Spatial distribution of Phytophthora nicotianaein citrus rhizosphere

Foot rot disease of citrus is a major limiting factor for flourishing citrus industry across the world. The population of Phytophthora nicotianaewas found to be significantly maximum in rhizosphere at 0–8 in. soil depth (96.9 cfu/cc soil) and lowest (0.6 cfu/cc soil) at 16–24 in.. A strong positive correlation of root density (+ 0.98) with the population counts was recorded. The immunostrips specific for Phytophthoraspp. also had positive reaction with the rhizosphere soil sample collected from 0 to 8 and 8 to 16 in while it was negative with soil collected from 16 to 24 in. depth. PhytophthoraDNA was amplified and detected from depth of 0 to 8 and 8 to 16 in. in rhizosphere of infected plants while no amplification was observed from DNA extracted from rhizosphere soil at 16–24 in. depth. It reveals that the population count of Phytophthoradecreases with increase in soil depth. Maximum population was recorded in the months of July–September receiving maximum rainfall and having temperature range of 28.0–32.5 °C along with relative humidity of 71.5–75.0%. A strong correlation of population propagule densities was recorded with weather factors like rainfall and soil temperature.