Variation for dry matter yield,seed yield and other agronomic traits in Ladino white clover landraces and natural populations

Summary A set of Ladino white clover ecotypes including the last available landraces and some natural populations collected from old permanent meadows, together with some white clover varieties of various origins, were evaluated as monocultures for dry matter (DM) and seed yield assessed in separate field experiments. Other agronomic traits were also recorded. The best performing variety, Espanso, was significantly outyielded by some ecotypes for DM and seed production. Compared to landraces, natural populations yielded on average far less seed but as much DM and tended towards higher persistence indicating that domestication of the native Ladino at the farm level only improved seed yield of the crop. Natural populations showed, besides lower values of most seed yield components, a distinct canopy architecture characterized by smaller leaves, longer internodes and denser stolons. Seed weight proved the best character discriminating between the two ecotype groups. Significant variation for most traits was found both among landraces, in which it was mostly relatable to differences among provenances, and among natural populations. The relations between the main multivariate patterns of phenotypic variation and a set of environment collecting variables suggested that evolutive adaptation to different agronomic practices was a major determinant of the overall variation found in landraces. Evidence is provided that a relevant part of the variation observed among ecotypes for some important traits could be genetic.Abbreviations DM dry matter - DMY dry matter yield - NRH number of ripe heads - NFH number of florets per head - PL petiole length - LS leaf size - IL internode length - NS number of stolons - PRO protein content - SY seed yield - TSW thousand seed weight - NSF number of seeds per floret - PCA principal components analysis - PC principal component     

Heritability of, and genetic correlations among, forage and seed yield traits in Ladino white clover

Sixteen white clover genotypes and their half-sib progenies were grown in pure stand. Each clover progeny was also grown in a mixed stand that also included three grass varieties of different species. Dry matter (DM) yield was measured over 2 years and seed yield at the second year. Competitive ability of clover families was defined as the ratio between mixed stand and pure stand for clover DM yield. Narrow-sense heritability from parent-offspring regression of pure stand data was high to moderate (h²0.50) for DM yield, seed yield and most of their components. Persistence as predicted by stolon density showed negative genetic correlations with seed yield (r_g= -0.70) and DM yield (r₂= -0.60), whereas seed yield and DM yield tended towards a negative correlation (r₂=0.45). Sizes of different vegetative or reproductive organs were generally correlated positively. Evidence was provided that the set of parent genotypes represents well the genetic variation available within the Ladino gene pool. The results highlighted the difficulty of combining relatively short-term DM yield, persistence and seed yield into a unique plant type. Differences in competitive ability emerged only in the second year, better ability being related mainly to petiole length among the traits assessed in pure stand.     

Farmers' seed management practices open up new base populations for pearl millet breeding in a semi-arid zone of India

Farmers in western Rajasthan (north‐west India) produce and maintain their landrace populations of pearl millet through their own distinct seed management practices. The objective of this study was to characterize morphological and agronomic variability of different traits between and within three farmers' populations using quantitative‐genetic parameters. Populations examined were a typical landrace and two modified landraces, which were generated through farmer introgression of modern varieties with different levels of subsequent selection. From these three populations, 100 random full‐sib progenies were evaluated in field trials at two locations in western Rajasthan over two years. Significant genetic variation existed within the three populations. Estimates of heritability were moderate to high for all observed traits. Predicted selection response for grain yield across environments was 1.6% for the typical landrace and 2.2% for both the modified landraces. Results suggest that the introgression of modern varieties into landraces had increased the genetic diversity. Therefore, farmers' current breeding activities could open up new resources for plant breeding programmes aiming at plant improvement for the semiarid zones of India.     

