Called NSIC Rc142 or Tubigan 7, the new rice variety is the country’s first product of a mid-level biotech technique called marker-aided selection. It is resistant to the dreaded bacterial leaf blight (BLB) disease, which is serious during the wet season.
Tubigan 7 is one of the offsprings produced in almost 10 years of rigorous breeding work initiated in 1995 by Dr. Leocadio S. Sebastian, PhilRice executive director, through a research grant from the Rockefeller Foundation. It is the first variety produced by the project.
Subsequent breeding works were handled by Dr. Rodante E. Tabien, MC Abalos, MP Fernando, Emily C. Abrogena, Yolanda A. Dimaano, GM Osoteo, Rolly C. San Gabriel, DA Tabanao, Thelma F. Padolina, Herminia Rapusas and Genero P. Rillon.
The BLB resistance of Tubigan 7 was derived from IRBB5-21, a line provided by the Asian Rice Biotechnology Network (ARBN) of the International Rice Research Institute (IRRI).
According to Sebastian, Xa21, the BLB resistance gene from IRBB5-21, is known to be effective against nine BLB races. It was introduced into IR64 using DNA markers, as IR64 is considered a good parent for yield and grain quality. The DNA markers help plant breeders locate genes of interest, usually those that are associated with desired traits like BLB resistance.
Through the use of DNA markers, plant breeders can readily identify the offspring [products of breeding work] that are resistant to the much dreaded disease without waiting for the plants to grow until a particular stage.
Dr. Antonio A. Alfonso, PhilRice plant breeding and biotechnology division head, said the use of DNA markers makes the selection of BLB-resistant plants easier, faster and more effective than the conventional breeding method.
In the conventional breeding method, BLB-resistant plants are selected at around 45 days after transplanting. This method requires that the plants are inoculated with the disease organism that causes BLB and then observed for disease occurrence after two to three weeks for eight to nine weeks.
In contrast, plant breeders using marker-aided selection do not need the tedious process in conventional breeding. All they need is to identify plants with the BLB resistance gene and then evaluate and select them in the screenhouse and in the field. As a result, "breeding efficiency is tremendously increased due to reduced cost owing from reduced number of test entries and time needed for selection," Alfonso said.
"The use of DNA as markers for selection has streamlined and facilitated the whole process even without inoculation," Tabien and his co-workers said earlier in a paper presented during the 13th national rice research and development conference in year 2000.
Actually, marker-aided selection started in the 1996 wet season and continued until the 1998 wet season. Field testing started in the 1999 dry season.
In the National Cooperative Tests Phase 1, the yield of Tubigan 7 under direct wet seeded culture was 24 percent higher than PSB Rc30 during the dry season and 32 percent higher during the wet season. Under transplanted condition, its yield was higher by 12.7 percent.
Although Tubigan 7 is more adaptable in direct wet seeded culture, it could also be used in transplanted culture, preferably during the wet season. The breeders, however, suggest that it should be frequently monitored for blast incidence.
This new variety matures early at 105 days with a height of 85 centimeters. It has intermediate resistance to major diseases of rice like BLB and sheath blight, as well as a wide spectrum of resistance to the insect green leafhopper, yellow stemborer and brown planthopper. Green leafhoppers transmit the tungro virus disease, while brown planthoppers could wipe out a whole crop under heavy infestation.
Tubigan 7 has good milling and eating qualities, as it is sticky and moist when cooked because of its low amylose content.