Arbuscular mycorrhizal fungi in papaya plantations of Espirito Santo and Bahia, Brazil

The aim of this study was to obtain knowledge on arbuscular mycorrhizal ( AM) associations in papaya ( Carica papaya, L.) in field soils and nursery conditions. Sixty seven soil and root samples were taken in February and May of 1996, from 47 commercial plantations in the North of Espirito Santo State and the West and South of Bahia State, in Brazil. Samples were used for direct spore counts, root colonization assessment and for trap culture with Sorghum bicolor ( L.) Moench and Crotalaria juncea L. Additional sampling was done in commercial nurseries to evaluate mycorrhizal colonization. Although papaya cropping systems are usually under high input of fertilizers and pesticides, papaya roots showed considerable arbuscular mycorrhizal ( AM) colonization, ranging from 6% to 83%. Colonization rates were most influenced by available soil P, correlated positively with percentage of sand and soil pH, but correlated negatively with soil clay content. AM colonization of nursery seedlings was very low in most samples. Field spore numbers varied from 34 to 444/30g of soil. All Glomerales families were represented and 24 fungal species identified. Glomus etunicatum, Paraglomus occultum, Acaulospora scrobiculata and Gigaspora sp. were the most common species.