Inheritance of resistance to Meloidogyne incognita race 3 in cotton accession TX 25/Heranca da resistencia do acesso TX 25 de algodoeiro a Meloidogyne incognita raca 3

Cotton producers worldwide suffer with the losses caused by the presence of phytonematodes. The aim of the present study was to investigate the inheritance of resistance to Meloidogyne incognita race 3 in Gossypium hirsutum variety punctatum accession TX 25. Accessions of Gossypium sp. were obtained from the germplasm bank of Embrapa Cotton. Two experiments were performed in two consecutive years. In the first experiment, a susceptible parental line, FiberMax 966, a resistant parental line, TX 25, and their [F.sub.1], [F.sub.2] and backcross generations were tested. In the second experiment, parental lines FiberMax 966 and TX 25, their [F.sub.2] generation, and genotypes M315 (resistant), LA887 and DeltaOpal (moderately resistant) were tested. In both experiments, plants were inoculated with 2000 eggs and J2 of M. incognita race 3. The gall index, egg mass index and reproduction factor were evaluated 120 days following inoculation. In the first experiment, plants from the [F.sub.1] and backcross generations were susceptible. Plants from the [F.sub.2] generation presented a 3:1 resistant-to-susceptible ratio in the two experiments, indicating oligogenic resistance. Keywords: Gossypium hirsutum, gall nematode, gene segregation. Os cotonicultores do mundo inteiro sofrem com as perdas causadas pela presenca de fitonematoides nas lavouras. Assim o objetivo deste trabalho foi estudar a heranca da resistencia do acesso TX 25 de Gossypium hirsutum raca punctatum a Meloidogyne incognita raca 3. Foram utilizados acessos de Gossypium sp. pertencentes ao Banco de Germoplasma da Embrapa Algodao. Foram realizados dois experimentos em dois anos consecutivos. No primeiro ano foram testados FiberMax 966 e TX 25 como parentais suscetivel e resistente, respectivamente, e as geracoes [F.sub.1], [F.sub.2] e retrocruzamento. No segundo experimento foram testados os parentais FiberMax 966 e TX 25, a geracao [F.sub.2] alem dos genotipos M315 (resistente) LA887 e DeltaOpal (moderadamente resistentes). Em ambos experimentos as plantas foram inoculadas com 2000 ovos e J2 de M. incognita raca 3. As avaliacoes ocorreram aos 120 dias apos a inoculacao, e avaliou-se indice de galhas, indice de massa de ovos e fator de reproducao. No primeiro experimento as plantas da geracao [F.sub.1] e do retrocruzamento se mostraram suscetiveis, As plantas da geracao [F.sub.2] nos dois experimentos apresentaram uma proporcao de tres plantas resistentes para uma suscetivel indicando resistencia de cara