Molecular Characterization of Selected Mutant Lines of Onion (Allium cepa L.) against Purple Leaf Blotch Disease Using SSR Markers

Aims: The purple leaf blotch (PLB) disease, for which there is no released resistant variety in Bangladesh, causes loss in production of onion in every year. The mutants of a released variety, BARI Piaz-2 has shown to possess resistance against PLB which is yet to be characterized at molecular level. An easy and simple molecular detection technique of the gene responsible for this disease will be of great use in future. The present study was thus carried out to molecularly characterize four mutant lines of onion using Simple Sequence Repeat (SSR) marker to detect the presence or absence of PLB gene conferring resistance against purple blotch disease in onion.
Place and Duration of Study: The research was carried out during the period from March, 2013 to April, 2014 in the Biotechnology Laboratory of Bangladesh Institute of Nuclear Agriculture (BINA) in Mymensingh, Bangladesh.
Methodology: DNA was extracted from the vigorously growing fresh leaf samples of 25 days old seedlings of four mutant lines namely, BP2-75/2, BP2 -100/1, BP2-100/2 and BP2-100/12 of onion using CTAB method. The molecular characterization was done using two sets of SSR markers, namely MatK-1RKIM-f/MatK-3FKIM-r and rbcLa-F/rbcLa-R.
Results: All the four mutant lines showed clear band for the primer MatK-1RKIM-f/MatK-3FKIM-r which indicates the presence of PLB gene inferring resistance against purple blotch. Clear band was also observed with the marker rbcLa-F/rbcLa-R in all mutant lines except BP2-100/12 indicating absence of PLB gene in BP2 -100/12 which inferred susceptibility against purple blotch of onion. An unknown allele was also detected in this experiment which may be either linked with the PLB gene or a candidate gene which triggers the PLB gene responsible for purple blotch of onion.
Conclusion: Both the primers seemed to be effective in detecting the presence or absence of PLB gene in the studied mutant lines of onion variety BP2. However, more number of primers should be tested for effective screening of diverse germplams that will be helpful in designing any future breeding programs.