COMPARING HEAT-STRESS EFFECTS ON MALE-FERTILE AND MALE-STERILE TOMATOES

To separate the effects of heat stress on male and female reproductive tissues, male-sterile (MSs) and male-fertile tomatoes (MFs) were plac ed in growth chambers at 12 h day/12 h night temperatures of 28/22, 30 /24 or 32/26 degrees C from newer appearance to seed maturation (daily mean temperatures of 25, 27 or 29 degrees C). pollen from MFs was app lied individually to MS flowers. As MFs were self-pollinated, heat str ess was experienced by both male and female tissues. At growth tempera tures of 29 degrees C fruit number, fruit weight per plant, and seed n umber per fruit were only 10%, 6.4% and 16.4%, respectively, compared with those at 25 degrees C, Heat stress also adversely affected fruits et in MSs, especially when experienced by donor pollen. No fruit at al l developed on MSs receiving pollen produced at 29 degrees C, even whe n ovule development, pollen germination and subsequent embryo developm ent all took place at 25 degrees C, Effects on fruitset in MSs were re duced if donor pollen had not experienced heat stress. MSs grown at 29 degrees C but receiving pollen developing at 25 degrees C produced 73 % as much fruit (both on number and weight basis), had 40% as high fru itset and produced 87% of the seed per fruit as MSs grown at 25 degree s C, This use of male-sterile and male-fertile lines of tomato provide s new evidence that impairment of pollen and anther development by ele vated temperature will be an important contributing factor to decrease d fruit set in tomato, and possibly other crops, with global warming.