Genetic Improvement Of Grain Yield Research Articles

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.

Correlation and path analysis in the F, generation of greengram (Vigna radiata (L.) Wilczek)

The correlation and path coefficients were worked out in seven parents and F, population of their 21 crosses in greengram for 13 characters. Seed yield had significant positive genotypic correlation with number of secondary roots at maturity, dry weighty of plants at maturity, plant height, clusters per plant, pods per plant, seeds per pod and hundred grain weight and harvest index. Number of pods, clusters per plant and harvest index showed high positive correlation on grain yield and also with each other. Path analysis revealed that pods per plant had the highest positive direct effect on grain yield followed by to hundred grain weight and number of seeds per pod. Plant height showed high indirect effect through number of pods, seeds per pod and hundred grain weight on grain yield. The study revealed that genetic improvement of grain yield is possible by selecting characters having high positive correlation and positive direct effect.

How can breeding contribute to more productive and sustainable rainfed lowland rice systems?

The contributions to this special issue have examined our current understanding of the adaptation of rainfed lowland rice to the abiotic stresses associated with drought, submergence and low soil fertility. Genetic variation has been identified for both broad adaptation across target rainfed lowland environments and specific adaptations to some of the abiotic stress environments, e.g. late season drought, and submergence during vegetative development. However, in general progress in genetic improvement of adaptation that contributes to higher and more stable yields has been extremely slow. The opportunities for increasing the rate of genetic improvement of grain yield is examined under the four headings: (1) the complexity of the target genotype–environment system; (2) the genetic resources available to the breeding programs; (3) clarity of the breeding objectives, capacity of the adopted breeding strategy to achieve the necessary genetic modifications and selection strategy; and (4) the physical and human resource capability to implement, evaluate and manage the necessary breeding strategies. Recommendations are made on priority research areas that are required to integrate the growing understanding of rainfed lowland rice adaptation and the needs of the breeding programs.

Physiological Basis of Genetic Improvement of Maize Hybrids in Ontario from 1959 to 1988

Genetic improvement in grain yield of North American maize (Zea mays L.) hybrids during the past three to five decades can be attributed to increased phytomass production. The objective of this study was to identify the physiological traits that have contributed to the improvement in dry matter production of maize hybrids in Ontario. Experiments were conducted during 1987 and 1988 at two locations in Ontario with nine maize hybrids representing three decades of yield improvement in Ontario. Hybrids were grown at 2, 4, 8, and 13 plants m‒2 and phenological development was studied from planting to maturity. Phenological development differed very little between old and new hybrids. Rates of leaf appearance, days from planting to silking and from silking lto maturity, and kernel moisture loss during the grain‐filling period did not show a consistent trend with year of release of the hybrid. The interval from tassel to silk emergence, however, tended to be shorter for new than for old hybrids. Differences in rate of dry matter accumulation among hybrids were largest at late stages of development (3 wk post silking to maturity). Effects of plant density and hybrid on leaf senescence and loss of stover weight from 3 wk post silking to maturity were additive, with older hybrids and higher plant densities showing greater losses of stover weight and higher rates of leaf senescence. The improvement in dry matter accumulation from old to new hybrids may be attributable, in part, to increased tolerance of high plant density.

Genetic Improvement in Grain Yield of Commercial Maize Hybrids Grown in Ontario from 1959 to 1988

Analysis of crop improvement during past decades can elucidate the factors that have contributed to the genetic gain of crop cultivars and the understanding of the factors underlying genetic gain may help to sustain or improve genetic gain in the future. The objectives of this research were to estimate the genetic gain in total and machine‐harvestable grain yield of maize (Zea mays L.) hybrids representing three decades of commercial maize production in Ontario and to quantify the effect of the plant‐density :grain‐yield interaction on the genetic gain. Nine maize hybrids that had been grown in Ontario during the period 1959 to 1988 were evaluated at two locations during 1987 and 1988 at four plant densities. Total above‐ground dry matter, total grain yield, and machine‐harvestable grain yield were determined at physiological maturity. The genetic gain in total grain yield at the optimum plant density for grain yield was 1.7% yr−1, whereas the genetic gain in machine‐harvestable grain yield was 2.6% yr−1. The optimum plant density for machine‐harvestable grain yield increased with year of hybrid introduction. The optimum plant density for total grain yield increased from old to more recent hybrids, but the increase in optimum plant density did not continue for hybrids from the 1970s era to hybrids of the 1980s era. Approximately one‐third of the genetic gain in machine‐harvestable grain yield can be attributed to reduced stem lodging. A comparison of the oldest and most recent hybrids indicates that approximately 15% of the genetic gain in total grain yield can be attributed to increased harvest index. Consequently, increase in total dry matter accumulation attributed 85% to the genetic gain in total grain yield.

Varietal response in wheat to water supply in the field, and male sterility caused by a period of drought in a glasshouse experiment

SUMMARYField experiments in 1961 and 1962 with four winter wheat varieties (Professeur Marchal, Cappelle‐Desprez, Hybrid 46 and Holdfast) compared three water regimes: irrigation to prevent the soil water deficit exceeding 2 in.; shielding from rain; and normal rainfall. The experiments were done on soils selected for their liability to drought. Grain yield was decreased by water deficit; the effects differed between varieties, but the varietal differences were not consistent in the 2 years.In glasshouse experiments, plants of Cappell‐Desprez were subjected to drought for 3–4 days during ear development and subsequently watered normally. When this treatment preceded pollen meiosis by a few days many of the lower florets of each spikelet were male‐sterile but female‐fertile. Also there was often proliferation, within the spikelet, of normally fertile florets above the male‐sterile ones, showing that the number of florets formed may increase until a late stage in ear development.The results of the field experiment suggested that grain yield was restricted by the capacity of the grains as sinks for photosynthates. If so, a genetic improvement in grain yield could be obtained by breeding for an increase in number of florets per spikelet.