Genetic variation and variety x environment interaction for digestibility, forage yield and protein content in alfalfa
Bernadette Julier, Christian Huyghe, and Christian Ecalle
INRA, Unité de Génétique et d'Amélioration des Plantes Fourragères,
F-86600 Lusignan, France
Nowadays, breeders include the energy value as a breeding criteria. We studied the digestibility of a very large set of varieties or populations of alfalfa originating from various countries over the world, in a range of environments. One hundred and forty-four varieties, with fall dormancy ranging between 3 and 5 were analyzed in two locations in France over 3 years, with a total of six cuts per location. In each cut, forage yield, plant digestibility, fiber contents, leaf to stem ratio, protein content, lodging score were measured.
Genetic variation for digestibility was as large as 8 points. For the top yielding varieties, the range of variation was of about 4 points. The correlation between forage yield and digestibility was significantly negative, but a few varieties combined to some extent a high yield and a high digestibility. The effects of environment (location, year, cut) were much larger than the effect of variety, for digestibility as well as for other traits. All interactions between environment (location, year, cut) and variety were significant but not very high. It was possible to identify varieties that contributed little to environment * variety interaction, i.e. stable varieties over environments. Some of the stable varieties were highly digestible, others had an average digestibility and the others had a low digestibility. However, the heritability of digestibility was low, as a consequence of the environment * variety interaction, and above all, to the high residual variance.
Genetic correlations between enzymatic digestibility and fiber contents (NDF, ADF, ADL) were higher than 0.9, indicating the redundancy between these four traits. We observed a significantly positive correlation between digestibility and protein content, but the two traits were clearly different. Lodging was not correlated to digestibility. Some cultivars, with thick stems, were lodging-resistant and digestible.
These results indicated that, without any breeding, it exists some genetic variation for digestibility. Digestible cultivars can combine a high yield, lodging resistance and high protein content. This offers valuable prospects for breeding.