Combining ability in the F1 and F2 generations of diallel cross in hexaploid wheat (Triticum aestivum L. em. Thell)

The F(1) and F(2) progenies of a ten-parent diallel cross (excluding reciprocals) of hexaploid wheat (Triticum aestivum L. em. Thell) were analyzed for combining ability for quantitative and quality traits. The results indicated significant differences among the parents for general combining ability (gca) and crosses for specific combining ability (sca) for all the characters studied. The gca and sca components of variance were significant for all the traits. However, the gca component of variance was predominant indicating the predominance of additive gene effects for the traits studied. Among the parents Durgapura 65, HD 2285, Lok-1, Raj 1972 and HD 2329 were the best general combiners for grain yield and average to high combiners for tillers per plant, grain yield per spike, grains per spike and 1000-grain weight. The best specific crosses for grain yield were Sonalika x WH 157, HD 2428 x Durgapura 65, Durgapura 65 x Sonalika, HD 2428 x Lok-1 and CPAN 3004 x Raj 1972. The parent Raj 1972, Lok-1 and HD 2285 were the best general combiners for grain yield and protein content, however, Raj 3077 was the best general combiner for protein content. The most suitable specific crosses for protein content were HD 2329 x HD 2285, HD 2428 x Raj 1972 and CPAN 3004 x WH 157. Most of the specific crosses for grain yield as well as protein content involved high x average, average x average and average x poor general combiners. To ensure further increase in grain yield along with high protein, combinations of desirable yield components is advocated. Inclusion of F(1) hybrids showing high sca and having parents with good gca, into multiple crosses and/or bi-parental mating, or diallel selective mating could prove a worthwhile approach for further improvement of grain yield in bread wheat.     

Heterosis studies for yield and its components in bread wheat over environments

A set of diallel crosses involving 10 parents was made to have information on the extent of heterosis over mid-parent and better parent and inbreeding depression for yield and yield contributing characters under three different environments. Marked heterobeltiosis for grain yield and its important components were observed. For grain yield, 83 crosses showed significant positive heterobeltiosis in all the three sowing dates, however, twenty crosses showed significant consistent heterobeltiosis for grain yield per plant over all the three environments. The maximum heterobeltiosis for grain yield per plant observed was 50.94% (Raj 3765 x HD 2285), 121.08% (PBW 373 x HD 2329) and 93.96% (PBW 373 x HD 2329) under early, normal and late sowing conditions, respectively. Cross PBW 373 x HD 2329 in both early and normal plantings and cross Raj 3765 x HD 2285 under late planting were observed most heterotic for grain yield. The crosses showing heterosis for grain yield were not heterotic for all the characters. Heterosis for grain yield per spike followed by tillers per plant and 1000-grain weight was independently associated with heterosis for grain yield in early and normal plantings. However, heterosis for grain yield per spike, dwarf plant height and tillers per plant contributed maximum towards yield heterosis. Significant inbreeding depression was recorded frequently for yield and yield contributing traits, however, in a few traits it was observed significant negative indicated that F(2) was superior to F(1) considered desirable combination for trait(s). The study reveals good scope for commercial exploitation of heterosis as well as isolation of pure lines among the progenies of heterotic F(1) for improvement of yield levels in bread wheat.     

