High-temperature effects on early development of tomato (Lycopersicon esculentum Mill.).

Abstract

In southern states, plantings for fall and winter tomato (Lycopersicon esculentum Mill.) production often have problems in stand establishment. Tomato seed sown in late summer or early fall often encounter soil temperatures greater than 40°C. This exceeds the generally accepted maximum germination temperature of 35°C, and is thought to contribute to poor seedling growth and vigor. Studies were conducted on tomato to evaluate the effects of high temperatures on germination and seedling development, and their physiological and anatomical responses. At the optimum temperature of 25°C, seed of all tested tomato lines had 85% or higher germination in petri dishes. Germination was reduced dramatically when the temperature was greater than 35°C, and in alternating temperatures of either 40/25 or 40/30°C, seed germination was also low. Seed imbibed for 24 to 48 hours at a constant temperature of 40°C, also showed the deleterious effects of high temperature and had reduced germination. Seed germination did not decrease dramatically if seed were imbibed for more than 24 hours at a constant temperature of 25°C. The time interval of 24 to 48 hours following imbibition was considered to be the most heat sensitive period in tomato seed germination. There were no differences in the banding pattern of heat shock proteins (hsps) from emerged seed of either heat sensitive or heat tolerant lines. However, at temperatures of 35 and 40°C the width of hsps bands increased. Testing for electrolyte leakage of emerged seed showed that leakage played a role in influencing the isotope absorption of root radicles. Normal seedling development was observed at 23/21°C in terms of secondary roots formation, and fresh weight of roots, cotyledons and leaves. Alternating temperatures of either 40/25, or 40/30°C resulted in delayed development of seedlings when seed were imbibed, germinated and grown two days at 23/21°C before heat treatments were applied. Secondary root and leaf primordia could be detected microscopically when seedlings were grown at 23/21°C for either two or three days. Yet, development was delayed at high temperatures, and a reduction in root number, leaf number, and fresh and dry weight of roots, cotyledons and leaves was observed.