Gene effects of Cicer reticulatum on qualitative and quantitative traits in the cultivated chickpea

The gene effects of Cicer reticulatum on both double‐podding as qualitative traits and yield criteria as quantitative traits in interspecific hybridization with cultivated chickpea (Cicer arietinum) have not yet been elucidated, despite the easy acquisition of hybrid progeny between two species. This study sought to answer three questions concerning qualitative and quantitative traits in reciprocal crosses between C. arietinum and C. reticulatum. (i) Is there a similarity in the gene effects of flower colour, pigmentation and double‐podded traits in reciprocal interspecific crosses? (ii) What are the expressivity and penetrance of the double‐podded trait in interspecific crosses? (iii) Which heterosis predicts the occurrence and the extent of transgressive variation? The materials for this study were F₁, F₂ and F₃ progeny derived from a reciprocal cross between C. arietinum and C. reticulatum. As qualitative traits, purple flower colour, pigmentation and single‐podded traits in C. reticulatum were governed by a dominant single gene. Purple flower colour and pigmentation were detected to be linked traits as all progeny had the same phenotypes. As quantitative traits, yield criteria in progeny which were double‐podded had higher values than the single‐podded counterparts. Expressivity and penetrance of the double‐podding trait were superior in progeny derived from C. reticulatum × C. arietinum. The results showed that fruitful heterosis was more useful than residual heterosis in F₃ as residual heterosis was mostly negative and fruitful heterosis was suggested in self‐pollinated species such as chickpea that lacks inbreeding depression. Interspecific transgression was significant with respect to chickpea improvement because it represented a potential source of novel genetic variation.     

Leaf shape × sowing density interaction affects chickpea grain yield

Modifying plant architecture is considered a promising breeding option to enhance crop productivity. Modern chickpea (Cicer arietinum L.) cultivars with either compound (wild‐type) or simple leaf shapes are commercially grown but the relationships between leaf shape and yield are not well understood. In this study, a random sample of ‘Kabuli’ type progeny lines of both leaf types, derived from two crosses between modern American simple leaf cultivars and early‐flowering wild‐type breeding lines, were planted at different sowing densities. Leaf area development and final grain yield in genotypes of the two leaf types responded differently to changes in sowing densities. Compound leaf lines attained higher leaf area indices and higher grain yields at both low and high sowing densities. Yield responses of the simple leaf lines to increasing sowing density were significantly higher compared to compound leaf genotypes in two of three field experiments. The prospects for utilizing the simple leaf trait as a breeding target for short‐season growing areas are discussed.     

Integrated breeding approaches for improving drought and heat adaptation in chickpea (Cicer arietinum L.)

Chickpea (Cicer arietinum L.) is a dry season food legume largely grown on residual soil moisture after the rainy season. The crop often experiences moisture stress towards end of the crop season (terminal drought). The crop may also face heat stress at the reproductive stage if sowing is delayed. The breeding approaches for improving adaptation to these stresses include the development of varieties with early maturity and enhanced abiotic stress tolerance. Several varieties with improved drought tolerance have been developed by selecting for grain yield under moisture stress conditions. Similarly, selection for pod set in the crop subjected to heat stress during reproductive stage has helped in the development of heat‐tolerant varieties. A genomic region, called QTL‐hotspot, controlling several drought tolerance‐related traits has been introgressed into several popular cultivars using marker‐assisted backcrossing (MABC), and introgression lines giving significantly higher yield than the popular cultivars have been identified. Multiparent advanced generation intercross (MAGIC) approach has been found promising in enhancing genetic recombination and developing lines with enhanced tolerance to terminal drought and heat stresses.     

Direct and indirect selection for yield in chickpea

Summary The efficiency of indirect selection for seed yield was compared with direct selection for yield per se in chickpea. A total of 2500 single F₂ plants, derived from 50 crosses with 50 plants from each cross, were divided into five sub-populations (SP1 to SP5) of 500 plants each by including 10 plants from each of the 50 crosses. The five sub-populations were advanced upto F₆ by exercising 10% selection intensity for four successive generations for number of pods per plant in SP1, number of seeds per pod in SP2, seed weight in SP3, seed yield in SP4 and random selection in SP5. The efficiency of direct and indirect selection for yield was evaluated by comparing groups of 50 F₆ lines from each sub-population. SP1 and SP3 F₆ lines showed higher mean grain yield than the other three methods. SP1 and SP3 were found to be almost equally efficient in developing F₆ lines which were significantly superior to the check. This suggests that indirect selection for yield via pod number and seed weight is more efficient than direct selection for yield.     

