The effect of temperature and relative humidity on the airborne concentration of Pyricularia oryzae spores and the development of rice blast in southern Spain

Abstract

The rice (Oryza sativa L.) cultivars Puntal and Thaibonnet were used in a field trial designed to investigate how temperature and relative humidity affect the airborne concentration of Pyricularia oryzae spores and the development of rice blast. A relative humidity of 95% and an average temperature of 26-27 deg C were optimum for infection and substantially favoured spore release. The first symptoms of infection were detected on the leaves when the crop was at the mid-tillering stage, the number of lesions increasing as the plant developed. After the onset of heading the number of leaf lesions decreased while the number of node and panicle base lesions increased. A temperature increase of 1 deg C in early August (mid-tillering stage) led to an increase in the mean intensity of disease. The presence of spores in the air from July 15th predicted the appearance of leaf lesions a few days later. The peak spore concentration in August could be used to forecast panicle blast. Assessing the airborne concentration of P. oryzae could help in understanding the population dynamics of this pathogen.