MYCORRHIZAL DEPENDENCY AND NUTRIENT-UPTAKE BY IMPROVED AND UNIMPROVEDCORN AND SOYBEAN CULTIVARS

Plants in nutrient-deficient soils often benefit when colonized by ves icular-arbuscular mycorrhizal fungi (VAMF). Plants vary, however, in r esponsiveness or mycorrhizal dependency (MD). The objective of this wo rk was to evaluate MD within corn and soybean cultivars. Three improve d and three unimproved corn (Zea mays L.) and three improved and two u nimproved soybean [Glycine soja Siebold and Zucc. and Glycine max (L.) Merr.] cultivars were evaluated for growth response, nutrient uptake (N, P, K, Ca, Mg, and Zn), and root phosphatase activity Greenhouse st udies were conducted with VAMF (Gigaspora margarita or Glomus intrardi ces) and without inoculation in a low-P soil. The VAMF colonization of roots with inoculation ranged from 62 to 87% for soybean and 49 to 68 % for corn. Soybean had a higher MD than corn, but considerable variat ion occurred within soybean cultivars. Relative growth of the two unim proved soybean cultivars was significantly greater with VAMF colonizat ion than without (Soja, >1900%; Mandarin, >400%). Among improved culti vars, relative growth was less enhanced with colonization (BSR 201, Ri chland, and Swift cultivars averaged approximate to 200% greater growt h with VAMF than without VAMF colonization). An unimproved corn cultiv ar, Reid Fellow Dent, was unresponsive to mycorrhizal colonization, wh ereas another unimproved cultivar, Argentine Pop, increased growth 400 % with colonization. Total uptakes of N, P, K, Ca, Mg, and Zn were sig nificantly greater (P<0.001) in mycorrhizal plants, but the concentrat ions (mg g(-1)) of N, Rig, and Ca were lower in mycorrhizal plants tha n in nonmycorrhizal plants. These results suggest that considerable va riability exists in MD of corn and soybean cultivars when grown in P-d eficient soils, and the variability extends across both improved and u nimproved cultivars.