Genetics of transgressive segregation for yield and yield components in wheat

Three crosses of spring wheat (Triticum aestivum L. em Thell) involving six cultivars (WC29, WH291, SGP 14, RAJ. 1972, WH377 and HD 2329) were selected on the basis of combining ability analysis to study genetics of transgressive segregation for tillers/plant, grains/spike, 1000 grain weight and grain yield/plant using various mating designs. Diallel analysis indicated that both additive and non- additive components were significant for all the characters. On the basis of general combining ability and specific combining ability effects, the parents WH 291 and WH 377 were found to be good general combiners for tillers/ plant, 1000 grain weight and grain yield/plant. For grains/spike SGP 14 was found to be a good general combiner. The cross WH 377 × HD 2329 for tillers/plant, SGP 14 × Raj. 1972 for grains/spike and grain yield/plant and WC 29 × WH 291 for 1000 grain weight were found to be good cross combinations. Generation mean analysis indicated that the additive-dominance model was inadequate for all the characters in all the crosses except for 1000 grain weight in WC29 × WH291. Additive component was more pronounced than non-additive components for all the characters in all the crosses except for tillers/ plant in WH 377 × HD 2329. Predictions for transgressive segregants from F₃ was more accurate than that from generation mean analysis. However, prediction from both the sources were equally efficient if additive-dominance model was adequate. In general, observed frequencies of transgressive segregants were more in F₂ and BIPi than F₄ but the majority of them were discarded on progeny testing. Biparental mating had an impact in increasing the frequencies of transgressive segregants for different characters in all the crosses. The crosses, WH 377 × HD 2329 for grain yield/ plant, SGP 14 × Raj. 1972 for tillers/plant and WC 29 × WH 291 for grains/spike and 1000 grain weight were found to be potential crosses for transgressive segregants. A comparison of combining ability of parents and crosses, and observed and predicted frequencies of transgressive segregants indicated that the potential crosses for transgressive segregants were those that had high sea effects and involved high and low general combiners. The crosses involving low general combiners irrespective of their sea effects showed poor performance with respect to transgressive segregation.     

Triple test cross analysis in F2 populations of four barley crosses

Summary The triple test cross analysis of Jinks and Perkins (1970) was used to study different components of genetic variation in four barley F₂ populations, C 164x IB 226, C 164xJyoti, IB 226xP 113 and DL 3xP 113, for final plant height, spike length, 100-kernel weight, grain yield per plant and harvest index. The overall epistasis (i type) was, in general, a minor component but the j & 1 type epistasis was an important element for all five characters in cross 3 (IB 226xP 113). Both the additive (D) and dominance (H) components were highly significant for all the five characters in all four crosses. The dominance was directional in all cases except for 100-grain weight in crosses 1 (C 164xIB 226), 2 (C 164xJyoti) and 4(DL 3xP 113).     

Inheritance of five quantitative characters of bread wheat

Summary Heritability estimates of five characters of the wheat plant were studied in five crosses involving six cultivars of bread wheat. Parents, F₁, F₂ and backcrosses to both parents were used in the estimation of the genetic parameters.Heritability was low for number of fertile spikes/plant, moderate for number of spikelets/spike, number of kernels/spike, 1000-kernel weight and moderately high for number of kernels/spike. Evidence for mainly nonadditive gene effects were observed in the expression of number of fertile spikes and 1000-kernel weight. Although nonadditives contributed to a lesser degree to the gene action, additives seemed to be the most important genetic expression regulating number of spikelets/spike, number of kernels/spike, and number of kernels/spikelet. Except for number of fertile spikes/plant, selection in F₂-populations seems to be promising.     

Epistatic,additive and dominance variation in a triple test cross of bread wheat (Triticum aestivum L.)

Summary Triple test cross progenies resulting from the crossing of three testers (Kloka, UP 368 and an f₁ intermediate between them) and 24 varieties of bread wheat have been studied for plant height (cm), peduncle length (cm), ear length (cm), number of spikelets per spike and harvest index (ratio between economic and total yield). Epistasis was not significant for any of the characters studied. The testers were inadequate for plant height and for peduncle length although the testers varied considerably for these traits. Additive variance played a significant role in the inheritance of all the characters except number of spikelets per spike. The dominance variance was important for plant height, ear length and harvest index. The degree of dominance was in the over-dominance range for plant height. Complete dominance was operative for ear length, number of spikelets per spike and harvest index whereas for peduncle length only partial dominance was observed. The possibility of the isolation of the recombinants with high harvest index has been stressed.     

