Variance component estimations and allocation of resources for breeding sweetpotato under East African conditions

In Africa, average sweetpotato storage root yields are low and breeding is considered to be an important factor in increasing production. The objectives of this study were to obtain variance component estimations for sweetpotato in this region of the world and then use these to determine the efficiency of variety trials and breeding systems. From an incomplete series of variety trials in Kenya and Uganda (comprising 15 genotypes, three locations, two crop durations and three seasons) variance components were estimated ‐ using the REML method ‐ for the following traits: storage root yield, biomass production, harvest index, storage root dry matter and the Elston index which was used to aggregate all four traits. The storage root yield of clones across all 12 environments ranged from 15.2 to 33.0 t/ha. The variance components were significant for all traits, except the genotype by season interactions for storage root dry matter. The efficiency of selection systems was determined for total test capacities of 450 and 900 plots and using not more than five locations. Two‐stage selection was 17‐81% more efficient than one‐stage selection after two seasons of testing. Two‐stage selection was optimized under the restriction of using at least two locations at step 1. Trials with two locations and one replication at step 1 and five locations and two replications at step 2 were appropriate both for selecting for storage root yield and for simultaneously selecting for storage root yield, biomass production, harvest index and storage root dry matter content by using the Elston index. There are indications that such an allocation of resources for breeding sweetpotato is also appropriate for other regions in Sub‐Saharan Africa.     

AMMI analysis of cassava response to contrasting environments: case study of genotype by environment effect on pests and diseases,root yield,and carotenoids content in Cameroon

Genotype by environment interaction remains a substantial issue in all breeding programs. Crop genotypes are generally developed in a central breeding location, but always require the evaluation of breeding products in different environments. This is particularly relevant in countries that have a wide range of climates. Eighteen cassava genotypes were evaluated in Cameroon in eight environments—varying in seasonal rainfall and temperature patterns and soil characteristics—over two cropping seasons. Soil nutrient content was analyzed and trials were established in a randomized complete block design in three replications. Response of genotypes to major cassava pests and diseases, yield and carotenoids content was evaluated. It was observed that four genotypes did not show cassava mosaic disease (CMD) symptoms irrespective of the environments. The local check had highest CMD incidence and severity across all environments. Average number of whitefly per plant across all environments was highest on TMS 96/0023. Average cassava green mite (CGM) infestation was low on all the genotypes. Fresh root yield of five genotypes ranged between 25 and 30 tons per ha for both years. Significant and positive correlation was found across locations between fresh root yield and soil K, P and Mg. AMMI analysis revealed highly significant differences among genotypes and environments and significant genotype?×?environment interaction for most of the estimated traits, indicating variability in genotypes performance with environment.     

Simple approach to the analysis of GxE interactions in a multilocational spaced plant trial with timothy

Summary Sixty genotypes of timothy, comprising 12 genotypes originating from each of five locations, were grown at the same locations in northern Scandinavia and Iceland, as a part of a joint breeding project in timothy. The trials were observed for two years and various characters were evaluated. Large genotype x environment interactions occurred for most characters and the response of individual genotypes. irrespective of origin contributed most to the variation. A superiority measure (P.), based on the genotype's response and the maximum response, averaged over all locations, was used to rank the genotypes with respect to yield and other morphological attributes. Based on this ranking it is possible to choose genotypes which are high yielding and show good stability over the area.     

Replicate allocation to improve selection efficiency in the early stages of a potato breeding scheme

Field data and simulation were used to investigate replication within trials and the allocation of replicates across trial sites using partial replication as an approach to improve the efficiency of early-stage selection in a potato breeding programme. Analysis of potato trial data using linear mixed models, based on four-plant (clonal) plots planted as augmented partially-replicated (p-rep) designs, obtained genetic and environmental components of variation for a number of yield and tuber components. Heritabilities, trial-to-trial genetic correlations and performance repeatability of clonal selections in p-rep trials and in subsequent fully replicated trial stages were high, and selection was effective for the economically important traits of marketable tuber yield and tuber cooking quality. Simulations using a parameter-based approach, pertaining to the variance components estimated from the p-rep field trials, and the parametric bootstrapping of historic empirical data showed improved rates of genetic gain with p-rep testing over one and two locations compared with testing in fully replicated trials. This potato breeding study suggests that the evaluation and selection of a clonal field crop in fully replicated trials may not be optimal in the early stages of a breeding cycle and that p-rep designs offer a more efficient and practical alternative.     

