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Rubber and resin are potentially important products of guayule (Parthenium argentatum A. Gray) that can assure the profitability of this crop as an agricultural alternative for the semi-arid areas of central and eastern Spain. This study analyzes, for the first time, the changes in rubber and resin production across 27 guayule accessions (traditional and modern) and along three cycles under the agroclimatic conditions of Castilla-La Mancha, simulating industrial management with a biannual harvest. The rubber content (% of dry mass) increased from 4.2% in one-year-old plants to 6.6% in two-year-old plants, but decreased after harvesting. Contrastingly, the rubber yield doubled in contiguous sampling, reaching a mean of 303.6 kg ha−1, with a maximum yield of 341.2 kg ha−1 after the first harvest. Three patterns of rubber production were established based on the production periods. A similar analysis was performed for resin production, which was heterogeneous across accessions belonging to the same rubber groups. In this case, three independent groups were established to classify the resin accumulation profiles following the same criteria of production periods. Here, we demonstrate that biannual harvesting has the potential to enhance rubber accumulation in summer, although more research is needed for its adaption to current harvesting techniques in this area. [ABSTRACT FROM AUTHOR]

Guayule, a plant native to the Mexican deserts of Chihuahua and southern USA, has attracted interest as a substitute source of natural rubber and other bioproducts, and is a promising alternative crop for the semi-arid regions of central and eastern Spain. The trials performed on guayule production in Spain in the 1960 s need to be updated following the emergence of climate change and the development of more productive guayule accessions. Accordingly, the objective of the present study was to search for those lines that best adapt to the agro-climatic conditions of Castilla-La Mancha with respect to biomass production when the crop is industrially managed. The adaptation of 27 guayule accessions was studied by comparing their vegetative development (height, width, volume, shape, branch number and diameter). Results revealed the contribution of genetic imprinting for growth in plants up to 24 months after transplanting, after which times environmental effects were dominant in the second and third cycle after harvesting every two years. Biomass production along the three cycles simulating industrial management with biannual harvest depended on the germplasm, the harvest management and the agro-climatic conditions. The accessions with higher biomass content in branches were CAL-7 and AZ-2. • Twenty-seven accessions adapted to Castilla-La Mancha agro-climatic conditions. • The genetic contribution is observed in plants up to 24 months after seeding. • Environmental effects were dominant after harvesting every two years. • Biomass production is dependent on many factors (germplasm, the harvest and clima). • The accessions with higher biomass content in branches were CAL-7 and AZ-2. [ABSTRACT FROM AUTHOR]