Plant competition and disease in genetically diverse wheat populations

Summary The direct and indirect effects of plant genetic diversity on epidemics and the influence of disease on plant competition were investigated using the wheat (Triticum aestivum)/stripe rust (Puccinia striiformis) system. Replacement series consisting of a susceptible and a resistant wheat genotype or two wheat genotypes susceptible to different races of stripe rust were grown in the presence and absence of the pathogen. Stripe rust severity, number of seed heads, seed yield, and seed weight were determined separately for each wheat genotype in the mixtures and the pure stands. The frequency of susceptible genotypes in a mixture explained up to 67% of the variation in disease severity. However, competitive interactions among plant genotypes sometimes appeared to alter susceptibility and obscured the relationship. In pure stands of single genotypes, disease severity explained between 52 and 58% of the variation in seed yield. In mixtures, coefficients of determination were only 10 and 31%, suggesting a strong influence of plant-plant interactions on seed yield. These results suggest that host-parasite coevolutionary models need to account for the strong effect that specific plant genotype combinations may have on disease severity and plant reproduction.Paper No. 9818 of the journal series of the Oregon Agricultural Experiment Station     

An analysis of association of components of yield and oil in safflower (Carthamus tinctorius L.)

Summary Inter-relationships of various component characters with yield and oil content were analysed using 215 entries of safflower from India and U.S.A. Correlation of capsule number per plant and capsule weight with yield per plant was pronounced and they showed large direct effects on yield. All other components influenced seed yield mainly through these two components. Seed size had little effect on yield while seed number exerted a positive influence. The proportion of hull expressed as per cent of the whole seed revealed a highly significant and inverse relationship with oil content and was mainly responsible for the observed variability in oil content in the material. Although negative association was indicated between seed size and oil content, it was observed to be due to the indirect effect of hull content and not due to direct effect of seed size. Interestingly, yield per plant and its major components, number of capsules and capsule weight, revealed a negligible relationship with oil content. Both direct as well as indirect effects of hull percent and yield per plant were responsible for the favourable effect of seed number on oil content. The correlation of plant height, days to first flowering and total crop growth period with yield and oil content was either negligible or low, offering scope for developing early maturing and dwarf varieties with high yield and oil content. Spine index showed a non-significant association with yield and oil content. Capsule number, capsule weight and hull per cent were observed to be the most important components in breeding for higher yield and oil content.     

Correlation and path-coefficient analyses of seed-yield components in pearl millet x elephantgrass hybrids

Correlation and path-coefficient analyses have been successful tools in developing selection criteria. Since increased seed yield is an important goal in our pearl millet x elephantgrass [Pennisetum glaucum (L.) R.Br. x P. purpureum Schum.] hexaploid breeding program, we used correlation and path-coefficient analyses on seed data. This study was conducted to develop appropriate selection criteria by determining the direct and indirect effects of seed-yield components on seed yield plant^-1. Number of tillers plant^-1, panicles tiller^-1, seeds panicle^-1, 100-seed weight, and seed yield plant^-1, were estimated for individual plants in seven families. Phenotypic (r_p) and genetic correlations (r_g) were calculated, and path analyses (phenotypic and genetic) were carried out according to predetermined causal relationships. Phenotypic and genetic correlations differed in several cases due to large environmental variance and covariance. Phenotypically, all components were positively and significantly associated with seed yield plant^-1. Genotypically, only seeds panicle^-1 and 100-seed weight were significantly correlated. These two components were also positively correlated (r _p=0.55, r _g=0.63), so simultaneous improvement for both components would be feasible. Panicles tiller^-1 and seeds panicle^-1 were negatively correlated (r _g=-0.97). In the path analyses, all direct effects of the components on seed yield plant^-1 were positive. Phenotypic indirect effects were not as important as genetic indirect effects. The components seeds panicle^-1 and 100-seed weight influenced seed yield plant^-1 the greatest, both directly and indirectly.Florida Agricultural Experimental Station Journal Series No. R-03339     

Path and ridge regression analysis of seed yield and seed yield components of Russian wildrye (Psathyrostachys juncea Nevski) under field conditions