Genetic diversity and its relationship to hybrid performance and heterosis in rice as revealed by PCR-based markers

Ten elite inbred lines (four japonica, six indica), chosen from those widely used in the hybrid rice breeding program at Human Hybrid Rice Research Center in China, were crossed to produce all possible hybrids excluding reciprocals. The 45 F₁ hybrids along with the ten parents were evaluated for eight traits of agronomic importance, including yield potential, in a replicated field trial. The ten parents were analyzed with 100 arbitrary decamer oligonucleotide primers and 22 microsatellite (simple sequence repeats, SSRs) primer sets via polymerase chain reaction (PCR). Out of the 100 random primers used, 74 were informative and amplified 202 non-redundant bands (variants) with a mean of 2.73 bands per polymorphic primer. All 22 microsatellite primer sets representing 23 loci in the rice genome showed polymorphisms among the ten parents and revealed 90 alleles with an average of 3.91 per SSR locus. Cluster analysis based on Nei's genetic distance calculated from the 291 (202 RAPDs, 89 SSRs) non-redundant variants separated the ten parental lines into two major groups that corresponds to indica and japonica subspecies, which is consistent with the pedigree information. Strong heterosis was observed in hybrids for most of the traits examined. For the 43 diallel crosses (excluding 2 crosses not heading), yield potential, its components (including panicles per plant, spikelets per panicle and 1000-grain weight) and their heterosis in F₁ hybrids showed a significant positive correlation with genetic distance. When separate analyses were performed for the three subsets, yield potential and its heterosis showed significant positive correlations with genetic distance for the 15 indica x indica crosses and the 6 japonica x japonica crosses; however, yield potential and its heterosis were not correlated with genetic distance for the 22 indica x japonica crosses. Results indicated that genetic distance measures based on RAPDs and SSRs may be useful for predicting yield potential and heterosis of intra-subspecific hybrids, but not inter-subspecies hybrids.     

Branching Shoots and Spikes from Lateral Meristems in Bread Wheat

Wheat grain yield consists of three components: spikes per plant, grains per spike (i.e. head or ear), and grain weight; and the grains per spike can be dissected into two subcomponents: spikelets per spike and grains per spikelet. An increase in any of these components will directly contribute to grain yield. Wheat morphology biology tells that a wheat plant has no lateral meristem that forms any branching shoot or spike. In this study, we report two novel shoot and spike traits that were produced from lateral meristems in bread wheat. One is supernumerary shoot that was developed from an axillary bud at the axil of leaves on the elongated internodes of the main stem. The other is supernumerary spike that was generated from a spikelet meristem on a spike. In addition, supernumerary spikelets were generated on the same rachis node of the spike in the plant that had supernumerary shoot and spikes. All of these supernumerary shoots/spikes/spikelets found in the super wheat plants produced normal fertility and seeds, displaying huge yield potential in bread wheat.     

Genetic analysis of chromosomes of common wheat. I. Analysis of chromosome 1B of Timstein,with respect to certain quantitative characters

Triparental group analysis (Aksel, 1967) was applied to measurements of six characters (days-to-head, plant height, tiller number per plant, kernel number per spike, single kernel weight and total grain yield per plant) of the wheat varieties Chinese Spring, Timstein, the substitution line SL (1B)Tim, and their crosses and backcrosses. Highly significant allelic and non-allelic interactions were found at the within-chromosome level only. The substituted chromosome pair 1B of Timstein was found to contain two or more genes conditioning plant height, tiller number per plant, kernel number per spike and total grain yield per plant.     

Soluble Carbohydrates and Floret Fertility in Wheat in Relation to Population Density Stress

Wheat, variety Sonalika, was grown at different densities inboth field and pots during the winter seasons 1983–84and 1984–85. Grain yield pattern of the spikelets of themain shoot inflorescence was similar in both the field and pots,the spikelets in the middle part of the ear contributed mostand yield per spikelet decreased progressively towards the apexand the base. Increased population density decreased yield ofgrain, primarily by decreasing spikelet number and the fertilityof florets. High population density accelerated growth of thespike for some time during the pre-anthesis period and the solublecarbohydrate concentration was also higher under these conditions.During both anthesis and post-anthesis, the soluble carbohydrateconcentration and the growth of the spike declined much fasterin the high-density population. High density also decreasedthe floret fertility and growth in dry weight in all the spikelets,but it was more severe on the basal spikelets, resulting incomplete sterility of the florets at these nodes. The solublecarbohydrate concentration of these slow-growing, sterile, basalspikelets was found to be higher in comparison to that of fertilespikelets in the middle and top positions within the ear. Soluble carbohydrates, spike, spikelet, fertility, grain number     

