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. herbaceu m L., are potentially important genetic resources for cotton breeding programs. The National Plant Germplasm System (NPGS) contains approxim ately 400 accessions of these species, but little information is avail able on the diversity within the collection or on characteristics of i ndividual accessions. This investigation was initiated to provide a mo rphological description of each accession. These data were used to eva luate the range of diversity represented within the collection and to address the questions of species and race distinctions. Multivariate t echniques were used to assess similarities among accessions and to eva luate morphological parameters contributing to the variation in each s pecies. Means for 41 of 53 characters were significantly different bet ween species, although high infraspecific variability resulted in rang e overlap for all characters. Principal component analysis separated t he two species. Accessions from southern Africa and racial designation s of africanum and wightianum formed clusters within G. herbaceum base d on the first two principal components; no clusters were noted within G. arboreum. Accordingly, the validity of infraspecific or racial cla ssifications for most of the accessions of this latter species in the current NPGS collection is questionable. Additional germplasm acquisit ions from under- or non-represented areas could expand genetic diversi ty in the collection.