Scientists at International Maize and Wheat Improvement Center (CIMMYT) at Hyderabad, India in collaboration with their counterparts in Nairobi, Kenya have conducted a genome-wide association study (GWAS) to identify regions in maize DNA that confer improved resistance to sorghum downy mildew disease in maize. SDM is an important foliar disease of maize caused by the fungus, Peronosclerospora sorghi.
We all relish corn- be it as popcorn, sweet corn or the breakfast staple- corn flakes. Maize or the Corn is the world’s leading cereal grain with a total production that has surpassed wheat or rice and India is one of the eight major maize growing countries in Asia. Unfortunately, during the monsoon season, the total productivity is limited due to the susceptibility to a number of diseases like downy mildews (DM), leaf blights, rusts, stalk rots and ear rots with DM spread throughout Asia.
In this report, the group conducted a genome-wide association study (GWAS) for sorghum downy mildew (SDM) resistance in a panel of 368 inbred lines adapted to the Asian tropics. Along with previously reported regions conferring resistance to SDM, they identified novel SNPs in the genome that are important. SNPs or Single Nucleotide Polymorphism is a variation in a single nucleotide (basic unit of the DNA) that occurs at a specific location in the genetic code and each change or variation is present to some degree within a population.
Six of these SNPs belong to significant regions reported to be associated with DM resistance and could be useful in maize breeding programs to develop DM-resistant maize varieties. The study was led by Dr. Sudha K Nair, Senior Molecular Geneticist, CIMMYT, Hyderabad.
“Downy mildew being a devastating problem for the entire Asian maize cultivation, understanding the genetics of the trait, and using that in breeding for resistant varieties is the most ecologically efficient way of managing the disease. It is for the first time that, a panel of about 400 maize inbred lines is being used in a genome-wide association study using high density, genome-wide SNP markers of more than 300,000 for identifying genomic regions responsible for the quantitative resistance towards downy mildew in maize”, explained Dr. Nair.
Metalaxyl, a chemical that is used to kill the fungus causing DM, is less effective now as the fungus has developed resistance to it owing to its extensive use. Thus, rather than using chemicals, farmers need a more sustainable and less expensive alternative to combat SDM in maize.
“On the basis of Genome wide association (GWAS), significant number of SNPs and haplotypes observed in Asiatic tropical maize breeding lines wherein eight novel genomic regions associated with Sorghum Downy Mildew (SDM) resistance were reported for the first time in the present study. In addition, ten marker-phenotypic trait associations identified were co-located within the genes associated with SDM resistance that could provide critical information for future empirical studies for improvement of breeding programs in maize”, explained Dr. Vishal Acharya, Scientist, Functional Genomics and Complex System Lab at CSIR-Institute of Himalayan Bioresource Technology, Palampur. Dr. Acharya is not connected with the study.
Dr. Nair and her team is quite hopeful, “We are in the process of validating the resistance-associated SNP markers in our maize breeding program, which could then be shared with all our partners, both public and private, for routine use in maize breeding programs in the region”.
“The International Maize and Wheat Improvement Center, known by its Spanish acronym, CIMMYT®, is one of the 15 independent, international, non-profit agricultural research organizations that make up the CGIAR (Consultative group on International Agricultural Research) with partners in over 100 countries (www.cimmyt.org). Head-quartered in Mexico, Hyderabad is the hub for CIMMYT’s tropical maize improvement activities for Asia”, Dr. S K Nair added.
The team comprised of Zerka Rashid, Pradeep Kumar Singh, Hindu Vemuri, Pervez Haider Zaidi, and Sudha Krishnan Nair from CIMMYT, Hyderabad and Boddupalli Maruthi Prasanna, Program Director, Global Maize Program from CIMMYT, Nairobi. The study was published in journal Scientific Reports.
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