Can Coir Pith-Starch-Plant Growth Promoting Rhizobacteria Composite Sustain Zea mays Seedling Survival and Growth under Flood (Waterlog) Condition?

Abstract

Aim: This study was conducted to formulate and evaluate the efficacy of a composite: coir pith + starch + plant-growth-promoting rhizobacteria (PGPR), in sustaining the survival and growth of Zea mays (maize) seeds cultivated under flood stress. Place and Duration of Study: Department of Microbiology Laboratory, Federal University Otuoke, Bayelsa State, Nigeria, between May and July 2024. Methodology: Rhizobacteria were isolated, screened for plant-growth-promoting (PGP) traits; phosphate solubilisation and indole-3-acetic acid (IAA) production and further tested for PGP activity via seed germination bioassay. Composites were prepared by homogenizing coir pith, starch gel and standardized PGPR inoculum at a ratio of 2:24:20 (w/v), pelleted and dried at 28 oC. The efficacy of the composites was examined in a pot experiment by measuring shoot length (SL), root length (RL) and plant height (PH), of the treated maize seeds. Treatments were conducted in two sets (single composite pellet and 4 composite pellets); Set 1 (seeds + 1 composite pellet/pot, Control 1 and Control 2), Set 2 (seeds + 4 composite pellets/pot, Control 1 and Control 2). Controls 1 and 2 were; seeds + coir pith + starch only and maize seeds only, respectively. Set 1 was monitored for 2 weeks, and Set 2 for 7 days. Flood conditions were simulated by saturating the pots with water, without drainage, for 3 days. Results: Five rhizobacteria were isolated; LCE tested positive for IAA production and phosphate solubilisation, SPP tested positive for IAA production only, and C tested positive for phosphate solubilization only. The growth performance of treated maize seeds under waterlogged condition in Set 1 indicated that the Control 1 (maize seeds + 1 coir pith + starch only pellet) was more effective than Control 2 and the other composites. The treatments in Set 1 did not support maize seed growth throughout the two-week monitoring period, except control 1 (maize seeds + 1 coir pith +starch only) which sustained seed survival and growth for 2 weeks. One way ANOVA indicated that the mean growth for control 1 was the same across the weeks as the p-value (p = 0.658) is greater than the 5% significance level (α = 0.05). In Set 2, at day 7, the observed survival and growth of maize seeds treated resulted from the application of 4 coir pith+starch+LCE (Priestia flexa) pellets. The mean SL, RL and PH recorded for the seeds were 2.6±0.2, 3.6±0.45 and 15.9±0.45 cm, respectively. LCE was identified by 16S rRNA sequencing as Priestia flexa. Conclusion: This study demonstrates the potential of coir pith+ starch+Priestia flexa to mitigate waterlogging stress, sustain survival and growth of Zea mays seedlings.