Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Genetic studies were conducted on heat tolerance, size of stigma, style and ovary in the tomato, Lycopersicon esculentum Mill. in a series of experiments. Several cultivars were compared under summer and spring growing conditions for fruit set, flower drop, dormant or undeveloped ovaries, fruit weight, seed number per fruit, mean weight of 100 seeds, percentage of seed germination and non-aborted or normal pollen grains. In the Summer of 1978 the average minimum temperature was 24(DEGREES)C and maximum was 34.6(DEGREES)C. In Spring 1979 the average minimum temperature was 15.6(DEGREES)C and the maximum was 25.3(DEGREES)C. 'BL6807' set the highest percentage of fruits (50.5%) in the summer; whereas, 'L401' had the lowest fruit set of 1.1%. 'BL6807' had the smallest number of flowers to drop or absciss in the summer and 'CL9-0-0-1' had the lowest percentage of dormant or undeveloped ovaries. 'BL6807' had the statistically highest percentage of stained pollen grains in the summer indicating good viable pollen. In general the cultivars had less pollen in the summer than in the spring; however, differences occurred among cultivars in the summer. The mean fruit weight of the cultivars during the summer was generally lower than in the spring with the exception of 'BL6807', 'Saladette', and 'S6916' which were the same. The same was true for mean seed weight and seed number except 'CL9-0-0-1' and 'Chico III' which had no significant difference in seed number between seasons. There was a highly significant positive correlation between fruit weight and seed number for the cultivars in both seasons. The percentage germination of the seeds produced in the summer season was lower than those produced in the spring with the exception of 'Saladette' which showed no difference. 'L401' have very low fruit set in the summer having many flowers with split antheridial cones and elongated styles. This test showed that 'BL6807' was the most heat tolerant cultivar and 'L401' was the most heat sensitive. 'Saladette', 'S6916' and 'CL9-0-0-1' cultivars also showed heat tolerance by the fairly high percentage of fruit set. 'Chico III' did not show an appreciable amount of heat tolerance because it had only 11% fruit set which was significantly lower than other cultivars except 'L401'. In a diallel test 'S6916' transmitted good fruit setting ability to its progenies having less flower drop and fewer dormant ovaries. 'BL6807' was the next best parent for transmitting fruit setting ability and less flower drop, however, it transmitted the character for dormant ovaries to its progenies. 'L401' had the lowest general combining ability value for fruit set indicating that this tomato cultivar consistently transmitted less fruit setting ability to its progenies at high temperature. Additive gene effect for fruit set, flower drop and dormant ovaries, was more important than non-additive effects. The ability to produce normal flowers and to set a relatively high percentage of fruits in the cross 'L401' X 'Chico III' appeared to be under a heritable mechanism with some dominance. This cross also showed that stigma diameter, style diameter and ovary shape are under a heritable mechanism showing a partial dominance of the small stigma diameter, style diameter and some dominance of the 'Chico III' ovary shape. Heritabilities were 40.2-49.4% for stigma diameter, 72.8-74.4% for style diameter and 72.8-80.7% for ovary shape.