Growth and survival of cowpea bradyrhizobia in various carrier materials

Abstract

Pakistan does not yet have the technology for commercial production ofRhizobium andBradyrhizobium inoculum. Therefore, investigations were undertaken to evaluate the suitability of different materials like compost, sawdust, rice husks, sugar cane, filter mud, and peat asBradyrhizobium carriers. The growth and survival of bradyrhizobia (strain TAL 441 of the cowpea type) was studied in sterilized and unsterilized carriers mixed with loam and enriched with lucerne meal and sucrose. Three different sterilization methods (autoclaving, gamma irradiation, and dry heating of the carriers) were used. The growth and survival of bradyrhizobia in the inoculants were studied at two different storage temperatures, 4° and 20°C. After 2–21 months of inoculation, maximum survival of rhizobia (7.6 × 109 cells g−1) was observed in autoclaved filter mud containing loam-lucerne meal and sucrose. The survival of rhizobia in autoclaved peat was 3.4x 109 cells g-t. The maximum viable number of rhizobia per seed of mungbean (Vigna radiata) was 7.7 × 108 in gamma-irradiated compost and least (1 × 107 cells seed−1) in rice husks.