The correlations among seed yield components, and their direct and indirect effects on the seed yield (Z) of Russina wildrye (Psathyrostachys juncea Nevski) were investigated. The seed yield components: fertile tillers m(-2) (Y(1)), spikelets per fertile tillers (Y(2)), florets per spikelet(-) (Y(3)), seed numbers per spikelet (Y(4)) and seed weight (Y(5)) were counted and the Z were determined in field experiments from 2003 to 2006 via big sample size. Y(1) was the most important seed yield component describing the Z and Y(2) was the least. The total direct effects of the Y(1), Y(3) and Y(5) to the Z were positive while Y(4) and Y(2) were weakly negative. The total effects (directs plus indirects) of the components were positively contributed to the Z by path analyses. The seed yield components Y(1), Y(2), Y(4) and Y(5) were significantly (P<0.001) correlated with the Z for 4 years totally, while in the individual years, Y(2) were not significant correlated with Y(3), Y(4) and Y(5) by Peason correlation analyses in the five components in the plant seed production. Therefore, selection for high seed yield through direct selection for large Y(1), Y(2) and Y(3) would be effective for breeding programs in grasses. Furthermore, it is the most important that, via ridge regression, a steady algorithm model between Z and the five yield components was founded, which can be closely estimated the seed yield via the components.     

Correlations and heritability of the characters determining the seed yield of the long-raceme alfalfa (Medicago sativa L.)

Phenotypic correlation coefficients and heritability of the characters controlling seed yield of long-raceme forms of alfalfa was determined. It was found that seed yield per plant, which was positively correlated with 10 out of 12 analysed characters, depended upon the number of pods per raceme and the number of seeds per pod. Variability of these characters determined about 60% of the variability of seed yield. Multiple linear regression and phenotypic correlations show that simultaneous selection for increased pod number per raceme and increased seed number per pod and raceme length resulted in enhanced seed yield potential. The share of the additive genetic effects in the phenotypic variance for number of pods per raceme was low and about 21-23%, while for number of seeds per pod and per raceme amounted to about 50%. The expected genetic progress in recombination breeding for number of seeds per pod and number of seeds per raceme will be of medium magnitude, while one cannot expect any rapid and considerable progress in the number of pods per raceme. Considering the high positive correlation between raceme length and number of pods and seeds per raceme, one should conclude that raceme length can be an important criterion in selection of plants showing a high seed productivity.     

Bottlenecks and spatiotemporal variation in the sexual reproduction pathway of perennial meadow plants

Sexual reproduction is important for the growth of populations and the maintenance of genetic diversity. Several steps are involved in the sexual reproduction pathway of plants: the production of flowers, the production of seeds and the establishment of seedlings from seeds. In this paper we quantify the relative importance and spatiotemporal variability of these different steps for four grassland perennials: Centaurea jacea, Cirsium dissectum, Hypochaeris radicata and Succisa pratensis. We compared undisturbed meadows with meadows where the top soil layer had been removed as a restoration measure. Data on the number of flower heads per flowering rosette, the numbers of flowers and seeds per flower head, and the seedling establishment probabilities per seed were collected by field observations and experiments in several sites and years. Combination of these data shows that H. radicata and S. pratensis have higher recruitment rates (1.9 and 3.3 seedlings per year per flowering rosette, respectively) than the more clonal C. dissectum and C. jacea (0.027 and 0.23, respectively). Seedling establishment is the major bottleneck for successful sexual reproduction in all species. Large losses also occurred due to failing seed set in C. dissectum. Comparison of the coefficients of variation per step in space and time revealed that spatiotemporal variability was largest in seedling establishment, followed closely by flower head production and seed set.     

Genetic basis of seed setting in alfalfa

Summary The genetic basis of seed setting was evaluated in seven clones of alfalfa selected under predominantly self-pollinating conditions. They were hand crossed in all possible combinations. Their compatibility was studied by the percentage of flowers forming pods and number of seeds per pod during crossing. The variances for GCA, SCA and reciprocal effects were significant for percentage of pod set with a narrow sense héritability of 64 %. This suggested maternal influence of clones on percent pod set, controlled primarily by additive genetic components. GCA was the only significant component for number of seeds per pod with a narrow sense heritability of 71%. There were wide differences between the clones in their relative magnitude of GCA, SCA and reciprocal effects for both traits used as compatibility indexes. Performance of the diallel crosses was judged by studying seed yield and its related characters, namely seeds per pod, dry matter per plant, frost resistance, plant vigor and plant height. Although GCA and SCA variances were significant for all characters, reciprocal differences in general were absent. The SCA values were very high as compared to GCA. Narrow sense heritability values were very low while broad sense heritability were much higher. This suggested that almost none of the variation was due to additive genetic components and all the variability is controlled by interactions of a digenic, trigenic and quadrigenic nature and heterzozygosity. Heterosis was evaluated by comparing the seed yield of single crosses with their mid-parent and high-parent, and very high values were observed. Thus selection of better genes may not be feasible and further improvement in selected clones may have to be brought about by utilization of various interactions and heterosis. An attempt was made to find combinations of characters that may be used for the selection of seed yield but none were found to be satisfactory.     