Contribution of autochthonous maize populations for adaptation to European conditions

Early vigor, earliness and cold tolerance are the main potential contributions of European maize (Zea mays L.) for breeding programs for adaptation to areas with short growing seasons and cold springs. The objective of this research was to determine the potential contributions of populations from different European regions to breeding for adaptation. Six Spanish and six French maize populations differing on variability for earliness, vigor and cold tolerance were crossed in a complete diallel without reciprocals. The populations and their crosses were evaluated in the field and in a cold chamber. Minimum temperatures were the main environmental trait affecting genotype × environment interaction, probably due to the cold sensitivity of the genotypes with the best performance in the field. The best population cross, based on specific heterosis for adaptation-related traits in the field, was Viana × Rastrojero, but this cross was cold sensitive. Tuy × Lazcano should be the best choice for a breeding program for adaptation, based on performance in the field and cold tolerance. As conclusions, there was variability for earliness, vigor and cold tolerance among the populations and crosses involved in this study, being tolerant to cold conditions the populations with medium growing cycle originated in areas with short growing seasons. The highest yielding crosses were cold sensitive.     

Characterizing the molecular and morphophysiological diversity of Italian red clover

Red clover (Trifolium pratense L.) is the third major forage species in Europe, but there is limited information on the biodiversity and the genetic structure of landraces and natural populations which evolved in this region. The objective of this study was producing such information for Italian germplasm on the ground of molecular and morphophysiological diversity. The study included 16 Italian natural populations from a wide range of environments, four landraces representing the four traditional commercial ecotypes, and two varieties. Eight morphophysiological traits were assessed in a replicated trial under field conditions, whereas two AFLPs primer combinations with 140 polymorphic markers were recorded on a random sample of 13 genotypes per population. Ordination and classification results based on morphophysiological data clearly kept track of the type of germplasm (i.e. landrace or natural population) and its geographic origin, unlike results based on molecular markers. Euclidean distances among populations based on morphophysiological traits were not correlated with Nei’s genetic distances based on molecular markers according to Mantel’s test. Geographical distances among landrace or natural population material was correlated with distances based on morphophysiological traits but not with those based on molecular markers. The average within-population variation estimated via molecular markers was about 2.6-fold higher than that among populations, preventing an acceptable discrimination among most populations. On average, natural populations tended to have within-population variation similar to varieties and somewhat lower than landraces. Our results have implications for collection, conservation, exploitation and registration in a sui generis system of red clover genetic resources.     

Genetic structure of landrace populations of the New World grain amaranths

Summary Grain amaranth populations from their centers of origin in the New World had shown a pattern of allozyme variation that suggested most landraces to be highly homozygous mixtures of genotypes. To compare this pattern of variation with the variation for morphological traits, 15 selfed families from each of six populations were grown in a replicated field experiment. Four pigmentation traits known to be smiply inherited were scored along 18 other morphological traits. Populations varied for the amount of polymorphism for marker loci, and exhibited little heterozygosity. Analysis of variance for the quantitative traits showed significant interpopulation differences for each of the observed characters. Populations differed for the number of metric traits showing significant between-family differences for just one of the metric traits whereas another had between-family differences for all ten. These results suggested high levels of homozygosity within these landraces; thus, variation for quantitative traits conformed well with the allozyme variation patterns.Stepwise multiple regression of all characters on yield as the dependent variable was used to compare the relative contributions of specific characters to yield within individual populations. Plant height, days to flowering, and leaf length were included in the regression equations for 6, 5, and 5, of the populations, respectively. Days to floweing was negatively correlated with yield, while plant height and leaf length were positively correlated. These correlations suggest the potential for developing early flowering, high yielding cultivars having short stature, selected by breaking its correlation with yield. Several breeding strategies based on these findings on genetic resources are discussed briefly.     

Indirect selection for persistence and seed yield in large-leaved white clover

High persistence and seed yield are important targets in white clover breeding but their assessment is expensive. The efficiency of indirect selection for these traits performed on characters recorded during a medium-term dry matter (DM) yield evaluation was verified for large leaved populations in separate experiments for medium-term (three-year) and long-term (fourth and fifth year) DM yield (Trial 1) and seed yield (Trial 2). The best results were provided by stolon density observed at the end of the third cropping year for prediction of long-term yield, and by the product of number of heads times number of florets per head assessed prior to mowing in Trial 1 for prediction of seed yield in Trial 2. Indirect selection was about as efficient as direct selection in these cases. Predictions of persistence from three-year or third year DM yield, and seed yield from single seed yield components in Trial 1 were less accurate.     

