Calcium Nutrition and Resistance of Alfalfa to Ditylenchus dipsaci

R. T. Sherwood, D. Huisingh

Abstract


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[sup+][sup+]/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[sup+][sup+] concentration within 2 days. Penetration was reduced at 12 mM Ca[sup+][sup+]/liter. Reproduction during 21 days following inoculation yielded 3-fold, or greater, nematode increases in 'Atlantic' buds at all Ca[sup+][sup+] 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[sup+][sup+] concentrations. Increased nutrient Ca[sup+][sup+] concentrations resulted in increased Ca[sup+][sup+] content, decreased Na[sup+] and K[sup+] content, and unchanged Mg[sup+][sup+] content of buds and cotyledons. Accordingly, increased nutrient Ca[sup+][sup+] resulted in increased divalent/monovalent cation ratios (Ca[sup+][sup+] + Mg[sup+][sup+]/Na[sup+] + K[sup+] ) . Resistance to reproduction was correlated more closely with the divalent/monovalent cation ratio than with Ca[sup+][sup+] content of tissue, At the four higher nutrient Ca[sup+][sup+] 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. Key Words: Ditylenchus dipsaci, Stem nematode, Alfalfa, Medicago sativa, Resistance, Reproduction, Calcium, Magnesium, Potassium, Sodium.

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