Environmental, irrigation and fertilization impacts on the seed quality of guayule (Parthenium argentatum Gray)

Guayule is a perennial shrub that originates from the Chihuahua desert. Currently stand establishment is by transplanting seedlings. In order for guayule commercialization to be more profitable, direct seeding methods need to be developed. For direct seeding to be practical factors affecting seed quality need to be identified. Guayule seed quality is highly variable. The objective of this study was to determine the seed quality of guayule (Parthenium argentatum Gray) grown under various field conditions in Arizona, USA, and to determine the influence of irrigation frequency and fertilization management practices on seed quality. In experiment I guayule lines AZ-2, AZ-4, AZ-R2 and 11591 were compared at four locations in Arizona (Marana, Maricopa, Yuma Mesa and Yuma Valley). In experiment II guayule lines AZ-2 and 11591 were compared under three irrigation frequencies (40%, 60% and 80%) field capacity and fertilization at low and high levels of nitrogen, at Maricopa. Germination, embryo viability, empty achene production and achene moisture content were determined for harvested achenes. In experiment I a line × location interaction occurred for normal germination, empty achenes and achene fresh weight. Line AZ-4 had the highest germination of 59% at the Yuma Valley location. Empty achenes were the highest in Marana for line 11591 at 56%. In experiment II normal germination was affected by the line, irrigation and fertilization factors. The highest germination of 66% with line 11591, 55% at 60% irrigation and 56% at high fertilization was recorded. Empty achenes were the highest with line AZ-2 at 27%. Correlations of normal germination vs. maximum temperature, empty achenes vs. total rainfall and empty achenes vs. average wind speed were positive. Negative correlations occurred for empty achene vs. maximum temperature, normal germination vs. total rainfall and normal germination vs. average wind speed. The quality of guayule seed under both experimental conditions is severely decreased by empty achene production, which seems due to genetic variability and environmental conditions during flower bloom.