Effects of High Temperature on Flowering and Pod Set in Soybean

Plants of soybean(cv.Enrei) were grown in pots(1/5000a) in a viny house. Temperature treatment was conducter for 10 days from the beginning of the flowering period(BFP) in the growth chambers under artificial light controlled at day/night air temperatures of 27/27, 32/27, and 37/27℃, respectively. the pollen viability at 37/27℃(89.4%) was significantly lower than 27/27℃(97.2%). In ouder to identify the sensitive stage to high temperature, the plants were treated for 2 days before BFP in the growth chambers controlled at 27/27 and 40/27 ℃, respectively, and the pollen viability of flowers opening after the treatment was investigates. By the treatment at 40/27℃, the pollen viability of flowers which opened at 4 days after the treatment(82.9%) was significantly lower than 27/27℃(97.3%). This indicates that floral buds at 4 to 5 days before flowering, which coincide with the microsporogenesis stage, are sensitive to high temperature. However, high temperature affected the pod setting ratio a little in both experiments. High temperature treatment was conducted by transferring the plants into the glasshouse under natural light before and after BFP. High temperature treatment at 7-1 days before BFP promoted vegetative growth and increased the pod setting ratio, while reducing the seed size. High temperature treatment at 14-8 days before BFP promoted floral differentiation on the second order racemes with compound leaves and increased the number of the floral buds, so that reduced the pod setting ratio. These results suggest that hight temperature at the microsporogenesis stage reduces pollen viabillity, however, pod setting ratio is affecter by the pollen viabillity.

ダイズ品種エンレイを供試し，雨除けハウス内でポット栽培を行った．開花始から10日間，昼/夜温を27/27，32/27，37/27℃に設定した人工光型グロスチャンバー内でダイズを育成し，処理９日目に開花前日の花蕾について花粉稔性を調査した．花粉稔性は27/27℃処理（97.2）に比べて37/27℃処理（89.4）で有意に低下した．高温に敏感な時期を特定するため，開花始前に２日間，昼/夜温を27/27，40/27℃に設定した人工光型グロスチャンバー内でダイズを育成し，処理後開花した花について花粉稔性を調査した．その結果，処理後４日に開花した花の花粉稔性が27/27℃処理（97.3）に比べて40/27℃処理（82.9）で有意に低下した．すなわち開花前４，５日が高温に特に敏感な時期であることが示され，この時期は雄性生殖細胞分裂期に一致した．しかし，両実験とも結莢率におよぼす高温の影響は小さかった．さらに，自然光下のガラス温室内で開花始前後の４週間について１週間ごとに高温処理を行い，収量成立過程におよぼす影響について検討した．開花始前７～１日の高温処理は栄養成長を促進し結莢率を高めたものの，百粒重を減少させたため，子実収量は対照区とほぼ同様となった．開花始前14～８日の高温処理は２次椏枝の花芽分化を促進しその花蕾数を著しく増加させた結果，結莢率が著しく低下した．以上の結果より，雄性生殖細胞分裂期の高温は花粉稔性を低下させるが，結莢率は花粉稔性よりも花蕾数や開花期の栄養条件によって大きく影響されることが示唆された．