CIMMYT种质对四川、云南、甘肃和新疆春性小麦产量遗传增益的贡献

研究历史品种产量潜力变化规律有助于提高小麦育种水平。2007—2009连续2年度将来自四川、云南、甘肃和新疆的代表性59个品种分别种植在四川成都、云南丽江、甘肃武威和新疆昌吉,在肥水供应充足、控制病虫害和倒伏的条件下分析了产量和相关农艺性状的变化趋势。结果表明,四川、云南、甘肃和新疆品种的产量随育成年份显著增加,年遗传增益分别为0.73%、0.34%、0.58%和1.43%。产量遗传增益四川品种表现与产量构成因子关系不密切;云南品种主要表现为减少穗数和增加穗粒数;甘肃品种主要表现为增加穗粒数;新疆品种主要表现为增加主穗粒重和收获指数,并与成熟期提早及株高降低有一定关系。各地区品种中Rht-B1b和Rht-D1b矮秆基因均来自CIMMYT种质,其产量潜力的提高主要得益于CIMMYT种质的引进和有效利用,在四川和云南,CIMMYT种质的主要贡献是提高品种的条锈病抗性;而在甘肃和新疆,其被利用的主要特性是矮秆、高产、穗粒数多及广泛适应性。     

Assessment of genotype × environment interactions for yield and fiber quality in cotton performance trials

Plant breeding programs involving a wide range of crop plants routinely practice selection (directly or indirectly) for genotypes that display stability for a given trait or set of traits across testing environments through the genotype evaluation process. Genotype stability for trait performance is a direct measure of the presence and effect of genotype × environment interactions, which result from the differential performance of a genotype or cultivar across environments. The genotype evaluation process also requires selection of the proper field trial locations that best represent the target environments the breeding program is directed toward. In this study, we assessed the extent to which genotype × environment interactions affected agronomic performance (lint yield, gin turnout) and fiber quality (fiber length, fiber strength, uniformity index, micronaire, fiber elongation) in a series of cotton (Gossypium hirsutum) performance trials in 12 location–year environments in South Carolina. Genotype × environment interactions affecting lint yield were larger in higher yielding environments, while interactions for fiber strength were greater for genotypes with lower mean fiber strength values. Two regions within the South Carolina cotton production areas were identified as proper testing locations for lint yield performance, while testing for fiber strength can be accomplished in any location within the statewide cotton production areas. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Associations between grain yield and carbon isotope discrimination in cowpea

Twenty cowpea (Vigna unguiculata L. Walp.) genotypes, comprising Kenyan cultivars and Kenyan and introduced breedings lines, were grown in 15 replicated field trials carried out at three locations in semi-arid eastern Kenya over four seasons. Grain and straw yields and the carbon isotope discrimination (Δ) of this material were determined, and days to flowering and maturity observed.None of the seasons in which the trials were conducted was appreciably drier than the long term average for the sites, and some trials received excessive rain. Averaging the data for the 15 trials, one genotype yielded much less grain (77 g m⁻²) than the 19 others, whose yield ranged from 125 to 177 g m⁻² (average 148 g m⁻²). Trial mean yield trials had a high straw Δ (r = +0.567) and had received more rain between flowering and maturity (r = +0.428) than lower yielding ones. Among genotypes, averaging over trials, the correlation coefficient (r) between grain yield and grain Δ was +0.394, and between grain yield and straw Δ, +0.460. Early genotypes had the highest grain Δ and straw Δ. The correlation among genotypes between date of flowering and grain Δ was −0.632 and with straw Δ, −0.502. When comparisons were made among trials, there was no clear relationship between the strength of the correlations among genotypes between grain yield and straw Δ or grain Δ and the degree of stress experienced by a trial (as indicated by the rainfall it had received). It appeared that this was because the variances of grain Δ and straw Δ were greater in the most droughted trials, whereas the variance of yield was greatest in the least droughted trials.It is concluded that the genetic correlation between grain yield and either grain Δ or straw Δ is unlikely to be strong enough to make either Δ a useful surrogate or adjunct in selecting for high yield in the segregating generations of a breeding programme for semi-arid eastern Kenya, but that Δ may be of value in the selection of parent genotypes.     

