Genetic variation and survival of Erysiphe necator in tropical India

Abstract

The heterothallic, biotrophic fungus Erysiphe necator causes powdery mildew on grapes which impacts the yield and quality of fruits and their processed products. Two genetic groups, A and B, have been described which overwinter either as flag shoots or chasmothecia. The genetic structure of the Indian isolates and their oversummering mode in tropical regions is not known. In this study, population genetic analysis of 26 and 134 E. necator isolates from temperate and tropical regions of India, respectively, was performed. PCR analysis showed presence of both genetic groups A and B in temperate regions and only genetic group B in tropical regions. Flag shoots were not observed in tropical region. Weather data analysis and temperature sensitivity of E. necator conidia indicate the possibility of the pathogen oversummering as conidia on bark. Sequence analysis of ITS (Internal Transcribed Spacer), IGS (Intergenic Spacer), TUB2 (Beta-Tubulin) and EF1-α (Translation Elongation Factor 1-α) genes covering 1762 nucleotides from 22 isolates showed the presence of four haplotypes, A-IN1, B-IN1, B-IN2 and B-IN3 in temperate regions and only haplotype B-IN3 in tropical regions. Haplotypes A-IN1 and B-IN1 were similar to haplotypes of group A and B, respectively, reported from USA, Europe and Australia. The other two haplotypes, B-IN2 and B-IN3 grouped with haplotypes from USA and are new reports from India. The diversity and haplotype structure suggest that powdery mildew was introduced in north India and then moved to tropical regions corroborating historical reports of the introduction of grapevines in India. Occurrence of a genetic group with lower fungicide sensitivity and greater aggressiveness might explain the difficulties to manage this disease in Maharashtra, India.

Population structure of Erysiphe necator on domesticated and wild vines in the Middle East raises questions on the origin of the grapevine powdery mildew pathogen

“…Groups I and III correspond to groups A and B, but group II which was found only once in India was not further examined. Ghule et al (2019) also reported on a new genetic group in India which they refer to American invasion. We suggest that there is great importance to examine E. necator populations' origin, especially in the sympatric regions of wild and domesticated grapevines, in the centre of domestication in Central Asia.…”

“…Ghule et al . (2019) also reported on a new genetic group in India which they refer to American invasion. We suggest that there is great importance to examine E .…”

“…The reasons for the scarcity of group A in Israel is not clear. Interestingly, the prevalence of group A is also low in other invaded regions of the world, like Chile, Portugal, New-Zealand and India (Araya et al, 2014;Cooper et al, 2015;Oliveira and Cunha, 2015;Ghule et al, 2019). Montarry et al (2008) showed that group A was less aggressive than group B in germination and infection efficiency.…”

Comprehensive analyses of the occurrence of a fungicide resistance marker and the genetic structure in Erysiphe necator populations

“…H3 and H4 are similar to genotype B2 from Hungary 17 , but, as EF1-α sequences were not analyzed in that study, the unambiguous identity could not be determined. Genotype H7 from Hungary is identical to genotype B-IN1, reported from India 24 . Genotype H13, which is identical to genotype 11 18 found in isolates from the United States 18 , was detected once.…”

“…The fungus is introduced to Europe, where two distinct genetic groups, designated as A and B, were identified first based on DNA-fingerprint techniques 20 , 21 . Afterwards single nucleotide polymorphisms (SNPs) were assigned to those genotypes, in sequences of the β-tubulin ( TUB2 ) 16 , 17 , 22 , translation elongation factor 1-a ( EF1 -a) 18 , 23 , 24 and eburicol 14α-demethylase ( CYP51 ) genes 21 , and also in the sequences of the nrDNA internal transcribed spacer (ITS) 21 and intergenic spacer (IGS) regions 18 .…”