The effects of light and a photosynthetic inhibitor on the expression of the Lr20 gene for resistance to leaf rust in wheat

Abstract

A possible relationship between photosynthetic activity and the occurrence of hypersensitivity was explored. Most of these experiments exploited the temperature-sensitivity of the Lr20 gene which is expressed at 20 °C but not at 30 °C. Colonies of avirulent rust were thereby grown at 30 °C before transfer to 20 °C where necrosis and limitation of fungal growth occurred under normal conditions. Necrosis was largely prevented in leaves held under coloured cellophanes which filtered out photosynthetically active wavelengths of light. Necrosis was also prevented by application of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU). Despite the prevention of necrosis by DCMU, the avirulent rust grew very litde in the presence of the Lr20 gene. These results suggested that photosynthesis is involved in processes leading to necrosis in this system and showed that necrosis is not essential for expression of resistance to rust growth.