Analysis of genotypic and environmental variation in international mungbean trials

Summary Two-way classification analysis, combined with analysis of variance and linear regression techniques, was applied to a set of yield data from twenty-one genotypes grown at twelve locations for two years in International Mungbean Nursery trials. Genotypes and environments with similar yield response patterns were grouped and differences between groups identified. Genotypes were also grouped on the basis of flowering time and the relation between days to flower and yield was examined. It was concluded that cluster and associated analyses are of value in determining response patterns of mungbean genotypes to a wide range of environments, and a useful aid in the selection of materials and locations for mungbean evaluation. In particular we note the adaptation of genotypes M409 and M1134 to high elevation locations, and the positive yield response of M374 (MG50-10A) to high yielding environments. Highest yielding lines were also the earliest to flower. Disease resistance was considered the most important breeding objective for mungbean yield improvement.     

Long-term association of locations for testing spring bread wheat

Summary The International Spring Wheat Yield Nursery (ISWYN) has been distributed annually since 1964 and the results provide a base for investigating relationships among locations. Ordination and clustering of locations was conducted using 26 years of grain yield data. Ordination and clusters based on the discrimination of germplasm were compared with mega-environments, which are groupings of locations defined by CIMMYT on the basis of climatic factors and perceptions of major biotic and abiotic stresses. Discrepancies among mega-environmental groupings, clusters and ordinations may identify locations for which major stresses affecting wheat yield are yet unidentified.Major environmental discriminators were latitude and the presence or absence of stress, although there was little association of locations due to limited moisture availability. We identified two major spring wheat environments, typified as Asian and European, and suggest the mega-environmental classification does not explain all significant associations among locations. Location groupings based on discrimination of germplasm should be considered in parallel to mega-environments on a regular basis and we propose breeding for a base of broadly adapted germplasm to which specific stress tolerances are incorporated.Abbreviations CIMMYT International Maize & Wheat Improvement Centre - ISWYN International Spring Wheat Yield Nursery - WANA West Asia and North Africa     

Comparison of lattice designs,check plots,and moving means in wheat breeding trials

Summary Efficiencies of lattice designs, check plot designs, and moving means were compared in seven environments for control of error in wheat breeding trials. Lattice analyses of lattice designs and check plot covariance analyses of check plot designs gave similar CV's and intra-site heritabilities and were superior to direct RCBD analyses of these designs. Moving mean covariance analyses were generally only slightly less efficient than lattice analyses or check plot covariance analyses. Differences between designs and methods of analysis, which were evident on an intra-site basis, were not evident from combined analyses indicating that genotype x environment interaction is much more important than intra-site error in limiting progress from selection. Moving mean covariance analyses with 2 replicates per location and as many locations as feasible is suggested as a useful strategy for early generation wheat breeding trials.     

Genetic improvement of agronomic and qualitative traits of spring barley

Five experiments, involving 24 genotypes, were carried out over three seasons to estimate the increase both in grain yield and other selected agronomic traits, and in potential malt extract of spring barley achieved by plant breeders during a period of over 160 years. In all experiments there was neither a chemical control of fungal diseases nor physical support of the tall, older genotypes to prevent yield losses from attack by fungi and lodging, respectively. In all experiments the most modern cultivars yielded more than the older ones. Significant breeding progress was also observed for plant height, resistance score, protein content and potential malt extract. The trend over time was generally of a curvilinear nature, showing no or only a slight increase till the 1950s and/or 1960s, and a greater rate of increase during the last 40 years of barley breeding. Using data from the official trials of cultivars and advanced breeding lines a linear increase in yield per year of 60 kg/ha since the 1950s was calculated for the low‐rainfall conditions of eastern Austria.     

