Repeatability of stability estimators for downy mildew incidence in pearl millet

Summary Repeatability of mean downy mildew (Sclerospora graminicola (Sacc.) Schroet.) incidence, regression coefficients and deviation mean squares were investigated for 25 pearl millet (Pennisetum typhoides (Burm.) Stapf. & Hubb.) genotypes in 20 environments by correlating arrays of these stability parameters over subsets of the 20 environments arranged according to the year-wise, random, stratified and extreme methods of environmental division. Correlation coefficients between arrays of mean downy mildew incidence from different pairs of subsets ranged from 0.57 to 0.98 and those of deviation mean squares from 0.58 to 0.96 indicating good repeatability of these parameters. Arrays of regression coefficients from different subsets, on the other hand, showed correlation coefficients that ranged from –0.58 to 0.96. Apparently, the regression index of stability was not repeatable for the genotypes and environments studied. Therefore, in order to identify a widely adapted genotype, testing is required to be carried out over a wider range of environments.     

Stability analysis over various filial generations in bread wheat

Summary Stability analysis on 7 parent varieties and all their possible crosses (excluding reciprocals) in generations F₁ to F₅ are reported. The regression coefficient (b) of the parents ranged from 0.66 (Sonalika) to 1.34 (Kalyansona). On the average the b value was lower in F₃ (.87) and F₂ (.88) followed by F₁ (1.04), F₄ (1.06) and F₅ (1.16). Phenotypic stability appeared to be associated with genetic constitution of the parents as well as level of heterozygosity and heterogeneity of the populations. Distinct differences were observed in general combining ability values for regression coefficients among the parents, indicating transmissibility of this trait. However, no such trend was observed for deviation mean squares. The data on yield and stability parameters showed that high mean yield is not necessarily associated with average regression, indicating the possibility of combining high mean yield with high stability.     

Effects of selection criteria on yield stability in chickpea (Cicer arietinum L.)

Summary Selection in the F₃ generation for seed yield, fruiting branches/plant, effective pods/plant, and seed index (100-seed weight) was carried out in two chickpea crosses. Sixty F₅ lines (15 lines/selection criterion) along with check variety were evaluated for seed yield in three distinct environments. The effects of selection criteria on yield stability was examined using linear regression approach and genotype-grouping technique. There were no differences between selection criteria for linear yield responses of F₅ lines to different environments. Within all four selection criteria the lines showed similar linear responses. The non-linear component was relatively higher for lines selected for effective pods and seed index than lines selected for yield and fruiting branches. On the basis of mean yield and coefficient of variation across environments, the seed index was the least effective selection criterion for developing high yielding and stable lines. When the results of stability parameters and genotype-grouping technique were considered together, selection for yield and fruiting branches was highly effective for isolating stable and high yielding lines.     

Regression analysis for general adaptation in pearl millet using different environmental indices

Summary Regression analyses on grain yield of 20 hybrid and 13 composite varieties of pearl millet (Pennisetum typhoides (Burm. S. & H.)) evaluated at 19 sites in India were performed to assess their relative stability and to compare different measures of environmental values. A large portion of the significant genotype X environment interactions was attributed to the non-linear component and deviations mean squares (S_di ²) were a very important parameter for selection of stable varieties. The mean grain yield was positively associated with regression coefficients and deviations mean squares. The hybrids MH 31, MH 35, MH 36 and MH 62 and composite populations MP 16, MP 31 and MP 36 possessed general adaptability. The use of dependent, independent and near-independent measures of environmental values has been found to have little influence on the general interpretation of regression analysis in pearl millet.     

Effect of genome combinations on stability of yield and yield components in wheats and triticales

Summary The data on number of grains/spike, 100 grain weight and grain yield/plant in eighteen genotypes of four genome combinations (AABB- 4 genotypes, AABBDD- 6 genotypes, AABBRR- 5 genotypes and AABBDDRR- 3 genotypes) were recorded for eight environments created by combining two dates of sowing, two fertilizer regimes and two spacings. Two stability parameters-regression coefficient (b) and deviation from regression (S_d ²) were computed. Joint regression analyses revealed that the genotypes differed significantly for these characters. A significant variation due to environments was also found. A comparative study of performance of genotypes belonging to four genome combinations revealed that the genes for stability are not uniformly distributed in these genome combinations. Stability may largely depend on gene combination rather than on genome combination.     

