Detection of QTL for forage yield,lodging resistance and spring vigor traits in alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.) is an internationally significant forage crop. Forage yield, lodging resistance and spring vigor are important agronomic traits conditioned by quantitative genetic and environmental effects. The objective of this study was to identify quantitative trait loci (QTL) and molecular markers associated with increased forage yield, resistance to lodging, and spring vigor. A backcross population composed of 128 progeny was developed by crossing the breeding parents DW000577 (lodging susceptible) and NL002724 (lodging-resistant) and back-crossing an individual F₁ plant to the maternal parent (i.e. DW000577). A linkage map of NL002724 was developed based upon the segregation of 236 AFLP, SRAP, and SSR markers among the backcross progeny. The markers were distributed among 14 linkage groups, covering an estimated recombination distance of 1497.6 centiMorgans (cM). Replicated clones of both parents and backcross progeny were evaluated in the field for estimated forage yield, lodging, and spring vigor in Washington and Wisconsin during 2007 and 2008. Significant QTL were found for all three traits. In particular, two QTL for lodging resistance were identified that explained ≥14 % of trait variation, and were significant in all years and locations. Major QTL explaining over 25 % of trait variation for forage yield were detected in multiple environments at two separate locations on chromosome III. Several QTL for spring vigor were located in the same or similar positions as QTL for forage yield, possibly explaining the significant correlation between these traits. Molecular markers associated with the aforementioned QTL were also identified.     

Performance of Avena sativa L./Avena fatua L. Backcross lines

Summary Although wild oats (Avena fatua L.) have been considered a potential source of genes for cultivated oat (Avena sativa L.) improvement, most progenies of A. sativa/A. fatua crosses have weak straw and are very susceptible to crown rust (Puccinia coronata CDA. var. avenae Fraser and Led.). Backcrossing to A. sativa has been suggested as a method of improving progeny lines while introducing new genes from wild oats to cultivated oats. In this study, A. sativa/A. fatua F₁ hybrids were backcrossed twice to A. sativa, and lines from three backcross populations were selected on the basis of agronomic performance in segregating generations. The A. sativa recurrent parents were Dal (tall and late) and Stout (short and early).Backcross lines and recurrent parents were evaluated in five performance trails from 1983 through 1985. There was significant variation among backcross lines for most traits, but most backcross lines did not produce higher grain and straw yields than their A. sativa parent. Several backcross lines were higher than their recurrent parent in test weight and groat percentage. A line derived from Stout, 175BC2-6, was considered the most promising backcross line in the study. This line produced more grain, had heavier kernels, and headed 3.3 days earlier than Stout. Although 175BC2-6 does not have sufficient straw strength and crown rust resistance to be released as a cultivar, it is considered to be a new source of high grain yield, high test weight and earliness for oat breeding.     

Inheritance of groat-oil content and high-oil selection in oats (Avena sativa L.)

Summary The potential for breeding for high groat-oil content in oats was investigated by (a) conducting generation means analyses on data from three matings among adapted Avena sativa L. cultivars, (b) practicing one cycle of phenotypic recurrent selection in a segregating population derived from eight species backcrosses (Avena sativa x (A. sativa x A. sterilis)) among 24 parents, and (c) identifying transgressive segregates from interspecific (A. sativa x A. sterilis) matings.Additive gene action was the most important component in explaining the variation among generation means for groat-oil content. Dominance and epistatic interactions involving dominance were not significant in any mating. Significant residual genetic variation occurred in one mating, even after additive, dominance, and three digenic interactions were fitted. The importance of additive genes action implies that desired allelic combinations for high groat-oil content can be obtained in pure-line cultivars.One cycle of phenotypic recurrent selection using single plants as the selection units resulted in a genetic gain of 1.7 to 2.1% in groat-oil content. Individual plants selected for initiating the second cycle had from 9.5 to 12.6% groat oil.Over all 12 interspecific matings, the F₂ progeny means were similar to the midparent values. Only two were significantly deviant. Transgressive segregates for high and low groat-oil content from these matings provided evidence that A. sterilis possesses alleles for high and low groat-oil content that are different from those in the gene pool of cultivated oats.Journal Paper No. J-11340 of the Iowa Agric. and Home ECon. Exp. Stn., Ames, Iowa 50011. Project 2447. This study was supported in parts by grants from the Iowa Committee for Agricultural Development and the International Harvester Company.     