The inheritance of fruit yield and stolon production in everbearing strawberries

Summary The everbearing progeny from crosses between three short-day and four everbearing genotypes were assessed for early fruit yield and stolon production. General combining ability (GCA) was found to be important for fruit yield but specific combining ability (SCA) was more important for stolon production. The results suggested that it should be possible to combine early fruiting and adequate stolon production in an everbearing genotype. The breeding strategy necessary to achieve this aim is discussed.     

Response of white clover genotypes to evaluation environments of dense and spaced planting, and implications for selection

Twelve genotypes were grown for two years asmonocultures in the evaluation environments (EE) ofspaced planting (SP) and dense planting (DP). Drymatter (DM) yield, seed yield and their contributingtraits were recorded. The environments were comparedfor: i) genotype performance, and selection efficiencyfor the target environment of DP, and ii) estimates ofgenetic correlations between traits. DP was obtainedby close transplanting of clonal cuttings. EE × Ginteraction occurred for DM yield over harvests, andstolon density, petiole length, inflorescenceproduction and number of florets per inflorescence averagedover repeated measurements. Interaction effectsleading to relatively higher DM yield in SP tended tobe associated positively with those for the othertraits and featured the genotypes with greater abilityto colonize bare soil by stolon production. Theinteraction effects decreased with time and generallydisappeared (p < 0.05) by the end of the experiment,when the environments reached a similar DM yield andstolon density. EE × G interaction also occurred forseed yield (p < 0.08), recorded at the second year.Indirect selection in SP for performance in DP waspredicted to be less efficient for DM yield (–40%),seed yield (–23%) and the other traits subject to EE ×G interaction, compared with direct selection in DP.Evaluation under SP led to identification of severalgenetic correlations that were not confirmed under DP.DP compared with the traditional SP evaluationtechnique is more labour-demanding but allows for i)increasing the selection efficiency and/or decreasingthe time needed for a reliable evaluation, and ii)obtaining a more reliable estimation of geneticcorrelations for ordinary agricultural environments.     

The relationship between the regeneration system and genetic variability in the cucumber (Cucumis sativus L.)

Durum wheat has been subjected to intense breeding in Italy due to its local economic importance. Four groups of Italian cultivars representative of different breeding eras were compared in northern Syria for yield potential and morphophysiological features at a moderately favourable site, and drought tolerance at a stressful site. Group 1 included indigenous landraces; Group 2 comprised genotypes selected from exotic landraces (released in 1920's–1930's); Group 3 included genotypes selected from crosses or mutagenesis involving Group 2 materials (1950's–1960's); Group 4 comprised genotypes selected from crosses between CIMMYT and Group 2 materials (from 1970's). Under moderately favourable conditions, a yield increase of 1.03 t ha–¹ was observed from Group 1 through Group 4, corresponding to a genetic gain of about 0.017 t ha–¹ per year. Such increase was only partly accounted for by a parallel increase in spike fertility and seed weight. Plant stature decreased dramatically from Group 1 to Group 4; a remarkable reduction of height was already attained in Group 3, before the introduction of dwarfing genes from bread wheat. Earliness of heading and grain filling duration increased consistently across breeding phases, the length of crop cycle remaining almost unaltered. No significant improvement of drought tolerance resulted from the breeding activity, suggesting the need to put more emphasis on selection for real stress tolerance rather than escape. Overall variation for morphophysiological traits, assessed by a principal components analysis, highlighted the great diversity among the Group 1 cultivars, while variation within Groups 3 and 4 was lower. Indigenous landraces, little used in the breeding history, as well as novel, unexploited exotic germplasm sources could contribute to broaden the crop genetic base in the region.     