A note on the application of diallel crosses for the analysis of genetic variation in natural populations

Summary The complete diallel cross among homozygous lines can be a useful tool to analyze the genetic architecture of natural populations. However, it represents the natural population only approximately, in particular if the number of lines is small and the analyzed traits exhibit inbreeding depression or other forms of directional dominance. Some incorrect expected mean squares that can be found in the literature suggest tests for genetic variance components that can be misleading under such circumstances. Expected mean squares for a factorial analysis and for a modified Hayman analysis are presented and the effect of the number of lines and directional dominance is discussed.     

Stability analyses for estimating relative durability of quantitative resistance

Summary Experiments in which a series of host cultivars are inoculated in all combinations with a series of pathogen isolates have been used to detect specificity in the host resistance. A theoretical model of polygenic resistance involving both general and specific interactions with pathogen virulence was developed to test the abilities of statistical analyses to discriminate between host genotypes with different levels of general and specific resistance. Estimates of levels of specific resistance could be obtained in regressions of disease severity scores for each host cultivar X pathogen isolate combination vs. the virulence index of each isolate. If the virulence index was based on the mean disease severity induced by the isolate over all host cultivars, the slopes of the regression lines were correlated with the levels of specific resistance in host cultivars. If the virulence index was based on the disease severity induced by the isolate on a host cultivar with a minimum of specific resistance, the mean squares for deviations from the regression were correlated with the levels of specific resistance in host cultivars. A method was developed to consistently choose host cultivars with minimum specific resistance. The two regression analyses gave estimates of specificity in randomly generated, model genotypes of approximately equal accuracy, although the second method appeared to be more accurate when the numbers of loci controlling resistance and virulence were small. The best estimates of numbers of genes for specific resistance were obtained by calculating a rating based on mean disease severity, the mean square for deviation from the regression on the virulence index based on disease severity on the cultivar with minimum specific resistance and the slope of the regression on the virulence index based on the mean disease severity. The best estimates of proportions of resistance genes that were specific were obtained by calculating a rating based on the above deviation mean square and slope alone.Cooperative investigation of the U.S. Department of Agriculture, Agricultural Research Service and the North Carolina Agricultural Research Service. Journal Series Paper No. 8326 of the North Carolina Agricultural Research Service     

A method of analyzing cultivar x location x year experiments: a new stability parameter

Summary Assessment of cultivar performance in a cultivar x location x year experiment is often difficult because of the presence of a location x year interaction. Our objective is to demonstrate a method on separation of environment effects (location x year) into predictable and unpredictabel components. The analysis consists of two parts: (1) a regression analysis based on location effects (averaged over years), assuming that the location means represent predictable environmental variation; and (2) the estimation of stability (denoted type 4) based on the years within location mean squares, assuming that years within location represent unpredictable environmental variation. From the regression analysis in (1), a breeder can determine the optimum range of locations in which a cultivar is well suited, and from (2) he can choose the most stable cultivars. The advantage of type 4 stability is that it is independent of the other cultivars included in the test and of the regression coefficient estimated for predictable variation. Three sets of published data are used to illustrate the analysis. Type 4 stability is compared with type 3 stability (deviation mean square from regression on environmental index) for genetic consistency. The analyses suggest that type 4 stability is consistent and is therefore a potential genetic parameter, but type 3 stability is not.Contribution No. I-806 from Engineering and Statistical Research Centre, Research Branch, Agriculture Canada, Ottawa, K1A OC6, Canada     

60份优质番茄自交系遗传多样性AFLP分析

本文以AFLP技术对60份优质番茄自交系的遗传多样性进行了分析。17对AFLP引物组合共扩增得到905条带,其中多态性条带251条,平均每对引物检测到约15个多态性位点,平均多态率为27.7%;仅用E7M4和E7M10两对引物组合就可以绘制60份番茄自交系的指纹图谱。60个自交系间的Jaccard遗传相似系数变幅为0.259-0.952,平均值为0.664。采用UPGMA方法聚类,遗传相似系数变幅为0.54-0.57时,60份番茄材料可以划分为7个类群。聚类结果与来源、果实大小、果形等性状未表现出明显的相关性。     

甘蔗品种主要性状的基因型与环境及其互作效应分析

用AMMI模型双标图对国家第六轮甘蔗品种区域试验5个试点的12个甘蔗品种试验数据进行分析,研究甘蔗区试中不同品种的产量稳定性问题。结果表明,参试品种的6个产量性状在品种间和地点间差异显著,品种与地点的互作效应差异显著;FN30、YG16蔗茎产量和含糖量高,稳定性强,属于高产、稳产性较好的品种。AMMI模型很好地解释了甘蔗品种产量性状的基因型效应、环境效应和GE互作效应。     