Dissection of a major QTL for seed colour and fibre content in Brassica napus reveals colocalization with candidate genes for phenylpropanoid biosynthesis and flavonoid deposition

A major quantitative trait locus (QTL) influencing seed fibre and colour in Brassica napus was dissected by marker saturation in a doubled haploid (DH) population from the black‐seeded oilseed rape line ‘Express 617’ crossed with a yellow‐seeded B. napus line, ‘1012–98’. The marker at the peak of a sub‐QTL with a strong effect on both seed colour and acid detergent lignin content lay only 4 kb away from a Brassica (H+)‐ATPase gene orthologous to the transparent testa gene AHA10. Near the peak of a second sub‐QTL, we mapped a copy of the key phenylpropanoid biosynthesis gene cinnamyl alcohol dehydrogenase, while another key phenylpropanoid biosynthesis gene, cinnamoyl co‐a reductase 1, was found nearby. In a cross between ‘Express 617’ and another dark‐seeded parent, ‘V8’, Bna.CCR1 was localized in silico near the peak of a corresponding seed fibre QTL, whereas in this case Bna.CAD2/CAD3 lay nearby. Re‐sequencing of the two phenylpropanoid genes via next‐generation amplicon sequencing revealed intragenic rearrangements and functionally relevant allelic variation in the three parents.     

Pollen selection for chilling tolerance at hybridisation leads to improved chickpea cultivars

The potential of pollen selection as part of the breeding efforts to increase chilling tolerance in chickpea was investigated. This alternative approach to apply selection pressure at the gametophytic stage in the life cycle has been proposed widely, but there are no reports of the technique being implemented in a crop improvement program. In this paper, we describe how we developed a practical pollen selection technique useful for chickpea improvement.Pollen selection improved chilling tolerance in crossbreds compared with the parental chickpea genotypes and compared with progeny derived without pollen selection. This is backed up by controlled environment assessments in growth rooms and by field studies. We also clearly demonstrate that chilling tolerant pollen wins the race to fertilise the ovule at low temperature, using flower color as a morphological marker. Overall, pollen selection results in a lower threshold temperature for podding, which leads to pod setting two to four weeks earlier in the short season Mediterranean-type environments of Western Australia. Field testing at multiple sites across Australia, as part of the national crop variety testing program, shows that these breeding lines have a significant advantage in cool dryland environments.The major factors which affected the success of pollen selection are discussed in the paper, from generation of variability in the pollen to a means to recover hybrids and integration of our basic research with an applied breeding program. We conclude that chilling tolerance observed in the field over successive generations are the result of pollen selection during early generations.     

Quantitative trait loci for fruit size and flowering time-related traits under domestication and diversifying selection in cucumber (Cucumis sativus)

In cucumber, the genetic basis of traits under domestication and/or diversifying selection is not well understood. Here, we reported QTL mapping for flowering time and fruit size-related traits with segregating populations derived from a cultivated × wild cross. Phenotypic data of flowering time (FT), fruit size (FS), fruit number (FN) and fruit weight per plant (FW) were collected in multiple environments. QTL analysis identified 19 QTL for these traits. We found that the major-effect QTL FT1.1 played an important role in regulating flowering time in cultivated cucumber, whereas the minor-effect QTL FT6.3 contributed to photoperiod sensitive flowering time during domestication. Two novel consensus FS QTL, FS1.4 and FS2.3, seem to be the targets of selection during breeding for the US processing cucumber. All other FS QTL were co-localized with previously detected QTL using populations derived from cultivated cucumbers, suggesting that they were under selection during both initial domestication and subsequent improvement. Results from this study also suggested that the wild cucumber is a useful resource for capturing positive transgressive segregation and novel alleles that could be explored in cucumber breeding.     

