Interactions of Glomus species and Meloidogyne arenaria on growth and development of Arachis hypogaea

Abstract

Four vesicular-arbuscular mycorrhizal fungi were evaluated for their ability to enhance growth of three peanut cutivars grown under conditions of low and high available phosphorus. Peanut cultivars Starr, Florunner, and Virginia 81B, representing Spanish, runner, and Virginia botanical types respectively, received one-half strength Hoagland's solution with either 0.1 mg/l or 12.5 mg/l available P for 7 weeks. When P was limiting (0.1 mg/l) inoculation with Glomus intraradices, Glomus deserticola, or an equal mixture of G .intraradices + Glomus etunicatum resulted in shoot dry weight approximately three times that of non-inoculated controls. When available P was optimal (12.5 mg/l) only inoculation with G. intraradices enhanced plant growth. This characteristic of G. intraradices is unique in that mycorrhizal enhancement of plant growth is usually observed only under conditions of low availible phosphorus. Inoculation with G. etunicatum failed to enhance plant growth at either level of applied P, although roots were highly colonized by the fungus. Enhancement of plant growth at 0.1 mg/l available P was attributed to increased uptake of N and P by mycorrhizal plants. The growth enhancement facilitated by inoculation with G. intraradices at the high level of applied P could not be attributed to increased uptake of any essential elements. The amount of VAM fungal colonization inside the root, although important, was not highly correlated with enhancement of plant growth. The possibility of G. intraradices increasing tolerance to the peanut root-knot nematode, Meloidogyne arenaria, was also investigated, as well as its effect on development and reproduction of M. arenaria within the root system. Greenhouse studies indicated inoculation with G. intraradices enhanced vegetative growth of peanut cultivar Florunner also colonized by M. arenaria. A field study revealed inoculation of M. arenaria infested plants with G. intraradices enhanced marketable yields over plants inoculated with nematodes alone or non-inoculated controls. When root systems were small and G. intraradices and M. arenaria were forced to inhabit the same site within the root, G. intraradices retarded development and reproduction of root-knot nematodes. When roots were large G. intraradices either had no effect on, or enhanced development and reproduction of M. arenaria, since nematodes chose to inhabit sites where G. intraradices was not present.