Heat Stress Trial with Tomato

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

A trial was conducted in 2019 at the University of Delaware Thurman Adams Research Farm, Georgetown, Delaware to evaluate 28 commercial and experimental tomato cultivars for yield and quality under heat stress. Plants were transplanted to the field on 31 May 2019. Field plots were one row (6’) wide and 10’ long. The experiment design was a RCB with four replications. In-row spacing for plants was 1.5’ with 6 plants per plot. Fruit were harvested five times: 8 August, 20 August, 4 Sept., 16 Sept., and 28 Sept. Fruits were graded into Extra Large (XL), Large (L), Medium (M), Small (S) sizes, Seconds (2nd) and Culls. Five large tomatoes in each plot were cut and evaluated for the appearance of white tissue. On the second harvest, tomatoes were also given a white tissue rating (0-10) and tested for soluble solids.

The top group in terms of marketable yield were Grand Marshall, XTM 2256, Red Snapper, STM 2255, Red Mountain, Red Bounty, and FTM 6281 and ranged from 19.6 to 15.5 lbs./plant. Most varieties had peak yield on harvest 2. Varieties that had peak yields on the first harvest were Red Mountain and FTM 6163. Varieties with peak yields on harvest 3 were Red Snapper, FTM 6281, Jamestown, Myrtle, and Saybrook. Varieties showing extended harvest (over 4 lbs./plant in harvests 4 +5) were Grand Marshall and XTM 2256. Grand Marshall and XTM 2256 had significantly higher numbers of tomatoes per plant compared to all varieties except Mountain Fresh, STM 2255, and Jamestown. Grand Marshall and XTM 2255 also had much higher numbers in harvests 4 and 5 than other varieties.

Varieties with low mean incidence of white tissue (less than 1.5) were Jamestown, FTM 6298, Primo Red, and Red Bounty. Varieties with incidence of white tissue over 3 were Camaro, FTM 6163, Mountain Merit, and Mountain Fresh. Varieties with all tomatoes sampled showing white tissue on harvest 1 were FTM 6163, Camaro, and Red Snapper. All samples of Mountain Fresh and FTM 6163 had white tissue in harvest 2. White tissue incidence decreased as temperatures decrease across all varieties; however, Grand 5 Marshall, Mountain Merit, and Myrtle had more than 2.5 tomatoes showing white tissue in harvest date 4 and Mountain Fresh was still showing 40% white tissue in harvest date 5.

XTM 2256, FTM 6281, Bella Rosa, and FTM 8011 had soluble solids 4.5 or greater. Camaro, Red Snapper, FTM 5187 Dixie Red, BHN 602, Mountain Fresh, Saybrook, Mountain Merit, Red Deuce, and FTM 6163 had white tissue severity ratings of 4 or greater. This corresponds to white tissue covering 40% or greater of the fruit. Camaro had a white tissue severity rating of 8.3. STM 2255, Roadster, and FTM 8011 had white tissue ratings under 2.

FTM 6281 had over 4 lbs./plant in the XL category. Red Snapper, Grand Marshall, Red Bounty, XTM 2256, SV 7101, STM 2255, FTM 6281, Red Mountain, and FTM 6298 yielded over 5 lbs./plant of Large tomatoes. Red Mountain, Grand Marshall, XTM 2256, and Red Snapper had over 5 lbs./plant of medium tomatoes. Red Mountain had 3.4 lbs./plant of Small tomatoes. Seconds which comprised mostly of tomatoes with some cracking were 2.8 lbs./plant in Primo Red. Varieties with over 2 lbs./plant in the Cull (misshapen) category were Biltmore, Red Deuce, Camaro, Roadster, and Mountain Merit. Mountain Majesty, Camaro, and Red Deuce had 7 or more fruits per plant in the cull category. Varieties with less than 5 % culls were Grand Marshall, Jamestown, and Mountain Fresh.

This trial is being repeated in 2020.

Some of the Varieties From the 2019 Tomato Trial

some of the varieties from the 2019 trial