Phenotypic variations, heritability and correlations in dry biomass, rubber and resin production among guayule improved germplasm lines

Gauyaule (Parthenium argentatum Gray) originated in the Southern Texas and Northern Mexico deserts, which suggests it as a good candidate for arid and semi-arid sustainable agricultural systems to produce natural rubber and other industrial byproducts. Continued improvement of guayule for higher biomass, rubber and resin production, and high resistance to environmental stresses, are required and necessary to meet the growing demand of guayule industry. The current study was conducted to evaluate the phenotypic variations in dry biomass, and rubber and resin content and production in nine improved guayule germplasm. The gentypes were grown in six environments and were harvested at one, two, and three years old. Results indicated that these germplasm has a good genetic variability at different growth stages in biomass rubber and resin production. The widest phenotypic variations were observed in plants harvested two year after transplanting. Significant genotypic by environmental interactions of these traits, suggest that evaluating guayule germplasm in multiple environments in order to select lines with the desired level of these traits is required. High heritability estimates of these traits suggest that selection is feasible in the first three years in general, and the highest after two years of transplanting, were plants reached maximum growth homogeneity with low competition among plants in the growing area. Positive correlation coefficients among these traits suggest the possibility of selection for more than one trait at a time, which could reduce guayule developing time and efforts to meet different industrial demands such as rubber and byproducts in the breeding programs.