R. Rodríguez-García

Correlation and path coefficient analyses of the agronomic trait of a native population of guayule plants

Abstract Correlation and path coefficient analyses have been successfully used for plant selection for increasing yields of different crops. This approach could be applied to increase guayule latex production. Natural stands of guayule ( Parthenium argentatum ) in Mexico may constitute a source for plant selection. This paper reports on the correlation coefficients for phenotypic characteristics and path coefficient analysis of guayule to evaluate the direct and indirect effects of the rubber production components. The variables evaluated were plant height, main stem diameter, dry weight, rubber and resin content, and yields. These were measured from different part plants of shrubs a wild stands of Gomez Farias, Mexico. Rubber yields of the first-year stem and the diameter of the main stem are the variables that relate to rubber yield per plant. Based on the correlations and path coefficient analysis results, we found that the dry weight of the first-year stems is a good indicator for selecting high rubber yielding plants in wild stands.

Seasonal growth, rubber and resin yield characteristics of guayule under natural environmental conditions

Abstract Knowledge of the growth characteristics of guayule ( Parthenium argentatum Gray) and the different co-products produced during plant development would be extremely useful for selecting guayule species with high rubber yields, productivity, and defining the best time for harvesting. In this work, the changes in biomass, rubber and resin characteristics of two Mexican accessions and a check variety with high rubber yields were monitored during a 3-year period, starting at the seeding stage. The plants were grown in an experimental dryland field and sampled almost every month for plant height, top spread, biomass, stem diameter, rubber and resin contents. The results show cycles of biomass accumulation which may be correlated with changes in rubber and resin content. The overall biomass increase was approximated using an exponential function of a growth constant and time. The constants obtained apparently depended on the accession.

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

Abstract 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 64×3 m belts at each site. Production variables in the Site A were evaluated from 45 shrubs classified into three diameter classes according to the shrubs dominant sizes. The Site A had a total shrub density of 7890 plants/ha, whereas the Site B had 31 900 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.

Critical Evaluation of Different Techniques for Determining Soil Water Content

To efficiently operate any type of irrigation system, it is necessary to know when to irrigate and the quantity of water to apply during irrigation. To achieve this, it is very important to know the previously available soil water content. A good on-farm irrigation water management requires a routine monitoring of soil water moisture. Soil water must be maintained between a lower and upper limit of availability for an optimum plant growth. Soil moisture is a very dynamic variable that depends on plants evapotranspiration, irrigation frequency, drainage and rainfall. Measuring soil water content for determining the water depth allows avoiding the economic losses due to the effect of underirrigation on crop yield and crop quality, and the environmentally costly effects of overirrigation on wasted water and energy, leaching of nutrients or agricultural chemicals into groundwater supplies.