Oligonychus coffeae (Acari: Tetranychidae), popularly known as red spider mite (RSM) is one of the major pests of commercial tea (Camellia sinensis (L.) O. Kuntze) plantation world over. Many attempts have been made in the past to control this devastating pest using a variety of microbial bioagents, however, area-wise field success is very limited. We carried out an in vitro study to explore the potential of rhizospheric Bacillus spp. (B. amyloliquefaciens BAC1, B. subtilis LB22, and B. velezensis AB22) against O. coffeae through adulticidal and ovicidal activity. The 100% adult and egg mortality was observed with bacterial suspension (1 × 10⁹ CFU/mL) by B. velezensis AB22, showing the lowest LC₅₀ values for both adults and eggs of O. coffeae, i.e., 0.28 × 10⁵ and 0.29 × 10⁵, respectively. The study also throws some insights into the underlying mechanism through electron microscopy study and identification of some putative pesticidal metabolites from all the species. The three Bacillus species were observed to have four commonly secreted putative bioactive secondary metabolites, brevianamide A, heptadecanoic acid, thiolutin, and versimide responsible for their bio-efficacy against O. coffeae. The outcome of our study provides a strong possibility of introducing Bacillus spp. as a biological miticide and developing synthetic metabolites mimicking the mechanistic pathway involved in microbial bioefficacy.

Plant-beneficial microbes are a perennial ally in an agroecosystems, providing multiple benefits to crop plants. The present study explored the potential of two microbial biocontrol agents (MBCAs), viz., Trichoderma asperellum and Pseudomonas fluorescens, against the bacterial blight pathogen of rice, Xanthomonas oryzae pv. oryzae. In vitro, MBCAs resulted in significant inhibition of X. oryzae pv. oryzae, as evidenced through the distortion of pathogen cell morphology and formation of a pathogen biofilm. Pot studies on the effect of MBCAs in rice showed increased germination, increased vigor index of seedlings, increased tiller numbers, a 10.29% reduction in percentage disease incidence (PDI), and low disease severity following individual inoculation. Activity of plant defense enzymes also increased with MBCA treatment (phenylalanine ammonia-lyase, 2.7-fold increase; peroxidase and polyphenol oxidase, 5-fold increase), establishing the priming effect of MBCAs on host defense. The quantitative polymerase chain reaction data revealed that pathogenesis-related genes (OsPR1a, OsPR1b, and OsPR10a) and X. oryzae pv. oryzae resistance genes (Xa1 and Xa26) were upregulated 4- to 14-fold in MBCA-treated rice plants over control plants. These results provide insights into the phenological, physiological, and molecular responses of rice crops treated with MBCAs in the presence of X. oryzae pv. oryzae and could be used to develop an effective field management strategy.

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is recognized as one of the most devastating diseases affecting banana cultivation worldwide. In India, Foc extensively affects Malbhog banana (AAB genomic group) production. In this study, we isolated 25 Foc isolates from wilt-affected Malbhog plantations inIndia. A pathogenicity test confirmed the identity of these isolates as Foc, the primary causative agent of wilt in bananas. The morpho-cultural characterization of Foc isolates showed large variations in colony morphological features, intensity, and pattern of pigmentation, chlamydospores, and conidial size. The molecular identification of these isolates using Race1- and Race4-specific primers established their identity as Race1 of Foc, with the absence of Tropical Race 4 of Foc. For a more comprehensive understanding of the genetic diversity of Foc isolates, we employed ISSR molecular typing, which revealed five major clusters. About 96% of the diversity within the Foc population indicated the presence of polymorphic loci in individuals of a given population evident from the results of Nei’s genetic diversity, Shannon’s information index, and the polymorphism information content values, apart from the analysis of molecular variance (AMOVA). The current findings provide significant insights toward the detection of Foc variants and, consequently, the deployment of effective management practices to keep the possible epidemic development of disease under control along the Malbhog banana growing belts of northeast India.

Fusarium wilt, caused by Fusarium oxysporum f.sp. cubense (Foc), is recognized as one of the most devastating diseases affecting banana cultivation worldwide. In India, Foc extensively affects the Malbhog banana (AAB genomic group) production. In this study, we isolated 25 Foc isolates from wilt-affected Malbhog plantations of India. Pathogenicity test confirmed the identity of these isolates as Foc, the primary causative agent of wilt in banana. Morpho-cultural characterization of the Foc isolates showed large variation in colony morphological features, intensity, and pattern of pigmentation, chlamydospores, and conidial size. The molecular identification of these isolates using Race-1 and Race-4 specific primers established their identity as Race- 1 of Foc, with absence of TR- 4. For a more comprehensive understanding of genetic diversity of Foc isolates, we em-ployed ISSR molecular typing which revealed five major clusters. Ahigh96% diversity within Foc population indicated the presence of polymorphic loci in individuals of a given population evi-dent from results of Nei’s genetic diversity, Shannon information index, and polymorphism in-formation content values, apart from analysis of molecular variance (AMOVA). The current findings provide significant insights towards detection of Foc variants, and consequently the deployment of effective management practices to keep the possible epidemic development of disease under control along Malbhog banana growing belts of northeast India.

Production sustainability of perennial fruit crops has always been challenged by changing dynamics of diseases, more so with ongoing patterns of climate change. Efforts have been made to analyze the reasons behind the repeated failures to address the management of many diseases in fruit crops using conventional approaches. The stronger application of nextgeneration sequencing and other biotechnological tools in disease resistance breeding, the role of microbial antagonists in developing wide spectrum bio-formulations, and elevating plant nutrition vis-s-vis plant immunity are suggested to come of age in developing some time-tested strategies for fruit crops to display production sustainability, besides the development of next-generation bio fungicides and nano-biofungicides. Understanding the interplay between hosts and pathogens concerning plant immunity in regulating or neutralizing the invading pathogen is still an enigma with many unresolved mysteries.