Observations on different mildew sources used in apple breeding at Ahrensburg

Fifty-six populations of common bean (Phaseolus vulgaris L.) were grown in Pontevedra (Northwestern Spain) in four different environments in order to study their genetic diversity in 18 agronomical traits. All characters showed significant differences among populations, and most of them had significant genotype-environment interactions. Broad-sense heritability for this pool of characters ranged from 0.87 (seed length) to 0.12 (seed yield). Sixteen populations which deserve special attention because of their breeding value for earliness, yield, pod and seed size have been identified.     

Genetic potential to improve seed and forage yield simultaneously in smooth bromegrass under water deficit conditions

This study was conducted to assess genetic potential of smooth bromegrass for water stress and to identify the association among different seed and forage production related traits. Thirty-six genotypes were clonally propagated and evaluated in the field under two moisture environments (normal irrigation and water stress) during 2013–2015. High variation was observed among genotypes for all of the measured traits. Water stress had negative effects on seed yield and its components and reduced genotypic variation of measured traits. On average, water stress reduced seed and forage yield by 38 and 14%, respectively. Genetic coefficient of variation for seed yield and its components was higher under stress, providing opportunities for a greater selection differential. The estimates of heritability were higher in normal condition than water stress condition for all of the evaluated traits, which is advantageous for successful selection. Moreover, the majority of seed yield components had higher heritability estimates than seed yield. The higher heritability estimates of some seed yield components, compared to SYP, suggests a potential for indirect selection. The results showed that selection for both forage and seed yield is possible simultaneously in normal irrigation as well as in water stress environment. Genotypes 7, 8, 26 and 27 had high forage yield, while genotypes 23 and 27 had high seed yield under both normal irrigation and water stress condition. Three genotypes ranked among the top three for both seed and forage yield and under both normal irrigation and water stress condition. They are promising parents for further use in developing improved cultivars by cross-breeding.     

Indirect Selection for Root Development of White Clover and Implications for Drought Tolerance

Improving white clover drought tolerance by selecting for more developed roots is controversial, labour‐consuming and complicated by the adventitious root system. This study aimed at assessing: (i) the value of thicker stolons as an indirect selection criterion for increasing root development, (ii) the relationship between root development and drought tolerance, and (iii) the consistency of population response for root and shoot traits between swards derived from seedlings or stolon cuttings. Thick‐ and thin‐stolon populations obtained by one cycle of divergent phenotypic selection within one ladino landrace, and one ladino natural population, were evaluated in metal containers (0.55 m × 0.12 m × 0.75 m deep) in a 1‐year experiment including vegetative material (seedling or stolon cutting) and drought stress (absent or present) as additional factors. Aerial dry weight (DW) was also assessed across two summer harvests under irrigated and rainfed field conditions for the thick‐stolon selection, two breeding populations selected from the same landrace regardless of stolon thickness, and the drought‐tolerant ladino ‘Brown Loam Synthetic no. 2’. The thick‐stolon selection had greater root DW (+21 %) than the thin‐stolon selection besides thicker stolons (+23 %). The natural population combined thinnest stolons with lowest root DW. Differences between populations were consistent across vegetative material. Primary and adventitious root systems did not differ for root DW in deeper soil horizons (>23 cm), above‐ground biomass and its reduction due to drought stress. Root DW increased under stress, particularly in deeper horizons. Aerial DW variation among populations evened up or narrowed much under stress, with no cross‐over interaction leading to an advantage of thick‐stolon material or ‘Brown‐Loam Synthetic no. 2’.     

