Morphological description of a novel synthetic allotetraploid(A(1)A(1)G(3)G(3)) of Gossypium herbaceum L.and G.nelsonii Fryx. suitable for disease-resistant breeding applications

Wild species of Gossypium ssp. are an important source of traits for improving commercial cotton cultivars. Previous reports show that Gossypium herbaceum L. and Gossypium nelsonii Fryx. have better disease resistance characteristics than commercial cotton varieties. However, chromosome ploidy and biological isolation make it difficult to hybridize diploid species with the tetraploid Gossypium hirsutum L. We developed a new allotetraploid cotton genotype (A(1)A(1)G(3)G(3)) using a process of distant hybridization within wild cotton species to create new germplasms. First of all, G. herbaceum and G. nelsonii were used for interspecific hybridization to obtain F(1) generation. Afterwards, apical meristems of the F(1) diploid cotton plants were treated with colchicine to induce chromosome doubling. The new interspecific F(1) hybrid and S(1) cotton plants originated from chromosome duplication, were tested via morphological and molecular markers and confirmed their tetraploidy through flowrometric and cytological identification. The S(1) tetraploid cotton plants was crossed with a TM-1 line and fertile hybrid offspring were obtained. These S(2) offsprings were tested for resistance to Verticillium wilt and demonstrated adequate tolerance to this fungi. The results shows that the new S(1) cotton line could be used as parental material for hybridization with G. hirsutum to produce pathogen-resistant cotton hybrids. This new S(1) allotetraploid genotype will contributes to the enrichment of Gossypium germplasm resources and is expected to be valuable in polyploidy evolutionary studies.