Press Release December 1999

As part of a program involving the Philippine-based International Rice Research Institute (IRRI), the farmers have been shown how to grow glutinous rice varieties with less pesticide by using a simple, easy-to-follow varietal diversification scheme. Glutinous rice is considered a premium variety in China and commands a higher price among consumers.

The farmers grow rice on the fertile Yunnan plateau in southern China, where a disease of rice known as blast is a constant threat. However, by intercropping high-value, but blast-susceptible glutinous rice, with hybrid indica rice varieties, the farmers appear to have overcome the problem. Intercropping involves the planting of different rice varieties in the same field.

Rice blast is caused by a fungus that infects rice plants at any growth stage. Although tremendous progress has been achieved in understanding this disease, blast continues to cause significant yield losses in both temperate and tropical areas.

Today, blast is one of the most serious diseases affecting rice production in China. It threatens the nation's ability to further increase and stabilize rice output for its one billion plus rice eaters. Research to overcome the problem has focused on intercropping for some time.

Scientists from the Yunnan Agricultural University and IRRI found that intercropping achieved 92-99 percent control of rice blast and produced 0.5-1.0 ton more grain per hectare compared with indica rice monocropping, which is the traditional way of growing rice in the region.

The experiments on interplanting diverse varieties to control rice blast were first carried out under a project called Exploiting Biodiversity for Sustainable Rice Pest Management. It was developed by IRRI in consultation with national agricultural research systems in China, Thailand, Vietnam, and the Philippines. Funding from the Asian Development Bank (ADB) started in 1997.

In Yunnan, monocropped glutinous rice, which commands a premium price in the Chinese market, suffered yield losses of more than 45 percent because of blast. As a result, farmers had to spray fungicides seven to eight times throughout the growing season to control the disease.

In 1998, farmers in Shiping County joined a demonstration trial on the sustainable control of pests and diseases through varietal diversification by planting four rows of hybrid rice and one row of glutinous rice in a 700-hectare rice field.

Hybrid rice yields ranged from 7.5 to 9 tons per hectare while glutinous rice achieved an additional 0.6 to 0.9 ton per hectare, with only one fungicide spray.

But even more impressive was the drop in rice blast incidence (from 55 to 5 percent) and glutinous rice yield losses (from 28 to 0 percent), confirming observations that diversification could control rice blast.

Support for the strategy grew when rice yields increased by 0.6 to 0.9 ton per hectare when varietal diversification was carried out in the Jiangshui towns of Xizhuang and Miandian, further north, on a consolidated 13-hectare farm in 1998.

The success of this cropping scheme has enticed more farmers to join the project. This year, four to six rows of hybrid varieties Shanyou 63 and Shanyou 22 and one row of glutinous varieties Huangkenuo and Zinuo were grown on 1,450 hectares.

In addition to controlling rice blast, the strategy boosted rice yields by about 0.6 ton per hectare, thereby increasing farmers' incomes to around 1,200 yuan (about $150) per hectare.

Capitalizing on the initial success of this experiment, the IRRI-Yunnan research team plans to extend the diversification strategy to cover 50,000 to 80,000 hectares of rice land in Yunnan by 2000.

Dr. Tom Mew, head of IRRI's Entomology and Plant Pathology Division and the ADB project coordinator, said "this project presents a classic case of scientist-policymaker-farmer cooperation in pushing a technology from the conceptual stage to actual practice. IRRI scientists originally raised the possibility of using varietal diversification for blast control. Partners at Yunnan Agricultural University led by Professor Hai-Ru Chen and Dr. Youyong Zhu adopted the general idea and formulated an implementation plan that took into account farmers' practices and inputs. Highly motivated farmers and members of the provincial and county plant protection stations then helped implement the project in farmers' fields."

The IRRI research team is composed of Hei Leung, a plant pathologist and the leader of the Institute's Cross-Ecosystems Research Program, and Chris Mundt, a visiting scientist at IRRI from Oregon State University.

Their counterparts are Chinese team leader Hai-Ru Chen, Youyong Zhu, Yunyue Wang, and Yueqiu He of the Phytopathology Laboratory, Yunnan Agricultural University. They work in collaboration with Jinxiang Fan and Jinyu Zhou of the Plant Protection Station, Department of Agriculture, Yunnan Province.

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