Identification of quantitative trait loci for resistance to bending-type lodging in rice (Oryza sativa L.)

Bending-type lodging is one of the most important factors affecting the yield and grain quality of rice. This study identified quantitative trait loci (QTLs) for physical strength of the upper culms, and evaluated QTL effects on lodging resistance. In 2010 and 2011, QTLs for breaking strength, length, and diameter of the top three internodes were identified by analyzing chromosomal segment substitution lines (CSSLs) developed from ‘Koshihikari’ and ‘Kasalath’. The QTL analysis indicated that ‘Kasalath’ had two types of QTLs: one to strengthen specific internodes and one to simultaneously improve the physical strengths of plural internodes or the top three internodes. A QTL for breaking strengths of the top three internodes (bsuc11) was detected on chromosome 11 in both years. This QTL did not overlap with that for internode length. To evaluate the effects of bsuc11 on lodging resistance, this study selected three CSSLs with bsuc11 and analyzed the breaking strengths of the top three internodes after heading and the pushing resistance of the lower part. Internodes of ‘Koshihikari’ showed decreased breaking strengths after grain filling, while those of CSSLs with bsuc11 did not show this decrease in breaking strength. The pushing resistance of the lower part at the fully ripe stage was the same in ‘Koshihikari’ and CSSLs with bsuc11. These results suggested that bsuc11 could be a target to improve the physical strength of the upper culms to resist bending-type lodging, and that the physical strengths of upper and lower parts are controlled by different genetic factors in rice.     

Direct and indirect selection for grain yield in oats (avena sativa L.)

Direct and indirect selection for increased grain yield were carried out on a population of 678 F₂-derived lines of oats. A selection intensity of 10% was used with direct selection (selection for grain yield itself) and with indirect selection using three criteria, harvest index, vegetative growth rate, and the index of harvest index + vegetative growth rate. Expected gains from 1978 evaluations were compared to actual gains measured in 1980. Actual grain yield increases were 4, 8, 7, and 6% from selection via harvest index, vegetative growth rate, grain yield, and harvest index + vegetative growth rate, respectively. Thus, indirect selection via vegetative growth rate gave a greater increase in grain yield than did direct selection. Heritability values computed via components of variance ranged from 0.50 to0.57 for the three traits, harvest index, vegetative growth rate, and grain yield, whereas regression heritabilities ranged from 0.41 to 0.55. Realized heritabilities were 0.33, 1.00 and 0.89 for the three traits, respectively. Selection via all criteria caused significant changes in nearly all agronomic traits except weight per volume. Vegetative growth rate, which gave the greatest gain in grain yield, caused less drastic changes in days to anthesis, plant height, biological yield, and vegetative yield than did direct selection for grain yield.     

Continued response through seven cycles of recurrent selection for grain yield in oat (Avena sativa L.)

Long-term selection experiments provide germplasm to study the effects of selection in a closed population. Recurrent selection to enhance grain yield in oat has been ongoing at the University of Minnesota since 1968. The objectives of this study were: (i) estimate the GCA and SCA effects for three agronomic traits in the seventh cycle of selection, (ii) assess the effect of the current methods of selection on parental contribution and unselected traits, and (iii) determine the direct and indirect responses to seven cycles of recurrent selection for grain yield. Progeny of the Cycle 6 parents and parents for Cycles 0 through 7 were grown in two separate tests. Grain yield, heading date and plant height were evaluated in each test. Grain yield was increased by 21.7% after seven cycles of selection. Evaluation of Cycle 6 progeny showed that GCA effects were significant for all three traits studied, and SCA effects were significant only for grain yield. Four Cycle 6 parents did not have any progeny selected as Cycle 7 parents. Results from this study indicate that long term recurrent selection has continued to increase grain yield. Alternative selection strategies may be necessary to maintain the genetic variability in this population, particularly when improvement of secondary traits is required. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relation of seed weight to grain yields in oats,Avena sativa L.