Genetic variation for secondary seed dormancy and seed longevity in a set of black‐seeded European winter oilseed rape cultivars

Secondary seed dormancy in oilseed rape is a phenomenon that allows seeds to survive in the soil for many years without germination. Following soil cultivation, dormant seeds may germinate in subsequent years, and they are the main reason for the occurrence of volunteer oilseed rape plants in successive crops. Inheritance of secondary dormancy may be related to seed longevity (SL) in the soil. Genetic reduction in secondary dormancy and SL could provide a mean to reduce the frequency of volunteer plants and especially the dispersal of transgenic oilseed rape. The aim of the present study was to analyse secondary dormancy, germination rate and SL of 28 black‐seeded winter oilseed rape cultivars using in vitro laboratory tests. The material was tested in field experiments at six different locations in Germany in 2008/2009. Significant effects of the genotype and the location on all traits were found. Heritability was high for secondary dormancy (0.97) and moderate for germination rate (0.70) and SL (0.71). Results indicate that a selection for low secondary dormancy would be effective.     

Mapping quantitative trait loci (QTLs) underlying seed vitamin E content in soybean with main,epistatic and QTL × environment effects

Soybean (Glycine max (L.) Merr.) seed contains small amounts of tocopherol, a non‐enzymatic antioxidant known as lipid‐soluble vitamin E (VE). Dietary VE contributes to a decreased risk of chronic diseases in humans and has several beneficial effects on resistance to stress in plants, and increasing VE content is an important breeding goal for increasing the nutritional value of soybean. In this study, quantitative trait loci (QTLs) underlying VE content with main, epistatic and QTL × environment effects were identified in a population of F_5 : 6 recombinant inbred lines from a cross between ‘Hefeng 25’ (a low‐VE cultivar) and ‘OAC Bayfield’ (a high‐VE cultivar). A total of 18 QTLs were detected that showed additive main effects (a) and/or additive × environment interaction effects (ae) in different environments. Moreover, 19 epistatic pairs of QTLs were found to be associated with α‐tocopherol (α‐Toc), γ‐tocopherol (γ‐Toc), δ‐tocopherol (δ‐Toc) and total VE (TE) contents. The QTLs identified in multienvironments could provide more information about QTL by environment interactions and could be useful for the marker‐assistant selection of soybean cultivars with high seed VE contents.     

Use of barley seed vigour to discriminate drought and cold tolerance in crop years with high seed vigour and low trait variation

Seed vigour is a precondition for early and homogenous field emergence of barley, in addition to effective malting. This study aimed to assess the selection of barley varieties by using seed vigour as the indicator. Seed vigour of barley (quantified as the germination percentage) was evaluated under drought (?0.2 MPa) and temperature stress (10°C). At two locations over a 3‐year period, 1 population of 133 Derkado × B83‐12/21/5 doubled haploid (DH) lines (and parents) was evaluated for seed vigour, of which 108 DH lines were assessed for three malting parameters. The relatively high values of vigour during the 3‐year period (overall average 94–95%) probably impeded high variations in genetic potential. A total of 27 DH lines of the 133 evaluated showed transgression for vigour (up to 98%) in comparison with the parents (Derkado: 96%; B83: 92%). In conclusion, caution should be applied when selecting for seed vigour, even in good crop years with high levels of seed vigour and low trait variations. Such selection might improve vigour, particularly in crop years with unsuitable weather conditions.     

Comparing mating designs to restore seed production of interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum

Interspecific hybrids between Trifolium uniflorum and cultivated white clover (Trifolium repens) have highly useful characteristics for temperate pastoral systems derived from both parent species. However, the early hybrids (F₁ and BC₁) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC₁F₁ generation produced lower‐than‐expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover corrected these deficiencies and created new variation. Seed numbers were also returned to near target levels by recurrent selection within the BC₁ generation. Thus, it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. The BC₁F₂ and BC₂F₁ generations produced high seed numbers per plant, along with reasonable variation. Both of these second‐generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits.     

Implications of the population effect in the selection of soybean progeny

The goal of this study was to verify the influence of the population effect in the estimates of genetic and phenotypic components and to identify the best soybean progeny or lines in a commercial soybean breeding programme. We evaluated 292 populations for grain yield and absolute maturity during three agricultural years. To quantify the efficiency of the inclusion of the population's effect in the model, we estimated genetic gain with the selection, the Spearman's correlation, the coincidence index, the realized gain and correlated response of selected genotypes with and without the effect of the population. It was found that the variance components, heritability and coefficient of experimental variation were better estimated when the effect of the population was included, providing greater gain with selection for grain yield and absolute maturity. Coincidence and ranking among the selected progeny with and without the effect of the population are of greater magnitude in more advanced inbreeding generations and at higher percentage of selected progeny. The use of the population effect has greater importance in earlier generations of inbreeding.     