Phenotypic Stability of Mixtures – Relations Between the Stability Parameters of a Mixture and Its Components

For each of the two stability parameters (‘regression coefficient’ and ‘sum of squared deviations from the regression’) of the common regression approach (= regression of the yield of population i in environment j on the environmental index of this evironment j which often has been estimated by the mean of all tested populations in this environment j) the phenotypic stability of a mixture and it's components have been analysed theoretically. It can be shown that in practical applications (for example: variety testing) the regression coefficient of a mixture often can be sufficiently approximated by the arithmetic mean of the regression coefficients of the components grown singly. This simple relation between a mixture and it's components don't hold for the second stability parameter ‘sum of squared deviations from the regression’. The exact relation has been deduced and useful and clear approximations are discussed. All the theoretical results are demonstrated and applied using the well-known experimental barley data of Sandfaer (1970).     

Increased Selection Response in Larger Populations. I. Selection for Wing-Tip Height in Drosophila Melanogaster at Three Population Sizes

The effect of population size on selection response was investigated with replicated selection lines of 40, 200 and 1000 selected parents, using Drosophila melanogaster homozygous for the mutant raised. Selection for increased wing-tip height was carried out for 55 generations, with an average selection intensity of 0.6 standard deviation. The rank order of responses in the seven individual lines was significantly in order of population size, and the variance of response among lines showed a significant effect of population size. The final mean responses (selected - controls, +/- standard errors) in the three treatments, in order of increasing population size, were 8.6 +/- 1.8 mils (three small lines), 15.1 +/- 1.3 mils (two medium lines), and 19.8 +/- 1.5 mils (two large lines). The differences between treatments seem to have emerged too rapidly to be the result of mutations, and are probably due mainly to the utilization of existing variation with greater efficiency by selection in larger populations.     

Adaptation of safflower genotypes Carthamus tinctorius L.

Summary Adaptation reactions of 33 genotypes of safflower Carthamus tinctorius L. were studied under 7 different climatic conditions. The genotpyes were divided into two sets. Set I consisted of 15 genotpyes selected from the local populations. Set II had 15 introduced and local varieties. Three control genotpyes, Ute, Ferio, and Local Arak, were common to both sets.Genotpye-environment interaction was not significant for Set I but it was highly significant for Set II. Three environmental indices were obtained and used in the adaptation analyses of the genotpyes in Set II. One of the environmental indices, designated EI, was dependent on the genotypes of Set II. The other two indices, designated EI-1 and EI-2, were independent of the genotpyes of Set II. The methods of Eberhart and Russell (1966) were used in analyses of adaptation by Index EI and the methods of Freeman and Perkins (1971) for Indices EI-1 and EI-2.The mean square associated with genotype-environment interaction was partitioned into two components, heterogeneity of regression and its residual, under EI-1 and EI-2. Both components were highly significant for both cases. However, the mean square of heterogeneity of regression was equal to its residual under EI-1 and even smaller than its residual under EI-2. These observations indicate that a major part of genotpye-environment interaction can not be accounted for by differences in the regressions of the individual genotypes. As well as this overall test, individual regression analyses for single genotypes were also considered. None of the genotypes had significant regression mean square under EI-1. Only two introduced genotypes had significant regression mean squares when EI-2 was used. The overall test of equality of the slopes of the regression for the genotypes of Set II was rejected at the 1% level under EI. This test indicated that genotypes of Set II were significantly different in their association with the EI. The significant differences among the genotypes of Set II were also shown by an F test of the pooled deviation mean square divided by the pooled error mean square. Individual regression analyses for single genotpyes of Set II were considered under EI. Mixed adaptation reactions were observed for different genotypes. Among 18 genotypes of Set II, regression mean squares were significant for only 10 genotpyes. Therefore, it appeared that the dependent environmental indices are more useful than the independent environmental indices when statistical theory of regression is used in the analysis of adaptation. Observations in the present study were not in agreement with the hypothesis that the relation between the performance of different genotypes in the various environments and some measure of these environments is linear or nearly so.Among the 12 introduced genotypes, only one, Ute, was identified as stable and high-yielding. Among the 15 selected from the locally adapted populations, eleven did not differ significantly from Ute in mean yield but four exceeded Ute significantly in mean productivity. The present study thus indicates that the Iranian safflower breeding project has been successful in identifying genotpyes which give high and stable yields under diverse environmental conditions. It does not indicate that introduced and exotic germplasms are unimportant in the breeding projects; it is quite possible that still more desirable genotypes can be developed by incorporating introduced genetic variability into the local germplasm.Associate Professors and Plant Breeder     

