The Pigeonpea-RhizobiumSymbiosis as Affected by High Root Temperture: Effect on Nodule Formation

The effect of elevated temperature on root hair formation, adsorption of rhizobia, and nodulation of pigeonpea was studied. Nodulation was adversely affected at both 28°C and 37°C, and the effect was more pronounced during the first 3 d of nodule formation. Temperatures above 32°C resulted in the reduction or even complete absence of root hairs. The root hairs formed at elevated temperatures were spheroid and stunted in growth. The number of loosely and firmly adsorbed cells of Bradyrhizobium spp. (Cajanus) strain CC1021 on pigeonpea roots were reduced to 49% and 38%, respectively, at 37°C.