Effect of temperature and inoculum density on disease intensity of Phytophthora parsiana

ABSTRACT- The effects of inoculum density and temperature on the disease intensity of Phytophthora parsiana on almond seedlings were investigated. Almond seeds (Rabie and Kaghazi cultivars) were placed in moist vermiculite at ۴°C for ۴۵ days. Germinated seeds were sown in a soil: sand mixture (۲:۱ v/v) and grown in greenhouse (۱۸°C-۲۵°C). One-month-old seedlings were transferred from the greenhouse to the growth chambers set at ۱۵, ۱۸, ۲۰, ۲۵,۳۰ and ۳۲°C. The seedlings were subsequently inoculated either with mycelium of P. parsiana grown for ۴-۶ weeks on vermiculite amended with hemp seed extract or with zoospore (۱۰۳, ۱۰۴, ۱۰۵ and ۱۰۶ ml-۱) by root dip method. The effect of temperature, inoculum density and their interaction on seedling mortality was measured. The results indicated that all three factors had significant effects on seedling mortality. While the highest disease incidence (۱۰۰% mortality in almond seedlings) occurred at ۳۰°C and ۳۲°C, no mortality was observed at ۱۵°C and۱۸°C. Increasing temperature from ۲۰°C to ۳۰°C and inoculum rate from ۱۰۳ to ۱۰۶ zoospores ml-۱ increased disease incidence significantly. Higher temperatures and inoculum densities also caused significant increases in the colonization level of the crown, main and lateral roots as well as reductions in the fresh and dry root weights of the seedlings.

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Keywords: ، Almond ، high temperature ، pathogenicity ، root rot