Testing Tomato Hybrids for Heat Tolerance at West Tennessee Experiment Station

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(NO₃)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 bc	114 b	124 b	287 c	41 b	68 b	69 b	178 c
Solar Set	91 b	108 b	138 b	337 bc	28 b	85 ab	82 b	195 bc
Heatmaster	179 a	144 ab	74 b	397 ab	115 a	59 b	10 c	184 c
Heatwave	52 bc	191 a	116 b	359abc	92 a	76 b	55 bc	223 bc
NC 96378	73 b	137 ab	154 b	364abc	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 bc
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 bc	373 b	1142 a	191 b	264abc	301 bc	756 b
Solar Set	299 b	468 bc	346 b	1113 a	180 bc	252 bc	379 b	811 b
Heatmaster	548 a	445 c	233 b	1226 a	279 a	313 ab	154 c	746 b
Heatwave	180 bc	684 a	366 b	1230 a	232 ab	262abc	304 bc	798 b
NC 96378	220 b	519 bc	421 b	1160 a	153 bc	365 a	299 bc	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	29abc	29 a	7 ab	65 ab
Solar Set	23 b	76 b	52 ab	151 bc	13 bc	17 ab	14 a	44abc
Heatmaster	79 a	60 b	28 b	167abc	38 a	12 b	3 b	53 ab
Heatwave	29 b	72 b	45 ab	146 bc	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 bc
	Mean fruit size (lbs per fruit)
Mt. Fresh	0.42 bc	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	0.52 bc	0.34 bc	0.28 a	0.34 bc
Solar Set	0.46 b	0.50 a	0.37 a	0.44 a	0.58 ab	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

^{zLarge=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
^{xEarly harvest - 6/29 to 7/14; midseason - 7/18 to 8/1;
late - 8/4 to 8/16
^{wEarly harvest - 8/15 to 8/22; midseason - 8/24 to 9/1;
late - 9/5 to 9/15
^{vMeans followed by the same letter are not significantly
different, Duncan’s multiple range test, 5% level.
^{uIncludes small and medium sized fruit}}}}}}

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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.