Abstract
Stunting of sour orange seedlings was observed in seedbeds which had been fumigated chemically, heat-treated, or planted in soil-less media. Mycorrhizae were consistently absent from stunted seedlings and present in vigorous seedlings in seedbeds and nurseries and also present in orchards. Inoculation with Glomus fasciculatus (Thaxter) Gerd. & Trappe increased seedling height more than 300% and increased foliar phosphorus concentrations in greenhouse experiments on sour orange seedlings grown in sand culture with complete nutrient solution. Preplant application of P at 200 mg/liter did not increase growth or foliar P concentrations under the same conditions. Inoculation of seedlings receiving 0 to 800 mg P/liter with G. fasciculatus increased growth where 0 or 100 mg P/liter was added, but not where higher rates of P were used. Application of high rates of P induced copper deficiency symptoms, which were more severe on non-mycorrhizal than on mycorrhizal plants.