Quality of guayule seeds separated by physical attributes

Guayule (Parthenium argentatum Gray) is being developed as a new commercial crop to be grown in arid and semiarid regions. Guayule stands are presently established using transplants; however, establishment by direct-seeding would reduce costs and make production more economical. A major difficulty in field establishment by direct-seeding is the variation in the quality of guayule seeds. Guayule seeds vary greatly in color, size, and weight, which are the attributes believed to be associated with the observed germination differences among and within seed lots. To determine the importance of these attributes, guayule seeds from different seed lots were separated by size (diameter) and color, each separation class was weighed and then seed quality determined by germination percentage and rate. X-ray analysis was used to distinguish filled from unfilled seeds, and this was related to the germination results. In six guayule breeding lines (N565, 11591, AZ-2, AZ-3, AZ-4, and AZ-5), the highest quality seeds were darker (opaque-black and gray), small to medium in diameter (1.4-1.6 mm), and were heavier (a greater proportion of filled seeds). Color appeared to be a more efficient separator for seed quality than seed size; however, separation by size may be acceptable on a large scale and still provide higher quality and more uniform seed lots.