Abstract
Apple scab caused by Venturia inaequalis Cooke (Wint.) is one the important diseases of trade and industrial significance in apple. In present study variability studies in pathogen isolates were studied, which is one of the most important factors for devising management studies of scab disease in apple. Genetic diversity of 30 Venturia inaequalis isolates from 12 districts of two geographical distinct regions of Jammu and Kashmir was calculated based on the allele frequencies of 28 SSR markers and the internal transcribed spacer (ITS) region of the ribosomal DNA. The ITS based characterized sequences were submitted to NCBI GenBank and accession numbers were sanctioned. Dendrogram showed that all the accessions formed 2 main clusters with various degree of sub clustering within the clusters. Analysis based on SSR study reveals that the heterozygosity ranged from 0.0 and 0.5, with an average value of 0.39. The expected heterozygosis or gene diversity (He) ranged from 0.0 to 0.50 with an average of 0.40. The Fst value ranges from 0 to 0.6 with an average of 0.194. Diversity within each population (HS) values ranging from 0.26 to 0.33. Average differentiation among populations (GST) was 0.11 and populations were isolated by significant distance (r 2 = 0.50, P < 0.01). From the AMOVA analysis, 25% of variation was observed among population, 9% among individuals and 66% within individuals observed in the population. Structure analysis grouped isolates into two populations. Principle coordinate analysis explained variation of 36.6% in population 1, 14.30% in population 2 and 13.10% in population 3(Admixture) with 64.07% as overall cumulative percentage of variation. This indicates that extensive short-distance gene flow occurs in Kashmir region that dispersal over longer distances also appears to occur frequently enough to prevent differentiation due to genetic drift. Also it is evident that Jammu and Kashmir most likely has V. inaequalis subpopulations linked to diverse climatic conditions of the Jammu region compared to the mountainous inland Kashmir region. The results of present study would help to understand the genetic diversity of V. inaequalis from Jammu and Kashmir that would lead in the development of more effective management strategies and development of new resistant cultivars through marker-assisted selection.
Highlights
Apple (Malus × domestica Borkh.) is most widely and commercially cultivated species in the genus Malus throughout temperate regions of world[1]
The current study identified taxonomic relationships or differences between 30 V. inaequalis isolates, which can help to identify characteristics such as resistance or susceptibility toward a particular anti-fungal agent
The present study undoubtedly shows that there is high diversity of V. inaequalis in the Kashmir valley and reveals that the larger part of variability existed within the individuals
Summary
Apple (Malus × domestica Borkh.) is most widely and commercially cultivated species in the genus Malus throughout temperate regions of world[1]. Scab is very severe and among one of the mainsignificant diseasesall through the world in terms of economic losses in temperate regions with cool and moist climate during spring[3]. It ranks number one disease in terms of yield loss, which poses potential threat to apple industry[4]. Scab disease is caused by Venturia inaequalis Cooke (Wint.) whichis an ascomycetous heterothallic and hemibiotrophicfungus. Earlier, this genus was included in the family Venturiaceae, order Pleosporales, according to its “Pleospora-type centrum and bitunicateasci” [7]. In early spring, when temperature and moisture are suitable, Ascospores start maturing and are released forcibly in air[11]
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