Harvest Time
Rice varieties for drought-prone areas
By Dr. Sosimo Ma. Pablico
MORE THAN 1 million hectares of ricefields in the Philippines are drought-prone. Farmers in these areas normally suffer from long periods without rain that should provide the much needed water for their rice crops. In many instances, yields are low whenever drought affected their crops.
It is for this reason that rice breeders are continuously breeding for adverse environments. The truth is that the bulk of the country’s rice breeding efforts are geared to the development of varieties for unfavorable environments.
Five lines are now being tested nationwide under the National Cooperative Tests. These tests are conducted by a group of researchers who compose the national Rice Technical Working Group. They come from the Department of Agriculture integrated research centers, state universities and colleges (SCUs), private breeding stations, UP at Los Banos (UPLB), and the Philippine Rice Research Institute (PhilRice), the leaf agency.
PhilRice breeders hope that the five drought-tolerant lines will be released as varieties in 2010.
At PhilRice, UPLB and IRRI (International Rice Research Institute), rice breeders are using at least three approaches in the development of more drought-tolerant rice varieties. These approaches are wide hybridization, molecular marker-aided breeding, mutation breeding, and anther culture.
Dr. Antonio A. Alfonso, PhilRice plant breeder and molecular biologist who received the TOYM [The Outstanding Young Men] award last December, explains that wide hybridization involves the crossing of cultivated rice with wild rice to transfer the latter’s desirable traits. Wild rice grows in swamps, river banks, and mountain sides without anyone planting and taking care of them.
“Many wild rice species are resistant to drought and other abiotic stresses,” says Dr. Alfonso. “We hope to transfer these traits to our new varieties.”
Dr. Alfonso and his team are using several accessions of Oryza glaberrima, the predominant wild rice species in Africa, and other selected drought-tolerant varieties in their breeding activities. They have already produced a considerable number of first generation offspring and backcross populations, which will be continuously tested for drought-tolerance until stable lines are selected. Stable lines with desirable traits in addition to drought tolerance are eventually released as varieties.
Biotechnology and other non-conventional approaches are also being used. One of them is the use molecular markers as guides in breeding.
Plant breeders led by Dr. Dindo Agustin Tabanao are on their toes identifying chromosome regions that are associated with drought tolerance. “A rice plant is tolerant to drought when its yield is not affected by prolonged drought stress,” says this plant breeder.
He stresses, however, that yield under prolonged drought stress is difficult to measure. This is because plant breeders would have to evaluate plants under stress and non-stress conditions. Other traits related to drought tolerance are also useful for breeding, but are muc more difficult to measure. These traits include root length, osmotic adjustment, and water use efficiency.
Dr. Tabanao points out, however, that selection would be much easier if molecular markers linked to chromosome regions controlling drought-tolerance mechanisms are identified.
“Once these are identified, these regions will be introgressed or transferred to popular rice varieties,” says Dr. Tabanao. “Those varieties will then become drought-tolerant while maintaining their other favorable characteristics like high yield and pest resistance.”
Another method is to change some genes of certain varieties to make their traits desirable. This mutation is induced by using gamma rays from Cobalt 60, according to Dr. Tabanao.
“Although mutation sounds grotesque, it is perfectly safe and allows breeders to speed up crop improvement,” Dr. Nenita Desamero stresses. “Gamma-irradiation changes the dominant undesirable allele to make the trait desirable. So far mutation has been most useful for inducing semi-dwarfism in tall cultivars and shortening the duration of mate-maturing varieties.”
Another technique that accelerates the breeding process is anther culture, according to Dr. Desamero. “In this process, anthers with immature pollen grains are placed in a culture medium with components that will eventually allow the production of seedlings,” she says.
At least 14 varieties are now available for rainfed farms, but PSB Rc14 is the most preferred. (With Erik-Ray Matthew S. Palomar)
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