Associations Among Forage Quality Traits, Disease Resistance, and Vigor in Alfalfa.
Carlos E. L. Fonseca, D.R Viands, J.L. Hansen, A.N.Pell, J.E. Miller-Garvin,and E.M. Thomas
Dept. of Plant Breeding, Cornell University, Ithaca, NY 14850
Much of the alfalfa breeding efforts in the USA aim at improving forage quality and multiple disease resistance. Little is known about the genetic relationship among diseases, quality traits, persistence, and vigor in alfalfa. We determined the associations among resistances to anthracnose (ANT), bacterial wilt (BW), Fusarium wilt (FW), Phytophthora root-rot (PRR), and Verticillium wilt (VW); concentrations of acid detergent fiber (ADF), acid detergent lignin (ADL), crude protein (CP), true in vitro dry matter digestibility (IVDMD), neutral detergent fiber (NDF), and neutral detergent-soluble fiber (NDSF); persistence; and vigor. Plants were scored for disease symptoms according to the Standard tests to characterize alfalfa cultivars (Fox et al., 1991). Simple (rS), phenotypic (rP), and additive genetic (rG) correlation coefficients were estimated for all possible pairs of traits from half-sib (HS) progeny tests of alfalfa populations NY9505 and NY9515. Both plant populations are of moderate fall dormency (rating 4) and are adapted to northern USA and eastern Canada.
Significant differences among HS families were detected for all traits, except for persistence. Resistances to BW and FW were significantly associated in NY9505 (rG = 0.61 ± 0.12). In both populations, NDSF (mostly pectin in alfalfa), was significantly associated with ADF (rG = -0.67 ± 0.11 and -0.86 ± 0.10), ADL (rG = -0.76 ± 0.11 and -0.86 ± 0.10), IVDMD (rG = 0.53 ± 0.15 and 0.71 ± 0.12), and NDF (rG = -0.71 ± 0.10 and -0.88 ± 0.09). Vigor was significantly associated with ADF (rG = 0.50 ± 0.16), ADL (rG = 0.55 ± 0.18), CP (rG = -0.42 ± 0.19), IVDMD (rG = -0.65 ± 0.17), and NDF (rG = 0.53 ± 0.16) in NY9515. Significant association was found between FW and CP (rP = -0.22 ± 0.11), NDSF (rP = 0.25 ± 0.11), and vigor (rS = -0.17 ± 0.07) in NY9505, and between ANT and both NDF (rG = 0.30 ± 0.14) and vigor (rG = 0.31 ± 0.15) in NY9515. We conclude that selection for BW resistance in some populations may have a positive impact on FW resistance. Selection for higher NDSF concentrations may decrease the concentrations of the other cell-wall fiber components and increase IVDMD. Selection for lower fiber and/or higher CP concentrations may decrease vigor. Significant correlations between quality traits, disease resistances, and vigor were not of sufficient magnitude to adversely affect the improvement of these traits. Response to direct selection may be effective for both populations, but other related traits may need to be monitored for indirect response from selection.
Reference
Fox, C.C. et al. 1991. Standard tests to characterize alfalfa cultivars. 3rd ed. North America Alfalfa Improvement Conference, Beltsville, MD.