Summary We measured yielding ability and weight per 100 seeds in 7 populations of oat lines, each derived from a different cross. The association between these two traits was curvilinear, with maximum yields occurring when 100-seed weights were between 2.75 and 3.10 g.In a simulated selection experiment conducted on a bulk population of 150 oat lines (i.e. only lines with seed weight between 2.75 and 3.10 g per 100 seeds were saved), the proportion of superior yielding lines was increased from 16% in the original to 32% in the new one. In the 100-seed weight class below 2.75 g, the proportion of high yielding lines was only 5%.Journal Paper No. J-6102 of the Iowa Agricylture and Home Economics Experiment Station, Ames, Iowa, U.S.A. Project No. 1176. In cooperation with the crops Research Division, Agricultural Research Service, U. S. Department of Agriculture.     

Changes in genetic diversity during seven cycles of recurrent selection for grainyield in oat, Avena sativa L.

Variability for desirable alleles within elite breeding populations is a requirement for long-term genetic improvement. Changes in genetic diversity were evaluated in a recurrent selection programme for enhanced grain yield in oat, Avena sativa L., using coefficient of parentage (r_p) and restriction fragment length polymorphism (RFLP) based genetic similarity (S) estimates. Both r_p and s increased during seven cycles of recurrent selection, indicating a reduction in the level of genetic diversity within the population. The relationship between genetic diversity and agronomic performance was also examined. Genetic similarity measures were poor predictors of the near-homozygous progeny performance and general and specific combining ability effects for three agronomic traits in the recurrent selection programme. In addition, there was no apparent trend for preferential selection of progeny from either more similar or more diverse parents within a given cycle of selection. The overall reduction in genetic diversity in this population has not affected selection response for grain yield. Variability remaining at important loci or de novo variation are possible explanations for the continued selection progress.     

Quantitative trait loci for quality and agronomic traits in two advanced backcross populations in oat (Avena sativa L.)

Using the advanced backcross quantitative trait loci (AB‐QTL) strategy, we successfully transferred and mapped valuable allelic variants from the high β‐glucan (BG) accession IAH611 (PI 502955), into the genome of cultivar ‘Iltis’. By backcrossing one BC₁F₁ plant to ‘Iltis’, we developed two BC₂F_2‐6 populations A and B, comprising 98 and 72 F₂‐individuals, respectively. Genotyping of BC₂F₂ individuals with predominantly AFLP markers resulted in 12 linkage groups with a map size of 455.4 cM for Population A and 11 linkage groups with a map size of 313.5 cM for Population B. Both populations were grown at three sites in Germany over a three‐year period. Individuals were then phenotyped for 13 traits including grain yield (YD) and β‐glucan content (BG). QTL analysis via stepwise regression detected a total of 33 QTLs, most of which were clustered in three linkage groups. Two dense linkage groups A1 and B13 were found to be putatively homologous to groups KO_6 and KO_11 of the ‘Kanota’/‘Ogle’ map, respectively.     

一种野生燕麦的染色体核型分析

对安徽风阳地区麦田里的一种野生燕麦的染色体核型进行了分析，结果如下：该物种的染色体数为2n=42，各染色体间形态差异明显，但均为中着丝粒染色体（m）或近中着丝粒染色体（sm），最长与最短染色体相对长度比为2．34，并在全套染色体中的第9号和16号染色体上发现了2对随体，核型公式为2n=6x-42=22m＋20sm（2SAT），核型类型舅比较对称的2B型。同时讨论了燕麦作为小麦遗传改良的重要种质资源，对普通小麦远缘杂交和品质改良的意义。     

Among and within-cultivar variability for histological traits of lucerne (Medicago sativa L.) stem