Assessing diversity in Triticum durum cultivars and breeding lines for high versus low cadmium content in seeds using the CAPS marker usw47

Cadmium (Cd) is a toxic heavy metal that occurs naturally in soils. Durum wheat is known to accumulate generally more Cd than other cereal crops. The uptake of Cd in durum wheat is governed by the gene Cdu1, which co‐segregates with several DNA markers, such as the co‐dominant marker usw47 and the dominant marker ScOPC20. A panel of 314 durum wheat cultivars or lines originating from 16 countries or regions were assessed with usw47. The plant material was mainly comprised of cultivars and modern breeding lines. From this set, 165 durum wheat lines were classified as low‐Cd accumulators, 144 high‐Cd accumulators and five were heterogeneous. A smaller subset of 16 cultivars had previously been evaluated for Cd accumulation in replicated field trials. Lines with the high‐Cd allele showed a 2.4‐fold higher Cd content in the seeds than lines with the low‐Cd allele. We also compared the utility of markers usw47 and ScOPC20 as selection tools. Marker‐assisted selection appears as a robust and practicable tool for breeding durum cultivars with low‐Cd content.     

User‐friendly markers linked to Fusarium wilt race 1 resistance Fw gene for marker‐assisted selection in pea

Fusarium wilt is one of the most widespread diseases of pea. Resistance to Fusarium wilt race 1 was reported as a single gene, Fw, located on linkage group III. The previously reported AFLP and RAPD markers linked to Fw have limited usage in marker‐assisted selection due to their map distance and linkage phase. Using 80 F₈ recombinant inbred lines (RILs) derived from the cross of Green Arrow × PI 179449, we amplified 72 polymorphic markers between resistant and susceptible lines with the target region amplified polymorphism (TRAP) technique. Marker–trait association analysis revealed a significant association. Five candidate markers were identified and three were converted into user‐friendly dominant SCAR markers. Forty‐eight pea cultivars with known resistant or susceptible phenotypes to Fusarium wilt race 1 verified the marker–trait association. These three markers, Fw_Trap_480, Fw_Trap_340 and Fw_Trap_220, are tightly linked to and only 1.2 cM away from the Fw locus and are therefore ideal for marker‐assisted selection. These newly identified markers are useful to assist in the isolation of the Fusarium wilt race 1 resistance gene in pea.     

Breeding cowpea for resistance to Striga gesnerioides in the Nigerian dry savannas using marker‐assisted selection

Historically, conventional breeding has been the primary strategy used to develop a number of Striga‐resistant varieties currently grown in the Sahel of Western Africa. In this study, we have successfully developed and applied a marker‐assisted selection strategy that employs a single backcross programme to introgress Striga resistance into farmer preferred varieties of cowpea for the Nigeria savannas. In this strategy, we have introduced the Striga resistance gene from the donor parent IT97K‐499‐35 into an elite farmer preferred cowpea cultivar ‘Borno Brown’. The selected 47 BC₁F₂ populations confirmed the recombinants with desirable progeny having Striga resistance gene(s). The 28 lines selected in the BC₁F_2:4 generation with large seed size, brown seed coat colour and carrying marker alleles were evaluated in the field for resistance to Striga resistance. This led to the selection of a number of desirable improved lines that were immune to Striga having local genetic background with higher yield than those of their parents and standard varieties.     

Genotypic differences in storage losses of sugar beet – causes and indirect criteria for selection

To improve the storability of sugar beets, this study aimed at determining reasons for genotypic variability in sugar losses and invert sugar accumulation during storage, and at identifying indirect criteria to select for varieties with low storage losses prior to storage. In 2011 and 2012, 18 genotypes, and in 2012 and 2013, six genotypes cultivated at two locations were stored for 8 and 12 weeks at 8°C under controlled conditions. The same 18 genotypes were grown under stress conditions in Spain in 2012/2013. Sugar losses were closely correlated with the invert sugar accumulation after storage. Genotypic differences in storage losses were primarily caused by differences in the level of infestation with microorganisms. The invert sugar accumulation was lower for genotypes with high marc concentration before storage, pointing to a non‐specific resistance. Additionally, the sugar concentration in dry matter before storage, and the invert sugar concentration after cultivation under stress conditions correlated with the invert sugar concentration after storage. These parameters are therefore suggested as criteria to select for improved storability of sugar beet genotypes.     

