Identification of molecular marker linked to purple blotch disease resistance in onion (Allium cepa L.)

Abstract

Investigations entitled “Identification of molecular marker linked to purple blotch disease resistance in onion (Allium cepa L)” was conducted at the Division of vegetable crops, Indian Institute of Horticultural Research, Hessaraghatta, Bangalore and at the Plant Molecular Biology Laboratory, Division of Horticulture, University of Agricultural Sciences, Bangalore. The salient achievement of the investigation is summarized. RAPD markers were used in onion due to the advantages over other kinds of markers to study its association with resistance. Identification of molecular linked to disease resistance included selection of resistance and susceptible parents, primer screening to identify the polymorphism between the parents and analysis of the mapping population segregating for resistance to associate DNA marker linked to resistance. Screening of onion germplasm for purple blotch disease resistance under natural and artificial epiphytotic conditions resulted in identification of one resistant genotype PBR 287(PDI 4.85) and other two moderately resistant genotypes viz., Arka Kalyan 704 (12.12) and MS-65- 268(14.91). These three resistant genotypes were utilized as source of resistance to purple blotch disease. Studies on growth, yield and quality parameters on these identified resistant genotypes revealed the similarities in plant growth and bulb qualities and they were also found superior over other genotypes. The three purple blotch resistant genotypes viz., PBR 287, Arka Kalyan 704 and MS 65-268 were fingerprinted using 20 selected arbitrary primers, which could effectively distinguish the resistant and susceptible genotypes. Further, genetic analysis of the four genotypes using RAPD markers revealed high polymorphism among the genotypes confirming the high heterozygous nature of the population due to its highly cross pollinated breeding behavior. Dendrogram analysis of three genotypes revealed the existence of high genetic similarity between MS-65-268 and PBR 287(40% dissimilarity). Further dendrogram also clustered Arka Kalyan 704 and Arka Niketan 709(65% dissimilarity) together but with comparatively lesser genetic similarity.Results revealed that the inheritance of resistance in PBR 287 was governed by single dominant gene and segregated according to classical Mendalian ratio 3:1 in F2 population derived out of cross between PBR 287(resistant) and Arka Niketan 709 (highly susceptible). A RAPD marker OPC12 900 was found closely linked to purple blotch disease resistance as indicated by bulked segregant analysis and analysis of F2 individuals. This marker could be effectively employed for MAS of large population for purple blotch disease resistance even in the absence of the pathogen and at the early stage of the life cycle of onion crop.