Rice blast fungus (Magnaporthe grisea) causes blast disease (also known as “rotten neck disease”), which has a catastrophic effect on rice. Rice blast disease—found in 85 countries worldwide—causes huge crop losses annually and is estimated to destroy enough rice to feed more than 60 million people. The fungus can infect the roots, leaves, and stems of the plant. Once embedded, the fungus can produce structures that can also invade the plant’s vascular system—blocking transport of nutrients and water and producing lesions on the aerial plant parts.
Scientists at the Rice Research Unit in Beaumont, Texas—led by plant molecular geneticist Robert Fjellstrom and research leader Anna McClung—have found genetic markers that tag a disease-resistance gene that has been effectively used to combat a broad-spectrum of races of M. grisea.
These DNA markers are linked to the Pi-z blast-resistance gene in rice. This gene confers resistance to many forms of the blast fungus, so these markers are quite valuable for selecting and breeding disease-resistant rice cultivars. Because the resistance genes are natural, their use represents an environmentally friendly way to combat the disease.
The markers presented in this research are located closer to the Pi-z gene than previously developed ones. This close proximity makes the new markers extremely accurate in predicting the presence of this useful gene. Rice breeders have already been able to use these markers to select for highly resistant rice cultivars in California (M-207 and M-208) and Texas (Presidio).
Preliminary analysis of a cross between the cultivars Zenith and Pi-2, which carry the Pi-z and Pi-2 resistance genes, respectively, indicate that the genetic factors encoding their separate resistance reactions are not the same but are very tightly linked. The Pi-z markers reported here provide rice breeders and geneticists with a valuable tool for marker-aided selection of the Pi-z gene. Most of the Pi-z marker alleles are unique to the Pi-z gene, making them easy to select for the Pi-z gene within most genetic backgrounds.—By Alfredo Flores, Agricultural Research Service Information Staff.
"DNA Markers for Rice Blast-Resistance Gene" was published in the September 2008 issue of Agricultural Research magazine.