had the lowest late season yield and the smallest mean fruit size. The highest yielding late-maturing hybrid was Mt. Fresh, which produced large amounts of large, extra large, and total fruit. NC 96378 and Heatwave had the highest amounts of total culls in the spring and fall, respectively. Sunsation had the highest mean fruit size in the spring planting; while in the fall study, Mt. Fresh and Solar Set had the highest early mean fruit size. Heatmaster had the smallest fruit in the study. Introduction Tomato prices in Tennessee have traditionally increased during the early fall due to continuing demand and decreasing supplies. This situation presents the possibility of a desirable marketing window, especially after Labor Day. Tomatoes are more difficult to grow during this season because of higher insect populations, climatic conditions more favorable to diseases, and failure to set fruit because of high temperatures prior to flowering. Several tomato hybrids are being marketed which are reported to be tolerant to high temperatures and to set fruit during hot summer months. Twelve of these hybrids were grown at the West Tennessee Experiment Station in 1999 and five of these were chosen for further testing in 2000 based on reasonably good yields and production of horticulturally acceptable fruit. The objectives of this study were to compare these five hybrids to a widely adapted, commercially grown hybrid and attempt to identify tomato hybrids which may be adapted to production during times when temperatures are highest. Materials and Methods Two plantings, designated spring and fall, were made using six tomato hybrids in each planting. The spring planting was transplanted on 27 April after danger of frost was past and about the time when many commercially grown tomatoes are transplanted in West Tennessee. The fall planting was transplanted on 16 June and developed fruiting buds and bloomed at a period when day/night temperatures were averaging 90E/69EF, respectively. The tomatoes were grown using currently recommended cultural practices for staked tomatoes in Tennessee. All plots received 400 lbs/acre of 15-15-15 fertilizer prior to
transplanting and 30 lbs/acre of nitrogen as Ca(NO 3 ) 2 was applied as a sidedressing when first tomato fruit were about one inch in diameter and again two weeks later. Plants were supported by a five ft stake driven between every other plant and with nylon string tied to the stakes. Supplemental water was supplied as needed with a drip irrigation system. Registered pesticides were applied on a regular schedule or as needed to control weeds, diseases and insects. Tomatoes were harvested at the mature green or breaker stage of maturity. Fruit from each plot were graded into small, medium, large and extra large sizes on a commercial grading machine and fruit from each category were counted and weighed. Fruit were classified as culls if they did not meet standards required for U. S. No. 2 grade. Harvest distribution for the spring planting was divided into early (6/29-7/14), midseason (7/18-8/1) and late (8/4-8/16) harvest periods while the fall harvest distribution was early (8/15-8/22), midseason (8/24-9/1) and late (9/5-9/15). Mean fruit weights for each period were calculated from fruit number and weight data. Data were analyzed by size and harvest period by appropriate statistical methods. Data presented are of large and extra large fruit classes since these are fruit with the highest value. Similar results were found with small and medium fruit. Results and Discussion Heatmaster had the highest yield of early large, extra large and total yield in both the spring and fall plantings (Table 1). It also had the lowest yield of these size categories during the late part of the season. This hybrid is best adapted to a spring planting when early maturity is desired; it should not be used when the objective is late fruit production. Mt. Fresh produced significantly higher late-season large, extra large and total yields in the fall planting and higher late-season large and total yields in the spring planting than any other hybrid. It could not be determined in this study if this character could be due to heat tolerance or to another factor such as plant vigor, disease tolerance, nutrient utilization, etc. Mt. Fresh did not suffer any apparent harm from being grown in the hottest part of the summer. Most of the culls were due to radial cracking around the stem/shoulder area of the fruit and did not constitute a major portion of the harvest. Uneven soil moisture due to a intermittent drought probably contributed to the cracking. NC 96378 had the highest total culls in the spring but was not significantly different from Mt. Fresh and Heatmaster. In the fall, the highest cull fruit was in Heatwave, followed by Sunsation, Heatmaster, and Solar Set. Sunsation had the highest mean fruit size in the spring planting. In the fall study, Mt.