Genetic variability of cassava progenies developed through introgression of cassava mosaic disease resistance into Ghanaian landraces

Availability of genetic diversity is important in selecting suitable cultivars for crop improvement. Progenies of crosses between 19 farmer-preferred cassava landraces and Cassava Mosaic Disease (CMD)-resistant cultivar TME 11 were evaluated and compared with their maternal parents to assess their genetic variability and genetic gains based on CMD tolerance, some growth variables and root yield. The combined analysis of variance for the traits showed significant genotypic differences amongst the progenies and the parents. Apart from a few instances, the differences in replications and years were also significant. Genetic variability components showed high heritability ranging from 92.3 to 99.6% and moderately high genetic gains of 54.1 to 99.6% for the parental cultivars. Apart from canopy spread and plant height, heritability and genetic gains of the progenies were slightly lower than the parents indicating high variability within families of the progenies. The phenotypic coefficient of variation was slightly greater than genotypic coefficient of variation indicating minimal influence of environment on the genotypes. For most of the characters evaluated, the mean performance of the progenies was higher than their corresponding parental lines. Although the genotypes differed significantly (P < 0.001) for all traits evaluated, cultivars such as Afebankye, Bosome nsia, Cedi bankye, 262 Debor, Kwadaso 25, Nkaakom 57 and Sisipe were found to constitute a pool of germplasm with adequate variability. The negative correlation between CMD incidence and other traits evaluated showed significant progress made in the breeding program.     

Early generation genetic variation and heritability of yield and related traits among tef populations

The extent of genetic variation and heritability of a trait are among the major determinants of selection gains in plant breeding programs. The aim of this study was to determine the magnitude of genetic variation and inheritance of grain yield, and component traits of newly developed tef populations under moisture-stressed and non-stressed conditions for drought tolerance breeding. Seventeen crosses along with the parents were evaluated in the F2 generation under moisture-stressed and non-stressed conditions in northern Ethiopia during 2015 and 2016. There were marked genotypic and phenotypic variation among the crosses in the F2 generation for plant height, panicle length, peduncle length, number of productive tillers per plant, main shoot panicle seed weight, biomass yield, and grain yield under both test conditions, important for successful selection and genetic advancement. The families of DZ-Cr-387 x 207832 and DZ-Cr-387 x 222076 were high grain yielders with early maturity under both test conditions.     

Productivity,persistence and traits related to drought tolerance in smooth bromegrass

This study was conducted to evaluate drought tolerance and persistence in a germplasm of smooth bromegrass and association of forage productivity with different traits. Thirty‐six genotypes of smooth bromegrass were clonally propagated and evaluated under two soil moisture environments for three years (2013–2015). High genotypic variation was observed among genotypes for all the measured traits. Drought stress decreased mean values for traits related to productivity. Also, the long‐term stress for three years reduced the persistence of plants. Results indicated that indirect selection based on components of forage yield, which had high heritability and high correlation with yield, would be more effective to improve drought tolerance in this germplasm. The results of principal component analysis showed that there was a negative relationship between phenological traits with the persistence‐related traits and yield production. This suggests that selection for earliness may indirectly promote persistent genotypes. The results showed that some Hungarian genotypes are valuable gene sources for persistence. The most persistent genotypes from both groups (Iranian and foreign) were identified using the biplot method. These genotypes may be useful for the development of populations for future studies.     

Long-term trends and genetic architecture of seed characteristics,grain yield and correlated agronomic traits in triticale (×Triticosecale Wittmack)

The aim of this study was to investigate long-term genetic trends and the genetic architecture of grain yield, seed characteristics and correlated agronomic traits in triticale. Therefore, a panel of 846 diverse triticale genotypes was assessed for three agronomic and three seed shape- and size-related traits. We observed a high genotypic variation and a high heritability for all traits. Analysing the development of these traits during the last decades revealed a continuous increase for grain yield and thousand-kernel weight, and a slight increase in seed width. The seed characteristics and thousand-kernel weight formed a complex of highly positive correlated traits. Genome-wide association mapping revealed many small-effect QTL and a few moderate-effect QTL. The allele frequencies of the moderate-effect QTL followed the same temporal trends as observed for the phenotype. In line with the phenotypic correlations, we identified several pleiotropic QTL for grain yield, thousand-kernel weight, seed width and seed area. Our results illustrate the continuous progress achieved in triticale breeding and suggest that triticale seeds have been selected to be more spherical in modern cultivars.     

