Some factors that contribute to poor survival of rhizobia on preinoculated legume seed

Abstract

Preinoculation of seed is a convenient alternative method to inoculating seed on-farm. With preinoculation, a range of plant-growth and protection agents, polymer adhesives, colour pigments or dyes, and powder materials may be incorporated into an inoculant adhesive-slurry prior to seed coating. However, our recent point-of-sale surveys support findings of previous studies that survival of rhizobia on preinoculated seed is variable and can be poor. We focussed our research, both in the laboratory and at commercial facilities, on some of the factors that may contribute to poor survival of rhizobia on preinoculated seed. We found that rhizobial survival was affected by water quality; filtration improved cell survival but was not equal to distilled water. We also found that polymers affected cell survival differently for each rhizobial strain, and that slowing the desiccation rate reduced the cell rate of decline. Although fewer in cell number, older inoculant afforded more protection for survival of rhizobial cells. There is a need to test each ingredient and stage in the seed-coating process for compatibility to determine the best practices to promote rhizobial survival on seed. Failure to act on these factors prolongs the status quo of the findings from recent retail surveys.