The value of grass-legume associations is still under discussion from both agronomic and breeding points of view, chiefly because of contrasting conclusions on the nature of interference effects. A set of experiments was carried out at Lodi in 1980-84, to determine the effect of interspecific interference on the single partners and on associations as a whole. The general conclusions drawn from these experiments and their consequences for breeding strategies are summarized and discussed in this paper. Comparison of different models for analysis of the experimental data suggested a possible explanation of the different opinions on the nature of interference effects.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

In an alfalfa (Medicago sativa L.) breeding study conducted under conditions of high competition between plants, combining ability [or forage yield was evaluated from diallel crosses among selected parents which had been partly inbred by selfing. The performance of first and second generation synthetics was studied as well. General combining ability (GCA) variance was considerably larger than specific combining ability (SCA) variance for all generations of parental inbreeding (S0, S1, S2, S3, and S4). In general both GCA and SCA increased with inbreeding. The best single crosses came from selected inbred parents. Selling and subsequent selection improved the genetic value of the parents and resulted in improved synthetic varieties. Breeding synthetic varieties based on four selected S2. plants might well be an efficient method to improve yield of alfalfa.

In a breeding program of luceme based on selfing in sward conditions general as well as specific combining ability was evaluated for diallel crosses made at different levels of inbreeding. The performance of the second generation synthetics was studied as well. The efficiency of selting and subsequent selection in improving the genetic value of parents is very important. The optimal solution for luceme breeding could well be the use of synthetic varieties which are based on 4 inbred clones.

In an alfalfa (Medicago sativa L.) breeding study conducted under conditions of high competition between plants, combining ability for earliness and mortality was evaluated from diallel crosses among selected parents, which had been partly inbred by selfing. The performance of first and second generation synthetics was also studied. For both earliness and mortality (percentage of blooming or dead plants, respectively), general combining ability (GCA) was considerably larger than specific combining ability (SCA) for all generations of parental inbreeding (S0, S1, S2, S3, and S4). GCA and SCA increased with the level of inbreeding. Significant correlations were noted between earliness and yield, between mortality and yield and between earliness and persistence. At each level of parental inbreeding the single crosses with the greatest forage yield were also the earliest and the most persistent. Syn 2 generation synthetics had the same response pattern.