Calcium Nutrition and Resistance of Alfalfa to Ditylenchus dipsaci

摘要

Stem nematode-susceptible 'Atlantic' and resistant 'Lahontan' alfalfa seedlings, grown in sand and watered with complete nutrient solutions containing 0.75, 1.5, 3.0, 6.0, or 12.0 mM Ca⁺⁺/liter, were inoculated with Ditylenchus dipsaci (the stem nematode) 5-6 days after emergence. Approximately equal numbers of nematodes entered the tissues of each variety/Ca⁺⁺ concentration within 2 days. Penetration was reduced at 12 mM Ca⁺⁺/liter. Reproduction during 21 days following inoculation yielded 3-fold, or greater, nematode increases in 'Atlantic' buds at all Ca⁺⁺ concentrations, in 'Atlantic' cotyledons at the four lower concentrations, in 'Lahontan' buds at the lowest concentration and in 'Lahontan' cotyledons at the two lowest concentrations. Reproduction was lower at the higher Ca⁺⁺ concentrations.Increased nutrient Ca⁺⁺ concentrations resulted in increased Ca⁺⁺ content, decreased Na⁺ and K⁺ content, and unchanged Mg⁺⁺ content of buds and cotyledons. Accordingly, increased nutrient Ca⁺⁺ resulted in increased divalent/monovalent cation ratios (Ca⁺⁺ + Mg⁺⁺/Na⁺ + K⁺ ). Resistance to reproduction was correlated more closely with the divalent/monovalent cation ratio than with Ca⁺⁺ content of tissue, At the four higher nutrient Ca⁺⁺ concentrations, 'Lahontan' buds had higher ratios than 'Atlantic,' and infected buds had higher ratios than noninfected buds. Although cation balance modifies disease expression, the basic resistance mechanism remains unknown.