Aspects of participatory plant breeding for quinoa in␣marginal areas of Ecuador

Summary Field trials were carried out in Ecuador with two indigenous communities, Ninín Cachipata and La Esperanza, to determine farmers’ preferences for quinoa (Chenopodium quinoa Willd.) cultivars and to improve PPB processes. More women than men participated, reflecting that quinoa, a primarily subsistence crop, is mainly managed by women. Farmers’ field selection criteria for quinoa in the field were mostly based on yield, earliness and plant colour; however only breeders’ measurements of yield and panicle height significantly correlated to farmer selection scores. Older women gave higher scores than younger women or men, apparently due to a concept of no cultivar being without value. Working in same gender pairs improved evaluation richness. INIAP technicians were more discriminating in their evaluations than farmers. They also used additional selection criteria of disease resistance and uniformity. At seed selection, farmers from Ninín Cachipata, where food security is not assured, chose lines based on yield, while farmers from La Esperanza, where resources are less limiting, also considered seed size, colour, saponin content and marketability. Field characteristics were not taken into consideration at seed selection, signifying that farmers are less interested in those characteristics, or that it was difficult for them to correlate field data when presented in tabular form with seed characteristics. Future trials with small farmers should have fewer lines or replications to avoid farmer fatigue during evaluation. Farmers who grow primarily for subsistence in semi-arid environments have more interest in growing quinoa, and more to gain from having improved cultivars; therefore future participatory efforts should focus on them.     

Genotypic and environmental influence upon the nutritional composition of barley grain

Summary The grain yield and contents of the quantitatively predominant nutritional constituents of barley grain were determined in nine adapted spring barley varieties each grown at seven European locations with three or four replications.The largest variation in nutritional composition was due to different environmental conditions, but genotypic effects were also present. Interactions between genotype and environment were small. The average protein content at different locations varied from 8.1 to 14.7 per cent of the grain dry matter, and was not simply related to the amount of fertilizer-N applied.The nutritional composition of the grain was influenced by the grain yield level. The percentage of dietary fiber and protein decreased with increasing grain yield, but some varietal differences which were independent of the grain yield level could be established.The protein quality depended upon the protein level, as the protein contained more prolamin relatively to non-prolamin protein at high than at low protein levels. A difference between two varieties in the prolamin/non-prolamin ratio was consistent over a wide range of variation in protein content.     

Interaction of common beans cultivars of the black group with years, locations and sowing seasons

The objectives of this study were to assess which environmental factors (local, season or years) are the most important to contribute for the interactions with genotypes of common black beans and to verify the existence of genotypes with broad and/or specific adaptation to the diverse planting seasons in Central Brazil. Data of grain yields for 13 genotypes in 18 field trials used for cultivar registration were utilized, across 2?years (2003 and 2004). Analyses of variance were carried out with decomposition of the genotype x environment interactions. Firstly, data of 18 trials were used, allowing a partial isolation of factors and, subsequently, eight trials were used to allow a complete isolation of the factors. The genotype x sowing seasons (R²?=?4.2?%) and genotype x year (R²?=?4.1?%) interactions were of the greatest important, while genotype x location was less important (R²?=?3.0?%). It was concluded that is more important to conduct evaluations of genotypes in different seasons and years rather than in different locations. The majority of the genotypes tested presented specific adaptation, although it was possible to identify superior lines with wide adaptation.     

Reaction of wild species of the geneus Lens to drought

Summary Susceptibility to drought stress is a key factor in dry land lentil (Lens culinaris Medikus) production in the Mediterranean region of West Asia and North Africa. This study examined the response to drought stress of 121 accessions representing all subspecies of the genus Lens; cultivated, and the wild L. culinaris ssp. orientalis (Boiss.) Ponert, L. culinaris ssp. odemensis (Ladiz.), L. nigricans M.B. Godr. ssp. nigricans Godr. and L. nigricans ssp. ervoides (Brign.) Ladiz. for their potential use in breeding for dry land conditions. Accessions were grown under two moisture regimes (dry land and dry land plus supplemental irrigation) at Breda, Syria during the 1990–91 and 1991–92 seasons. The cultivated lentil had markedly superior seed and straw production than did the wild Lens species. Time to flowering accounted for less than 10% of the variation in yield of wild accessions under rainfed conditions in the two seasons, showing that, in contrast to the cultivated germplasm, drought escape was relatively unimportant in wild lentil. Performance under drought in wild lentil, measured in terms of dry land seed yield or drought susceptibility index (S), was randomly distributed among collection locations with little relation to collection site aridity. Direct selection of wild lentil germplasm for biomass yield under dry conditions is of little value and an evaluation of wild accessions in hybrid combination is needed.     

