Variation within and among Ladino white clover ecotypes for agronomic traits

Summary One set of 285 genotypes from three landraces and one natural population and a second set of 165 genotypes from two landraces and one natural population were evaluated in separate trials. Variation among populations was mostly accounted for by the difference between landrace and natural population genotype groups, the former showing features related to higher seed yield and short-term aerial dry matter (DM) yield and to lower persistence, cold tolerance and protein content. Compared to variance among ecotypes, that within ecotypes was never lower and it was at least four-fold higher for important traits such as aerial and total (aerial plus stolon) DM yield, stolon density, production of seed heads and cold tolerance. Landraces and natural populations showed similar levels of intra-population variation for all traits except cold tolerance, for which landraces tended to somewhat greater variation. Trait associations were less definite at the genotype level than what previously found in terms of mean values of the ecotypes. This finding and the relatively high broad sense heritability which was observed for all components of DM and seed yield can support the breeding activity on this clover. The level of variation and of heritability found for protein content do not suggest the routine evaluation of this trait in breeding programmes.     

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.     

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.     

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 variability and interrelationships of seed yield and yield components in switchgrass

Information on the genetic variability of seed yield and yield components is limited and no information is available on correlations among seed yield and yield components and direct and indirect effects of the yield components on seed yield in switchgrass, Panicum virgatum L. Accordingly, we conducted replicated experiments at Chickasha and Perkins, OK, in 1998 involving 11 lowland type switchgrass populations to assess genetic variation for seed yield and yield components, quantify interrelationships among them, and determine direct and indirect effects of yield components on seed yield through path coefficient analysis to identify traits for indirect selection of seed yield. Significant (P ≤ 0.01) variation existed among the 11 populations over locations for percent seed set and 100-seed weight. Seed yield/plant and the seed yield components panicle number/plant, spikelet number/panicle, and seed number/panicle had significant (P ≤ 0.05) population × location interactions, indicating substantial environmental influence on these traits for these populations. Accordingly, data for these traits were analyzed separately for each location revealing significant (P ≤ 0.01) differences among populations at both locations for each of these traits. Phenotypic correlation between seed yield/plant and seed number/panicle was positive (r = 0.76** at Chickasha and r = 0.72** at Perkins). Path coefficient analyses revealed that seed number/panicle had the highest positive direct effect on seed yield at both locations. Ample genetic variability was present among the switchgrass populations studied to allow breeding improvement of seed yield. Selection for increased seed number/panicle would be the most effective means of indirectly selecting for higher seed yield within this germplasm. Correlation and path coefficient analyses among biomass yield, seed yield, and harvest index indicated that, at least within the switchgrass germplasm studied, it would be possible to breed switchgrass cultivars with enhanced biomass yielding ability and sufficient seed production capability for their commercial propagation.     

Effect of generation of inbreeding, cutting treatment and year on agronomic traits in berseem populations

The selfing effect in berseem clover (Trifolium alexandrinum L.) was analysed by comparing generation means for nine agronomic traits (dry matter yield, plant height, leaf-stem ratio, harvest index, seed yield and its components). Parents, S₁, S₂, S₃, and S₄ generations of six populations of different geographical origin (3 from Egypt and 3 from southern Italy) were investigated to estimate the relative changes with increasing homozygosity and to prove the effectiveness of selfing in a breeding program. The experiment was carried out at Foggia (Italy) under field conditions for two years (1995 and 1996) adopting two cutting treatments: at fifth internode elongation (A) and flowering (B). The mean values decreased with the advancement in selfing generations in both years and cutting treatments for the most of the traits. Treatment B yielded more biomass and seed yield than treatment A in both years. Cutting treatments did not affect the adaptability of the selfed progenies of populations with different geographical origin, in fact, the Italian populations were more productive for dry matter under both cutting treatments (856.6 g m^-2 on average), whereas Egyptian populations proved superior for seed yield particularly under treatment B (62.5 g m^-2 on average). Inbreeding depression was greater for forage dry matter and seed yield (−62and −79% on average, respectively), whereas the plant height and 1000-seed weight were the least susceptible traits (−26 and −19% on average, respectively). Estimates of the parameters of the stability analysis showed that not all populations responded to inbreeding level and environment variations to the same degree. Differences were evident under treatment A, only. Development of self-fertile, relatively vigorous inbred lines of berseem clover with different degrees of homozygosity appears possible. Genotypes tolerant to selfing from Egyptian and Italian groups have been obtained by inbreeding and selection for self-fertility; they could be utilised as basis for producing new breeding activities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Climatic adaptation in subterranean clover populations

