Relationship between Japanese Pear Scab Development and Nutrients Content in Leaves on Trees Given Different Amounts of Nitrogen Fertilizer.

Abstract

The correlation between the development of Japanese pear scab (caused by Venturia nashicola) on leaves and the content of total nitrogen, total carbon, phosphorus, potassium, calcium, magnesium, iron and manganese in the leaves on trees given different amounts of nitrogen fertilizer was investigated. With an increase of nitrogen fertilizer, the content of total nitrogen and manganese in leaves increased while calcium content decreased. The content of total carbon, phosphorus, potassium, magnesium and iron did not show any obvious change. The ratio of diseased leaves, degree of disease development and degree of conidial formation increased with increasing amounts of given nitrogen fertilizer. Significant correlation (P=0.05) were recognized between total nitrogen content and the degree of disease development on 3rd and 7th position leaves from top leaf, the degree of conidial formation on 11th position leaf, calcium content and degree of disease development on 7th position leaf, and manganese content and degree of conidial formation on 7th position leaf. These results show that with an increase in nitrogen fertilizer there is an increase in total nitrogen and manganese content and a decrease in calcium content in leaves, and a higher susceptibility to Japanese pear scab was induced.