Pyramiding of partial disease resistance genes has a predictable,but diminishing,benefit to efficacy

Partial resistance genes often need to be ‘pyramided’ into a crop cultivar to obtain commercially acceptable levels of disease resistance. Analysis of data from four different wheat mapping populations, segregating for partial resistance to four contrasting foliar pathogens, showed a diminishing benefit to disease control from increasing the numbers of resistance loci in wheat lines. To test whether a general function could describe the efficacy benefit from pyramiding, a simple multiplicative survival model (MSM) was used to predict disease severities on mapping population lines carrying various combinations of two, three or four resistance loci. The effectiveness of each resistance locus was expressed as the disease severity in lines carrying resistance alleles at one locus, as a proportion of the severity in lines carrying no detectable resistance alleles. The predicted severity from any given combination of multiple resistance loci was calculated as the product of the proportional severities for the relevant single loci. A regression line fitted to transformed observed against predicted values explained 93% of the variation, with a slope and intercept not significantly different from 1 and 0, respectively. MSM may therefore provide a simple method to test contrasting types of partial resistance and search for synergistic combinations. The analysis suggests that diminishing returns are a general feature of partial resistance to foliar pathogens in wheat, a finding that is likely to apply to other crop pathosystems. Identifying and combining ever more QTL is likely to provide limited gains. The consequences of these findings for QTL analysis are described.     

甘蓝型油菜隐性上位互作核不育系的选育及其细胞学研究

【目的】利用甘蓝型油菜隐性上位互作细胞核雄性不育材料的杂种优势,阐明其雄性不育的机理。【方法】以引进的油菜杂交种"皖油14"为材料,采用自交、姊妹交、测交的方法,对其后代进行选育;通过石蜡切片法,对选育得到的纯合两型系中的可育株1740B、不育株1740A及全不育系1740CA植株的雄蕊发育特点进行细胞学观察。【结果】选育得到甘蓝型油菜隐性上位互作细胞核雄性不育材料的临保系1740C和纯合两型系1740AB。细胞学观察结果表明,可育株1740B的雄蕊发育正常,可形成成熟的花粉粒,花药发育过程主要包括孢原细胞时期、造孢细胞时期、花粉母细胞期、减数分裂期、单核花粉期、二核花粉期和三核花粉期;纯合不育株1740A的雄蕊败育发生在四分体后期,由于四分体周围的胼胝质不能解体和绒毡层细胞的径向肥大,使得四分体被挤向药室中央且原生质体浓厚,然后逐渐解体死亡,最后整个花粉囊萎缩变形;全不育系1740CA的花粉败育过程从小孢子时期到二核期均有发生,花粉细胞外只能形成极薄的一层花粉壁,绒毡层脱落并径向肥大,将花粉细胞挤向药室中央,花粉细胞质逐渐降解,细胞变形,最终变成一个无内容物的空壳。【结论】利用"临保系"进行测交选育是从定性的角度来辨别遗传分离比例的差异;甘蓝型油菜隐性上位互作细胞核雄性不育材料中,纯合不育株与杂合不育株的雄蕊败育时期及特征存在差异。     

水稻单穗重和千粒重的QTL定位

用基于混合线性模型的统计方法对一套来源于亲本IR64/Azucena的加倍单倍体群体在两个生产季节的水稻单穗重和千粒重进行了分析,各检测到15个QTL分别控制这两个性状,其中有6个QTL同时与这两个性状有关。所有QTL分布在除第11、12染色体以外的其余10条染色体的相应标记区间内。在控制千粒重的QTL中,12个QTL有加性效应,6对QTL带有加加上位性效应,它们不受环境条件的影响。在控制单穗重的QTL中,7个QTL具有加性效应,但其中4个QTL的表达随环境而异;6对QTL具有加加上位性,但其中1对对环境敏感。qTGW2的加性效应对千粒重的贡献率超过10%;3个QTL（qGW1、qGW7和 qGW8 1）在早季环境的加性效应对单穗重的贡献率亦都大于10%,但对环境敏感。     

甘蓝型油菜隐性上位互作核不育系9012A与6AB和S45AB遗传对比

研究结果表明：（１）甘蓝型油菜核不育系９０１２Ａ与显性上位互作核不育６ＡＢ在恢复关系上明显不同,是不同于显性上位互作核不育的一种新的互作核不育类型。其育性受２对隐性重叠不育基因与一对隐性上位抑制基因互作控制。（２）控制９０１２Ａ和Ｓ４５Ａ的不育基因是非等位的,在甘蓝型油菜中存在至少２套隐性重叠不育基因。进一步的研究显示隐性上位基因与隐性重叠不育基因之间的互作可能是非专一性的。这对现有双隐性核不育杂种优势利用具有重要的意义。     

作物杂种优势机理研究进展

杂种优势是农业生产中非常重要的遗传现象之一.杂种优势虽然已经被成功应用了数个世纪,但其形成的机理仍不十分明了.不同时期的学者在不同层次上进行了大量的研究和探索并相应地提出了一些解释或假说,但至今都没有形成一个较为一致的解释.本文综述了作物杂种优势机理相关的重要假说以及近年来国内外的相关研究进展.     

