International Rice Research Institute Farm Research Articles

Lodging-related morphological traits of hybrid rice in a tropical irrigated ecosystem

Hybrid rice ( Oryza sativa L.) has been proven to be effective in increasing yield potential, but lodging often limits its yield in high-yielding environments. This study was conducted to determine genotypic variation in lodging resistance and lodging-related morphological traits among hybrid and non-hybrid check varieties, and to identify the key morphological traits associated with lodging resistance. Lodging behavior of 16 rice genotypes, including 12 hybrids and four inbreds, was studied at the International Rice Research Institute farm during the 2004 wet season (WS) and 2005 dry season (DS). Grain yield and visual score of lodging were determined at maturity. Lodging-related morphological traits were measured at 30 days after flowering. Large genotypic differences in lodging-related morphological traits were observed. Among these traits, dry weight per unit length, breaking resistance, and lodging index (bending moment/breaking resistance × 100) of lower internodes were significantly correlated with visual score of lodging. Several hybrids demonstrated high lodging resistance although their average plant height was over 120 cm. The lodging-related morphological traits and visual score of lodging in these hybrids were comparable with those of the non-hybrid check varieties with strong lodging resistance. These results suggest that increases in dry weight per unit length and breaking resistance of lower internodes are primary targets for reducing lodging index, thus improving overall lodging resistance of hybrid rice in a breeding program.

Comparison between aerobic and flooded rice in the tropics: Agronomic performance in an eight-season experiment

Yield penalty and yield stability of aerobic rice have to be considered before promoting this water-saving technology in the tropics. The objectives of this study were (1) to compare crop performance between aerobic and flooded rice continuously over several seasons, and (2) to identify yield attributes responsible for the yield gap between aerobic and flooded rice. Field experiments were conducted at the International Rice Research Institute farm in dry and wet seasons. Grain yield and its components were compared between aerobic and flooded rice continuously for eight seasons from 2001 to 2004 using the best available aerobic rice varieties in the tropics. The yield difference between aerobic and flooded rice ranged from 8 to 69% depending on the number of seasons that aerobic rice has been continuously grown, dry and wet seasons, and varieties. When the first-season aerobic rice was compared with flooded rice, the yield difference was 8–21%. The yield difference between aerobic and flooded rice was attributed more to difference in biomass production than to harvest index. Among the yield components, sink size (spikelets per m 2) contributed more to the yield gap between aerobic and flooded rice than grain filling percentage and 1000-grain weight. Yield decline was observed when aerobic rice was continuously grown and the decline was greater in the dry season than in the wet season. The yield decline of aerobic rice was attributed more to changes in biomass production than in harvest index. Our data suggest that new aerobic rice varieties with minimum yield gap compared with flooded rice and crop management strategies that can reverse the yield decline of continuous aerobic rice have to be developed before aerobic rice technology can be adopted in large areas in the tropics.

Rice yields decline with higher night temperature from global warming.

The impact of projected global warming on crop yields has been evaluated by indirect methods using simulation models. Direct studies on the effects of observed climate change on crop growth and yield could provide more accurate information for assessing the impact of climate change on crop production. We analyzed weather data at the International Rice Research Institute Farm from 1979 to 2003 to examine temperature trends and the relationship between rice yield and temperature by using data from irrigated field experiments conducted at the International Rice Research Institute Farm from 1992 to 2003. Here we report that annual mean maximum and minimum temperatures have increased by 0.35 degrees C and 1.13 degrees C, respectively, for the period 1979-2003 and a close linkage between rice grain yield and mean minimum temperature during the dry cropping season (January to April). Grain yield declined by 10% for each 1 degrees C increase in growing-season minimum temperature in the dry season, whereas the effect of maximum temperature on crop yield was insignificant. This report provides a direct evidence of decreased rice yields from increased nighttime temperature associated with global warming.

Effect of Panicle Size on Grain Yield of IRRI-Released Indica Rice Cultivars in the Wet Season

Grain yield under wet season (WS) conditions has gradually received more attention due to looming scarcity of irrigation water, which limits the area for planting to flooded lowland rice in the dry season in the tropics. This study was conducted to determine (1) grain yield of IRRI (International Rice Research Institute)-released rice cultivars under WS conditions and (2) if panicle size (spikelet number per panicle) is an important trait that influences grain yield in the WS. Field experiments were conducted at the IRRI farm in the 2000 WS and 2001 WS using 14 IRRI-released conventional and two F1 hybrid cultivars under irrigated lowland conditions. Grain yield and yield-related traits were measured at maturity. Grain yield of tested cultivars ranged from 4.5 to 7.0 t ha−1 in the 2000 WS and from 4.1 to 5.6 t ha−1 in the 2001 WS. Large differences in panicle number and panicle size were observed among cultivars. All cultivars had small to intermediate panicle size ranging from 63 to 114 spikelets per panicle. Among all the measured yield-related traits, panicle size had the most consistent and closest positive correlation with grain yield. These results suggest that it is possible to improve maximum attainable yield in WS by breeding cultivars with larger panicle size. However, whether other cultivar groups such as the tropical japonica with large panicles (150-200 spikelets per panicle) would confer high yield in WS remains to be studied.

