Correlations and Path Analyses of Agronomic Traits in Guayule

Successful breeding of guayule ( Parthenium argentatum Gray) for increased rubber yield requires knowledge about the traits that influence rubber production directly and indirectly. This study was undertaken to examine the interrelationships of several agronomic traits through path‐coefficient analyses, to determine broad‐sense heritability, and to estimate genetic advance under selection. Plant height, width, dry weight, rubber content, resin content, rubber yield, and resin yield from guayule selections planted at two locations (Riverside, CA, and Maricopa, AZ) were used for analyses. The guayule selections exhibited significant differences for all traits at both locations, except for plant dry weight and plant width at Maricopa. Broad‐sense heritability estimates ranged from a low of 75.1% (for rubber content) to a high of 96.5% (for resin content) at Riverside, and from 6% (for plant width) to 93.1% (for resin content) at Maricopa. Expected netic advance ranged between 18% (for plant width) and 76% (for resin yield) at Riverside, and between 0.72% (for plant width) 41% (for resin content) at Maricopa. Rubber yield, the most critical trait for economic commercialization of guayule, showed expected genetic advance of 58% at Riverside and 37% at Maricopa. Path‐coefficient analyses indicated plant height to be less important than plant width as a component of dry weight at Riverside. Dry weight and percent rubber content had positive direct effects on rubber yield and accounted for 99% of its variation at Riverside and 85% at Maricopa.