Seed quality of guayule (Parthenium argentatum Gray)

Abstract

The germination potential of guayule seed is considered too poor for direct seeding. Relating seed quality to field conditions could provide information on suitable locations and management to improve seed quality. The study objective was to determine seed quality of guayule grown under different field conditions in Arizona. Two trials were evaluated: experiment I, compared lines AZ-2, AZ-4, AZ-R2, and 11591 at locations Marana, Maricopa, Yuma Mesa, and Yuma Valley, and experiment II compared lines AZ-2, and 11591 under integrated irrigation of 40%, 60%, and 80% field capacity, and fertilization of high and low nitrogen. Seed germination, empty achene production, viability of ungerminated seeds and moisture content was determined. In experiment I, a line x location interaction occurred for normal germination, empty achenes, and achene wet weight. Yuma Valley location and line AZ-4 had the highest seed germination at 59%. Empty achenes were higher in Marana for 11591 at 56%. Achene wet weight was higher at 0.041g/50 achenes in Yuma Mesa with 11591 and in Yuma Valley with AZ-R2. In Experiment II, line, irrigation, and fertilization were significant for normal seed germination. Only line was significant for empty achene production. Line x fertilization and irrigation x fertilization interactions were significant for achene wet weight. Seed germination was higher with line 11591 at 66%, 55% at 60% irrigation, and 56% at high fertilization. Empty achenes were higher with AZ-2 at 27%. Achene wet weight was at 0.033g/50 achenes, and higher for 11591 at high and low fertilization levels, and higher at 40% irrigation and high fertilization, and at 60% irrigation and low fertilization. Experiment I had overall seed germination at 44%, and experiment II was at 39%. Empty achene production was at 36% in experiment I, and 31% in experiment II. The quality of guayule seed under both trial conditions were severely decreased by empty achene production. There is not any indication that soil moisture and nutrient applications improves the seed germination potential. The main reason for empty achene production seems due to the genetic variability of guayule seed production, and related to the environmental conditions of high temperature, rainfall and winds during flower bloom at the trial sites.