Variation in cold tolerance and spring growth among Italian white clover populations

Seven populations collected at different altitudes in northern Italy, two Ladino breeding populations and two control cultivars (AberHerald and Grasslands Huia) of white clover (Trifolium repens L.) were included in a series of experiments analysing: (i) levels of cold tolerance using artificial and field-based methods; (ii) relationships between these measures of cold tolerance; (iii) components of spring yield, various physiological traits, and their relationships with cold tolerance. Rates of seedling and growing point mortality in the populations over winter, assessed in separate field experiments, were closely related (r = 0.85). Grasslands Huia showed the highest death rates, and material originating from high altitudes the lowest. The LT₅₀ value, i.e., the temperature at which 50% of the growing points would die, estimated by an artificial freezing test, was significantly correlated with field-based measures of seedling (r = 0.64) and growing point (r = 0.84) mortality. The existence of these correlations is of potential interest for the development of indirect selection criteria for complex and expensive-to-evaluate traits such as winter survival in field plots. Besides being reliable, in this study the artificial assessment was also sensitive, providing a greater degree of separation of the populations means than field-based measures. Of the several physiological traits (water content,concentrations of water soluble and total non-structural carbohydrate, and water soluble protein content of stolons) measured at a mid-winter sampling date under field conditions, the only character showing significant variation between populations was soluble protein content. There was a slight trend for material with a higher protein content to exhibit greater field-based values of cold tolerance. High altitude populations tended to have low spring yields. The highest spring yield was found in one of the Ladino populations. The study identified two populations which combined, to differing extents, cold tolerance and spring yield characteristics that would be of potential use in breeding for specified agronomic/climatic zones. This revised version was published online in August 2006 with corrections to the Cover Date.     

The inheritance of the cold induction response with respect to floral initiation in white clover (Trifolium repens L.)

Summary The inheritance of the cold induction response in the UK cultivar of white clover Menna, was assessed in controlled environments.Only 50% of the population flowered without prior cold induction. The cold period increased the number of stolons which became reproductive.All families from the crosses between induction and non-induction requiring genotypes produced progeny lacking a cold requirement for flowering.Heritability estimates for the number of flowers per plant, reproductive buds per stolon and stolon number were high.The necessity of eliminating the cold induction requirement in potentially valuable white clover cultivars in relation to seed production at lower latitudes is discussed.     

Study of genetic diversity in safflower genotypes using agro-morphological traits and RAPD markers

This research was conducted to study the genetic diversity in safflower (Carthamus tinctorius L.) using agro-morphological traits and RAPD markers. Sixteen selected lines derived from landraces growing in various agro-climatic regions of Iran along with four exotic genotypes were evaluated in a randomized complete block design with three replications under field conditions. Days to emergence, days to initial flowering, days to flowering, days to maturity, plant height, branches per plant, capitula per plant, seeds per capitulum, 1,000-seed weight, seed yield per plant, seed yield, and reaction to powdery mildew (Leveillula taurica Arnaud) were evaluated in this study. Genetic diversity of the genotypes was assessed by RAPD markers. The results indicated significant differences among genotypes for the agro-morphological traits and clustering based on these traits classified the genotypes into five groups. Analysis of the RAPD markers revealed 15 polymorphic primers out of 50 used primers. Based on RAPD data, the highest genetic similarity was observed between the cultivars of “AC Sunset,” “AC Sterling” from Canada and the lowest relatedness observed between a local breeding line “E₂₄₂₈” and genotype “GE₆₂₉₂₃” from Germany. Cluster analysis based on RAPD markers and 54% coefficient of similarity divided the genotypes into five distinct groups. Comparing the clusters based on agro-morphological traits with those from molecular markers showed slight similarities. The finding of high genetic variation for agro-morphological traits and polymorphism at DNA level reveal that agronomic traits can be improved by selection programs.