冬小麦产量性状的遗传效应分析

以农大139等7个冬小麦品种进行4×3不完全双列杂交,采用加性-显性及其与环境互作的遗传模型对亲本、F_1和F_2的株高、主穗穗长、单株穗数、主穗小穗数、千粒重和单株粒重6个性状进行遗传分析．结果表明,株高和主穗长主要受加性效应控制,而单株穗数、主穗小穗数、千粒重和单株粒重主要受显性×环境互作效应影响．矮2杂交后代易选到矮株,奥里生杂交后代易得到大穗材料,农林10号和奥里生的杂交后代分蘖力将加强,814的杂交后代小穗数增多,814杂交后代千粒重增高．所有产量性状未表现明显的杂种优势．     

Grain number determination in durum wheat as affected by drought stress: An analysis at spike and spikelet level

Yield studies show that increases in grain yield are always accompanied by an increase in grain number and, hence, further increases in yield potential may require additional improvements in grain number. The improvement of modern durum wheat was mainly based on the introduction of semidwarf genes. A 2‐year field drought stress experiment, concerning two different genotype groups (landraces vs modern cultivars), was carried out under a rainout shelter in order (a) to assess the effect of water deficit on floret dynamics and grain number determination, (b) to explore the relationship between plant water status with grain number per spike and its components (i.e., spikelets per spike, fertile florets per spikelet and grain set) and (c) to quantify the importance of several plant traits in determining the final number of grains per spike and fertile florets per spike when the main source of variation is water availability. Compared to control (well irrigated), grain number per spike was reduced, depending on year, genotype and water availability level, by 12.4–58.7% and this reduction was evident almost in all spikelet positions along the spike. Although there were some doubts in the past about the increased sensitivity of semidwarf cultivars to drought stress, they were not confirmed from our results. In most of the cases, the variation in plant water status (by means of water potential index [WPI]) during floret primordia phase (FPP) explained most of the variance in grain number per spike, fertile florets per spikelet, grain set and fertile spikelets per spike. In general, increasing water stress intensity decreased grain number per spike by an average rate of 13.5 and 9.4 grains per 0.2 MPa decrease in WPI, in modern cultivars and landraces, respectively. However, seasonal and genotypic effects were evident by modifying the slopes of the linear regressions between WPI and the studied plant traits. Commonality analysis revealed that the number of fertile florets per spikelet was the best predictor of grain number per spike, indicating that there is still much space for further improvement for this trait in landraces. However, this trait has been clearly improved in modern cultivars, especially at the basal and central spikelets. Although the number of spikelets per spike was the best unique predictor of the number of grains per spike in modern cultivars, grain set presented the highest total effect.     

西藏小麦资源在都江堰试种的表现及评价

对125份来源于西藏的小麦地方品种进行农艺性状分析和评价。结果显示,西藏小麦植株高度总体偏高,少数适中。分蘖数多数在10个以下,少数偏多。穗长、小穗数的单位长度着生的小穗数存在明显差异,存在一些密穗类型和多小穗类型。多数小麦品种穗粒数不少,但千粒重明显偏低。性状相关分析表明,随着分集数增多、穗长增长、小穗数增多,株高有增加的趋势,而株高的增加又导致了千粒重的降低。小穗数多其穗长通常比较长。中时西藏小麦资源进行了评价、利用方式进行了探讨、在都江堰与西藏表现差异的原因进行了分析。     

Exploration of Genetic Pattern of Phenological Traits in Wheat (<i>Triticum aestivum</i> L.) under Drought Stress

