Effects of soil temperature, seeding depth, and seeding date on rhizoctonia seedling blight and root rot of chickpea

Rhizoctonia solani Kuhn, a prevalent fungal pathogen in cultivated prairie soils, can be an important factor affecting seedling establishment of chickpea (Cicer arietinum L.). Studies were undertaken to determine the impact of different soil conditions on seedling establishment, development of root rot, and productivity of desi (Tyson) and kabuli (Sanford) chickpea plants sown in the presence of R. solani AG-4. The impact of soil and air temperatures and seeding depth was studied under controlled conditions, and the influence of seeding date was investigated at three field sites. The host responded to warm soils by increasing its growth rate, and the pathogen by increasing its virulence. The kabuli cultivar, Sanford, showed greater susceptibility to root rot caused by R. solani than the desi cultivar, Tyson. Root rot and shoot infection levels increased with soil temperature for both cultivars, but reached maximum values at substantially lower temperatures for Sanford. Shoot biomass of infected treatments for this cultivar was substantially lower than the controls, while the biomass of Tyson was affected to a lesser degree. Air temperatures of 17/3degreesC day/night allowed relatively unhindered plant growth, even of the more susceptible cultivar, Sanford, in the presence of R. solani, while warmer and cooler temperatures resulted in high mortality and diminished plant growth in surviving plants. Seedling emergence and seedling dry weight were greater at a seeding depth of 2 cm than at 5 cm for seedlings grown in infested soil. In inoculated field plots, seedling emergence was greatest in treatments seeded in late May to early June compared those seeded in early or mid-May; in noninoculated treatments, both emergence and yield were lower in treatments seeded in late May than at the earlier seeding dates. Seeding date did not affect the occurrence of root rot.