Distribution and diversity of Fusarium oxysporum f.sp. cubense TR4 causing banana wilt in Sub-tropics of India and comparative analysis of TR4 specific molecular detection methods

Abstract

Fusarium wilt caused by Fusarium oxysporum f.sp. cubense (Foc) is regarded as the most recurring and deadliest threat to banana cultivation worldwide. Among three physiological races of the pathogen capable of infecting Musa spp., Tropical race 4 (TR4) is considered the most virulent race of Foc without any known source for resistance. In India, race 1 was commonly observed to affect the cultivars of Pisang Awak, Rasthali (Silk), and Malbhog (Silk) while the Grand Naine (G9) the most popular and extensively grown cultivar of Cavendish banana in subtropics of Uttar Pradesh (U.P.) and Bihar was free from the disease till 2018. But in 2018, the incidence of wilt was first time observed in Sohawal, Ayodhya (U.P.) later in Katihar (Bihar) of India. The Association of TR4 was later confirmed with diseased samples. In the current study, the distribution and incidence of TR4 was assessed in the subtropics covering the states of U.P. and Bihar. Forty-one isolates pathogenic to the banana plant were collected from 6 states, which varied in terms of aggressiveness, and morphological characteristics like colony color, spore size, and shape. The isolates from U.P. and Bihar were characterized as TR4 using two primer sets targeting the SIX1a (secreted in the xylem) gene however isolates from Gujarat, Assam, Andhra Pradesh, and Tamil Nadu (TN) were identified as Race 1 using two primer sets targeting SIX6b and a hypothetical protein (XM_018394505.1). Genetic variability was assessed using 8 ISSR markers and divided all 41 isolates into two major groups, with a set of isolates from the U.P. and Bihar in group A and isolates from other states in group B. In the comparative analysis of three TR4-specific primers, only 1 out of 3 primer sets was confirmed to be more accurate in the characterization of the TR4. Analysis of molecular variance revealed that genetic variations among the regions and within the region accounted for 37.0 per cent and 63.0 per cent. The current study signified that the spread of the TR4 in U.P. and Bihar suggests the need for efforts for management with emphasis on biosecurity practices and the use of antagonistic biological agents to prevent further spread.