Higher Leaf Area Growth Rate Contributes to Greater Vegetative Growth of F1 Rice Hybrids in the Tropics

The early vigor of hybrid rice (Oryza sativa L.) developed in temperate areas has been mainly attributed to its higher tillering rate. The objective of this study is to identify factors that contribute to greater vegetative growth of Fi hybrid rice recently developed in the tropics. We analyzed data from field experiments conducted from 1994 to1997 in both dry and wet seasons at the International Rice Research Institute farm. Each experiment had one to four pairs of comparisons between best hybrids and best conventional varieties. Parameters used for comparison were tillering rate, leaf area growth rate (LAGR), and crop growth rate (CGR) between transplanting (TR) and midtillering (MT) and also between MT and panicle initiation (PI). In most cases, the hybrids exhibited greater CGR than the conventional varieties, either between TR and MT or between MT and PI or both. The difference in CGR was associated with the difference in LAGR between hybrids and conventional varieties. However, the tillering rate of hybrids was significantly lower than or equal to that of conventional varieties. Therefore, the higher LAGR, independent from tillering, contributed to greater CGR of recently developed F1 hybrid rice in the tropics. The difference in LAGR and CGR between hybrids and conventional varietieswas not associated with tillering. The higher LAGR of the Fl hybrids than that of the conventional varieties could be attributed to their thinner leaf blades.

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

Genetic improvement in grain yield has been intensively studied in wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), maize (Zea mays L.), and soybean [Glycine max (L.) Merr.]. Such information is limited in rice (Oryza sativa L.). The objective of this study was to determine the trend in the yield of rice cultivars–lines developed since 1966. Twelve cultivars–lines were grown at the International Rice Research Institute (IRRI) farm and the Philippine Rice Research Institute farm during the dry season of 1996. Seven cultivars–lines were grown at IRRI farm in the dry season of 1998. Growth analyses were performed at key growth stages, and yield and yield components were determined at physiological maturity. Regression analysis of yield versus year of release indicated an annual gain in rice yield of 75 to 81 kg ha−1, equivalent to 1% per year. The highest yields obtained with the most recently released cultivars was 9 to 10 Mg ha−1, which is equivalent to reported yields of IR8 and other early IRRI cultivars obtained in the late 1960s and early 1970s at these same sites. Therefore, the 1% annual increase in yield may not represent genetic gain in yield potential. The increasing trend in yield of cultivars released before 1980 was mainly due to the improvement in harvest index (HI), while an increase in total biomass was associated with yield trends for cultivars–lines developed after 1980. Results suggest that further increases in rice yield potential will likely occur through increasing biomass production rather than increasing HI.

Long-term effects of tillage, cultivar and herbicide on weed shift and control in broadcast-seeded flooded rice

Chemical and nonchemical control of a heterogenous weed community in broadcast-seeded rice was studied at the International Rice Research Institute farm from 1984 to 1986 during both dry and wet seasons. Increasing tillage frequency from one to three harrowings substantially reduced the stand of Paspalum distichum L. but increased that of Scirpus maritimus L. Increasing the number of harrowings from one to three also significantly increased yield. Cultivar type did not affect weed infestation, although IR29723-143-3-2-1 consistently outyielded IR36 in weed-infested plots. Bensulfuron-methyl (methyl-2[(4,6-dimethoxy-pirimidin-2-yl) aminosulfonyl-methyl] benzoate) and propanil (3′4′-dichloropropionanilide) + 2,4-D ((2,4-dichlorophenoxy) acetic acid) adequately controlled S. maritimus and the annual weeds Echinochloa glabrescens Munro ex Hook.f., E. crus-galli (L.) Beauv. ssp. hispidula (Retz.) Honda, Cyperus difformis L. and Monochoria vaginalis (Burm.f.) Presl, increasing yield significantly. However, herbicide application also significantly increased the P. distichum population. The long-term result from continuous tillage and herbicide use was an increase in weed population.

Modern Technology and Economic Efficiency of Philippine Rice Farmers

Farmer's recent study and Frankel's review of Griffin's book suggest that belief in a between actual and potential agricultural production in developing countries has regained currency in the development community., Timmer's concern with measuring technical efficiency and the attempts of Shapiro and Miiller to relate modernization and information to technical efficiency focus on differences in productivity among farmers as indicators of such a gap.2 Among technologists the hypothesis has a number of faithful adherents, including the former director of the International Rice Research Institute (IRRI), who could not understand the Asian farmer who had adopted the new rice varieties was not doing better. Somehow [he felt that] the rice scientists who had obtained yields of 5 to 10 metric tons per hectare on the IRRI farm still could not explain why so many Filipino farmers [for example] obtained, on the average, less than one metric ton per hectare increase in after shifting from the traditional to the high yielding varieties.3 In response to these persistent questions, in 1974 scientists at IRRI began a research project to measure the and to understand the factors responsible for it. The yield gap was defined by biologists as the difference, under farmers' conditions, between the maximum possible

Comparative study on yield and yield attributes of hybrid, inbred, and NPT rice genotypes in a tropical irrigated ecosystem

Yield potential of 16 rice genotypes including 12 hybrids, 3 inbreds, and I new plant type (NPT), were studied at the International Rice Research Institute farm under optimum crop management to achieve maximum attainable yields during the wet season (WS) of 2004 and dry season (DS) of 2005. Yield and yield components were determined at maturity. 1R76712H produced the highest grain yield (7.7 t/ha) followed by 1R75217H and Magat (7.6 t/ha) in WS; in DS, 1R79118H produced the highest grain yield (9.17 t/ha) followed by 1R73855H (8.9 t/ha) and SL-8H (8.8 t/ha. The high yield of hybrid rice was due to high harvest index (0.50). Hybrid produced significantly higher productivity (80.2 kg/ha/day) than inbred in DS, but the difference was not significant in WS. Hybrid produced higher spikelets/panicle and 1000-grain weight than inbred rice. Spikelet filling percent was higher in inbred than hybrid rice. The NPT rice genotype had the lowest spikelet filling percent, but the highest 1000-grain weight across the season. Keywords: Yield; yield attributes; hybrid and inbred rice genotypes. DOI: 10.3329/bjar.v35i2.5897Bangladesh J. Agril. Res. 35(2) : 343-353, June 2010