The histological structure of lucerne stems is a limiting factor for digestibility of the forage. Two experiments were carried out to compare cultivars and genotypes within cultivars for histological traits of the stems. In the first one, the among-cultivar genetic differences were assessed on 6 cultivars differing indigestibility. In the second one, the within-cultivar differences were evaluated on twenty genotypes belonging to two cultivars. Two sets of quantitative histological traits were measured using image analysis on the basal portion of the stems corresponding to the mature zone: the proportions of the different tissues of the lucerne stems (cortex, xylem, pithparenchyma), and the traits describing the xylem in vascular bundles (xylem cell wall thickness, xylem cell wall surface density, mean area of xylem vessel and mean area of fibre lumen). Few significant differences were observed among-cultivars, where as numerous within-cultivar differences were observed for histological traits. When the stem length was introduced as covariate, the differences among- and within-cultivars remained significant. Xylem proportion was negatively correlated to pith parenchyma proportion only. Xylem cell wall surface density and thickness were correlated to the cross-section radius but not to xylem proportion. As digestibility of lucerne is limited by histological structures, the large within-cultivar differences for histological traits of lucerne stems could be used in a breeding program for improved digestibility. This revised version was published online in July 2006 with corrections to the Cover Date.     

玉米抗茎倒伏能力相关性状与评价研究进展

茎倒伏造成玉米产量和品质下降,收获成本增加,籽粒生理成熟后无法继续田间站秆脱水,影响玉米机械化籽粒收获。关于玉米抗茎倒伏相关的性状,前人从植株形态、节间形态、解剖结构和化学成分等方面进行了大量研究,但结果不完全一致,同时这些性状对茎秆抗倒性作用大小的定量研究较少。本文综述了玉米抗茎倒伏能力的评价方法和指标、茎秆力学测定方法、抗茎倒伏能力相关性状的分析方法及其影响因素,提出了抗茎倒伏能力相关性状及评价研究中存在的问题和需要进一步关注的内容,希望为进一步研究玉米抗茎倒伏相关性状及其评价方法,培育抗倒伏品种和优化栽培措施提供参考。     

Identification and characterization of quantitative trait loci related to lodging resistance and associated traits in bread wheat

Lodging is a major constraint to increasing yield in many crops, but is of particular importance in the small‐grained cereals. This study investigated the genetic control of lodging and component traits in wheat through the detection of underlying quantitative trait loci (QTL), The analysis was based on the identification of genomic regions which affect various traits related to lodging resistance in a population of 96‐doubled haploid lines of the cross ‘Milan’בCatbird’, mapped using 126‐microsatellite markers. Although major genes related to plant height (Rht genes) were responsible for increasing lodging resistance in this cross, several other traits independent of plant height were shown to be important such as fool and shoot traits, and various components of plant yield. Yield components such as grain number and weight were shown to be an indicator of plant susceptibility to lodging. QTL for lodging and associated traits were found on chromosomes IB, ID. 2B. 2D. 4B, 4D. 6D and 7D. QTL for yield and associated traits were identified on chromosomes IB, ID. 2A. 2B. 2D. 4D and 6A,     

不同燕麦品种田间倒伏性状研究

在青藏高原东缘四川红原高寒地区,分析了燕麦（Avena sativa L.）倒伏与品种、株高、单株干重、茎秆强度、茎粗、第一茎节间长、第一茎节间干重、穗位高及根系条数的关系。结果表明,所测定7个燕麦品种均在孕穗期出现部分倒伏,花期倒伏率最大;燕麦品种抗倒伏能力为林纳>青燕1号>青海444>青引1号>青引2号>青海甜燕麦>青引3号莜麦;其中单株重、第一茎节间干重是影响燕麦倒伏的主要因子（P<0.01）,株高和穗位高对燕麦倒伏影响次之（P<0.05）。研究认为在燕麦品种选育过程中,可以适当放宽对株高的限制,重点选育单株干重大、基部第一茎节间干重大的品种。     

Evaluation of Major Dietary Ingredients in Diverse Oats (Avena sativa L.) Germplasm

Journal of Crop Science and Biotechnology - Oat (Avena sativa L.) is one of the world’s most important cereal crops, owing to its use as an important source of essential nutrients for both...     