水稻抽穗期 QTLs 的检测及上位性和环境互作效应分析

利用所构建的Lemont?特青重组自交系 (RIL)，采用混合线性模型和复合区间作图法，对不同季节获得的水稻抽穗期性状进行 QTL 定位及上位性和环境互作效应分析。检测到 3 个控制抽穗期的 QTL，分别位于 3、7 和 11 号染色体上，共解释 18.86% 的遗传变异，单个 QTL 的表型贡献率为 2.95%?10.56%，其中 qHD7-1 与环境存在显著互作，贡献率为2.18%；另检测到 9 对具有上位性效应显的互作位点。本研究表明上位性效应对水稻抽穗期具有重要的作用，抽穗期的一些QTL对环境敏感，在实际育种上应利用在不同环境稳定检测到的 QTL 进行分子标记辅助选择。     

玉米穗部性状遗传分析

以两组PA 种质改良系J1255、J1401 与S122 杂交所形成的6 个世代为试验材料,采用郭平仲提出的世 代平均数分析方法对玉米穗长、穗粗、籽粒长、百粒重、穗粒重进行了遗传分析。结果表明;玉米穗长与百粒重的遗传 受基因的加性效应为主,显性效应次之;穗粗、籽粒长和穗粒重的遗传受基因的显性效应作用为主,加性效应次之; 上位性效应明显存在于穗部各性状的世代遗传变异中,其中,对于百粒重的遗传变异,上位性效应明显大于显性效 应,并以加性伊加性的上位性互作为主。     

Generation means analysis of <Emphasis Type="Italic">wheat streak mosaic</Emphasis> virus resistance in winter wheat

Wheat streak mosaic virus (WSMV; Family: potyviridae; Genus: Tritimovirus) is a major threat to winter wheat (Triticum aestivum L. em. Thell) production worldwide, yet little is known about the genetic control of resistance. Our objective was to determine the mode of inheritance and type of gene action of WSMV resistance in two winter wheat crosses involving a resistant line, OK65C93-8, and two susceptible cultivars, Tandem and Vista. For each cross, parents, F₁, F₂, and backcross plants were inoculated and evaluated for WSMV resistance in two replicated greenhouse experiments. Generation means analysis indicated that additive, dominance, and epistatic effects were all involved in the inheritance of WSMV resistance. Broad-sense heritability estimates for visual symptom rating and ELISA values were high for both crosses (0.84–0.91). Narrow-sense heritability estimates were low in the Tandem/OK65C93-8 cross (0.43–0.45) and moderate in the Vista/OK65C93-8 cross (0.71–0.74). Due to the presence of greater non-additive gene effects combined with low narrow-sense heritability in the Tandem/OK65C93-8 cross, selecting for WSMV resistance in this cross would be complex if using conventional methods. On the other hand, the significant contribution of additive gene effects combined with moderate narrow-sense heritability in the Vista/OK65C93-8 cross suggested that it could be exploited to select for WSMV resistance. Progress from selection for WSMV resistance in early generations of winter wheat may vary among populations as indicated in this study. Therefore, evaluating genetic control of parental combinations may be warranted prior to selecting for WSMV resistance from this source.     

Quantitative trait loci for grain yield and yield components in a cross between a six-rowed and a two-rowed barley

Summary The positions of quantitative trait loci (QTL) for yield and yield components were estimated using a 85-point linkage map and phenotype data from a F₁-derived doubled haploid (DH) population of barley. Yield and its components were recorded in two growing seasons. Highly significant QTL effects were found for all traits at several sites in the genome. A major portion of the QTL was found on chromosome 2. The effect of the alleles in locus v on thousand grain weight and kernels per ear explained 70–80% of the genetic variation in the traits. QTL × year interaction was found for grain yield. Several different QTL were found within the two-rowed DH lines compared to those found in the six-rowed DH lines. Epistasis between locus v and several loci for yield and yield components indicates that genes are expressed differently in the two ear types. This may explain the difficulties of selecting high yielding lines from crosses between two-rowed and six-rowed barley.Abbreviations DH doubled haploid - QTL quantitative trait locus/loci - RAPD random amplified polymorphic DNA - RFLP restriction fragment length polymorphism - T. Prentice Tystofte Prentice - V. Gold Vogelsanger Gold     

Gene action in the resistance of peppers (Capsicum annuum) to Phytophthora stem blight (Phytophthora capsici L.)

Summary The variation among single and three-way crosses derived from seven lines of pepper (Capsicum annuum) selected for resistance to Phytophthora capsici was analyzed into statistical-genetic components due to general and specific combining abilities and additive-by-additive epistasis. Indirect evidence of higher order epistasis was also estimated. Epistasis was a principal source of variation. It was correlated with the level of aggressiveness of the pathogen. A breeding method such as recurrent selection seems to be the most appropriate to improve resistance to the fungus.