Enhancing Resistance to Cercospora Leaf Spot in Mung Bean (Vigna radiata L.) through Bradyrhizobium sp. DOA9 Priming: Molecular Insights and Bio-Priming Potential

Mung bean (<i>Vigna radiata</i> L.), a vital legume in Asia with significant nutritional benefits, is highly susceptible to Cercospora leaf spot (CLS) caused by <i>Cercospora canescens</i>, leading to significant yield losses. As an alternative to chemical fungicides, bio-priming with rhizobacteria can enhance plant resistance. This study explores the potential of <i>Bradyrhizobium</i> sp. strain DOA9 to augment resistance in mung bean against CLS via root priming. The results reveal that short (3 days) and double (17 and 3 days) priming with DOA9 before fungal infection considerably reduces lesion size on infected leaves by activating defense-related genes, including <i>Pti1</i>, <i>Pti6</i>, <i>EDS1</i>, <i>NDR1</i>, <i>PR-1</i>, <i>PR-2</i>, <i>Prx</i>, and <i>CHS</i>, or by suppressing the inhibition of <i>PR-5</i> and enhancing peroxidase (POD) activity in leaves. Interestingly, the Type 3 secretion system (T3SS) of DOA9 may play a role in establishing resistance in <i>V. radiata</i> CN72. These findings suggest that DOA9 primes <i>V. radiata</i> CN72's defense mechanisms, offering an effective bio-priming strategy to alleviate CLS. Hence, our insights propose the potential use of DOA9 as a bio-priming agent to manage CLS in <i>V. radiata</i> CN72, providing a sustainable alternative to chemical fungicide applications.