Identification of molecular marker linked with bacterial wilt resistance in marigold (Tagetes erecta L.)

Abstract

The annual flower crop marigold has gained popularity due to its easiness of cultivation and wide adaptability. It is grown for loose flowers for garland making, wreaths and religious offerings and is ideal for garden display. It is a rich source of some value added compounds - essential oils, carotenoid pigments etc. Bacterial wilt is a major reason for low productivity, especially in Kerala, causing a yield loss up to 65 - 70 per cent under conducive climatic conditions. Moreover, the pathogen being soil borne, management of this disease is very difficult and development of resistant varieties is the most promising strategy. Bulk sergeant analysis (BSA) is a quick strategy to find molecular markers associated with a trait. In this, plants from segregating population are grouped according to their phenotypic response to the target trait and the marker pattern will be associated with the expression. Usually, F2 population has been used for BSA because it provides the best recombination and segregation in the population so that extreme phenotypes can be easily distinguished upon artificial inoculation (Michelmore et al., 1991). The study entitled “Identification of molecular marker linked with bacterial wilt resistance in marigold (Tagetes erecta L.)” was carried out at the Centre for Plant Biotechnology and Molecular Biology and Department of Floriculture and Landscape Architecture, College of Agriculture, Thrissur during 2019 to 2021. The objective of this research programme was to identify inter simple sequence repeat (ISSR) marker for resistance to bacterial wilt disease in marigold (Tagetes erecta L.). To develop the mapping population, pollen from the resistant line M1 was used to pollinate the susceptible cv. Double Yellow. F1 seeds were collected and the hybrids were found to have moderate resistance. Flowers of F1 plants were selfed by bagging and the seeds obtained were sown to raise the F2 population. Two hundred and four F2 plants, resistant and susceptible parents were artificially screened (using fresh bacterial wilt inoculum having an OD value of 0.9 at 600 nm) for bacterial wilt resistance and the most susceptible and most resistant plants in F2 were identified. Wilting in plants was checked daily and infection was confirmed by ooze test. DNA was isolated from the parents and 10 plants each from most susceptible and most resistant F2 plants and S- and R-bulks were prepared. Fifty ISSR primers were initially screened and 21 primers yielding amplification were selected for BSA. BSA was carried out using parental DNA and Sand R- DNA bulks. A total of 179 amplicons were produced from 21 primers in ISSR marker analysis. From these 11 primers, yielded 23 polymorphic bands and four molecular markers were able to produce eight polymorphic bands segregating with bacterial wilt resistance. The markers ISSR 12 (750 bp), ISSR 16 (370 bp), ISSR 30 (150 and 800 bp) and UBC 866 (400 and 350 bp) were found segregating with the expression of resistance. Of these, markers ISSR 12 and ISSR 30 were associated with the susceptibility and the rest were associated with the resistance. Six markers identified in this study through BSA can be used in marker assisted selection for bacterial wilt resistance in marigold.