カキ'西条'における樹上軟化発生の原因と早生系統間差(栽培管理・作型)  [in Japanese] Cause of Pre-harvest Fruit Softening and Comparison among Early-Ripening Strains of Japanese Persimmon 'Saijo'(Crop Production & Cropping Type)  [in Japanese]

カキ'西条'の早生6系統における樹上軟化発生の系統間差とその原因および防止方法について検討した.7〜9月の降雨が多い年においても,"遠藤","山坂"および"安部"の各系統は細根活性の低下がみられず,果実のエチレン発生量が低く推移し,樹上軟化の発生が少なかった.湛水処理後10日頃に,果実のエチレン発生量が極めて多くなり,その後著しい落葉と落果がみられた.これに対して,遮光処理では,果実のエチレン発生量が少なく,落葉および落果は対照区と同程度に少なかった.したがって,樹上軟化発生は土壌の過湿により促進されるものの,日射不足はほとんど影響を及ぼさないと考えられた.7月下旬以降の多孔質マルチの土壌全面被覆によって,土壌の水分変動が少なくなり,pF値2.3程度で推移した.それにより,果実のエチレン発生が抑えられ,樹上軟化発生が抑制される傾向がみられた.以上より,樹上軟化は次の2過程が続いて生じた場合に起こりやすいと考えられた. (1)果実発育後期の長雨により地下部の通気不足が生じる(2)その後の高温や強風による蒸散,水ストレスによる果実のエチレン生成が高まる.

Pre-harvest fruit softening, so-called "On-tree early softened fruit", in which maturation is abruptly accelerated and over-ripened prior to harvest for certain physiological reasons, was compared among 6 strains of the "Early B" types of Japanese persimmon 'Saijo'. We also examined the cause and methods of preventing this phenomenon. Pre-harvest fruit softening was less frequently observed in the "Endo", "Yamasaka", and "Abe" strains than in "Koto" strain, even in years with heavy rain during July to September. In these strains, relatively higher activities were found in the fine roots, and except in "Koto", there were lower levels of ethylene evolution in the fruit during early September to late October. A remarkable ethylene evolution was observed in fruit on about day 10 of flooding treatment, then heavy falls of leaf and fruit were observed. On the contrary, however, shaded trees did not show increased ethylene production in fruit, and caused few or no falling leaves and fruit. This was also observed in untreated trees. Accordingly, the disorder might be promoted not by shortage of sunshine, but by high moisture in the soil. Soil moisture in late July to October was little changed by a "White porous water proof sheet" covering the soil under the tree crown, the pF value of soil at a depth of 15cm was 2.3 through out the period. Ethylene release from fruit, and the occurrence of pre-harvest fruit softening were considerably reduced by mulching with a water proof sheet. From the above results, it was considered that the pre-harvest fruit softening was induced mostly through the following 2 process; (1) At the late stage of fruit maturity, flooding condition by continuous rainfall blocks aeration in root, and the ethylene precursors (ACC) are accumulated in fruit. (2) Thereafter, waters are actively vaporized from fruits by exposure to high temperature during the following fine and windy days, and ethylene release in fruit under water stress, resulting in rapid fruit softening.