Source Year: 1996

Guayule (Parthenium argentatum) produces a high quality hypoallergenic latex that is of interest for use in the medical industry. In order to meet the anticipated demand, guayule will need to be planted in mild climatic zones over a wide geographic area, and often following cotton (Gossypium sp) or other crops susceptible to the root-invading fungus Verticillum dahliae. As guayule has been previously shown to be susceptible to V. dahliae, the goals of this work were: (1) to develop through mass selection a diploid guayule line that is tolerant to V. dahliae, and (2) to evaluate improved guayule lines for Verticillium tolerance. A diploid guayule population was subjected to three cycles of selection, with only the plants with the greatest tolerence and the highest rubber yields used in the subsequent cycles of selection. Also, 15 improved polyploid and 3 diploid lines were evaluated for tolerance to V. dahliae under green house conditions. Cuttings were more tolerant than seedilings, and tolerance increased with age of the plant at the time of inoculation. The screened diploids expressed greater tolerance than an unscreened diploid population in both greenhouse and field trials. Among the 18 improved lines, 13 of which had not been previously evaluated, a screened diploid line (418-6) had the highest tolerance ranking, but was not significantly better than 4 unscreened polyploid lines. Continued evaluation of improved lines will help growers in making informed decisions about which lines to plant for their specific locations. The Verticillium tolerant diploid germplasm material developed in this study is available to plant breeding programmes.