Seed Endophytic Bacteria from Manilkara zapota L. and Their Influence as Rice Seed Priming Agents

In recent years, seed endophytes have gained significant attention due to their impact on the ecology, health, and productivity of host plants. Extensive research is being conducted to explore novel endophytic bacteria for sustainable crop improvement. Manilkara zapota L. P. Royen (Sapotaceae) is a highly stress-tolerant tree widely cultivated in tropical countries, yet its associated endophytes remain unexplored. In this study, nine bacterial isolates were obtained from M. zapota seeds, of which three (LA2, LA4, and NS1) were selected based on their IAA production capability which ranged from 2.3, 6.34, and 16.1 µg mL^-1, respectively. Identification through 16S rRNA sequencing confirmed LA2 as Pseudomonas rhodesiae, LA4 as Bacillus cereus, and NS1 as Enterobacter cloacae. All isolates exhibited nitrogen-fixing ability, while NS1 uniquely solubilized potassium and phosphorus with KSI and PSI value as 2.9 and 2.3, respectively. Further, the efficacy of the bacterial isolates in promoting rice seedling growth was evaluated, and novel bioformulation was prepared from the consortia of LA2 + LA4, LA2 + NS1, LA4 + NS1, and LA2 + LA4 + NS1. All the isolates and bioformulations were tested as biopriming agents. Rice seedling growth experiments revealed a significant increase in germination percentage, root length, and shoot length following biopriming with individual isolates and consortia. Among treatments, the LA2 + LA4 combination exhibited the highest growth promotion, with a root length increase of 2.1-fold and shoot length increase of 2.3-fold as compared to control. Thus, our results highlighted that bioprospecting microbes from M. zapota seeds can help in nutrient management and seedling establishment.