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Foot rot or gummosis is considered one of the most devastating diseases of citrus plants responsible for orchard decline. Disease incidence of 20.50 to 37.27% was recorded in orchards and nurseries of different districts of Punjab. Soil samples were collected from the rhizosphere of orchard plants and nursery seedlings for identification of Phytophthoraspp., using morphological and molecular approaches. P. nicotianaewas found as the sole causal agent of foot rot/ gummosis in all the 40 isolates collected from different citrus growing regions of Punjab. The 40 isolates were grouped into two different clusters by UPGMA clustering using 17 SSR primer pairs. All the isolates from regions of Sri Muktsar Sahib, a few isolates from Hoshiarpur, Ludhiana and Sangrur were grouped in one cluster while all the isolates of Bathinda, Fazilka, a few isolates from Hoshiarpur and Ludhiana were in the second cluster. The representative isolates of P. nicotianaefrom these regions should be included in screening of planting material for disease resistance breeding programmes.

The intensity of scab caused by Streptomyces scabieson mother seed tubers significantly impacts the scab severity in the harvested crop. In the current study, it is revealed that scab severity on infected mother seed tubers and duration of crop directly affects the disease severity in progeny crop. Mother seed tubers with disease severity grade of 0, 1, 2, and 3 were sown with different crop duration periods of 70, 80 and 90 days. Significantly greater disease incidence and severity were recorded when seed tubers of infection grades 2 and 3 were sown (59.41 and 64.26% incidence; 6.7 and 7.2% severity, respectively). Significantly lesser scab incidence and severity were recorded at 70 DAP (35.64 and 2.4%, respectively) than at 80 and 90 DAP. It was also found that the disease incidence in 80 and 90 days old crop from mother seed tuber of infection grade 0 was statistically similar to disease incidence in 70/80/90 days old crop of mother seed tubers with infection grade of 2 and 3. Significantly maximum lesion grade was found in 90 days old crop sown from mother seed with scab severity grade 3. This shows that the scab incidence and severity increases in the crop with increase in the disease severity grades of mother seed tubers and increased duration of crop by delaying the harvesting interval. Hence, the strategy of planting seed tubers with minimum scab severity grade and harvesting the crop earlier, preferably at 70 DAP, can be utilized to lower the disease severity in progeny crop.

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.

Survival of Phytophthora nicotianaein relation to host, irrigation and rhizosphere soil was studied at Punjab Agricultural University, Ludhiana, between 2016 and 2018. Largest pathogen populations were recorded in the rhizosphere of seedlings grown in soil from infested orchards 21 months after transplanting. After fifteen months, the P. nicotianaepopulation density dropped to 0 cfu/ml of soil in inoculated and irrigated sandy and sandy loam soils without seedlings. The pathogen's propagules survived for 18 months in presence of irrigation water and for 9 months without irrigation and seedling in orchard infested soil. The seasonal population fluctuation was also influenced by environmental conditions including soil temperature and relative air humidity. The largest population was detected in the months of July–September, with temperature of 24 to 33 °C and relative humidity of 71 to 75%, while the smallest population was detected in April-June, with temperatures of 26 to 37 °C and relative humidity of 50 to 53%. Seedlings infected by P. nicotianaedisplayed a variety of symptoms including stem lesions, gummosis and retarded shoot and root growth.