Increasing the benefits of species diversity in multispecies temporary grasslands by increasing within-species diversity.

BACKGROUND AND AIMS: The positive effects of species diversity on the functioning and production of ecosystems have been discussed widely in the literature. In agriculture, these effects are increasingly being applied to mixed-species crops and particularly to temporary grasslands. However, the effects of increases in genetic diversity (i.e. within-species diversity) on productivity in multispecies crops have not been much studied. Nevertheless, genetic diversity may have strong positive effects on agricultural ecosystems and positively influence production and species abundances in multispecies covers. We examine here the effects of genetic diversity on temporary multispecies grasslands. METHODS: From a real situation, a breeder's field trial, we describe a study with five seed mixtures, each containing seven species (three grasses and four legumes) but with three different levels of genetic diversity (low, medium and high) created by using different numbers of cultivars per species. From the perspective of a plant breeder, we analyse measurements of biomass production over a 5-year period. KEY RESULTS: We show a positive effect of genetic diversity on production, on production stability and on the equilibrium of species abundances in the mixtures over the 5-year period of the experiment. The legume/grass proportions were best balanced, having the highest within-species diversity. CONCLUSIONS: For the first time in a field-plot study, we demonstrate the major role played by within-species genetic diversity on the production, stability and species composition of temporary grasslands. Our key results seem to find their explanation in terms of shifts in the peaks of species biomass production during the season, these shifts likely leading to temporal species complementarity. Our study suggests major benefits will arise with increases in the genetic diversity of multispecies crops. Genetic diversity may be useful in helping to meet new crop-diversification challenges, particularly with multispecies grasslands. Genetic and species diversity will likely provide additional levers for improving crops in diversified systems.

Detection of favorable alleles for plant height and crown rust tolerance in three connected populations of perennial ryegrass (Lolium perenne L.).

Plant height, which is an estimator of vegetative yield, and crown rust tolerance are major criteria for perennial ryegrass breeding. Genetic improvement has been achieved through phenotypic selection but it should be speeded up using marker-assisted selection, especially in this heterozygous species suffering from inbreeding depression. Using connected multiparental populations should increase the diversity studied and could substantially increase the power of quantitative trait loci (QTL) detection. The objective of this study was to detect the best alleles for plant height and rust tolerance among three connected populations derived from elite material by comparing an analysis per parent and a multipopulation connected analysis. For the studied traits, 17 QTL were detected with the analysis per parent while the additive and dominance models of the multipopulation connected analysis made it possible to detect 33 and 21 QTL, respectively. Favorable alleles have been detected in all parents. Only a few dominance effects were detected and they generally had lower values than the additive effects. The additive model of the multipopulation connected analysis was the most powerful as it made it possible to detect most of the QTL identified in the other analyses and 11 additional QTL. Using this model, plant growth QTL and rust tolerance QTL explained up to 19 and 38.6% of phenotypic variance, respectively. This example involving three connected populations is promising for an application on polycross progenies, traditionally used in breeding programs. Indeed, polycross progenies actually are a set of several connected populations.