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CROP BREEDING, GENETICS & CYTOLOGY

Associations among Forage Quality Traits, Vigor, and Disease Resistance in Alfalfa

^a EMBRAPA-Cerrados, Rodovia BR 020 Km 18, Planaltina-DF, Brazil 73301-970
^b Dep. of Plant Breeding, 523 Bradfield Hall, Cornell Univ., Ithaca, NY 14853-1902 USA
^c Dep. of Animal Science, 325 Morrison Hall, Cornell Univ., Ithaca, NY 14853-4801 USA

drv3{at}cornell.edu

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.

Abbreviations: ADF, acid detergent fiber • AN, anthracnose • ASI, average severity index • BW, bacterial wilt • CP, crude protein • FW, fusarium wilt • HS, half-sib • IVDMD, true in vitro dry matter digestibility • NDF, neutral detergent fiber • NDSF, neutral detergent-soluble fiber • NIRS, near infrared reflectance spectroscopy • PRR, phytophthora root rot • VW, verticillium wilt

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