栽培温度がダイズの生育および感染ダイズ根粒菌の群集構造に及ぼす影響

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地球温暖化に伴う気候変動の作物生産への影響に関する基礎的知見の蓄積の一環として，異なる栽培温度環境下におけるダイズの生育と有用ダイズ根粒菌の接種効果および感染ダイズ根粒菌群集構造への影響について調査を行った．供試ダイズ品種として，‘オリヒメ’，‘ボンミノリ’，‘フクユタカ’を用い，供試菌株としてBradyrhizobium diazoefficiens USDA110Tを用いた．栽培は温度傾斜型チャンバー内で行い，低温区，中温区，高温区を設けた．異なる温度環境下での栽培試験の結果，無接種区と比較して，USDA110の接種により主茎長，主茎節数，茎葉乾物重，莢数，莢乾物重，地上部乾物重，根粒数が有意に増加したが，栽培温度の上昇により根粒数を除く項目が有意に減少した．各調査項目間の相関係数は根粒数と茎葉乾物重との関係など多くの組み合わせにおいて有意な正の相関関係を示した．USDA110の根粒占有率は，全ての温度区で接種したUSDA110が優占したが，低温区と中温区，低温区と高温区を比較すると栽培温度の上昇により減少する傾向を示した．以上の結果から，高温環境下では根粒数が減少することでダイズの生育が抑制され，その後の生育や収量に影響すると考えられた．しかし，根粒数とUSDA110の根粒占有率を確保することができれば栽培温度の上昇によるダイズの生産性低下を抑制することができると考えられる．

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We investigated the growth of soybean (Glycine max (L.) Merr.) under different cultivation temperature conditions, and the inoculation effect of useful bradyrhizobial strain and the community structure of infected soybean-nodulating bradyrhizobia to elucidate the effects of climate change on crop production due to global warming. “Orihime,” “Bonminori,” and “Fukuyutaka” were used as the test soybean cultivars, and Bradyrhizobium diazoefficiens USDA110T was used as the test strain. The soybean was grown in a temperature-gradient chamber with low-temperature zone, middle-temperature zone, and high-temperature zone. The results of cultivation test under different temperature conditions showed that inoculation with USDA110 significantly increased plant height, number of nodes, stem and leaf dry weight, the number of pods, pod dry weight, total plant dry weight, and number of nodules. However, all investigation items, except for the number of nodules were significantly reduced with increasing cultivation temperature. Correlation coefficients were significantly positive in many combinations, including the relationship between the number of nodules and stem and leaf dry weight. The occupancy of USDA110 was dominated by inoculated USDA110 in all cultivation temperature zones. However, the occupancy tended to decrease with an increase in cultivation temperature when comparing low- and middle-temperature zones and low- and high-temperature zones. These results suggest that the decreased number of nodules under high-temperature conditions inhibited soybean growth, reducing the growth and yield of soybean. However, the reduction of soybean productivity due to the increase in cultivation temperature may be reduced by ensuring the number of nodules and occupancy of B. diazoefficiens USDA110T．