Implications of early selection for grain colour on iron and zinc content and productivity of common bean

Brazilian consumers prefer beans of the beige grain colour. Common beans help supply dietary requirements for iron and zinc. The objectives of this study were (i) to determine whether early selection for grain colour affects the iron and zinc content and the grain yield in common beans and (ii) if an association between these characteristics was found, to obtain lines of carioca‐type grains with a high iron and zinc content and good grain yield. We evaluated 96 F_3:4, F_3:5 and F_3:6 progeny at two locations for iron and zinc content and grain yield. We selected 48 progeny for grain colour and chose 48 others at random. We found that early selection for grain colour does not affect the zinc content and grain yield. A positive and high association was found between iron and zinc content, and both iron and zinc content were slightly negatively correlated with grain yield. It is possible to obtain common bean lines combining a high iron and zinc content with good grain yield as long as a selection index is used.     

Leaf,canopy and agronomic water‐use efficiency of field‐grown sugar beet in response to potassium fertilization

Potassium (K) fertilization is important to maintain adequate concentrations of plant available K in agricultural soils to achieve best yields and improve crop stress tolerance and water‐use efficiency (WUE). Water‐use efficiency (WUE) can be expressed on various spatiotemporal scales, and it is known that responses of WUE to external stress are not uniform across scales. Multiscale evaluations of the impact of varying K fertilization on the WUE of C₃ crops under field conditions are missing so far. In the present field study, we evaluated effects of K fertilization on WUE of sugar beet (Beta vulgaris L.) on short‐termed leaf‐ (WUE_Leaf) and canopy‐scales (WUE_Canopy) and as the agronomic ratio of white sugar yield (WSY) to in‐season water use (i.e. WUE_WSY). In K‐fertilized plots, WUE_WSY was enhanced by 15.9%. This effect is attributed to increased beet yield and WSY, as no differences in total in‐season water use between fertilized and unfertilized plots were observed. Potassium (K) fertilization significantly enhanced the leaf area index, resulting in a more efficient depletion of soil moisture by roots in K‐fertilized plots. As a consequence, WUE_Leaf was increased due to stomatal adjustment. Potassium (K) improved WUE_Canopy only by tendency. It is concluded that K fertilization improves the WUE of field‐grown sugar beet across scales, but processes that regulate WUE are highly scale dependent.     

Phenotypic and seed structural comparison in hybrids of different Brassica rapa and B. oleracea

Brassica napus is an important oil species with short history and narrow genetic background. Interspecific hybrids from crosses between B. oleracea and different B. rapa were obtained. We found the hybrids with white petal resembling B. oleracea, the flavonoid and phenolic content decreased in hybrids, agreeing with the expressional changes of flavonoid biosynthesis genes. Seed coat of hybrids resembled diploid parents, or partly resembled to each parent with a clear outline. The palisade layer in hybrids was thicker than parents, with similar pigment accumulation as B. oleracea but more than B. rapa. Differentially sized protein bodies (PBs) were found in hybrids. The radical and inner cotyledon of all hybrids were identified with larger but less PBs than parents. The average size of PBs in outer cotyledon of resynthesized B. napus was also larger than parents, but the number of PBs was not significantly reduced. The phenotypic and seed structural variations after polyploidization of B. napus would be interesting for genetic broadening and breeding of rapeseed.     

Genetic evaluation and selection index in tetraploid Brachiaria ruziziensis

Half‐sib progenies of congo signal grass (Brachiaria ruziziensis Germain & Evrard, syn.: B. eminii, Urochloa ruziziensis) were analysed using a mixed model methodology. The objective was to estimate genetic and phenotypic parameters, predict individual genetic values, estimate correlations between characters associated with biomass production and forage nutritive value and use this information to determine the economic weights to compare three multiplicative selection indices. Individual narrow‐sense heritabilities corrected for inbreeding varied from 0.14 to 0.91 for characters associated with biomass production and from 0.04 a 0.24 for nutritional value characters. The correlations among characters associated with annual biomass production were of high magnitude. In contrast, biomass production characters were negatively correlated with crude protein, acid detergent fibre and lignin. Total dry matter yield, crude protein and regrowth ability were weighted separately in evaluations during wet and dry season or annually in selection indices. Index that considered characters annually resulted in better distribution of forage production along the year than indices that separated wet and dry season production.