Abstract
Red clover is a valuable forage crop, but often copes with unsatisfactory seed yield. Management practices to increase seed yield include fertilization, adequate weed and pest control, the synchronization of flowering through pre-cutting in spring, and the application of plant growth regulators to prevent lodging. Seed yield problems may have variable underlying reasons, such as inadequate pollination, fertility or genetic problems, or a combination of such traits. In this review paper, we summarize the results of recent publications that shed new light on the traits explaining seed yield differences between red clover genotypes. The main seed yield components are the number of flower heads per plant and the seed yield per flower head. Seed yield differences between diploid and tetraploid red clover are largely explained by the lower seed number per head. Recent research showed that, although inadequate pollination can lead to poor seed yield in certain areas, pollination cannot explain differences in seed yield between genotypes, cultivars, or ploidy levels. Correspondingly, corolla tube dimensions are not associated with seed yield, in spite of what is often believed by seed producers. On the other hand, fertility problems such as aberrations during male meiosis tend to occur more frequently in tetraploid genotypes and/or genotypes with low seed yield. A recent genetic study revealed 34 candidate genes for seed development, which opens perspectives for marker-assisted breeding. A final and remarkable finding is the occurrence of self-fertility in tetraploid red clover and its association with high seed yield. Breeders should be aware that selection for seed yield in tetraploid red clover may lead to unintentional selection for self-fertility, with possible consequences for inbreeding. The implications of recent findings for seed yield breeding and for the creation of novel tetraploids are discussed. Future research opportunities are considered.
Highlights
Red clover (Trifolium pratense L.) is a perennial forage legume belonging to the Fabaceae family.This crop is the second largest forage legume crop in the world in terms of production area, after alfalfa (Medicago sativa L.) [1]
Breeders should be aware that selection for seed yield in tetraploid red clover may lead to unintentional selection for self-fertility, with possible consequences for inbreeding
We summarize the results of recent publications that shed new light on the complex process of seed yield in red clover and discuss possible directions of future research and venues to improve seed yield in red clover through breeding
Summary
Red clover (Trifolium pratense L.) is a perennial forage legume belonging to the Fabaceae family. Higher forage yields and is generally more tolerant to biotic and abiotic stresses compared to diploid red clover [6,9,10]. In order to keep red clover on the market against competitive prices, seed yield needs to be improved, especially in tetraploid cultivars. Given its relevance for breeders and farmers, in recent years, several studies have investigated diverse aspects of seed yield in red clover. It remains unclear, if unsatisfactory seed yields are due to poor cultural practices during seed production, inadequate pollination, fertility problems, or any other genetic problems. We summarize the results of recent publications that shed new light on the complex process of seed yield in red clover and discuss possible directions of future research and venues to improve seed yield in red clover through breeding
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