Rice blast, caused by a fungus Magnaporthe oryzae, is one of the major diseases of the rice crop. Now, researchers from ICAR-National Rice Research Institute (NRRI), Odisha have mapped out the diverse genes in rice that help in disease resistance.
By characterising over 150 rice varieties from nine States across the country they also identified new markers associated with blast resistance.
Blast endemics
From 1980-1987, seven blast endemics have occurred in India causing severe losses. Fungicides are very expensive, harmful for the environment and inappropriate application can cause health issues. So researchers around the globe have been on a hunt for resistant genes against the pathogen and so far, more than 100 resistance (R) genes in the rice genome have been identified.
“The rapid changes in pathogen virulence pose a constant challenge to the success of existing blast-resistant rice varieties. Therefore, there is always a need to identify new broad-spectrum blast resistant genes/alleles in rice germplasm such as landraces, wild rice, etc,” explained Manoj Kumar Yadav from NRRI and the first author of the paper published in PLOS ONE.
The seeds of landraces grown over nine states were collected from the National Gene Bank, ICAR-NRRI, Cuttack. Leaves’ resistance to blast disease was checked by growing the seeds in uniform blast nursery for two wet seasons (2015 and 2016) at the experimental farm of the institute. This farm is considered as the hot spot for leaf blast disease and the disease was recorded 25 days after sowing.
The present study showed that the rice landraces collected from north-eastern states of India had the highest resistance. Dr. Yadav explains that this may be due to co-evolution of resistance genes along with the fungal pathogen over several centuries.
Gene hunt
Specific DNA markers were used for accurate identification of specific resistant genes. The researchers found the presence of 24 previously pin-pointed resistant genes in the 161 rice landraces. The landraces were found to harbour 5-19 resistant genes.
The landraces from Tripura had the highest number of resistant genes, followed by those from Maharashtra. The study also pointed out that rice varieties in the same ecological conditions can have different resistant/susceptible behaviours.
The combination of screening and molecular characterization will help in the identification of potential donors for leaf blast.
“The identified associated marker could be used for the selection of parental materials for the improvement of existing varieties with blast resistance,” adds P.C. Rath, Head Crop Protection Division and co-author of the paper in an email to The Hindu.
