SUMMARY Cowpeas, inoculated with one of five effective strains of Rhizobium isolated from African soils, were grown at root temperatures of 30 oC continuously or at 36, 38, 40, 42 and 44 oC for 5 h/day and returned to glasshouse ambient for the intermediate period. Growth was best at 30 and 36 oC; above 40 oC growth was poor and no nodules formed. At 40 oC two strains failed to nodulate. Symbiotic performance was not dependent only on nodule production as nodule efficiency varied inversely with temperature. The number of nodules formed by strain R5000 after exposure of inoculated seed or seedlings to 40,42 or 44 oC for 5 h/day on each of 3 or 6 days depended on the age of plant and the duration of exposure to stress. When exposed to 42 or 44 oC during the first 3 days after sowing nodulation was reduced from 18 to 1–3 nodules/plant even after a further 40 days growth at ambient (30 day, 20 oC night). Nodulation was unaffected when 10–15‐day‐old seedlings were exposed to the same conditions. Numbers of strain R5000 on seed declined rapidly following three daily exposures of 5 h at 39 and 42 oC; at 45 oC less than three bacteria survived on each seed. Other rhizobia of the cowpea group varied greatly in their toleration of high temperatures, some survived well at 45 oC whereas others behaved like R5000.
No takes yet. Share an insight, caveat, or question.
Day et al. (1978) studied this question.