Relationship of weather and plant microclimate parameters to rhizoctonia aerial blight development in soybean

Rhizoctonia aerial blight (RAB), caused by Rhizoctonia solani Kühn, is a major constraint to soybean production. This study evaluated weather and plant microclimate effects on RAB development using a split-plot design (two genotypes as main-plot, five sowing dates as sub-plot) over two kharif seasons (May-October, 2022–2023) at Jorhat, Assam, in India. Minimum temperature and evaporation showed the strongest negative correlations with disease severity ( r = − 0.86 to − 0.87, p < 0.01); soil moisture was positively correlated ( r = 0.68–0.91, p < 0.01). Disease severity, AUDPC, infection rate, weather, and microclimatic parameters were monitored weekly. Disease severity increased progressively with crop age ( p < 0.001) and was higher under early sowing. The highest severity occurred in JS 335 sown on 17 May (35.61% PDI; AUDPC 237.90), while the lowest occurred in KDS 753 sown on 1 and 16 July (16.34% and 14.73% PDI; AUDPC 102.92 and 105.16; p < 0.001). Treatment-specific stepwise regression equations explained 73.3–92.7% of the observed severity variability (adjusted R² = 0.706–0.900), but they were fitted and evaluated using the same two-season, single-location dataset and therefore represent exploratory fitted relationships rather than independently validated forecasting models. Lower disease severity in late-sown treatments is interpreted as reflecting a shorter epidemic window and altered weather exposure across phenological stages rather than an independent causal effect of sowing date. This study would support in the development of forecast models to assess soybean RAB risk in the hot and humid areas.