Nutrients and the Reaction of Two Alfalfa Clones to the Spotted Alfalfa Aphid12

Cuttings from resistant alfalfa clone 4956 and susceptible clone 4959 were grown for 9-14 weeks in white silica sand watered with solutions that contained an excess, a medium, or a deficient amount of calcium, magnesium, nitrogen, potassium, phosphorus, or sulfur before they were infested with Therioaphis maculata (Buckton). None of the treatments made the susceptible clone more resistant. Resistance was significantly decreased but not eliminated when the resistant clone was treated with deficient levels of calcium or potassium or excess levels of magnesium or nitrogen, but resistance was significantly increased in plants receiving deficient levels of phosphorus. Sulfur did not affect resistance.