Mixing ability analysis of wheat cultivar mixtures under diseased and nondiseased conditions

Summary Mixing ability analyses, adapted from combining ability analyses used in plant breeding, were performed on yield and stripe rust (Puccinia striiformis) severity data for two-way mixtures among either four or five club wheat (Triticum aesitivum) cultivars grown in five environments. Initially, two statistics were calculated for each trait: general mixing ability (GMA), the average performance of a cultivar over all of the mixtures, and specific mixing ability (SMA), the deviation of a mixture from the estimated performance of the pair based on its average performance in mixtures. General mixing ability was further divided into two components: genotype performing ability (GPA), the innate ability of a cultivar to yield and resist disease in pure stand, and true general mixing ability (TGMA), the average ability of a cultivar to influence yield and disease when mixed with other cultivars. Significant mean squares for genotypes, GMA, SMA, and TGMA were found for all of the traits in most environments. Examination of TGMA and SMA revealed cultivars and cultivar combinations that were statistically better mixers than the others. Some of the significant effects were probably due to the use of cultivars that differed in height and stripe rust resistance, but for other combinations there was no apparent explanation for enhanced mixing ability.Paper No. 9132 of the Oregon Agricultural Experiment Station. Supported in part by USDA Grants 88-34106-3631 and 88-37151-3662     

Resistance of wild wheat to stripe rust: Predictive method by ecology and allozyme genotypes

From 114 accessions of wild emmer wheat from 11 sites in Israel, known for their allozymic variation (Nevo & al. 1982), individual genotypes were tested for resistance to one isolate of stripe rust both in the seedling stage in a growth chamber and in the adult plant stage in the field. The results indicate that resistance to stripe rust in seedlings and adults are significantly correlated (r_s = 0.40, p < 0.001). Genetic polymorphisms of resistance to stripe rust vary geographically and are predictable by climatic, as well as allozymic markers. Three variable combinations of rainfall, evaporation, and temperature explain significantly 0.40–0.53 of the spatial variance in disease resistance to stripe rust, suggesting the operation of natural selection. Several allozyme genotypes are significantly associated with disease resistance. We conclude that natural populations of wild emmer wheat in Israel contain large amounts of disease resistance genes. These populations could be effectively screened and then utilized by the phytopathologist for identifying resistant genotypes and producing new resistant cultivars.Patterns of Resistance of Wild Wheat to Pathogens in Israel II.     

Very high CO2 reduces photosynthesis, dark respiration and yield in wheat

Although terrestrial CO2 concentrations, [CO2] are not expected to reach 1000 micromoles mol-1 for many decades, CO2 levels in closed systems such as growth chambers and glasshouses, can easily exceed this concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1 (1%). Here we studied the effect of six CO2 concentrations, from ambient up to 10000 micromoles mol-1, on seed yield, growth and gas exchange of two wheat cultivars (USU-Apogee and Veery-l0). Elevating [CO2] from 350 to 1000 micromoles mol-1 increased seed yield (by 33%), vegetative biomass (by 25%) and number of heads m-2 (by 34%) of wheat plants. Elevation of [CO2] from 1000 to 10000 micromoles mol-1 decreased seed yield (by 37%), harvest index (by 14%), mass per seed (by 9%) and number of seeds per head (by 29%). This very high [CO2] had a negligible, non-significant effect on vegetative biomass, number of heads m-2 and seed mass per head. A sharp decrease in seed yield, harvest index and seeds per head occurred by elevating [CO2] from 1000 to 2600 micromoles mol-1. Further elevation of [CO2] from 2600 to 10000 micromoles mol-1 caused a further but smaller decrease. The effect of CO2 on both wheat cultivars was similar for all growth parameters. Similarly there were no differences in the response to high [CO2] between wheat grown hydroponically in growth chambers under fluorescent lights and those grown in soilless media in a glasshouse under sunlight and high pressure sodium lamps. There was no correlation between high [CO2] and ethylene production by flag leaves or by wheat heads. Therefore, the reduction in seed set in wheat plants is not mediated by ethylene. The photosynthetic rate of whole wheat plants was 8% lower and dark respiration of the wheat heads 25% lower when exposed to 2600 micromoles mol-1 CO2 compared to ambient [CO2]. It is concluded that the reduction in the seed set can be mainly explained by the reduction in the dark respiration in wheat heads, when most of the respiration is functional and is needed for seed development.     

