Meet the tungro-resistant rice varieties

By Sosimo Ma. Pablico

THE RICE TUNGRO disease is the major rice diseases that can cause yield losses up to 90 per cent. Although the incidence of this disease in Northern Luzon is not as serious as in Mindanao, rice farmers in Regions 1 and 2 and the Cordillera Administrative Region may do well to know that tungro-resistant lines have been developed already. In case the disease strikes hard, they would have something to fall back.

Called Matatag lines by PhilRice [Philippine Rice Research Institute], these tungro-resistant lines started to be known in Mindanao in the late 90s when serious tungro outbreaks occurred in North Cotabato, South Cotabato, Davao del Norte, Bukidnon, Lanao del Norte, and Zamboanga del Sur.

At that time, the branch station of PhilRice in Midsayap, North Cotabato was conducting field trials on IR71031-4-5-5-1, the first tungro-resistant line bred by IRRI [International Rice Research Institute]. This line yielded 3.5-4.8 tons a hectare (t/ha) in farmers’ fields in 1998. PhilRice baptized it as Matatag 1. Together with IR69726-116-1-3, which was baptized Matatag 2, seeds were given to farmers during their graduation in a farmers’ field school on rice tungro disease management.

Matatag seed production and distribution efforts resulted in a dramatic decrease in tungro incidence starting year 2000. “The tungro-affected areas were significantly reduced as a result of the seed distribution under the leadership of PhilRice-Midsayap,” noted an external team of experts that PhilRice impact since its creation in 1987.

Tungro virus disease is transmitted by green leafhoppers that have been feeding on tungro-infected rice plants. When the population density of the nymphs (young leafhoppers) in rice fields increases, the rice leaves turn yellow to orange as a result of heavy feeding. The leaves become mottled and the plants exhibit mild to severe stunting.

Consequently, the plants do not develop well. Heavily affected farmers would be lucky if they would be able to recover their cost of production. Thus, tungro disease is a nemesis of farmers in tungro hot spot areas. Although the average life cycle of rice leafhoppers is 20-30 days, several generations could occur in one season. Thus, it is very difficult to predict severe infestations way ahead.

The best method of combating this disease is by planting varieties with intermediate resistance to tungro. The National Seed Industry Council (NSIC) has released three varieties for commercial planting – NSIC Rc118 (Matatag 3), NSIC Rc120 (Matatag 6), and IR73885-1-4-3-2-1-6 (Matatag 9). Matatags 3 and 9 were bred by IRRI, while Matatag 6 was bred by PhilRice. However, it was PhilRice that led in the nationwide field testing of IRRI’s lines before these were released as commercial varieties.

Matatag 3 is considered a stop gap variety for Panay Island (Region 6), as well as Regions 10, 11, 12 , 13 and ARMM in Mindanao. It has a fairly early maturity (107 days when transplanted; 101 days when direct seeded). It is suitable for transplanted and direct seeded cultures with fairly acceptable yields – 4,666 – 4,910 kg/ha when transplanted and 4,837 – 5,014 kg/ha when direct seeded.

Although Matatag 3 also has intermediate resistance to blast and bacterial leaf blight, as well as moderate resistance to dead hearts, caution must be taken because it is moderately susceptible to the green leafhopper, which transmits the tungro virus disease.

Matatag 6, on the other hand, was released as a stop variety for Panay Island, Negros Occidental, Misamis Occidental, Misamis Oriental, Bukidnon, Sultan Kudarat, South Cotabato, the Davao provinces, and ARMM. It matures in 90 – 92 days in transplanted and direct wet-seeded cultures. It yields higher when transplanted (5,015 – 5,185 kg/ha) than when direct wet-seeded (4,657 – 4,839 kg/ha).

If ever the diseases strikes in Northern Luzon, which we pray will not, farmers hopefully can use these information.

(Readers may reach columnist at spablico@yahoo.com. For past columns, click http://sundaypunch.prepys.com/archives/category/opinion/harvest-time/ For reactions to this column, click “Send MESSAGES, OPINIONS, COMMENTS” on default page.)

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