Summary Long-term persistence and, hence, agronomic success as a pasture of the annual species subterranean clover depend primarily on seed yield and seed survival over seasons. In natural populations, plant characteristics influencing seed setting and formation of seed reserves in the soil are expected to be adjusted to the prevailing environmental conditions of the sites of origin. Knowledge on plant/environment relationships may provide information on adaptive strategies of persistence, and guidelines for selecting adapted varieties to specific conditions. On pure lines from a number of populations such relationships were assessed for flowering time, seed yield, burr fertility, individual seed weight, initial hardseededness, and rate of hardseededness breakdown over summer. Flowering time decreased on decreasing annual rainfall, i.e., on shortening the growing season, as adaptive response to the need of producing adequate seed before the onset of the dry season. Individual seed weight decreased on decreasing rainfall, and increasing temperatures. Hard-seed maintenance over summer was higher in populations from hot and dry environments, where the marked effect of temperature on hardseededness breakdown exerts a strong selective pressure. Within-population variation, assessed on flowering time, was particularly wide, with early genotypes occurring even in populations from long-season environments. The adaptive relevance of maintaining high levels of within-population polymorphism to cope with unpredictable climatic fluctuations is discussed. Number of constituent lines as a measure of the population structure, and intra-population variation were both influenced by altitude and rainfall, tending to decrease as the climatic selective pressure becomes severe, under both low-rainfall, hot conditions and high-elevation, cold-prone environments.     

Morphological variation in Astragalus hamosus L. and Coronilla scorpioides L. populations of Tunisia

Morphological variation between Astragalus hamosus and Coronillascorpioides populations was studied using local germoplasm collected in northern and central Tunisia. Twenty-one morphological traits were recorded and data were analysed using complementary statistical analysis. Considerable variation based on morphological and agronomical traits was found between populations and for both species. Pod and peduncle lengths as well as flowers number were the most discriminant variables between populations. Differences were also found for variables like seed number per pod, seed yield and dry matter production. Significant correlations were found between plant traits and the environmental parameters of the origin sites. This study revealed enough variation among populations to initiate a selection programme for pasture improvement in arid and semi-arid areas of Tunisia, where the two species are well adapted. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Variation among and within Italian alfalfa ecotypes by means of bio-agronomic characters and amplified fragment length polymorphism analyses

Three accessions, corresponding to different ‘foundation’ farms, of each of the alfalfa (lucerne) Italian ecotypes ‘Vogherese’ and ‘Marem‐mano’, and two varieties were studied in order to evaluate: (1) the among‐ and within‐ecotype variation; and (2) the possibility of distinguishing the populations by means of bio‐agronomic characters and molecular markers (amplified fragment length polymorphisms, AFLPs). The two ecotypes could be distinguished by the differences in persistency after 15 cuttings in 3 years cultivation and by the seasonal distribution of the dry matter yield. Within‐ecotype variation was always of minor importance as compared with the among‐ecotype differences. The AFLP analyses generated 20 polymorphic fragments in ‘bulk’ samples: none was able to distinguish the two ecotypes, while variety‐specific fragments were found. The same analysis on an individual plant basis (485 polymorphic fragments) confirmed the absence of differences among ecotypes, while 10% of the total variance was attributable to variation among accessions within ecotype. The results of the analyses using agronomic traits and molecular markers are discussed in relation to the possibility of ecotype identification.     

Seed yield related to crop development and to yield components in nine cultivars of perennial ryegrass (Lolium perenne L.)

Summary We had previously found differences for seed yield among nine perennial ryegrass cultivars which were not associated with variation for seed weight. To detect the physiological basis of these genetic differences for seed yield, growth analyses were carried out. We related crop development and components of seed yield to seed yield during three years on clay and sandy soil. No significant differences occurred among cultivars for accumulation and partitioning of dry matter or the pattern of tiller production. Seed yield of the cultivars was not associated with ear number or total dry matter yield of the seed crop. Seed yield was more correlated with the number of seeds per unit area than with seed weight. The number of seeds as calculated after harvest from seed yield and seed weight was much lower than the number of seeds as estimated prior to harvest from seed yield components. The number of spikelets differed significantly among the cultivars, but the ranking was different from that for seed yield. The physiological basis of the genetic differences for seed yield is not clear. Implications for breeding perennial ryegrass are discussed.     

