In Brazil, which is one of the world`s principal banana production regions, almost all production is consumed within the country. Consumers show high preference for the cultivar Maca (AAB group). However, it is becoming increasingly difficult to produce bananas of this type because of their high susceptibility to Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense. Sexual breeding, which consists of recombination and selection, is limited in the banana because of polyploidy and sterility. Spontaneous somatic mutations are an important source of new cultirvars, and mutation breeding might be particularly important to generate genetic variation. Because of this, the mutation breeding approach has been used in Brazil. The objective of this research was to induce gamma ray mutations for resistance or to increase the level of tolerance to Fusarium wilt in the banana cultivar Maca on the basis of screening under field conditions. 4 refs.