Transgenic Pm3 multilines of wheat show increased powdery mildew resistance in the field

Resistance (R) genes protect plants very effectively from disease, but many of them are rapidly overcome when present in widely grown cultivars. To overcome this lack of durability, strategies that increase host resistance diversity have been proposed. Among them is the use of multilines composed of near-isogenic lines (NILs) containing different disease resistance genes. In contrast to classical R-gene introgression by recurrent backcrossing, a transgenic approach allows the development of lines with identical genetic background, differing only in a single R gene. We have used alleles of the resistance locus Pm3 in wheat, conferring race-specific resistance to wheat powdery mildew (Blumeria graminis f. sp. tritici), to develop transgenic wheat lines overexpressing Pm3a, Pm3c, Pm3d, Pm3f or Pm3g. In field experiments, all tested transgenic lines were significantly more resistant than their respective nontransformed sister lines. The resistance level of the transgenic Pm3 lines was determined mainly by the frequency of virulence to the particular Pm3 allele in the powdery mildew population, Pm3 expression levels and most likely also allele-specific properties. We created six two-way multilines by mixing seeds of the parental line Bobwhite and transgenic Pm3a, Pm3b and Pm3d lines. The Pm3 multilines were more resistant than their components when tested in the field. This demonstrates that the difference in a single R gene is sufficient to cause host-diversity effects and that multilines of transgenic Pm3 wheat lines represent a promising strategy for an effective and sustainable use of Pm3 alleles.     

Potential gain from selection for yield stability in two grain sorghum populations

Summary Maximum yield under highly unpredictable environments should be associated with selection of genotypes with superior performance across good and poor environments. Several stability parameters have been proposed to identify superior genotypes over a wide range of environments. None of these has been used as selection criteria, however, because of their low heritability. The objective of the study presented here was to compare the relative efficiency of predicted gain from indirect selection among three stability parameters: the coefficient of regression (b), deviation from regression (S _d ² ), and principal components scores (PC) from the AMMI model; two indices including mean yield and a stability parameter; and three indices involving yield at the best, the worst, and an intermediate environment. Two hundred S₁ families from each of two sorghum populations (TP24D and KP9B) were evaluated at four dry-land evironments over 2 years. The low heritability estimates and the low genetic correlation between the various stability parameters and mean yield resulted in their low relative efficiency as indirect selection criteria for high yield across environments. However, when the parameters were combined with mean yield over all to create indices, the relative efficiency increased for all the environments. In terms of resource allocation, these indices were not as efficient as mean productivity, rank summation, and selection index that involved fewer environments in their estimation.Contribution no. 9820 of Agricultural Research Division, Univ. of Neb. and no. 92-203-J of Kansas Exp. Stn.     

分子标记辅助选择改良水稻不育系臻达A及其杂交种的稻瘟病抗性

水稻抗稻瘟病基因Pi25是一个遗传传递能力强的广谱抗性基因。本研究以携带抗稻瘟病基因Pi25的BL27为抗源供体,与优质、配合力强、感稻瘟病的水稻保持系臻达B为受体亲本进行杂交、回交创制水稻抗病保持系新种质,再与臻达A测交和回交进行不育系转育,结合分子标记辅助选择和农艺性状筛选,获得3个抗性基因纯合、农艺性状和开花习性均与臻达A相似的改良不育系株系。利用福建省近年来致病性代表的22个稻瘟病菌株对3个改良不育系及其15个杂交种进行抗性鉴定,3个改良不育系的抗性频率为95.45%~100%,15个杂交种的抗性频率均达75%以上,而原始对照臻达A及其杂交种的抗性频率仅为54.55%和40.91%~63.64%。自然病圃诱发鉴定表明,3个改良不育系的叶瘟和穗颈瘟均为0级,表现高抗,而对照臻达A的叶瘟为5级,穗颈瘟为7级,表现感病;15个杂交种均表现良好的稻瘟病抗性。进一步分析比较15个杂交种的产量、农艺性状和稻米品质表现,结果表明臻达A-Pi25-3改良不育系的综合性状表现最优,继续回交转育,于2015年育成了稻瘟病抗性强、配合力好、群体整齐和性状稳定的不育系,命名为157A。研究表明,抗稻瘟病基因Pi25不仅在水稻不育系臻达A的遗传背景下的抗性表达完全,且在不同水稻恢复系测交种的背景下同样表现出较高水平的抗性,说明抗性基因Pi25对不育系稻瘟病改良的效果明显。创制的新不育系157A的稻瘟病抗性显著提高,还基本保留了原来不育系高配合力等优良特性,为选育高产、优质、抗病杂交稻新品种提供了不育系新种质。     