Morphologische und agronomische Merkmale autochthoner annueller Medicago-Arten in Marokko

Morphological and agronomic characteristics of autochthonous annual Medkago species in Morocco
Autochthonous annual Medicago species were collected on non-alkaline soils and evaluated as to their potential agricultural use. 411 Medicago ecotypes were found at 108 sites. With increasing rainfall and altitude of collecting sites, a decrease was recorded in the length of sprouts, in sward height, in leaf size, and in dry matter yield. High rainfall regions were found to select late flowering ecotypes. All Medicago ecotypes tested showed broad intraspecific variation in seed yield, leaf size and seed weight. Coumestrol content of leaves at flowering was generally low; on average 115 ppm of dry matter. No relationship was found between collection sites and coumestrol content. In a field trial comparing 112 ecotypes with nine introduced cultivars at two contrasting sites, thirty ecotypes proved to be better adapted to local conditions than the cultivars.     

Genetic variability in herbage and seed yield in selected half-sib families of berseem clover, Trifolium alexandrinum L.

Berseem clover Trifolium alexandrinum L. is an annual forage legume commonly grown in pure stands and in grass mixtures in the Medi-terranean basin. Six populations were naturally cross-pollinated in 1990 and 1991 by a half-sib breeding method. In 1992 and 1993. 54 half-sib maternal plants, six original populations, and six advanced populations were field evaluated for forage (short cycle, harvest made at seven or eight inlernodes: long cycle, harvested at flowering) and seed yield (no forage harvest) in experiments at the Forage Crop Institute at Foggia, Italy (typical Mediterranean location). Genetic variability, narrow-sense herilability, genetic and phenotypic correlations among forage and seed yield component trails were investigated. The genetic variance in dry matter among maternal half-sib populations in short cycle was 51% greater than in long cycle. Narrow-sense heritabilily was 35% higher in short cycle than long cycle for dry matter and 26% higher for seed weight than seed yield. The magnitude of the genetic variance components and genetic correlations suggested that selection among plants of maternal half-sib populations would be more effective for improving dry matter in short than in long cycle harvests. The selection applied in the study was not effective for increasing seed yield per se however, the trait may be increased by selecting indirectly for seed weight.     

Genetic variation in a Norwegian germplasm collection of white clover (Trifolium repens L.)

Genetic variation and genotype × environment interactions for important agronomic characters were estimated for eleven Norwegian populations of white clover (Trifolium repens L.), originating from between 58^°52′N and 69^°30′N latitude, and from altitudes of 10 to 450 m a.s.l. The populations were evaluated in monoculture clonal field plots for two years at two locations in Norway. The medium-leaved Danish cultivar Milkanova was also included in the experiment as a standard market cultivar. Considerable variation between populations was observed for winter survival, spring growth, morphological characteristics, dry matter yield, general performance, earliness and seed yield. Winter survival, measured as plant cover after two years, was significantly different at the two locations. All the populations had sufficient winter survival at the southern, continental highland site (61^°07′N).At the northern coastal location (69^°30′N),where the winter climate is unstable with physical stresses such as frost, ice-encasement and water-logging frequently occurring, only the northernmost, coastal populations showed sufficient winter survival. Highly significant interactions were found between populations and locations, and between populations and years for all characters measured at both locations and in both years, respectively. Interaction effects between populations, locations and years were significant only for leaflet length. The largest leaf lamina's were observed in the most southern populations. However, genotypes possessing relatively long leaflets were also found in the northernmost populations, although at low frequencies. In general, the populations originating from the northernmost locations had lower biomass production, and were smaller-leaved, more prostrate and exhibited shorter internodes and stolons compared to the populations from South and Middle Norway. These populations also initiated inflorescences earliest, and were among the lowest seed yielding populations. Otherwise, no clear clinal variation in growth characteristics was observed which could be related to the latitude or altitude of origin of the populations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Condensed tannins in birdsfoot trefoil: Genetic relationships with forage yield and quality in NC-83 germplasm