Mutations in Barley Row Type Genes Have Pleiotropic Effects on Shoot Branching

Cereal crop yield is determined by different yield components such as seed weight, seed number per spike and the tiller number and spikes. Negative correlations between these traits are often attributed to resource limitation. However, recent evidence suggests that the same genes or regulatory modules can regulate both inflorescence branching and tillering. It is therefore important to explore the role of genetic correlations between different yield components in small grain cereals. In this work, we studied pleiotropic effects of row type genes on seed size, seed number per spike, thousand grain weight, and tillering in barley to better understand the genetic correlations between individual yield components. Allelic mutants of nine different row type loci (36 mutants), in the original spring barley varieties Barke, Bonus and Foma and introgressed in the spring barley cultivar Bowman, were phenotyped under greenhouse and outdoor conditions. We identified two main mutant groups characterized by their relationships between seed and tillering parameters. The first group comprises all mutants with an increased number of seeds and significant change in tiller number at early development (group 1a) or reduced tillering only at full maturity (group 1b). Mutants in the second group are characterized by a reduction in seeds per spike and tiller number, thus exhibiting positive correlations between seed and tiller number. Reduced tillering at full maturity (group 1b) is likely due to resource limitations. In contrast, altered tillering at early development (groups 1a and 2) suggests that the same genes or regulatory modules affect inflorescence and shoot branching. Understanding the genetic bases of the trade-offs between these traits is important for the genetic manipulation of individual yield components.     

Inheritance of seed protein content and other agronomic characters in long bean (Vigna sesquipedalis Fruw.)

Summary Seven varieties of long bean, which included three local and four exotic, were crossed in a complete diallel. This was an attempt to study the inheritance of crude protein content, protein yield, flowering date, pod yield and yield components.Both additive and non-additive gene effects were responsible for the genetic variation in the diallel population. However, dominance variance was more important than additive variance in crude protein content, number of pods per plant and number of seeds per pod. For seed weight and pod length, additive variance was more important.The crude protein content, protein yield and number of pods per plant appeared to be controlled by overdominance effects. Partial dominance seemed to be the case for flowering date, pod length and seed weight; complete to overdominance for pod yield. High protein appeared to be associated with recessive genes whereas there was a general trend of high yielding parents carrying more dominant genes.     

Origins of variance in seed number and mass: interaction of sex expression and herbivory in Lomatium salmoniflorum

Summary As in many plant species, Lomatium salmoniflorum (Umbelliferae) individuals produce many flowers, only a subset of which produce mature seeds that escape seed parasitism and enter the seed bank. The interrelationships between the timing and number of flowers produced, sex expression, seed set, and seed parasitism were studied for their direct and indirect effects on the numbers and masses of viable seeds produced by individual plants. In a sample population of 369 plants that produced 161 386 flowers, 76% of the plants produced some hermaphroditic flowers. The percentage of hermaphroditic flowers increased significantly with the total number of flowers produced by a plant. Seed set was 65–90% in plants producing >600 flowers, but was highly variable in plants producing fewer flowers. Hand-pollinated plants showed the same pattern of seed set, suggesting that variable seed set in small plants may result from insufficient resources for seed development. The majority of schizocarps was produced by only 12% of the plants. Parasites killed 24.5% of the seeds prior to dispersal. Another 14.5% of the seeds lacked endosperm. Hence, the initial 161 386 flowers, which included 25874 hermaphroditic flowers each capable of producing two seeds, produced 42 468 seeds of which an estimated 25906 entered the seed bank as undamaged seeds with fully developed endosperm. Path analysis indicated that the number of hermaphroditic flowers on a plant and the percentage of seeds attacked by seed parasites had the greatest direct effects on the number of viable seeds entering the seed bank. The date at which a plant began flowering and the percentage of flowers setting seed had smaller or only indirect effects on viable seed production. Mean seed mass for plants was not significantly related to any of the factors that affected seed number, but little of the variance in seed mass occurred among plants. Masses of intact seeds in the population ranged 9-fold in both 1987 and 1988. Thirty-five percent of the variance was among seeds within umbels, 46% was among umbels within plants, and only 19% was among plants. The large variation among umbels within plants resulted from a seasonal pattern in which seeds from umbels produced late in the spring had lower mean seed masses than seeds from umbels produced early in the spring. Overall, the results indicate that both direct and indirect interactions between number of flowers, the date of initiation of flowering, seed set, and seed parasitism affect the number of viable seeds entering the seed bank. These interactions strongly bias viable seed output to a small minority of plants that produce many seeds with a wide range of masses over the growing season.     

