The influence of high temperatures on the growth and survival of Rhizobium spp. in peat inoculants during preparation, storage, and distribution

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Abstract
.gamma.-Irradiated peat was used to prepare inoculants for 10 spp. of tropical legumes. These inoculants were sent to cooperators in 14 cities in 13 tropical countries. Each cooperator received a package containing maximum recording thermometer, plating-media components, special instruction sheets and inoculants. Control experiments were pursued in the laboratory by exposing the various inoculants to 28.degree., 37.degree. and 46.degree. C. Temperatures reached in the inoculants during their transportation varied from 26.degree. (Mexico) to 45.degree. C (Kenya). Arrival time of the inoculants ranged from 6 days (Hissar, India) to 54 days (St. Augustine, West Indies). Although a total loss of variability was reported for chick-pea inoculant (Saudia Arabia) and a severe decrease in 2 others (bean and lentil inoculants in Kenya and Suadi Arabia, respectively), > 90% of the inoculants received had viable counts > 1 .times. 108 cells/g of moist peat. Laboratory data indicated that 28.degree. C was optimal for multiplication to maximal numbers > 1 .times. 1010 cells/g of moist peat. Six inoculants studied for long-term storage showed excellent quality for 24 wk at 28.degree. C. At 37.degree. C the cell multiplication was comparable with that at 28.degree. C with 8 of the 10 strains only during the 1st wk. For all strains, 46.degree. C was lethal. Large reductions in viable counts were observed during inoculant preparation when broth cultures were added to peat.