EFFECT OF NIGHT TEMPERATURE ON POLLEN CHARACTERISTICS, GROWTH, AND FRUIT-SET IN TOMATO

Lycopersicon esculentum Mill, 'Laura' plants were grown in the North C arolina State Univ, phytotron at 26C day temperature and 18, 22, 23, o r 26C night temperatures to determine the effects of night temperature on pollen characteristics, growth, fruit set, and early fruit growth, Total and percentage normal pollen grains were higher in plants grown at night temperatures of 18 and 22C than at 24 and 26C, but germinati on was highest in pollen produced al 26C, Seed content was rated highe r on the plants grown at 18C night temperatures than in any of the oth er treatments, Numbers of flowers and fruit on the first cluster were lower in the 26C night treatment than in the other night temperature t reatments, Plant height was greatest but total shoot dry mass was lowe st in the 22C night temperature treatments, Fruit fresh mass increased ,vith night temperature, reflecting more rapid development, but the ex periment was not continued to fruit maturity, so the effect of night t emperature on final fruit size and total plant production could not be determined, Night temperatures of 26C reduced fruit number and percen tage fruit set only slightly at a day temperature of 26C, even though these temperatures were above optimal for pollen production and seed f ormation, To separate temperature effects on pollen from direct or dev elopmental effects on female reproductive structures, pollen was colle cted from plants in the four night temperature treatments and applied to stigmas of a male-sterile cultivar kept at 24-18C minimum temperatu res in adjacent greenhouses, In the greenhouse-grown male sterile plan ts, no consistent effects of night temperature treatment given the pol len could be seen in fruit set, fruit mass, seed content (either on a rating or seed count basis), seedling germination, or seedling dry mas s.