Effects of Vesicular-Arbuscular Mycorrhizal Fungi on Satsuma Mandarin Tree Growth and Water Stress Tolerance and on Fruit Development and Quality.

Abstract

The effects of vesicular-arbuscular mycorrhizal (VAM) fungi were studied at low concentrations of applied phosphorus (P) on satsuma mandarin (Citrus unshiu Marc. cv. Okitsu wase) trees which were grafted on trifoliate orange (Poncirus trifoliata Raf) rootstock. The VAM. fungi used were Glomus ambisporum Smith and Schenck, Glomus fasciculatum (Thaxter) Gerdemann and Trappe emend. Walker and Koske, Glomus mosseae (Nicolson and Gerdemann) German and Trappe, and Gigaspora ramisporophora Spain. The trees that were inoculated with the VAM fungi grew larger and had better fruit quality as compared with non VAM control trees. The fruit of former were larger, had higher sugar contents in the juice, and better peel color in both 1992 and 1993 than did the latter. In the non VAM control trees, there was a significant difference between seasons in fruit size and quality. This difference is attributed to the low rainfall in 1992 resulting in high sugar content while fruit development was retarded. In 1993, however, heavy precipitation from June to November produced large fruit, but with lower sugar content. After water shortage treatment of 10 days, the water stress tolerance of satsuma mandarin trees was improved by the inoculation of a VAM fungus (Gigaspora ramisporophora).