PHYSIOLOGICAL, GENETIC, AND BREEDING STUDIES OF TOLERANCE TO HIGH TEMPERATURE AND HIGH RELATIVE HUMIDITY IN TOMATOES (LYCOPERSICON ESCULENTUM MILL.)

Two greenhouses, located in Lincoln, Nebraska, were used in testing the performance of 14 cultivars/lines and 24 F(,1)\u27s under different conditions of relative humidity (RH) and temperature. The high temperature, 29-35(DEGREES)C (85-95(DEGREES)F) day and 22-23(DEGREES)C (72-73(DEGREES)F) night reduced fruit set, flower numbers, seed set, and pollen viability as well as quantity. The number of flowers with elongated styles increased at high temperature in all cultivars except Saladdette which showed no style elongation above the antheridial cone. The response of the cultivars to high temperature was variable. S6916, Saladdette, CL(,1), and Burgess were highly tolerant. N59 F(,1) and Carmello F(,1) had low tolerance. The F(,1)\u27s had more tolerance than the parents; F(,1) S6916 x Burgess, F(,1) Y207 x Burgess, F(,1) Helani x Burgess, F(,1) Y297 x Bonus, and F(,1) Saladdette x Burgess were highly tolerant. High humidity reduced yield and quality of tomato at both normal and high temperatures. High humidity induced cracking and surface dullness. These defects reduced yields of marketable fruit by about 37%. The response of the cultivars was variable. Saladdette, Burgess and Bonus were highly tolerant to high humidity and produced good-quality fruits, while S6916 and CL(,1) were the highest in fruit-set, but susceptible to cracking. Carmello F(,1) and N59 F(,1) were lowest in fruit-set. The F(,1)\u27s had higher yield than the parents with better quality. The F(,1) Helani x Burgess, F(,1) Y207 x Burgess, and F(,1) Saladdette x Burgess had the best yield and quality of all F(,1)\u27s at high RH. In general, high RH reduced fruit-set, flower number, seed-set and pollen viability. Also, the number of cracked fruit was increased at high RH. The combined effect of high temperature and high relative humidity was greater than the effect of each factor alone. Some cultivars, as well as F(,1)\u27s, showed high tolerance to the combined effect of high temperature and high humidity. In the present work, general combining ability (GCA) was used to determine which was the best line, Burgess (male 1) or Bonus (male 2), when they were crossed to 12 females. Burgess (male 1) had high breeding value (good GCA) for most of the characters such as yield, flower number, fruit set, seed set, lower number of flowers with style elongation and lower number of cracked fruits, while Bonus (male 2) showed poor GCA. Based on the results of this study, a breeding scheme is proposed utilizing specific combining ability using the best genotypes in this experiment. The procedure should lead to combining the physiological strengths of several cultivars with tolerance to high temperature and high relative humidity resulting in high-yielding cultivars of good quality