41 J. Japan. Soc. Hort. Sci. 76 (1): 41–46. 2007. Available online at www.jstage.jst.go.jp/browse/jjshs JSHS © 2007 Partial Fertility Restoration as Affected by Night Temperature in a Season-dependent Male-sterile Mutant Tomato, Lycopersicon esculentum Mill. Masaharu Masuda 1,2 *, Kenji Kato 1 , Kenji Murakami 1 , Hiroshi Nakamura 2 , Christopher Ochieng Ojiewo 1,3 and Peter Wafula Masinde 3 1 Graduate School of Natural Science and Technology, Okayama University, Tsushima Naka, Okayama 700–8530, Japan 2 Faculty of Agriculture, Okayama University, Tsushima Naka, Okayama 700–8530, Japan 3 Department of Horticulture, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi, Kenya This study was conducted to investigate the influence of night temperature on the restoration of fertility in a season-dependent male-sterile tomato mutant (T-4). Plants were grown in greenhouses, in which minimum and maximum temperatures were set at 10°C and 28°C by heating and ventilation, respectively. Flowers were hand- pollinated and the fruit-set, seed-set, and number of seeds were examined. The rate of fruit-set was high and did not differ much from October to February; almost all fruits formed in October had self-fertile seeds, but 80% of the fruits from November to February were parthenocarpic. The rate of fruit-set dropped from 70% in March to below 10% in May. During this period, most of the fruits were seeded, though fruit-set was low. The number of seeds per seeded fruit varied with the season, being as high as 50 seeds in October, 1–2 seeds per fruit between November and March, and 1–20 seeds per fruit between April and June. A low night temperature of 12°C did not affect fruit-set but resulted in a better seed-set than a high night temperature of 18°C in the greenhouse. Further, pollination of the plants in phytochambers also resulted in a better fruit- and seed-set at 12°C than 24°C. In all cases, the influence of low temperature was more pronounced in autumn than in spring. Fruit-set was 70% at 12°C and 46% at 24°C. Of these fruits, 50% at 12°C and 10% at 24°C were seeded. It was inferred that partial fertility restoration in T-4 can be achieved by manipulation of night temperatures. The female organ was shown to be normal, functional, and compatible with wild-type pollen. From these results, the potential of the male- sterile T-4 mutant for use in a two line hybrid-seed production system was apparent. Key Words: male-sterile mutant, night temperature, partial fertility, tomato hybrid-seed. Introduction Hybrid-seed production of hermaphrodite or monoe- cious plants requires the maintenance of separate lines of male and female parents. Emasculation must be per- formed on the seed parents before pollination with the desired pollen (George, 1985). Whether by hand or using chemicals, emasculation is expensive, time consuming, and labour intensive, thereby contributing significantly to the high cost of hybrid-seeds (Lasa and Bosemark, 1994; Sawhney, 2004). Induction of male-sterility in the seed parent has been a useful way to circumvent the problems of high emasculation costs in F 1 tomato hybrid-seed production (Lasa and Bosemark, 1994). A number of male-sterile tomato lines have been developed and are currently being used with some level of success in hybrid-seed production (Dhaliwal et al., 2004). However, most of these lines are genic male-sterile mutants (GMS), and hence face the problem of mainte- nance. Normally, a GMS line is maintained by backcross- ing with a heterozygous maintainer line, but the progeny produced are 50% fertile and 50% sterile. In addition to the need for a third line, the maintainer line, an extra problem is created of roguing the fertile plants. Ideally, the male-sterile parent should be facultative so that it can be induced to self-pollinate when desired, thereby avoiding the maintenance of the male-sterile trait in the heterozygous condition. The ability to manipulate the restoration of fertility in GMS lines by environmental control is a desirable approach for the maintenance of these lines. This can lead to the production of 100% male- Received; March 13, 2006. Accepted; June 22, 2006. * Corresponding author (E-mail: mmasuda@cc.okayama-u.ac.jp).