MSc

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.