Four Decades of Breeding for Varietal Improvement of Irrigated Lowland Rice in the International Rice Research Institute

Abstract

Since the establishment of the International Rice Research Institute (IRRI) in 1960, IRRI’s breeding effort in varietal improvement for irrigated lowland has passed four decades. Breeding of semi-dwarf rice varieties such as IR8 at IRRI during first decade from 1960 to 1969 resulted in quantum leaps in yield potential, which marked the green revolution in Asia. During the second decade from 1970 to 1979, the primary emphasis of rice improvement has been directed towards incorporation of multiple disease and insect resistance and shortening of growth duration. Grain quality was the main target of crop improvement at IRRI during the third decade from 1980 to 1989. The fourth decade from 1990 to 1999 and beyond was focused again on the improvement of yield potential by developing hybrid rice and new plant type. Up to 1999, 46 indica inbred varieties and 2 indica/indica hybrid rice varieties were developed by IRRI and released in the Philippines for the irrigated lowland rice systems. Large-scale adoption of these improved varieties under modern crop management practices has resulted in a dramatic increase in rice production in major rice-growing countries. The hybrid varieties between indicas increased yield potential by 9% under the tropical conditions. New plant type (NPT) breeding has not yet resulted in an increase in yield potential. The second generation NPT developed by crossing tropical japonica with indica has demonstrated some promising results in terms of improvements in yield potential, disease and insect resistance, and grain quality.     

Genetic Diversity in Crop Improvement

SUMMARY

The use of genetic diversity to form modern crops is one of the most remarkable accomplishments of agriculture. Even in the age of genomics, genetic diversity remains the cornerstone of crop improvement. There is extensive diversity in soybean and its ancestors. Much of this diversity has been collected though opportunities to extend collections remain. Genetic diversity has been used extensively in Asian breeding but utilization of exotic germplasm has been limited in North America. Capturing the value of diversity is easy for some traits but quite difficult for other traits, such as yield. New procedures and technology may greatly facilitate understanding and effective use of these exotic yield alleles. For the foreseeable future though, progress in capturing yield value from exotic germplasm through traditional breeding will continue to outstrip our scientific understanding of the alleles themselves. Public institutions will need to facilitate access to germplasm to increase utilization of diversity so it favorably impacts humanity.     

A serial cross-sectional study of the prevalence of rabbit haemorrhagic disease on three farms in the lower North Island of New Zealand

AIM: To estimate over a 3-year period following the first release of rabbit haemorrhagic disease virus (RHDV) the prevalence of rabbit haemorrhagic disease (RHD) and the abundance of rabbits (Oryctolagus cuniculus) in an area that historically had low rabbit densities.

METHODS: Three farms grazing predominantly sheep and beef cattle, located close together and with low initial rabbit densities, were selected for study. RHDV had been deliberately released on all farms in December 1997. Farms were visited 2–3 times per year between June 1998 and April 2001. At each visit, rabbits were shot with the aid of spotlights at night and blood samples were collected for detection of RHDV antibodies. Rabbit carcasses were necropsied and the age of the animals was determined. Rabbit abundance on each property was measured throughout the study using spotlight night counts. Logistic regression was used to identify factors associated with the risk of carcasses being seropositive for RHDV.

RESULTS: Rabbit density differed initially between farms (8.2, 9.9, 2.3 rabbits per spotlight km in June 1998), and declined on all three properties over time (1.2, 2.4, 1.1 rabbits per spotlight km in November 2000). Highest antibody titres to RHDV were initially evident on the farm on which rabbits were most abundant. The average prevalence of seropositive rabbits overall was 21% (95% CI=15–28%). Female rabbits tended to be less likely to be seropositive for RHDV than males (OR=0.47; 95% CI=0.21–1.02). The odds of becoming seropositive were reduced for rabbits born in the breeding season of 1999–2000 (OR=0.17; 95% CI=0.05–0.64).

CONCLUSIONS: The temporal pattern of outbreaks measured by peaks of seroprevalence differed between closely-spaced farms when they had different rabbit densities, but were similar when rabbit densities were similar. Microclimate and vegetation influencing abundance of insect vectors for RHDV and intrinsic population-related factors like rabbit breeding behaviour are also likely to be involved in local patterns of spread.     

