Agriculture Business Week

Rice grows best when planted in a favorable environment. Some varieties, however, can cope with adverse conditions and give favorable yields.

“These varieties are continually developed and tested by PhilRice plant breeders,” said Dr. Nenita Desamero, PhilRice project leader of rice variety development for unfavorable rainfed lowland.

Rainfed lowland farms, by definition, are unfavorable for rice. This is because they don’t have installed irrigation systems. “However, there are rainfed farms that can provide a suitable environment as far as water is concerned,” said Dr. Desamero.

The plant breeder refers to areas with sufficient rainfall to provide. irrigation with a depth of 2-5 cm. In these areas, farmers may plant varieties released for irrigated farms.

“Farmers should plant varieties that are suitable for their areas,” she reminded. “The varieties should be high-yielding and resistant to pests in the locality. Also, farmers need to be more vigilant in their management of the available water. This includes fixing dikes for maximum water retention and scheduling field activities according to availability of water.”

While some rainfed rice fields have sufficient water, other farms are not as lucky. In fact, more than 1 million hectares of the ricefields in the Philippines are drought-prone: This means that there are long periods without rain to provide the much needed irrigation water.

Varieties for these areas compose the bulk of the rice breeding efforts for unfavorable environments. In fact, five lines are under National Cooperative Testing and may be released by 2010.

WIDE HYBRIDIZATION
The plant breeding team is using a variety of approaches to develop more drought-tolerant rice varieties. Wide hybridization is one.

“Wide hybridization,” according to Dr. Antonio Alfonso, PhilRice plant breeder and molecular biologist, “involves crossing cultivated rice with wild rice to transfer desirable traits. Wild rice are varieties that grow in swamps, riverbanks, and mountain slopes without anyone planting or tending for them.”

“Many wild rice species are resistant to drought and other abiotic stresses, insect pests, and diseases. We hope to transfer these characteristics to our new varieties,” Dr. Alfonso explained.

Using several accessions of Oryza glaberrima the predominant cultivated species in Africa, and other selected drought tolerant varieties, Dr. Alfonso and his team have produced F 1 and backcross populations, which will be further tested for drought-tolerance.

The plant breeders are also using biotechnology and other non-conventional approaches. Dr. Dindo Agustin Tabanao, PhilRice plant breeder and molecular geneticist, and his team are identifying chromosome regions that are associated with drought tolerance traits.

“A rice plant is tolerant to drought when its yield is not affected by pro-longed drought stress. This is impractical to measure because plant breeders would have to evaluate plants under stress and non-stress conditions. Other traits related to drought tolerance that are also useful for breeding, like root length, osmotic adjustment, and water use efficiency, are much more difficult to measure. But if molecular markers linked to chromosome regions controlling drought-tolerance mechanisms are available, selection will be much easier,” Dr. Tabanao explained.

“Once these are identified, these regions will be introgressed or transferred to popular rice varieties,” he added. “Those rice varieties will then become drought-tolerant while maintaining their other favorable characteristics like high yield and pest-resistance.”

Other varieties had genes which were changed to make their traits desirable. This mutation was induced using gamma rays from 60Co.

“Although mutation sounds grotesque, it is perfectly safe and allows-breeders to speed up crop improvement,” stressed Dr. Desamero. “Gamma-irradiation changes the dominant undesirable allele to make the trait desirable. For example, we want to make a tall variety shorter. We expose this variety to the gamma rays to change the gene from `tall’ to `short’. So far, mutation has been most useful for inducing semi-dwarfism in tall cultivars and shortening the duration of late-maturing varieties.”

Another technique that accelerates the breeding process is anther culture. “In this process, anthers with immature pollen grains are placed on a culture medium with components that will eventually allow the production of seedlings,” Dr. Desamero explained.

“A variety for irrigated lowland farms, NSIC Rc130 (Tubigan 3), was developed by PhilRice through anther culture. We hope to develop a variety for rainfed lowland farms as well,” she said.

At present, there are at least 14 varieties that can be planted in rainfed farms. PSB Rcl4 or Rio Grande is one of the most preferred varieties for these areas.

AQUA-RICE
“Normally, complete submergence for more than 3-5 days can be highly damaging to the crop. But some lines are able to survive and recover even after being submerged for 10-12 days.” said Dr. Desamero.

One of them is IR64-Subl. This is the popular variety IR64 inserted with the submergence tolerance gene (Sub 1). The gene was discovered by IRRI and the University of California-Davis from the Indian variety FR13A.

“With or without the submergence gene and planted under favorable condition, IR64 will have the same yield performance. However, when both are submerged under water for 10 to 12 days, IR64-Sub 1 can survive and recover,” Dr. Desamero explained.

Pilot-testing is currently on-going in Brgy. Papaya, San Antonio, Nueva Ecija and in North Cotabato.

So far, farmer-partners are giving positive feedback. According to Allan Balagtas, one of the farmer-partners, “the Sub l variety is planted the same way as all other varieties of rice. But since it survives even when submerged, we do not need to replant so we are able to save on time, labor, and cost.”

“Besides evaluating its performance on-farm, we would like to determine its acceptability among farmers,” Dr. Desamero said. “However, IR64-Subl is susceptible to rice blast and other diseases that are prevalent in rainfed rice areas, but PSB Rc82 is resistant to most races of rice blast.”

Meanwhile, the project team is also developing PSB Rc82-Subl using marker-aided backcrossing and selection.

According to Dr. Desamero, PSB Rc82 is crossed with IR64-Sub l to develop the variety. The resulting hybrid is backcrossed with PSB Rc82. Using marker aided selection, the top selections from the progenies with the Sub 1 gene and the desirable characteristics of PSB Rc82 are planted and the process is repeated until a stable line is developed.

“Elite lines of PSB- Rc82-Subl will hopefully be available in 2010,” she said.

DRY THEN FLOODED
Another rainfed lowland subecosystem is drought-submergence-prone. In this type, flooding and drought recur frequently.

“We are trying to develop a high-yielding variety that is submergence and drought-tolerant, pest-resistant, and with good grain and eating qualities,” Dr. Desamero said.

With the many problems in rainfed lowlands and other unfavorable ecosystems, why continue planting rice there?

“Improving the productivity in these areas would significantly contribute to the rice supply in our country. In 2007, production reached more than 3.7 M tons, with an average yield of 3.18 tons per hectare,” said Dr. Desamero.

“Poor farmers in those areas would also benefit with the improvement of technologies for their farms,” she added.