Drought is the major detrimental environmental factor for wheat (Triticum aestivum L.) production. The exploration of genetic patterns underlying drought tolerance is of great significance. Here we report the gene actions controlling the phenological traits using the line × tester model studying 27 crosses and 12 parents under normal irrigation and drought conditions. The results interpreted via multiple analysis (mean performance, correlations, principal component, genetic analysis, heterotic and heterobeltiotic potential) disclosed highly significant differences among germplasm. The phenological waxiness traits (glume, boom, and sheath) were strongly interlinked. Flag leaf area exhibits a positive association with peduncle and spike length under drought. The growing degree days (heat-units) greatly influence spikelets and grains per spike, however, the grain yield/plant was significantly reduced (17.44 g to 13.25 g) under drought. The principal components based on eigenvalue indicated significant PCs (first-seven) accounted for 79.9% and 73.9% of total variability under normal irrigation and drought, respectively. The investigated yield traits showed complex genetic behaviour. The genetic advance confronted a moderate to high heritability for spikelets/spike and grain yield/plant. The traits conditioned by dominant genetic effects in normal irrigation were inversely controlled by additive genetic effects under drought and vice versa. The magnitude of dominance effects for phenological and yield traits, i.e., leaf twist, auricle hairiness, grain yield/plant, spikelets, and grains/spike suggests that selection by the pedigree method is appropriate for improving these traits under normal irrigation conditions and could serve as an indirect selection index for improving yield-oriented traits in wheat populations for drought tolerance. However, the phenotypic selection could be more than effective for traits conditioned by additive genetic effects under drought. We suggest five significant cross combinations based on heterotic and heterobeltiotic potential of wheat genotypes for improved yield and enhanced biological production of wheat in advanced generations under drought.     

Detection and estimation of components of genetic variation for some metric traits in tomato (Lycopersicon esculentum Mill)

Summary Sixty families from two tomato triple test crosses (S120 x EC61747 and EC31513 x Tusa Ruby) were raised in complete randomized blocks in two replications and two environments (two fertilizer levels). Jinks and Perkins' (1970) analysis was used to detect and estimate the additive, dominance and epistatic components of genetic variation for flowering time, maturity period, number of branches per plant, final height, shape index of fruit, locule number, number of fruits per plant, yield per plant and weight per fruit. The j & 1 type epistasis was more important than the i type epistasis in the first cross, while in the second cross the two components of epistasis played almost equal roles in the control of characters studied. Both the D (additive) and H (dominance) components were significant for most of the characters in both crosses and in both the environments. The D component was relatively more important than the H component in the first cross, while the situation was just the reverse in the second cross. Dominance was directional in 8 out of 36 cases. Ambidirectional dominance was observed in 27 cases. A real absence of dominance was observed in one case only.     

小麦体细胞无性系矮秆变异体AS34株高构成和育种潜力探讨

创制和利用矮秆资源对于小麦品种改良具有重要意义。到目前为止,在小麦属中虽然已鉴定了多个矮秆资源,但多数矮秆资源在小麦中的利用价值有限。本研究对利用无性系变异途径获得的小麦矮秆材料AS34及其与模式小麦品种中国春杂交F1、F2材料进行了株高构成和主要农艺性状分析。结果发现,AS34共有4个节间,比其野生型豫麦66少了1个节间,各个节间长度按相似比例缩短,穗下节长度短于第2节长度;F1株高、节间长度指数介于2个亲本之间,节数与AS34相同,穗长、小穗数、穗粒数超过2个亲本;F2株高、穗长、穗粒数、小穗数变异范围广泛,约70%植株株高为60~89 cm,穗长6.0~9.9 cm、穗粒数50~79粒、小穗数20~24个。结果表明,AS34的矮秆变异由多基因控制,表现为数量性状,其矮秆性状对杂交后代穗长、小穗数、穗粒数等主要农艺性状有正向遗传效应,F2选择穗大、粒多、株高适中优良单株的机率较大,具有很好的育种利用价值。     

Genetic insight into yield-associated traits of wheat grown in multiple rain-fed environments

Background

Grain yield is a key economic driver of successful wheat production. Due to its complex nature, little is known regarding its genetic control. The goal of this study was to identify important quantitative trait loci (QTL) directly and indirectly affecting grain yield using doubled haploid lines derived from a cross between Hanxuan 10 and Lumai 14.