Inheritance of groat protein percentage in Avena sativa L. × A. Fatua L. Crosses

Summary Gene action and heritability of groat protein percentage were determined in F₁, F₂, and F₃ generations of nine crosses between three Avena sativa L. cultivars and three A. fatua L. selections. Relationships among groat protein percentage, grain yield, and 100-seed weight also were evaluated. The three A. sativa parents were Dal (high grain yield and intermediate groat protein percentage), Goodland (low grain yield and high groat protein percentage), and Stout (high grain yield and low groat protein percentage). The three A. fatua parents were chosen for the study on the basis of vigorous plant growth and high groat protein percentage. The study was conducted at Madison, Wisconsin in 1979 and 1980.There was partial dominance towards low groat protein percentage. Narrow sense heritability estimates for groat protein percentage were low in Dal and Goodland crosses and intermediate in Stout crosses. In the F₂ generation, groat protein percentage was significantly higher in shattering than in nonshattering plants in 1979, but not in 1980. There were significant, positive correlations between groat protein percentage, 100-seed weight, and grain yield in F₁ and F₂ generations, but they were not large numerically. Relationships among these traits were either negative or nonsignificant in the F₃ generation. Although our results indicated that selection for higher groat protein percentage is possible when a low protein A. sativa cultivar is used, most of our simple cross progenies from A. sativa x A. fatua crosses had weak straw and were susceptible to crown rust (Puccinia coronata Cda. var. avenae Fraser and Led.).     

Stability Indices for Weed Management Systems in Forage Oat (Avena sativa L.)

A set of integrated weed management systems was assessed in forage oat ( Avena sativa L.), cv. Kent, to compare efficiencies inter se in terms of mean forage productivity over different locations and different years, and relative agronomic effectiveness. Results for seven weed management systems were obtained for three consecutive years, i.e. 1995–96, 1996–97 and 1997–98, at five locations of the Indian subcontinent. Two systems – use of weeder-cum-mulcher at the 3- and 6-week crop stages (WCS) and use of weeder-cum-mulcher at the 4 WCS plus application of 2, 4-D at 0.37 kg a.i. ha^–1 at 6 WCS – were found to be effective and consistent over locations from year to year and over years from location to location. Pooled analysis over years and locations showed manual weeding at 4 WCS plus application of 2, 4-D at 0.37 kg a.i. ha^–1 at 6 WCS, on the one hand, and use of weeder-cum-mulcher at 3 WCS plus manual weeding at 5 WCS, on the other, to have equal efficiencies and to be more beneficial than the other treatments. Recommendation of the latter system is of particular interest as this system merely involves mechanical operations which provide the benefits of soil mulching and carry no risk of biotoxicity due to herbicides in crop plants or adverse effects on soil through uninterrupted use of chemicals.     

Association between certain stalk traits related to lodging and grain yield in maize (Zea mays L.)

Summary Thirty-five varieties of maize from different ecogeographical regions were planted to study the relationship between stalk characters and grain yield in maize. Grain yield was positively correlated with three stalk traits under investigation. Highly significant positive correlations existed among weight of a 5 cm stalk section, crushing strength and rind thickness. In general, genotypic correlation coefficients were higher than the phenotypic correlation coefficients. The present study indicates that it is possible to develop a high-yielding variety with superior stalk strength.     

Relationship between genealogical distance and breeding behaviour in oats (Avena sativa L.)

Summary Eight oat cultivars and experimental lines from four germplasm sources were crossed in a diallel mating design without reciprocals. F₁ heterosis for grain yield was evaluated in two experiments, and 48 F₂-derived lines from each of the 28 matings were evaluated for bundle weight, grain yield, straw yield, harvest index, height, and heading date in two experiments. Number of transgressive segregates per trait and generalized genetic variance were calculated for each mating. Genealogical distance for each mating was obtained by using coefficient of kinship based on the pedigree of the parents. The relationship between genealogical distance and the three types of breeding behaviour was examined via correlation and regression. Significant correlations occurred only for genealogical distance with numbers of transgressive segregates for height and with generalized genetic variances. Both were positive. Significant heterosis was observed for matings of more distantly related parents. Regressions on genealogical distance, when significant, were linear. Genealogical distance between parents was positive associated with diversity on the basis of breeding behavior.Journal Paper No. J-11874 of the Iowa Agriculture and Home Economics Station, Iowa State Univ., Ames, IA 50011. Project 2447.