ARBUSCULAR MYCORRHIZAL COLONIZATION OF LIME IN DIFFERENT AGROECOSYSTEMS OF THE DRY TROPICS

Tecoman, in the Mexican state of Colima, had the world's greatest prod uction of lime Citrus aurantifolia Swingle. Typical farming systems in the area include: (a) high-input monoculture, (b) a high-input system in which lime trees grow together with coconut palms, (c) a low-input system called ''Family Farms'' or ''Family Gardens''. In the Family G ardens, cultural practices are minimal and other fruit trees (about 16 species) coexist with the lime trees. This traditional minimal input system makes use of locally available resources and they are structura lly very diverse. Arbuscular mycorrhizae may be crucial for sustainabl e production in Family Gardens. Root colonization and spore population s of fungi were scored at 2-week intervals in the three agroecosystems during a 6-month period. First samples were taken after the applicati on of chemical fertilizer and irrigation in the high-input systems. Ro ot colonization of lime was much higher and consistent in the low-inpu t plots than in conventionally farmed plots, with colonization levels of 50-62% that remained the same throughout the sampling time; the hig h-input systems showed a high variation and lower level of colonizatio n, 36% and 27% in associated and monoculture systems, respectively. Sp ore abundance was higher in the high-input systems but showed constant variation. The results suggest a strong effect of agroecosystem on my corrhizal colonization of lime roots.