Adaptation and stability analysis of sweet potato varieties for low-input systems in Uganda

Sixteen sweet potato varieties were evaluated for fresh storage root yield in 20 trials during 2000–2001 for three seasons in four locations in Uganda. Of the 16 varieties, 11 were developed by farmers and five by a central breeding programme. The behaviour of the varieties was quantified in terms of wide adaptation (genotypic mean across trials), specific adaptation (genotypic predictions for specific locations) and stability (Shukla stability variance). With respect to all three aspects of yield behaviour, farmer varieties performed on average better than the official varieties. The results illustrate the potential that farmer varieties can have in the improvement of sweet potato in Uganda and other regions where high diversity of sweet potato landraces exists.     

The relative contributions of yield components to lint yield of upland cotton,Gossypium hirsutum L.

Summary Stepwise regression analyses provided an estimate of the net effect of yield components on lint yield of Upland cotton. Data from strain tests in the Pee Dee, South Carolina, cotton breeding program for crop years 1968 and 1969 were used in these analyses. Lint yield/m² was the dependent variable. Independent variables were: bolls/m², lint/seed, and seeds/boll.Correlation analyses indicated the relationships among yield components. Partial correlation coefficients were utilized to show the order of variable addition in the regression equations. We found that bolls/m² assumes the major role in determining yield. The lint/seed component assmes the secondary role in the development of lint yield. Seeds/boll made a relatively larger total contribution only after lint/seed had made its contribution.These data indicate that selection pressure should be placed on prolificacy (bolls/m²) and seeds/boll, concommitantly with selection to maintain or increase lint/seed. Although the lint/seed component makes a relatively smaller total contribution to lint yield, it is necessary to maintain or increase this component to secure the increased contributions of seeds/boll.Cooperative investigations of the Plant Science Research Division, Agricultural Research Service, US Department of Agriculture and the Tennessee and South Carolina Agricultural Experiment Stations. South Carolina Technical Contribution No 954.     

Components of resistance to late leaf spot and rust among interspecific derivatives and their significance in a foliar disease resistance breeding in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of Yield Attributes of Isogenic Tall, Semidwarf, and Doubledwarf Winter Wheats to Nitrogen Fertilizer and Seeding Rates

Relationships between grain yield attributes and response to agronomic practices of dwarf and tall genotypes in the major U.S. wheat region were investigated. Isogenic tall, semidwarf, and doubledwarf (Norin 10/5/Pawnee) 'Pawnee' winter wheat ( Triticum aestivum L.) lines were planted in a split-split-plot design with nitrogen fertilizer rates of 0, 50, and 100 kg ha⁻¹ as main plots and seeding rates of 30, 60, and 90 kg ha⁻¹ as subplots in four replications at Hutchinson and Manhattan, Kansas, during 1980–1981. There was no evidence that dwarf lines responded better than the tall line to nitrogen fertilizer; however, percentage fertile spikelets, spike length, harvest index, and kernel number per spike of the semidwarf line were favored by high nitrogen rates. Grain yield was more responsive to seeding rate in the doubledwarf line than in the other lines, and test weight and spike number per unit area were more responsive to seeding rate in one or both dwarf lines than in the tall line. Grain yield of each genotype depended highly on the predominant yield attributes — usually spike number per unit area and/or kernel weight — at one or both locations.     

Genetic mapping for resistance to gray leaf spot in maize

The molecular marker technology has been used on mapping of quantitative trait loci (QTLs) associated with plant resistance. The objectives of this research were to estimate genetic parameters and to map genomic regions involved in the resistance to gray leaf spot in maize. Ninety F₃ families from the BS03 (susceptible) and BS04 (resistant) cross were used. Field trials were performed using a 10 × 10 square lattice design with three replications. Data from 62 SSR markers were used for linkage analysis. The locations of the QTLs on the linkage groups were determined by composite interval mapping method and the phenotypic variance explained by each marker was determined by regression analysis. Several QTLs associated to disease resistance were identified in the population BS03 × BS04. Some QTLs showed significant effects over the different environments studied. The existence of significant QTLs in common among different environments indicates these genomic regions as possible new tools for marker-assisted selection in maize breeding programs.