Multiline as a Strategy to Reduce Damage Caused by Colletotrichum lindemuthianum in Common Bean

The aim of the study was to verify whether a mixture of lines containing equal amounts of seven lines of Carioca‐type common bean, all agronomically uniform but each presenting different patterns of resistance to Colletotrichum lindemuthianum, would be less damaged by anthracnose than the individual pure lines. Plants cultured in experimental plots in Lavras, Minas Gerais, Brazil, in the dry harvest seasons of 2007 and 2008 were inoculated with a mixture of races 65, 81, 87, 89 and 337 of the pathogen, and the severity of anthracnose was evaluated at 10‐ day intervals commencing 12 days after inoculation. The progress of the disease was estimated from the coefficients of the linear regression equations (b₁) and from the areas under the disease progress curves (AUDPC). The mean grain yields were determined in both experimental periods. The value of b₁ for the multiline was not different from that presented by the resistant line MA‐II‐22 and indicated a slower progress of the disease over time compared with susceptible lines. There were no differences in AUDPC values between the multiline and the resistant lines. The multiline presented a grain yield that was similar to those of the most productive lines even though susceptible lines comprised more than 28% of the mixture and such lines showed the lowest yields of grain. It is concluded that the use of the mixture of lines represents a good strategy for reducing the progress of anthracnose in the field and, as a consequence, reducing loss of grain yield.     

杂交水稻结实率稳定性的遗传分析

本文采用三套同核异质不育系与５个恢复力不同的恢复系按Ｐ×Ｑ模式配组、分５期播种的试验设计,在ＡＭＭＩ模型分析结实率稳定性的基础上,进一步剖析了不育胞质、保持系、恢复系及其工作的各种遗传效应。     

METHODS FOR THE STUDY OF BLOWFLY POPULATIONS

The variance of groups of traps sampling the blowfly populations of areas of different degrees of complexity is examined from data for three representative types of pasture—semi-arable, reclaimed peat bog, and upland sheepwalk.
For mean catches of under twenty flies the coefficient of variation was less for limited areas of homogeneous vegetational cover than for larger areas and greater diversity of vegetation; at intermediate mean levels the difference was negligible, hut it reappeared at mean levels of 40 and upwards.
Throughout the range of catches examined the variance was much greater than the mean. For very low catches even the standard deviation exceeded the mean, and at no level of mean was it less than 40%.
Even for uniform areas such as association fragments the high variance made results with less than six traps difficult to interpret, and ten or more traps are advised.
Two methods of comparative sampling of populations are discussed—stratification of the area to be sampled into subunits of relatively uniform vegetational or edaphic facies, and random distribution of the traps over the whole area. For the mean catches by these methods standard regression lines are suggested, from which variance estimates may be made when comparing observed means. Both regressions consist of two straight lines, the lower in each case having a steeper slope. The lines are:
Sections S.D. =+ 1 and 0·5+7.
Subsection blocks S.D. = 0·8+ 1 and 0·4+9     

Environmental stability and heritability estimates for grain yield and test weight in triticale

Hexaploid triticale has many advantages over both parental species for both grain and forage production in certain environments. Additional information on environmental stability and heritability would be desirable to develop appropriate selection strategies in the production of superior widely-adapted cultivars. The grain yield of 22 diverse genotypes grown at four ecologically-distinct geographical locations [Quincy, FL, USA (approximate geographical coordinates (AGC) = 30 degreesN 84 degreesW, approximate elevation (AE) = 58 m), Plains, GA, USA (AGC = 32 degreesN 84 degreesW, AE = 76 m), Bozeman, MT USA (AGC = 45 degreesN 111 degreesW, AE = 1458 m), and Aberdeen, ID, USA (AGC = 42 degreesN 112 degreesW, AE = 1360 m)] was measured in two years with winter and spring planting dates only at Bozeman and Aberdeen. Test weight (grain weight in a given volume) was determined for two years at Bozeman and Aberdeen at both planting dates and one year at Quincy. Stability analyses indicated that significant (P < 0.01) variation in means, regression coefficients, and deviation mean squares of the genotypes were present for both characters. Realized heritability (h2) estimates were as follows: grain yield ranged from -0.02 to 0.80 with a mean of 0.57; test weight ranged from 0.63 to 1.05 with a mean of 0.93. The results indicated that substantial genetic variation is present and selection for widely-adapted cultivars would be effective for both characters especially test weight.