Comparative Floral Fertility in Heat Tolerant and Heat Sensitive Tomatoes1

The heat tolerant tomatoes ( Lycopersicon esculentum Mill.) breeding line AU 165 and ‘Nagcarlang’ were compared with the heat sensitive ‘Floradel’ in fruit set, pollen abortion, and embryo sac abortion. The 2 heat tolerant cultivars had a significantly higher percentage fruit set under both moderate and high temperature in spring and summer than did ‘Floradel’, but fruit set of all 3 cultivars was significantly lower at high temperature. The fruit set of all 3 cultivars was markedly improved by hand pollination, indicating that insufficient pollination probably was a major cause of heat sterility at high temperature. Both pollen and embryo sac abortion were minor factors in the reduced fruit set observed. Heat tolerance in the cross AU 165 × ‘Floradel’ appeared to be partially dominant.