Influence of paclobutrazol on growth and yield of Brassica carinata A.Br.

Foliar spraying of Brassica carinata (cv. PC 5) with paclobutrazol (PP 333) at 5, 10 and 20 g ml^-1 concentrations, reduced plant height significantly and modified the canopy structure by enhancing the number of branches (primary, secondary and tertiary) and the angle of insertion of primary branches on the main axis. The seed yield per plant also increased mainly due to increase in the number of siliquae per plant. Paclobutrazol increased total dry matter of plants and partitioning coefficients. The leaves in paclobutrazol-treated plants exhibited higher chlorophyll content, and they remained intact on plants for longer than the controls. The seeds from paclobutrazol-treated plants had higher levels of proteins, strarch and total soluble sugars but less total seed oil content.     

Long term exogenous putrescine application improves grain yield of a salt-sensitive rice cultivar exposed to NaCl

In order to determine the impact of polyamines on the yield-related parameters of rice (Oryza sativa L.) exposed to NaCl, the plants belonging to a salt-sensitive cultivar I Kong Pao were maintained from the young seedling stage until harvest on nutrient solutions containing 0 or 30 mM NaCl in the presence or absence of 10 μM putrescine (Put), 10 μM spermidine (Spd) or 10 μM spermine (Spm). Exogenous Put and to a lesser extent exogenous Spd improved growth and yield of salt-treated plants in relation to an increase in K⁺/Na⁺ ratio of shoots and roots as compared to plants exposed to NaCl in the absence of exogenous polyamines. Exogenous Put also improved the net CO₂ assimilation, at least partly as a consequence of an increase in the stomatal conductance. Yield increase of salt-treated plants exposed to Put was related to an improvement of floral morphogenesis leading to a higher number of fertile tillers per plant and a higher number of spikelets per panicle. Putrescine also improved the pollen viability in salt-treated plants, allowing a higher seed set and thus a higher grain yield per plant. Although polyamines accumulated in the shoots to some extent in response to exogenous application, neither Put nor Spd accumulated in the seeds. In contrast, Spm did not afford any protection of salt-treated plants but was translocated to the seeds during maturation. Seeds with a high internal Spm concentration exhibited delayed germination in the presence of NaCl. These data are discussed in relation to the implication of polyamine in the metabolism and physiology of salt-treated plants.     

Genetic basis of variation of yield, and yield components in mungbean (Vigna radiata (L.) Wilczek)

Additive, dominance, and epistasis genetic basis of seed yield per plant, number of pods per plant, number of seeds per pod, and 1000 seed weight in mungbean (Vigna radiata (L.) Wilczek) have been examined, using Triple Test Cross (TTC) analysis. The material for TTC test was evaluated in two seasons i.e., kharif (July-October) and spring/summer (March-June), at the research station of the Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan. Epistasis was present significantly for number of pods per plant and number of seeds per pod when grown in the spring/summer season (March to June). Partition of epistasis showed that additive x additive ('i' type) interaction was an important component of number of pods per plant, and number of seeds per pod was found to be of both types 'i' type, and additive x dominance, and dominance x dominance ('j' and 'l' type) interactions. This indicated that epistasis might be a non-trivial factor in the inheritance of pods per plant, and seeds per pod in mungbean. The expression of epistasis was influenced differentially by particular genotypes, indicating that a limited number of genotypes may not be sufficient to detect non-allelic interactions for a trait in mungbean. Additive and dominance genetic components were significant for all four traits in kharif season (July to October) but only for seed yield and 1000 seed weight in spring/summer season. This suggests that the genes controlling seed yield per plant, and 1000 seed weight are equally sensitive to the environment. The predominance additive gene action in those traits is not significantly influenced by epistasis, suggesting that improvement of the traits can be achieved through standard selection procedures.     

