Phenotypic diversity of USDA guayule germplasm collection grown under different irrigation conditions

Authors: Luo, Zinan; Abdel-Haleem, Hussein

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2019
Publication Date: 12/15/2019
Publication URL: https://handle.nal.usda.gov/10113/6739295
Citation: Luo, Z., Abdel-Haleem, H.A. 2019. Phenotypic diversity of USDA guayule germplasm collection grown under different irrigation conditions. Industrial Crops and Products. 142. https://doi.org/10.1016/j.indcrop.2019.111867.
DOI: https://doi.org/10.1016/j.indcrop.2019.111867

Interpretive Summary: Natural rubber (NR) is a critical industrial natural resource. Its outstanding properties such as elasticity, resilience, heat dispersion and abrasion resistance cannot be completely replaced by petroleum-derived synthetic rubber. However, the current production of NR, mainly harvested from Hevea brasiliensis, is faced with many obstacles, including the shortage of supply due to increased demands, the risks of fatal diseases, changes in economic and social behaviors in rubber-producing regions, and the allergic reactions triggered by Hevea’s NR latex. Guayule is considered as a domestic source for NR as well as hypoallergenic latex that is suitable for semi-arid and arid sustainable agricultural systems for rubber, resin and latex production. Our study is the first to explore phenotypic diversity in important agronomic traits in a global USDA guayule germplasm that include improved germplasm as well as wild accessions collected from natural habitats at Mexico and United States. The results summarized their responses and stability grown under different irrigation regimes, in which water-stressed condition increased resin and rubber accumulation while well-watered condition increased dry weight biomass. The study also estimated moderate to high entry-mean heritability for the studied traits, suggesting the feasibility of selection to improve genetic gain and reasonable expectations for breeding targets at early generations of breeding cycles. Significant correlations between biomass-related traits and resin (or rubber) yield might suggest the possibility of selection for multiple traits at one time. Th results and significant correlations between ploidy level and resin (or rubber) content indicated the possibility of polyploidy breeding to achieve specific breeding goals. This study lays the foundation for guayule breeding efforts to select parental candidates in breeding programs to grow guayule under different growing conditions and to achieve different production goals.

Technical Abstract: Parthenium argentatum (guayule), originated from northern Mexico and southern Texas deserts, is a good candidate for arid and semi-arid sustainable agricultural systems to produce domestic natural rubber and other industrial byproducts. Exploring the genetic and phenotypic diversities of guayule germplasm collections is required for continuous genetic improvement of guayule characteristics to meet the growing demand of guayule for rubber, resin and latex industries. The current study phenotypically evaluated a larger guayule USDA germplasm collection than before, with 56 accessions for 10 important morphological and agronomic traits evaluated, which include plant biomass, rubber and resin content, rubber and resin yield. The accessions were grown under two different irrigation conditions: well-watered and water-stressed environments. Significant genotypic effects were found for all studied traits indicating the wide genetic variability of this collection. Significant Environmental effects were found in rubber content, resin content, rubber yield and dry weight biomass. No significant genotype-by-environment interactions (GEI) were observed indicating the similarity of those accessions across growing conditions. Moderate to high entry-mean heritability values were estimated for these traits, suggesting that selection is feasible to enhance the genetic gain. Significant inter-trait correlations were found between biomass-related traits and resin/rubber yield, as well as ploidy levels and resin/rubber content, indicating the possibility of improving multiple traits at one time. To conclude, this study explored the phenotypic variations of the USDA guayule germplasm under ifferent irrigation conditions, which will provide recommendations for parent and off-spring selections to enhance the breeding values in guayule breeding programs.