2018 ASHS Annual Conference

Guayule (Parthenium argentatum) is a woody perennial shrub native to Northern Mexico and the Southwest United States. Because of its ability to grow in hot dry environments, it is replacing more water intensive crops in the arid southwest, such as cotton. Guayule is being commercialized on a large scale because of its ability to produce rubber needed by the domestic tire industry. It also produces resins and biomass with potential uses as pharmaceuticals, industrial chemicals, and biofuels. Phymatotrichum omnivorum, known as Cotton Root Rot, Texas Root Rot, or Phymatotrichum root rot, is an economically important fungal pathogen in eudicot crops, such as cotton, alfalfa, fruit and nut trees, along with a number of ornamental plants grown across the Southwestern U.S. As more acreage of guayule is being planted, cotton root rot has been observed, having the potential to drastically affect this new industry. The best solution to this problem is to develop guayule lines resistant to P. omnivorum. Toward developing resistant lines, five guayule germplasm accessions (AZ-1, AZ-2, AZ-5, AZ-6, and 11591) were evaluated for resistance to the fungus. Two-hundred plants per line were inoculated with a solution containing the scleroeca of P. omnivorum. Plants were rated on the degree of infection from 0 – dead to 5 – no damage. Cotton was grown as a control to test the viability of the inoculum.