Grain Yield of Rice Cultivars and Lines Developed in the Philippines since 1966

limited, investments in irrigation have virtually ceased, high fertilizer use is causing concern about environmenGenetic improvement in grain yield has been intensively studied tal pollution from fertilizer losses, and rice lands are in wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), maize (Zea mays L.), and soybean [Glycine max being lost to non-rice uses in the major rice-growing (L.) Merr.]. Such information is limited in rice (Oryza sativa L.). The areas of Asia. Over the next 30 yr, Asia must increase objective of this study was to determine the trend in the yield of its rice production by at least 60% to meet the needs rice cultivars–lines developed since 1966. Twelve cultivars–lines were of population growth (Cassman and Pingali, 1995). To grown at the International Rice Research Institute (IRRI) farm and achieve this goal, our best option is to develop rice the Philippine Rice Research Institute farm during the dry season of cultivars with higher yield potential through crop im1996. Seven cultivars–lines were grown at IRRI farm in the dry season provement. of 1998. Growth analyses were performed at key growth stages, and IR8, the first high-yielding modern rice cultivar, was yield and yield components were determined at physiological matureleased by IRRI in 1966. This event marked the start rity. Regression analysis of yield versus year of release indicated an of the “green revolution” in Asia. IR8 is a semidwarf annual gain in rice yield of 75 to 81 kg ha21, equivalent to 1% per year. The highest yields obtained with the most recently released with profuse tillering, stiff culms, erect leaves, photocultivars was 9 to 10 Mg ha21, which is equivalent to reported yields period insensitivity, high N responsiveness, and high HI of IR8 and other early IRRI cultivars obtained in the late 1960s and compared with traditional cultivars (Chandler, 1969). early 1970s at these same sites. Therefore, the 1% annual increase in During the past 30 yr, rice breeding efforts have been yield may not represent genetic gain in yield potential. The increasing directed towards incorporation of disease and insect trend in yield of cultivars released before 1980 was mainly due to the resistance, earlier maturity, and improving grain quality improvement in harvest index (HI), while an increase in total biomass (Khush, 1990). To date, 44 semidwarf indica cultivars was associated with yield trends for cultivars–lines developed after developed by IRRI for the irrigated lowland ecosystem 1980. Results suggest that further increases in rice yield potential have been released in the Philippines. These cultivars will likely occur through increasing biomass production rather than and their derivatives have been widely grown in South increasing HI. and Southeast Asia and account for more than 80% of total rice production in this region. However, the yields of these rice cultivars have not been compared when D the past 30 years, rice production in Asia grown under the same field conditions at the same time. more than doubled as a result of the adoption of It is important to determine the contribution of plant modern cultivars, increased investments in irrigation, breeding to yield improvement because it may provide greater use of fertilizer, and some expansion in cultiinsights into the optimum strategy for attaining further vated area. The production environment in the future gains (Wych and Stuthman, 1983). is projected to be very different. Expansion of area is Genetic improvement in grain yield has been intenS. Peng, R.C. Laza, R.M. Visperas, and A.L. Sanico, Agronomy, Plant sively studied in wheat, barley, oat, and maize (Austin Physiology and Agroecology Division, International Rice Research et al., 1980; Wych and Rasmusson, 1983; Wych and Institute (IRRI), P.O. Box 3127, MCPO, 1271 Makati City, PhilipStuthman, 1983; Tollenaar, 1989; Feil, 1992). Most of pines; K.G. Cassman, Dep. of Agronomy, Univ. of Nebraska, Lincoln, these studies reported a positive historical cultivar trend NE 68583; G.S. Khush, Plant Breeding, Genetics, and Biochemistry Division, IRRI. Contribution of IRRI. Received 4 March 1998. *CorAbbreviations: CGR, crop growth rate; HI, harvest index; IRRI, Interresponding author ([email protected]). national Rice Research Institute; LAI, leaf area index; PhilRice, Philippine Rice Research Institute. Published in Crop Sci. 40:307–314 (2000).