Predicting Mycorrhizal Dependency of Troyer Citrange on Glomus fasciculatus in California Citrus Soils and Nursery Mixes

Abstract

AbstractIn a greenhouse experiment the mycorrhizal fungus, Glomus fasciculatus, significantly increased growth of Troyer citrange (Poncirus trifoliata L.) (TC) seedlings in 20 of 26 methylbromide‐fumigated citrus soils from southern California. Of the six soils in which G. fasciculatus provided no growth increase, two were greenhouse soils, three were nursery soils, and only one was a field soil. Glomus fasciculatus increased foliar P, K, and Cu concentrations and decreased foliar Mg and Na concentrations of TC grown in the majority of the 26 citrus soils. Foliar concentrations of P, K, Ca, Na, Zn, Mn, Cu, and Fe from either mycorrhizal or nonmycorrhizal TC could not be significantly correlated with the mycorrhizal dependency of TC in the soils studied. A positive correlation was observed between foliage concentrations of Mg in nonmycorrhizal TC and mycorrhizal dependency. Mycorrhizal dependency of TC was also positively correlated with soil pH and inversely correlated with extractable soil P (bicarbonate), Zn, Mn, Cu, percent organic matter, and cation exchange capacity. In the fumigated soils studied, it was highly probable that inoculations with G. fasciculatus would induce significant growth response in TC provided the soils had <34 ppm extractable P, 27 ppm extractable Mn, 12 ppm extractable Zn, or 3% organic matter. The magnitude of the mycorrhizal dependencies of TC on G. fasciculatus in the 26 citrus soils were accurately predicted with equations which used soil P, Mn, Zn, and also Cu and pH as independent variables.