Effects of climatic factors on native arbuscular mycorrhizae and Meloidogyne exigua in a Brazilian rubber tree (Hevea brasiliensis) plantation

The cost-knot nematode Meloidogyne exigua and arbuscular mycorrhizal (AM) f ungi may both occur in the roots of Brazilian rubber trees (Hevea brasilien sis). AM fungi may stimulate plant growth whereas nematodes usually reduce it. Variations of native AM fungi and M. exigua populations in soil and roo ts of rubber trees were studied for one year in a Brazilian plantation. The number of AM spores in the soil was generally greater in the rainy season than in the dry season, although AM colonization of roots was unaffected bl season. During the dry season, numbers of juveniles and eggs of M. exigua in roots were lower than in the rainy season. A site without nematodes in t he soil or roots showed the greatest numbers of AM spores in soil and highe st AM colonization of roots. A negative correlation was observed between th e percentage of AM colonization and the number of second-stage juveniles in soil and second-stage juveniles and eggs in roots. Microscope observations revealed (i) tissue specificity for each of the microorganisms in the root s, with a cortical location of mycorrhizae and a mainly vascular cylinder l ocation of nematodes, and (ii) that Gigaspora was the most abundant AM genu s in the plantation soil.