Rubber yield and guayule populations' attributes in naturally reestablished wild stands in Mexico

Medical latex goods provide opportunity for the commercial exploitation of hypoallergenic guayule (Parthenium argentatum, Gray). This, however, requires an adequate latex supply. Wild stands of guayule exist in Mexico. These have naturally reestablished over the last 15 years from previous harvesting of the whole plant. These stands constitute an excellent source of genetic material for selection, cropping and industrialization of guayule. The objectives of this study were: (a) to evaluate plant density and the spatial distribution pattern of the naturally occurring guayule shrubs in two types of topography within a wild stand at the Gomez Farias locality, at Coahuila, Mexico; (b) to determine the effect of main stem diameter on biomass, rubber and resin content, rubber and resin yield, and height for plants naturally occurring in slopes of less than 8% (Site A) and between 8 and 20% slope (Site B); and (c) to correlate total rubber yield with the other variables. Plant density was evaluated using the point centered quarter (PCQ) method based on a sample size of 40 random points per site. The spatial distribution pattern was estimated by the block quadrant variance method with two 64 x 3 m belts at each site. Production variables in the Site A were evaluated from 45 shrubs classified into three diameter classes according to the shrub's dominant sizes. The Site A had a total shrub density of 7890 plants/ha, whereas the Site B had 31900 plants/ha. The distribution of guayule plants was uniform for the Site A and clumped for the Site B. The plant branches showed high biomass production and the greatest rubber content was found in the main stem. Resin content was higher than rubber content in all the three diameter classes with a high positive correlation between these two parameters.