Partial Fertility Restoration as Affected by Night Temperature in a Season-dependent Male-sterile Mutant Tomato, Lycopersicon esculentum Mill

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℃ and 28℃ 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℃ did not affect fruit-set but resulted in a better seed-set than a high night temperature of 18℃ in the greenhouse. Further, pollination of the plants in phytochambers also resulted in a better fruit- and seed-set at 12℃ than 24℃. In all cases, the influence of low temperature was more pronounced in autumn than in spring. Fruit-set was 70% at 12℃ and 46% at 24℃. Of these fruits, 50% at 12℃ and 10% at 24℃ 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.

トマトの雄性不稔 T-4 の部分稔性回復に及ぼす夜温の影響について調査した．2001年10月～翌年 6 月の期間，最低気温10℃以上に維持し28℃換気のビニールハウス内において，順次開花してくる花について開花当日に自家人工授粉を行って着果率，有種子果率ならびに種子数を調査した．10月～2 月は，ほぼ100％着果し，10月に着果した果実は有種子果であり，11月～2 月に着果した果実は，その80％近くが無種子の単為結果であった．3 月以降，着果率が徐々に低下し 5 月では着果率が10％以下で単為結果はなかった．有種子果 1 果当たりの種子数は，10月には50粒に達することもあったが，11月以降の低温期には数粒となり，気温が上昇する 4 月～6 月には 1～20数粒であった．秋季ビニールハウスの最低夜温12℃と18℃下で人工授粉を行ったところ，着果率に差はなく，有種子果率は12℃で高く種子数も多かった．さらに，ビニールハウス内で育成した T-4 株を夜温12℃と24℃の人工気象器内に搬入して人工受粉し，10日後にハウス内に戻した．その結果，春季は両温度区ともほとんど着果しなかった．秋季は夜温12℃で約70％（24℃では46％）着果し，その50％（24℃では10％）は有種子果であった．1 果当たりの種子数は 7～9 粒で両温度区間に差はなかった．また，野生型花粉の人工受粉により1果実当たり50～180粒の種子が得られたことから，雄性不稔 T-4 には雌ずい側に問題はないことが示されトマト 2 系ライン F1 種子生産の種子親として利用できる可能性が示唆された．

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