Morphological Diversity and Relationships in the A-Genome Cottons, Gossypium arboreum and G. herbaceum

The Asiatic or A-genome cottons, Gossypium arboreum L. and G. herbaceum L., are potentially important genetic resources for cotton breeding programs. The National Plant Germplasm System (NPGS) contains approximately 400 accessions of these species, but little information is available on the diversity within the collection or on characteristics of individual accessions. This investigation was initiated to provide a morphological description of each accession. These data were used to evaluate the range of diversity represented within the collection and to address the questions of species and race distinctions. Multivariate techniques were used to assess similarities among accessions and to evaluate morphological parameters contributing to the variation in each species. Means for 41 of 53 characters were significantly different between species, although high intraspecific variability resulted in range overlap for all characters. Principal component analysis separated the two species. Accessions from southern Africa and racial designations of africanum and wightianum formed clusters within G. herbaceum based on the first two principal components; no clusters were noted within G. arboreum. Accordingly, the validity of intraspecific or racial classifications for most of the accessions of this latter species in the current NPGS collection is questionable. Additional germplasm acquisitions from under- or non-represented areas could expand genetic diversity in the collection