PATHOLOGICAL STUDIES ON DOWNY MILDEW OF PEA CAUSED BY PERONOSPORA VICIAE (BERK.) CASP.F.SP.PISI (SYDOW) IN EGYPT

Six pea cultivars including those commercially important in Egypt were tested for their susceptibility to infect with Peronospora pisi. Sugar pea was the most susceptible cultivar to P. pisi followed by Mange tout and Little marvel cultivars. On the other hand, the lowest infection was found on Master B cultivar followed by Lincoln and Relavil cultivars. Examination of senescent foliage of severily mildewed plants of Sugar, the highly susceptible pea cultivar, indicated the presence of oospores stage of this pathogen under greenhouse and open field conditions in Egypt. Microscopic examination indicate that the oospores were observed in naturally and artificially infected leaflets, stems, petioles and tenderls. Artificial inoculation with co~ nidia suspention of P. pisi on Broad bean ( Vicino faba L) cv. Giza 153, onion (Allium cnpn) cv. Giza 1 and Green bean (Plwseolns vulgaris L.) cv. Branco proved to be immune to infect by pea downy mildew throughout the whole growing period, as no symptoms were noticed. So, the pathogen causing downy mildew on pea was identified as Peronospora viciae f.sp.pisi. Conidia survived better at lower temperature than at higher temperatures when an artificial inoculation was used in survival tests. Conidia deposited on pea leaves stored at lab temperature lost their viability after a week. However, conidia deposited on pea leaves stored in refrigerator carried viable conidia for 3 weeks. This means that P.pisi conidia survived best at 10°C and poorest at 25-28°C. Oospores either stored at lab conditions or in refrigerator recorded higher percentages of disease severity during winter season and survived during summer season, host - free periods, and recorded new infection on pea plants after a year .This means that conidia lost their viability during summer season and it is not responsible for disease occurrence from season to another. So, oospores formed in infected pea plants are important for the survival of the pathogen during host - free periods. Effect of spraying different fungicides for controlling pea downy mildew disease under field conditions in two locations during 2007-2008 seasons indicated that Privicure - N, Ridomil Gold plus 42.5% and Ridomil Gold Mz 68 % were the most effective fungicides in reducing percentage of infection and disease severity of downy mildew.