Pathological and physiological studies of Downy Mildew of Basil (Ocimum basilicum) Caused by Peronospora belbahrii in Egypt

Document Type : Original Research Papers

Authors

1 Plant Protection Dept., Desert Research Center, Cairo, Egypt

2 Plant Pathology Dept., Faculty of Agriculture in Moshtohor, Benha Univ., Benha, Egypt

Abstract

Basil is the most commercially significant medicinal and aromatic plant, used both fresh and dried, as well as a source of essential oil for perfume and food flavor manufacture. Basil's main composition includes a significant amount of antioxidants and antimicrobial agents. The obligate, biotrophic oomycete pathogen Peronospora belbahrii Thines causes basil downy mildew (BDM). It became a very destructive disease that has caused severe damage and crop loss of sweet basil in Egypt and worldwide. A field survey for disease severity (DS) and disease incidence (DI) of BDM was done in basil cultivation areas in Egypt during two successive growing seasons 2019-2020. The highest percentage of (DS) and (DI) of BDM was (93% and 100%) in 2019 and (95% and 100%) in 2020 in Nassir city of Beni Suef Governorate. Laboratory studies indicated that the highest percentage of spores germination was 33% at temperatures 18oC and the lowest was 3% at 12oC, while no spores germinated at 10oC., the relative humidity percentages 100% and 95% were the most suitable for the highest germination percentage (35% and 33%). The effect of light and dark hours interval (12 hours of light and 12 hours of darkness) was the most suitable for the highest percentage of spores germination (30%). Pathogenicity test by detached leaves method explained that the sporangiophores of P. belbahrii appeared after two days from infection and the severity increased until the 4th day when the whole leaf was infected. Pathogenicity test under greenhouse condition revealed that P. belbahrii severity and incidence reached (96.6 and 100%, respectively) 7 days post-inoculation in case of sowing basil (Baladi cv.) by seeds while in case of using transplants the disease severity and incidence reached (91.4 and 100%, respectively) at 10 days post-inoculation. The varietal reaction of some basil cultivars to BDM under greenhouse showed that Lemon Basil O. americanum var. citriodorum had the lowest disease severity and incidence (11.0% and 21.6%)

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