Identification and Distribution of Meloidogyne incognita in Common Bean Cultivation: A Case Study from Eastern Dry Zone of Karnataka, India

Aims: This study aimed to identify and characterize the Meloidogyne species affecting common bean (Phaseolus vulgaris L.) fields in the Eastern Dry Zone of Karnataka, India and to assess the relationship between nematode population and environmental factors influencing their distribution. Study Design: A field survey-based study with morphological, molecular and ecological analysis. Place and Duration of Study: The study was conducted in sixteen locations across the Eastern Dry Zone of Karnataka, India, over a one-year period (2023). Methodology: A roving survey was carried out in common bean fields and root and soil samples were collected from rhizosphere of the common bean plants. Nematode populations were quantified and species identification was conducted using morphological traits of second-stage juveniles (J2) and adult females, including the perennial pattern technique. Molecular validation was performed using 18S rRNA primers, followed by sequencing and phylogenetic analysis. Correlations between nematode populations and factors such as plant age, soil moisture, pH, electrical conductivity and temperature were analysed. Results: The highest nematode infestation was recorded in Nandi (NAD) village, with populations of 112.6 J2/200 cc soil and 65 J2/5 g root. Morphological characterization confirmed the presence of Meloidogyne incognita, which was further validated through molecular analysis, showing more than 97.94% sequence identity with M. incognita. Phylogenetic analysis confirmed the evolutionary relationship of isolates from NAD, GTH, DNH, GKVK_PB, HDH, and ARH villages with M. incognita. A positive correlation was observed between plant age, nematode populations and gall formation, indicating increased reproduction with plant maturity. Soil moisture and pH significantly influenced nematode abundance, while electrical conductivity and temperature had minimal or negative effects. Conclusion: The study highlights the widespread distribution of M. incognita in common bean fields, emphasizing its potential to cause significant economic losses. These findings underscore the need for targeted nematode management strategies to mitigate yield losses in common bean production.