Genetic dissection of grain yield in bread wheat. II. QTL-by-environment interaction

The grain yield of wheat is influenced by genotype, environment and genotype-by-environment interaction. A mapping population consisting of 182 doubled haploid progeny derived from a cross between the southern Australian varieties ‘Trident’ and ‘Molineux’, was used to characterise the interaction of previously mapped grain yield quantitative trait locus (QTL) with specific environmental covariables. Environments (17) used for grain yield assessment were characterised for latitude, rainfall, various temperature-based variables and stripe rust infection severity. The number of days in the growing season in which the maximum temperature exceeded 30°C was identified as the variable with the largest effect on site mean grain yield. However, the greatest QTL-by-environmental covariable interactions were observed with the severity of stripe rust infection. The rust resistance allele at the Lr37/Sr38/Yr17 locus had the greatest positive effect on grain yield when an environment experienced a combination of high-stripe rust infection and cool days. The grain yield QTL, QGyld.agt-4D, showed a very similar QTL-by-environment covariable interaction pattern to the Lr37/Sr38/Yr17 locus, suggesting a possible role in rust resistance or tolerance. Another putative grain yield per se QTL, QGyld.agt-1B, displayed interactions with the quantity of winter and spring rainfall, the number of days in which the maximum temperature exceeded 30°C, and the number of days with a minimum temperature below 10°C. However, no cross-over interaction effect was observed for this locus, and the ‘Molineux’ allele remained associated with higher grain yield in response to all environmental covariables. The results presented here confirm that QGyld.agt-1B may be a prime candidate for marker-assisted selection for improved grain yield and wide adaptation in wheat. The benefit of analysing the interaction of QTL and environmental covariables, such as employed here, is discussed.     

Pollination thoroughness and maternal yield regulation in wild radish,Raphanus raphanistrum (Brassicaceae)

Summary Under conditions where resources are limited, there are often negative correlations between components of maternal yield, or between fruit and flower production. Pollination, in turn, may vary among individuals and influence total maternal expenditure. We examined the impact of variation in pollination thoroughness upon yield components and overall plant growth in wild radish (R. raphanistrum) plants grown in the greenhouse. Plants received different pollination treatments in which 0% to 100% of all flowers produced were hand-pollinated. Fruit set was increased by hand-pollination, but rarely exceeded 30%, even when more than 50% of the flowers were pollinated. Plants receiving more thorough pollination or having greater proportion fruit set produced significantly smaller seeds. Seed number per fruit was not influenced by pollination treatment. Mean values of yield components and interactions between components often varied among plants from different maternal families. Increasing pollination thoroughness also resulted in dramatic decreases in flower production. If male fitness is related to flower number, there may be a tradeoff between maternal fecundity and successful pollen export operating at the whole-plant level in this species.     

COMPONENTS OF REPRODUCTIVE EFFORT AND YIELD IN GOLDENRODS

Four components of reproductive yield (the weight of reproductive tissue) were examined in relation to their effect on reproductive effort and their relative contributions to reproductive yield in five species of goldenrods (Solidago, Compositae). The yield components were number of flowing stems per plant, number of flowering branches per stem, number of flowering heads per branch, and number of seeds per seed head. Individuals within populations increase their reproductive effort by increasing their reproductive weight, not by decreasing their vegetative weight. Each species shows a different pattern of positive correlations of yield components with reproductive yield and reproductive effort, indicating that each species has its own mechanisms for regulating reproduction. The yield components were not significantly intercorrelated.     

QTL analysis of seed yield components in red clover (Trifolium pratense L.)

Cultivars of red clover (Trifolium pratense L.), an important forage crop in temperate regions, are often characterised by an unsatisfactory level of seed yield, leading to high production costs. This complex trait is influenced by many components and negatively correlated with other important traits, such as forage yield or persistence. Therefore, seed yield has proven to be difficult to improve. Thus, the objectives of this study were to assess association among seed yield components and to provide the basis for identifying molecular markers linked to QTLs for seed yield components to assist breeding for improved red clover cultivars. A total of 42 SSR and 216 AFLP loci were used to construct a molecular linkage map with a total map length of 444.2 cM and an average distance between loci of 1.7 cM. A total of 38 QTLs were identified for eight seed yield components. The traits seed number per plant, seed yield per head, seed number per head, head number per plant and percent seed set were highly correlated with seed yield per plant, and QTLs for several of these traits were often detected in the same genome region. Head number per plant may present a particularly useful character for the improvement of seed yield since it can easily be determined before seed maturity. In addition, two genome regions containing four or five QTLs for different seed yield components, respectively, were identified representing candidate regions for further characterisation of QTLs. This study revealed several key components which may facilitate further improvement of seed yield. The QTLs identified represent an important first step towards marker-assisted breeding in red clover.