Lipa Deb

Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt in tomato, posed a significant threat to tomato cultivation. This study investigated the biocontrol potential of yeast isolates and Arbuscular Mycorrhizal Fungi (AMF) against this pathogen. Soil and phyllosphere samples were collected from tomato fields in Tamil Nadu, India, leading to the isolation of 120 yeast strains using serial dilution and leaf imprinting techniques. Morphological characterization grouped the isolates with 35 unique colonies were selected for further analysis. Molecular characterization identified three key yeast isolates: Rhodosporidium toruloides (Y2), Moesziomyces antarcticus (Y14) and Pichia kudriavzevii (Y16). Under pot culture conditions, the combined application of AMF and yeast isolates significantly reduced Fusarium wilt incidence. Treatment T5 (AMF liquid-based inoculum + soil yeast Y14) exhibited the highest root colonization (86.66 %), maximum spore load (10397 spores) and minimal disease incidence (11 %), with an 89 % disease reduction compared to the control. This treatment also enhanced tomato plant growth metrics, including height (121.00 cm), root length (61.10 cm) and antioxidant enzyme activity (peroxidase: 0.392 min/g, polyphenol oxidase: 0.791 min/g). Yield parameters were also improved, with maximum fruit weight (19.45 g) and fruit count (6.24) observed in T5-treated plants.

Beauveria bassiana, a potential entomopathogenic biocontrol agent, has recently drawn attention worldwide for its other additional beneficial roles such as plant disease antagonist, beneficial rhizosphere colonizer, plant growth promoter and an endophyte. In the present study, endophytic colonizing behaviour of five (5) B. bassiana isolates viz., Bb4, Bb16, Bb25, Bb44 and Bb53 were studied in rice following three (3) artificial inoculation techniques viz., seed treatment, root inoculation and foliar spray and the endophytic colonizing ability were determined by culture-based assay. After B. bassiana inoculation, rice plants were challenged with Rhizoctonia solani and disease incidence and plant growth promotion were assessed. Per cent colonization of rice stems, leaves and roots were influenced by inoculation technique, post-inoculation time (7th, 14th, 21st and 28th dpi) and plant growth medium (sterile soil, non-sterile soil), recorded maximum on 14th-day post-inoculation (dpi) i.e., 96% in stems, 92% in leaves and 28% in roots, whereas, lower colonization was recorded on 7th, 21st and 28th dpi. Whereas, the foliar spray was found best as compared to seed and root inoculation techniques, and maximum fungal recovery was observed in stems and leaves and least in roots. Upon colonization, the physical presence of B. bassiana in rice was localized by light microscopy-based studies. Potential B. bassiana strains with endophytic ability were re-isolated and their identity was determined based on morphometric and PCR-based techniques. Further, the present study also identified several virulent genes viz., BbChit1, Cdep1, Bbhog1 and Bbjen1 and extracellular hydrolytic enzymes viz., α-amylase, cellulase, lipase, pectinase and xylanase secreted by endophytic B. bassiana strains as determinants responsible for establishing the endophytic association in rice. On the other hand, a significant reduction in disease incidence was observed in the endophytic B. bassiana Bb4-, Bb16- and Bb44-inoculated plants as compared to the non-endophytic B. bassiana Bb25- and Bb53-inoculated plants along with enhanced plant growth promotion. This is one of the few studies investigating the colonization of B. bassiana in rice and its promising role as a plant disease antagonist and plant growth promoter in rice.