INTERACTIVE EFFECT OF SALINITY AND VERTICILLIUM-ALBO-ATRUM ON VERTICILLIUM-WILT-DISEASE SEVERITY AND YIELD OF 2 ALFALFA CULTIVARS

The interaction between the fungus Verticillium albo-atrum and soil sa linity was evaluated for two alfalfa (Medicago sativum) cultivars, Moa pa-69 and NK-89786, differing in susceptibility to Verticillium wilt. Salinity treatments (NaCl, CaCl2) were imposed by drip irrigation of 7 -week-old plants which were then inoculated by soil drench with differ ent concentrations of V. albo-atrum. In the absence of V. albo-atrum, a salinity of 7.5 dS/m significantly (P<0.05) reduced yield of both cu ltivars relative to the nonsaline control. Thresholds for reduction in relative yield with increasing salinities were 0.8 for NK-89786 and 1 .6 dS/m for Moapa-69, indicating that NK-89786 was more sensitive to s alinity than Moapa-69. In the absence of salinity, the percentage of s tems infected with V. albo-atrum and the severity of root xylem necros is were significantly greater for Moapa-69 than for NK-89786. Inoculat ion with V. albo-atrum did not significantly reduce yield of either cu ltivar when grown in nonsaline soil; however, when infected NK-89786 p lants were irrigated with saline water of 3.0, 5.0, or 7.5 dS/m, yield was significantly reduced relative to yield loss due to the effects o f V. albo-atrum inoculation alone. A similar yield reduction occurred for Moapa-69, but only at 7.5 dS/m.