Summary Genetic relationships of condensed tannins (CT) with other forage quality parameters have not been adequately studied in birdsfoot trefoil (Lotus corniculatus L.). The objectives were to bidirectionally select for CT concentration in birdsfoot trefoil to determine selection response and to create populations for examination of genetic relationships of CT with forage quality parameters, principally lignin. High-and low-tannin parental clones were selected from NC-83 birdsfoot trefoil germplasm and intercrossed to produce Syn₁ populations. Herbage samples, harvested for two years at two locations, were analyzed from high-tannin, low-tannin, and parental populations for CT concentration, herbage yield, and forage quality parameters. The mean condensed tannin concentrations in the high-and low-tannin populations were 69.3±0.8 and 21.1±0.8 g catechin equivalent (CE) kg^-1 dry matter (DM) compared with 36.4±0.8 g CE kg^-1 DM in the parental population. The selection response exhibited a quadratic relationship, with selection for increased CT concentration more effective than for reduced CT concentration. Compared with the parental population, acid detergent lignin (ADL) was higher, and crude protein (CP) and in vitro digestible dry matter (IVDDM) concentrations were lower for the high-tannin population and the converse was true for the low-tannin population. Lignin concentration was positively correlated with CT concentration (r_g=0.66 P0.01).Abbreviations ADF acid detergent fiber - ADL acid detergent lignin - CP crude protein - CT condensed tannins - IVDDM in vitro digestible dry matter - NDF neutral detergent fiber - NIRS near infrared reflectance spectroscopy     

Exotic barley germplasm: variation and effects on agronomic traits in complex crosses

Summary Utilization of exotic germplasm offers an approach to broaden genetic variability in breeding populations. This study was conducted in order to 1) compare germplasm of exotic origin with adapted Swedish barleys with respect to genetic differences and 2) to evaluate how exotic material affected agronomic performance in complex crosses. Allozyme studies showed the following Nei's gene diversities among parents: 0.13 (adapted parents), 0.16 (landraces) and 0.25 (H. spontaneum). Cluster analysis indicated that parental groups were genetically divergent. Earliness, straw length, number of ears per plant and thousand kernel weight (TKW) were studied. Variation in agronomic traits showed the following pattern: landraces > H. spontaneum > adapted lines. The best sources for earliness were adapted parents and landraces. Mean straw length was greatest in H. spontaneum lines. Number of ears per plant was quite similar in all groups. The highest TKW was among landraces and adapted parents. Hybrids from the complex crossing programme exceeded parents in earliness and TKW. An index composed from the four traits showed the most favorable frequency distributions for adapted parents and hybrids. Both genetic and agronomic studies indicate that new valuable variation from exotic germplasm may be introduced into barley breeding material.     

Variability in Namibian landraces of watermelon (Citrullus lanatus)

An on-station experiment was carried out in northern Namibia to compare local landraces of watermelon to modern varieties. Three groups of local watermelon are distinguished by farmers in Namibia: watermelons for fresh consumption, cooking melons used for porridge, and seed melons for oil pressing. The present study was carried out to estimate agronomic potential of the local landraces and verify whether agronomic characteristics would justify the local groupings. Important agronomic and fruit-quality traits (yield, earliness, fruit weight, fruit number, rind thickness, soluble solids, seed weight, and tolerance to biotic and abiotic stress) were measured in seven landraces (three watermelons, three cooking melons and one seed melon)and compared to three modern cultivars frequently grown in Namibia. The study revealed that well-adapted, productive Citrullus lanatuslandraces are available, and cultivated by local farmers throughout the northern regions of Namibia. Based on a combination of agronomic characteristics these local varieties could be grouped into three distinct types: watermelons, cooking melons, and seed melons, in agreement with farmers classification. Landrace water melons were characterized by smaller, less sweet fruits with larger seed and a thicker rind compared to modern varieties. Yield level was comparable but development was later and fruit number in some cases higher. Cooking water melons were less sweet than local water melon with large fruits comparable in size to modern cultivars. The only included seed watermelon had small fruits with large seeds and low soluble sugars. Yield varied from 118 t/ha for a giant cooking melon, out yielding all other accessions, to only 10t/ha for the seed melon type, but with considerable variation within groups. The earliness of commercial varieties maybe of interest in developing a mixed portfolio of short- and long-cycle landraces, whereas plant vigour, resistance and seed characters in some of the Namibian landraces may be important traits for breeding for both local purposes and for commercial varieties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analyses of agronomic and seed quality traits of doubled haploid population in Brassica napus through microspore culture

