Associations among forage quality traits, vigor, and disease resistance in alfalfa

Major objectives for alfalfa (Medicago sativa L.) breeding include improving forage quality and levels of disease resistance. Little is known about the associations between forage quality characteristics, including pectin (the main component of neutral detergent-soluble fiber [NDSF]), and disease resistance and vigor in alfalfa. Our objectives were to determine, in two alfalfa populations, the (i) correlations among NDSF and other forage quality traits; (ii) correlations of forage quality traits with plant persistence, vigor, and levels of resistance to diseases; and (iii) heritabilities and expected gains from selection for the aforementioned traits. Simple, phenotypic, and additive genetic correlation coefficients were estimated from half-sib (HS) progeny tests of two alfalfa populations (NY9505 and NY9515). In both populations, NDSF was negatively correlated with acid detergent fiber (ADF), lignin, and neutral detergent fiber (NDF), and positively correlated with true in vitro dry matter digestibility (IVDMD). Vigor was positively correlated with ADF, lignin, and NDF, and negatively correlated with IVDMD and crude protein (CP) only in NY9515. Of 144 correlation coefficients computed between forage quality traits and resistances to five major alfalfa diseases, only six were significant, and they were low in magnitude (-0.22 +/- 0.11 to 0.30 +/- 0.14). In an alfalfa improvement program, selection for forage quality is not expected to indirectly affect levels of disease resistance, but it may reduce vigor.