Fresh and Solar Set had the highest early mean fruit size. Fruit size held up well on all of these hybrids into the latter part of both seasons. Heatmaster is a small-fruited hybrid which may have a place in a niche market. Table 1.Tomato yields and mean fruit weights from spring and fall plantings of 5 putative heat tolerant hybrids and a widely grown commercial hybrid, West Tennessee Experiment Station, Jackson, TN. Large z fruit yield (20 lb boxes per acre) Hybrid Spring planting y Fall planting y Early x Mid- season x Late x Total Early w Mid- season w Late w Total Mt. Fresh 22 c v 175 a 251 a 448 a 18 b 62 b 194 a 274 a Sunsation 49 114 b 124 b 287 c 41 b 68 b 69 b 178 c Solar Set 91 b 108 b 138 b 337 28 b 85 ab 82 b 195 Heatmaster 179 a 144 ab 74 b 397 ab 115 a 59 b 10 c 184 c Heatwave 52 191 a 116 b 359a 92 a 76 b 55 223 NC 96378 73 b 137 ab 154 b 364a 41 b 116 a 80 b 237 ab Extra large z fruit yield (20 lb boxes per acre) Mt. Fresh 39 b 340 a 155 a 534 ab 80 a 86 b 115 a 281 a Sunsation 171 a 334 a 108 ab 613 a 136 a 69 b 40 b 245ab Solar Set 165 a 309 a 77 ab 551 a 142 a 74 b 53 b 269 a Heatmaster 171 a 107 b 25 b 303 b 103 a 23 b 2 b 128 c Heatwave 63 b 365 a 68 ab 496 ab 85 a 33 b 44 b 162 NC 96378 114 ab 298 a 84 ab 496 ab 94 a 162 a 48 b 304 a
Total u fruit yield (20 lb boxes per acre) Mt. Fresh 74 c 620 ab 689 a 1383 a 103 c 204 c 706 a 1013 a Sunsation 248 b 521 373 b 1142 a 191 b 264a 301 756 b Solar Set 299 b 468 346 b 1113 a 180 252 379 b 811 b Heatmaster 548 a 445 c 233 b 1226 a 279 a 313 ab 154 c 746 b Heatwave 180 684 a 366 b 1230 a 232 ab 262a 304 798 b NC 96378 220 b 519 421 b 1160 a 153 365 a 299 817 b Cull fruit yield (20 lb boxes per acre) Mt. Fresh 31 b 97 ab 66 a 194 ab 8 c 8 b 5 b 21 c Sunsation 33 b 61 b 29 b 123 c 29a 29 a 7 ab 65 ab Solar Set 23 b 76 b 52 ab 151 13 17 ab 14 a 44a Heatmaster 79 a 60 b 28 b 167a 38 a 12 b 3 b 53 ab Heatwave 29 b 72 b 45 ab 146 33 ab 21 ab 13 a 67 a NC 96378 35 b 132 a 65 a 232 a 10 c 24 ab 5 b 39 Mean fruit size (lbs per fruit) Mt. Fresh 0.42 0.47 a 0.36 a 0.41 a 0.59 a 0.41 a 0.31 a 0.35 ab Sunsation 0.52 a 0.50 a 0.37 a 0.45 a Solar Set 0.46 b 0.50 a 0.37 a 0.44 a 0.52 0.58 ab 0.34 0.28 a 0.34 0.36 ab 0.29 a 0.35 ab Heatmaster 0.36 d 0.36 b 0.31 b 0.35 b 0.41 d 0.27 d 0.20 b 0.29 d
Heatwave 0.38 cd 0.46 a 0.34 ab 0.40 a 0.40 d 0.30 cd 0.27 a 0.31 cd NC 96378 0.44 b 0.48 a 0.36 a 0.42 a 0.49 c 0.41 a 0.30 a 0.37 a z Large=2.6 through 3.0 inches in diameter; extra large= >3.0 inches in diameter y Spring transplanted 27 April, 2000; fall transplanted 16 June, 2000 x Early harvest - 6/29 to 7/14; midseason - 7/18 to 8/1; late - 8/4 to 8/16 w Early harvest - 8/15 to 8/22; midseason - 8/24 to 9/1; late - 9/5 to 9/15 v Means followed by the same letter are not significantly different, Duncan s multiple range test, 5% level. u Includes small and medium sized fruit Copyright 1999 by The University of Tennessee. All rights reserved. This research represents one season's data and does not constitute recommendations. After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.