Methodology/Principal Findings

Ten yield-associated traits, including yield per plant (YP), number of spikes per plant (NSP), number of grains per spike (NGS), one-thousand grain weight (TGW), total number of spikelets per spike (TNSS), number of sterile spikelets per spike (NSSS), proportion of fertile spikelets per spike (PFSS), spike length (SL), density of spikelets per spike (DSS) and plant height (PH), were assessed across 14 (for YP) to 23 (for TGW) year × location × water regime environments in China. Then, the genetic effects were partitioned into additive main effects (a), epistatic main effects (aa) and their environment interaction effects (ae and aae) by using composite interval mapping in a mixed linear model.

Conclusions/Significance

Twelve (YP) to 33 (PH) QTLs were identified on all 21 chromosomes except 6D. QTLs were more frequently observed on chromosomes 1B, 2B, 2D, 5A and 6B, and were concentrated in a few regions on individual chromosomes, exemplified by three striking yield-related QTL clusters on chromosomes 2B, 1B and 4B that explained the correlations between YP and other traits. The additive main-effect QTLs contributed more phenotypic variation than the epistasis and environmental interaction. Consistent with agronomic analyses, a group of progeny derived by selecting TGW and NGS, with higher grain yield, had an increased frequency of QTL for high YP, NGS, TGW, TNSS, PFSS, SL, PH and fewer NSSS, when compared to low yielding progeny. This indicated that it is feasible by marker-assisted selection to facilitate wheat production.     

Morphological analyses of spring wheat (CIMMYT cv. PCYT-10) somaclones

The objectives of this study were to induce callus from single immature wheat embryos, produce multiple seedlings from the induced callus, and analyse the somaclonal regenerants for potential grain production in a space garden. Immature wheat, Triticum aestivum L. (cv. PCYT-10), embryos were excised 10 to 12 days post-anthesis and cultured on modified Murashige & Skoog's inorganic salts. Embryos cultured on medium containing kinetin (6-furfurylaminopurine) at 0.5 mgl^–1 plus 2 or 3 mgl^–1 dicamba (1-methoxy-3,6-dichlorobenzoic acid) or 0.2 mgl^–1 2,4-dichlorophenoxyacetic acid produced calli from which 24, 35 and 39% of the explant tissue exhibited regenerants, respectively. The size of flag leaves, plant heights, tillers per plant, spike lengths, awn lengths, and seeds per spike were significantly different in regenerants of two-selfed recurrent generations (SC₁, SC₂) than in parental controls. However, there were no significant differences in spikelets per spike between the SC₂ and parental controls. Desirable characteristics that were obtained included longer spikes, more seeds per spike, supernumerary spikelets, and larger flag leaves, variants that should be useful in wheat improvement programs.Contribution from the Plant Science Dept., Utah State University, Logan, UT 84322-4820. Utah Agricultural Experiment Station Journal Paper No. 3611     

小麦新型不育类型利用潜力分析

K、L、Sh、T、A型 5类小麦杂种 F1研究表明 :1 K、L、Sh、T4类细胞质对杂种 F1不育的恢复度和单株产量均存在不同程度的不良效应 ;2不育系易恢复性能为 K>L≥ Sh>T型 ;3 K型不育系恢复度高的一个重要原因在于小穗中部小花结实性好 ;4研究 K、L、Sh型恢复度时 ,利用国际法表示恢复度较为合理 ;5F1单株籽粒产量普遍存在优势 ,平均超双亲杂种优势为 8.57% ,具有 1 5%以上的杂种组合占总组合 2 3.33%。单株籽粒产量优势为 A>K>Sh>L>T;6产量构成因素超双亲优势为千粒重 >单株穗数 >单穗粒数 ,其中千粒重优势为 K、L、Sh≥ A>T,单穗粒数优势为 A>K>L>Sh>T,单株穗数优势为 A>L>K>Sh>T;7K、L、Sh比 T型细胞质不育类型具有更大利用潜力。