Genetic variations among the isolates of Bipolaris Maydis based on phenotypic and molecular markers

A Nadeem,A Akbar,M Fahim,R Karim,S Hussain,Z Ahmad,A Fareed,T Iqbal,Saeedullah Saeedullah

doi:10.1590/1519-6984.253147

Abstract

Abstract Maydis leaf blight, caused by Bipolaris maydis, is an important disease of maize crop in Khyber Pakhtunkhwa (KP) Pakistan. Fifteen isolates of the pathogen, collected across KP, were studied for variability based on phenotypic and molecular markers. Significant variability among the isolates was observed when assessed using phenotypic traits such as radial growth, spore concentration, fungicide sensitivity and virulence. The isolates were classified into six culture groups based on colour, texture and margins of the colony. Conidial morphology was also variable. These were either straight or slightly curved and light to dark brown in colour. Fungicide test showed significant variation in the degree of sensitivity against Carbendazim. Isolate Bm8 exhibited maximum radial growth on carbendazim spiked plates. Conversely, isolate Bm15 showed the lowest radial growth. Variations in virulence pattern of the isolates were evident when a susceptible maize variety Azam was inoculated with spores of B. maydis. Genetic variability amongst the isolates was also estimated by RAPD as well as sequencing of ITS region. The RAPD dendrogram grouped all the isolates into two major clusters. Average genetic distance ranged from 0.6% to 100%, indicating a diverse genetic gap among the isolates. Maximum genetic distance was found between isolates Bm9 and Bm10 as well as Bm2 and Bm8. Conversely, isolates Bm13 and Bm15 were at minimum genetic distance. Phylogenetic dendrogram based on sequencing of ITS region grouped all the isolates into a single major cluster. The clusters in both the dendrogram neither correlate to the geographical distribution nor to the morphological characteristics.

Highlights

Maydis leaf blight (MLB)), caused by Bipolaris maydis (Telomorph: Cochliobolus heterostrophus), is an important disease of maize throughout the world
Fifteen isolates of Bipolaris maydis collected from diverse geographical regions of Khyber Pakhtunkhwa (KP) (Table 1) were selected for estimation of genetic variability
Genetic variability of Bipolaris maydis based on phenotypic markers

Summary

Introduction

Maydis leaf blight (MLB)), caused by Bipolaris maydis (Telomorph: Cochliobolus heterostrophus), is an important disease of maize throughout the world. Prevalence of the disease has been documented from tropical and subtropical maize growing regions of the world with warm and humid weather (Alim Shah et al, 2007; Martinez et al, 2010). Existence of variability in this pathogen has been reported previously (Karimi, 2003) which is of significant importance. The pathogen may evolve to break down the host resistance. It can adapt itself to changes in climatic conditions, crop practices and fungicides (Stanković et al, 2007). In plant-pathogen interactions, plants need to be sturdy enough to cope with the ever changing pathogen. Monitoring and constant surveillance of the pathogen divergence is important in this scenario (Gafur et al, 2002)

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Results

Conclusion