人工接種条件下におけるチャ赤焼病の病斑拡大と葉中の全窒素含有量及び葉の成熟度の関係

摘要

注射器を用いた人工接種条件下における赤焼病の病斑拡大と葉の全窒素含有量の関係を調べた．すべての接種日において，‘静印雑131’が‘やぶきた’より病斑が大きかった．各接種日とも上位葉ほど病斑が大きい傾向がみられたが，葉が成熟するほど上位葉と下位葉の差は小さくなった．葉中の全窒素含有量は上位葉ほど高かった．葉中の全窒素含有量と病斑の大きさとの間には，正の相関関係が見られた．以上の結果から，葉中の全窒素含有量が多い，未成熟なステージの茶葉は赤焼病感受性が高いことが推察された．%Tea bacterial shoot blight caused by Pseudomonas syringae pv. theae (Pst) is one of the major diseases in tea cultivation in Japan. The bacterial shoot blight resistance of Japanese tea cultivars has not yet been clarified with the exception of that of 'Shizu Inzatsu 131' , which has been shown to be extremely susceptible. Because epidemics of bacterial shoot blight occur irregularly, it is difficult to determine disease resistance from field observations. To developing a reliable inoculation assay, we investigated the effects of inoculation date, leaf position, and total nitrogen content of tea leaves on the development of bacterial shoot blight lesions. From 10 May to 28 June 2010, shoots of 'Shizu Inzatsu 131' (susceptible) and 'Yabukita' (moderately resistant) were collected and injected with Pst by using a syringe. The lesions on 'Shizu Inzatsu 131' were larger than those on 'Yabukita' after each inoculation. Lesions on the upper leaves were larger than those on the lower leaves after each inoculation, in each cultivar. Nitrogen content decreased from the upper leaves to the lower ones. There was a significant positive correlation between nitrogen content of tea leaves and lesion size in each cultivar at the 1% level. Total nitrogen content and maturity of tea leaves are among the environmental factors determining susceptibility to bacterial shoot blight.