Heritability of Flower Number and Fruit Set under Heat Stress in Tomato

The growing volatility of the climate, and its potential impact on crop production, has prompted several physiologic and genetic analyses under high-temperature conditions. Tomato is grown in warm temperate, subtropical, and tropical regions of the world, where daytime and nighttime temperatures regularly exceed the optimum temperatures for tomato growth during the summer, exerting stress on tomato production. Recent trends indicate more frequent extreme summer temperatures, which may grow even greater in the future, impacting crop growth. The objective of the current study was to estimate the heritability of flower and fruit set ability of tomato populations under heat stress conditions so that improvement for these traits can be planned. We developed two tomato populations using contrasting parents from the North Carolina State University (NCSU) tomato breeding program and the World Vegetable Center (formerly Asian Vegetable Research and Development Center). The F-2 and F-2-derived F-3 families (F-2(:3) populations) were grown at the Piedmont Research Station (PRS), Salisbury, NC, where summer growing temperatures are warmer than optimum for tomato production. Heritability estimates of the number of flowers per cluster, the number of fruit per cluster, and fruit set (measured as a percentage) were determined in two populations of tomato-NC10137 (NC714 X CLN-2413A) and NC10418 [230 HS-1(99) X NC 1CS]-by regression analysis using the offspring-on-parents method. Broad-sense heritability across the traits was high (47.2%-100%), whereas narrow-sense heritability was very low (1.4%-22.5%). There was a positive correlation between the number of flowers and the number of fruit per cluster (r = 0.50, P < 0.05), which was in close agreement with previous findings. These findings will be useful in investigating the genetic control of heat stress tolerance in tomato and in facilitating crop improvement in the future.