Breeding Tomatoes for All Seasons J. W. Scott IFAS, University of Florida Gulf Coast Research and Education Center 5007 60th Street East, Bradenton, FL 34203 Tomato genotypes have been field screened for fruit setting ability under high temperature (>30 day >21" night) and humidity conditions. Several genotypes have had good fruit set, but Cl 1 Id from the AVRDC in Taiwan is the most prom- inent heat tolerant source in current breeding lines. Fruit characters being selected are: large size, firmness, jointless stems, good shape, good color, even ripening, blossom-end smoothness, and no cracks. Disease resistance being incor- porated include Fusarium wilt (F. oxysporum f. sp. lycopersici) races 1, 2 and 3, gray leaf spot (Stemphylium solani Weber), bacterial wilt (Pseudomonas solanacearum E. F. Smith), and bacterial spot (Xanthomonas campestris pv. W. L. George, Jr. Horticulture Department University of Illinois Urbana, IL 61801 vesicatoria). To further enhance fruit setting, a parthenocarpy gene (pat-2) has been incorporated into heat tolerant genotypes. In 1983, two such lines had yields equal to and greater than Cl lid under high and low temperature condi- tions, respectively. This gene combination could result in hor- ticulturally acceptable, multiple disease resistant breeding lines which will set fruit under both high and low temperatures and/or high humidity conditions not conducive to pollination. Keywords: cold tolerance, disease resistance, fruit set, heat tolerance, Lycopersicon esculentum Mill., parthenocarpy, vegetable breeding. One objective of the tomato breeding program at the Universi- ty of Florida is to develop varieties or breeding lines which could be either grown as a summer tomato crop in Florida and other tropical areas, or utilized in obtaining varieties with earlier fruit set for fall crop tomatoes in these regions. It has been well documented by Kuo et al. (1978) and others that high temperatures limit tomato (Lycopersicon esculentum Mill.) fruit set, and this reduces production in many tropical and sub-tropical regions of the world. Villareal (1980) points out ad- ditional difficulty in attaining fruit set under high rainfall condi- tions which accompany high temperatures in many tropical areas. Breeding of tomatoes for such adverse conditions has been com- plicated the lack of high heritability for heat tolerant fruit setting ability (El Ahmadi and Stevens, 1979; Villareal and Lai, 1978). It has been extremely difficult to obtain heat tolerant lines with large fruit size, which probably relates to inefficient pollination. Fruit quality defects such as blotchy ripening and inadequate shelf life have also been problems in tropical regions (Villareal, 1980). Furthermore, fruit cracking increases under high rainfall conditions, especially with greater fruit size. Tropical tomato production is also limited by diseases. Bacterial wilt (Pseudomonas solanacearum E. F. Smith) is pro- bably the most prevalent disease problem in these regions (Yang, 1979). Other destructive diseases in the tropics, depending on location, include: Fusarium wilt (Fusarium oxysporum f. sp. lycopersica), races 1 and 2 (F2), gray leafspot (Stemphylium solani Weber (S), and bacterial spot (Xanthomonas cempestris pv. vesicatoria). Recently Fusarium wilt race 3 has been discovered in Florida (Jones et al., 1982), and sources of resistance are being evaluated (Scott et al., 1983). A source of resistance to bacterial spot has been reported recently (Scott and Jones, 1984) which should aid in development of varieties resistant to this pathogen. These resistances need to be incorporated into tomato lines with good heat tolerance, crack resistance, shelf life, ripening, and flavor. This is not an easy task, as evidenced by the general lack of available heat tolerant cultivars to date. One genetic system which might prove useful in developing improved fruit set under temperature stress is parthenocarpy. VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY Genetic parthenocarpy in tomato is a facultative trait whereby the expression of seedless fruit is greatest under periods of en- vironmental stress such as high temperatures (George et al., 1984; Lin et al., 1983). These fruits have normal locule gel, but no seeds. This trait could be useful in enhancing fruit set, not on- ly under high temperatures, but also under humid, rainy condi- tions or cool temperatures. Cool temperatures can inhibit fruit set during winter months in Florida, or in higher altitudes of some tropical areas. The sporadic occurrence of cool weather in Braden- ton would preclude an effective cold tolerance breeding program. The purpose of this paper is to report on some breeding ap- proaches being utilized at the University of Florida to develop tomatoes which will set fruit under temperature and humidity stress. MATERIALS AND METHODS General Characteristics. Fruit characteristics being selected for the total breeding program are large size, good shape, smooth blossom ends and shoulders, crack resistance, black shoulder resistance, firmness, good color, even ripening, good flavor, and no defects such as pox, gold fleck, or zippers. Vines are determinate (commonly termed semi- determinate), with adequate vine cover to protect fruit. Standard disease resistances being incorporated into all new varieties are Fusarium wilt races 1 and 2, Verticillium wilt race 1 (Verticillium albo-atrum Reinke and Berthold) (Ve) and gray leafspot. Of these, Verticillium wilt is not as important to the heat tolerance program since it is a cool weather disease. New disease resistances being bred are Fusarium wilt race 3, Fusarium crown rot (F. ox- ysporum f. sp. lycopersici radicus), bacterial spot, and bacterial wilt. Of these, Fusarium crown rot is probably not important to the heat tolerance program since it is a cool weather disease. Heat Tolerance Selection takes place in the field under high temperature (>30' C day, >21" C night) and high humidity conditions prevalent at Bradenton, Florida from mid-May through September. It is rare for night temperature to be less than 21 C 267