Summary The results showed that the F1 genotype from the cross (Brassica napus cv. Zheshuang 758 × cv. Z-4115) had good response to embryogenesis, and their embryo yield and rate of plant regeneration reached 69.8 embryo/bud and 46.9%, respectively. Characters from the doubled haploid (DH) populations in B. napus were analyzed and it was showed that the means of each agronomic trait were between their parents, but they were nearer to the paternal in 6 agronomic traits (plant height, branch position, number of pods in the main raceme, length of pod, number of pods/plant and number of seeds/pod). The number of genes controlling each agronomic trait was analyzed based on the DH populations. The results showed that the number of genes controlling number of pods in the main raceme was the highest (15.6), and the least number of genes was involved for stem width (only 7.9). According to estimated coefficients of skewness and kurtosis of the traits tested, gene interaction was found to be absent for stem width, plant height, length of main raceme, number of primary and secondary branches, pod density in the main raceme and seed weight/plant. Complementary interaction was also observed in five agronomic traits (number of pods in the main raceme, length of pod, number of pods/plant, number of seeds/pod and 1000-seed weight). A significantly positive correlation was observed between seed yield/plant and four agronomic traits (length of main raceme, length of pod, number of pods/plant and 1000-seed weight). The experiment also showed that the erucic acid, glucosinolate, oil and protein contents of DH populations were 34.23%, 87.09 μmol/g, 44.09% and 42.67%, respectively. The numbers of genes controlling each quality trait were 7.8, 9.7, 9.4 and 8.7, respectively. Partial correlations between the seed quality traits and the agronomic characters of DH populations were analyzed. In this experiment, the partial correlations among seed quality traits were also analyzed and it was found that the oil content had a negative correlation with the other three seed quality traits.     

Genetic diversity in a germplasm collection of Brassica rapa subsp rapa L. from northwestern Spain

In Galicia (northwestern Spain), Brassica rapa subsp. rapa L. includes turnips, turnip greens, and turnip tops. The objectives of this study are (i) to determine the genetic diversity and morphological resemblances among the B. rapa landraces of northwestern Spain in order to have information relative to the resources preserved, and (ii) to evaluate their agronomic characteristics, considering the three potential products that can be harvested. A collection of 120 landraces was evaluated for 34 morphological and agronomical traits by an augmented design at two locations. Two landraces were the most promising for turnips production (MBG-BRS0183 and MBG-BRS0256), two showed the best characteristics for turnip greens (MBG-BRS0082 and MBG-BRS0184), and three were the most appropriate landraces for turnip tops production (MBG-BRS0143, MBG-BRS0173 and MBG-BRS0401). Landraces were classified into five clusters (A–E) using the Ward–MLM (Modified Location Model) strategy: (A) included plants with the worst agronomic potential, (B) included most of the turnip populations with rosette growth habit, (C) included turnip populations without rosette growth habit, having more vigorous plants than cluster B, (D) gathered the most vigorous local varieties, with the highest early vigor, fresh matter content per leaf, and number of secondary stems per plant, and (E) landraces characterized by their earliness, large flowering periods, high numbers of secondary stems, and large seed weights. As conclusion, landraces evaluated in this work displayed enough variability to differentiate among appropriate populations for each one of the distinct crops. Their classification, using the Ward–MLM strategy, grouped accessions with similar characteristics into homogeneous categories.     

Genetic diversity in red clover (Trifolium pratense L.) revealed by morphological and microsatellite (SSR) markers

The NPGS-USDA core collection with 85 accessions of red clover, an important forage species, is little described. The goal of the present study was to evaluate the diversity of a set of accessions from the core collection at the morphological and molecular level in order to extract some valuable accessions for Brazilian red clover breeding programs. Twenty-one morphological traits, collected in field and greenhouse in South Brazil, and seven SSR markers were used to describe 57 accessions from the U.S. core collection and one population cultivated in Southern Brazil. Variation between accessions was large for most of the 21 morphological traits. A cluster analysis based on the morphological traits revealed five distinct clusters that separated the populations according to flowering earliness, as already described, but also according to persistency, growth habit and dry matter productivity. Over seven SSR loci, the number of alleles averaged 11.1 alleles per locus. Genetic diversity measured with SSR markers was high, with a mean expected heterozygosity of 0.86. An analysis of molecular variance revealed that the largest proportion of variation (83.6%) resided at the within population level. Although the molecular markers also separated accessions into five clusters, there was no coincidence between the composition of groups found with morphological and molecular data. Use of genetic diversity in breeding programs requires to use the most promising populations, to combine positive traits such as persistency and forage yield, and probably to use within population variation to detect valuable genotypes that could be used as parents of synthetic varieties.