Effect of Carrier Materials, Coinoculation and Sterilization on Survival of Plant Growth Promoting Microbes

Abstract

The study was conducted to investigate diverse carrier materials out of agricultural and environmental waste, that plays a role in maintaining the shelf life of plant growth promoting microbes (PGPM) at room temperature for locally produced inoculants in Malawi. Five different formulations divided into sterilized and unsterilized were prepared, using different carrier materials namely; rice bran plus plant extract (RBP), biochar plus plant extract (BP), Filter mud plus plant extract (FMP), rice bran, biochar and plant extracts (RBCP), filter mud, biochar and plant extracts (FMBP). Carrier materials were packed in polyethylene pack (six per each treatment), thereafter each treatment was divided into sterilized and unsterilized. Each treatment was inoculated with either single or multiple inoculants. Survival of PGPM, was based on colony forming units (CFU) on specific selective media namely: modified yeast extract mannitol, pikovskaya’s, Alexandria and basal media for nitrogen fixing microbes, phosphate, potassium and zinc solubilising media respectively. Results revealed that encapsulated formulation of based combination formulation of RBCP in both single and multiple inoculants exerted high stable numbers of PGRM along the storage compared to other formulations. The results also show that unsterilized formulations exert high numbers compared to sterilized which is as a result of hydrogen peroxide accumulation during sterilization. The study reveals that filter mud based formulations currently used in both single and multiple inoculants is not favorable for local environments because microbial numbers decrease after 20 days at room temperature. This makes filter mud formulations usage not favorable for rural smallholder farmers with no refrigeration facilities.