Influence of shading on the development of podosphaera leucotricha under field conditions

Abstract

The influence of shading on the incidence and development of P.leucotricha was examined at the locality of Belgrade, during 2008 and 2009. Investigation was carried out on two-year old apple nursery trees, cultivar Idared, sensitive to causal agent of apple powdery mildew. The experiment included three variants, two with different conditions of reduced light (24h and 48h shading, with 24h in the natural photoperiod) and the third variant, which included the cultivation of plants in natural photoperiod, without shading. Reduced light conditions were achieved by growing the plants under wooden experimental boxes. The boxes provided minimum differences in air temperature and RH values, inside and outside them. Inoculum was provided from two trees that were close to the experimental boxes, and the infection was carried out by direct application of conidia from infected young shoots and naturally, during growing period. Four assessments were made, three during shading period and one after removal of the experimental boxes. In both. years of investigation, the highest intensity of infection was manifested in the first variant (48h shading, 24h natural photoperiod), (14.0 - 100%), slightly lower in the second (24h shading, 24h natural photoperiod), (12.7 - 93.5%) and the lowest in variant of normal photoperiod, (0.1 - 16.6%). In shading variants, intensity of infection was rapidly increasing from the first to the third assessment, while in the fourth assessment, after the removal of boxes, it significantly decreased. The results of these studies indicate that light intensity significantly affects the appearance and development of P. leucotricha, and that apple powdery mildew develops intensively in the shade environmental conditions.