Antifungal and Organic Matter Degradation Activities of Rhizobacteria Associated with Pseuderanthemum palatiferum (Nees) Radlk in Tay Ninh Province, Vietnam

Pseuderanthemum palatiferum (Nees) Radlk is an indigenous Vietnamese medicinal plant cultivated extensively in Tay Ninh province for the production of health-supplement. Building upon a previous discovery of beneficial rhizosphere bacteria, this study evaluated 27 plant growth-promoting rhizobacteria (PGPR) strains for their organic matter degradation and antifungal capabilities. Organic matter decomposition was assessed using the agar well diffusion method. Among the 27 isolates, 13 degraded protein, 16 degraded starch, 20 degraded chitin, and 19 degraded cellulose, with maximum hydrolysis zone diameters reaching 22 mm, 35 mm, 19 mm, and 18 mm, respectively. Antifungal activity against two phytopathogens, Colletotrichum sp. and Fusarium sp., was evaluated via parallel streak co-culture assays. Only two strains, HNR10 and HNR13, exhibited antifungal activity. Strain HNR10 demonstrated superior efficacy, achieving 7-day inhibition rates of 50.00% against Colletotrichum sp. and 55.80% against Fusarium sp. Based on MALDI-TOF MS analysis, the prominent isolates HNR10, HNR13, and the high-performing degrader HNR27 were identified as Lysinibacillus sphaericus, Alcaligenes sp., and Enterobacter bugandensis, respectively. These findings highlight the potential applications of P. palatiferum-associated PGPR in sustainable agriculture.