Analysis of genetic diversity in Bolivian llama populations using microsatellites

South American camelids (SACs) have a major role in the maintenance and potential future of rural Andean human populations. More than 60% of the 3.7 million llamas living worldwide are found in Bolivia. Due to the lack of studies focusing on genetic diversity in Bolivian llamas, this analysis investigates both the genetic diversity and structure of 12 regional groups of llamas that span the greater part of the range of distribution for this species in Bolivia. The analysis of 42 microsatellite markers in the considered regional groups showed that, in general, there were high levels of polymorphism (a total of 506 detected alleles; average PIC across per marker: 0.66), which are comparable with those reported for other populations of domestic SACs. The estimated diversity parameters indicated that there was high intrapopulational genetic variation (average number of alleles and average expected heterozygosity per marker: 12.04 and 0.68, respectively) and weak genetic differentiation among populations (F_ST range: 0.003–0.052). In agreement with these estimates, Bolivian llamas showed a weak genetic structure and an intense gene flow between all the studied regional groups, which is due to the exchange of reproductive males between the different flocks. Interestingly, the groups for which the largest pairwise F_ST estimates were observed, Sud Lípez and Nor Lípez, showed a certain level of genetic differentiation that is probably due to the pattern of geographic isolation and limited communication infrastructures of these southern localities. Overall, the population parameters reported here may serve as a reference when establishing conservation policies that address Bolivian llama populations.     

Estimation of accuracies and expected genetic change from selection for selection indexes that use multiple‐trait predictions of breeding values

Procedures are described for estimating selection index accuracies for individual animals and expected genetic change from selection for the general case where indexes of EBVs predict an aggregate breeding objective of traits that may or may not have been measured. Index accuracies for the breeding objective are shown to take an important general form, being able to be expressed as the product of the accuracy of the index function of true breeding values and the accuracy with which that function predicts the breeding objective. When the accuracies of the individual EBVs of the index are known, prediction error variances (PEVs) and covariances (PECs) for the EBVs within animal are able to be well approximated, and index accuracies and expected genetic change from selection estimated with high accuracy. The procedures are suited to routine use in estimating index accuracies in genetic evaluation, and for providing important information, without additional modelling, on the directions in which a population will move under selection.     

玉米新品种通单258选育与应用研究

[目的]为玉米(Zea mays L.)新品种通单258今后大面积推广及在玉米育种中的应用提供科学依据。[方法]介绍通单258的选育经过、特征特性、产量表现、适应区域、栽培技术及制种技术。[结果]通单258是通化市农业科学研究院玉米研究所以自选系通2127作母本、通1702作父本杂交选育而成的中熟玉米杂交种,该品种在吉林省2011～2012年玉米区域试验和生产试验中表现出高产、稳产、品质优良、抗逆性好、适应性广等特点,2013年通过吉林省农业委员会审定。[结论]通单258综合性状优良,具有广阔的应用前景。     

大麦遗传育种技术研究进展

大麦是主要的栽培作物之一,有着悠久的栽培历史。在大麦栽培过程中,大麦遗传育种工作是影响其栽培面积和栽培方式的关键因素之一。相对于大麦的栽培历史,国内外的大麦遗传育种工作起步较晚,从常规育种方法到花药培养技术,再到分子标记辅助选择,大麦遗传育种技术的发展,使大麦产量和品质都得到了很大的提升。大麦遗传育种技术在大麦产业的发展中起到了举足轻重的作用,结合大麦育种实际对大麦遗传育种技术进行了分析和阐述。     

水稻光温敏核不育系LY172S的选育

[目的]为籼型光温敏核不育系LY172S在水稻育种中的进一步应用奠定基础.[方法]介绍LY172S选育过程、特征特性、育性表现、抗病性、米质、可繁性与繁殖技术要点、配组情况.[结果]LY172S是以1892S为母本,以协青早B为父本杂交选育而成的籼型光温敏核不育系,不育性稳定、起点温度低、异交结实率高、米质好、配合力强.2012年安排了华中农业大学植物科学技术学院组织的人工光温育性鉴定,2012年8月通过安徽省品种审定委员会组织的专家鉴定.[结论]LY172S在今后的水稻育种中有广阔的应用前景.     

优质高产多抗杂交油菜新品种T9034的选育与应用

[目的]探讨优质高产多抗杂交油菜新品种T9034的生产潜力和推广应用价值。[方法]介绍T9034的选育经过、特征特性、高产栽培技术要点、配套高产制种技术。[结果]T9034是安徽省铜陵县农业科学研究所用不育系铜A01与恢复系0337C配组育成的杂交油菜新组合,具有产量高﹑品质优﹑抗性强等特点,2008年通过安徽省审定。[结论]该研究可为T9034的大面积推广应用奠定基础。     

梭鱼养殖群体与自然群体的遗传结构研究

[目的]掌握渤海地区梭鱼种群的种质资源状况。[方法]应用随机扩增多态DNA(RAPD)技术,对梭鱼养殖群体与自然群体的遗传多样性进行了分析。[结果]从45个随机引物中选出20个扩增效果稳定的引物进行群体分析。其中,梭鱼自然群体共检出了204个扩增位点,多态位点136个,多态位点比例为66.7%;养殖群体中共检出了217个扩增位点,多态位点130个,多态位点比例为59.9%。[结论]目前梭鱼群体的遗传多样性较为丰富,人工养殖还未对其造成明显的影响。