|Ray, D - THE UNIVERSITY OF ARIZONA|
|Lorenz, G - ARIZONA STATE UNIVERSITY|
Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 7, 2000
Publication Date: N/A
Interpretive Summary: Plant traits of guayule associated with yield have not been improved as effectively as predicted or desired through plant breeding. Although variation for plant traits exist, progress has been hampered by lack of understanding of the environmental and genetic variation. In this study we calculated, using a novel approach, the proportion of measured variability of plant height, width, resin, rubber, and latex due to the environmental components and the proportion due to genetic influences. We found that a large portion of the variation is attributed to genetic effects in years one and two of growth. In the third year, the environmental effects compound and mask the genetic effects, making it more difficult to make effective selections for plant improvement. This information is very important for plant breeders to optimize their efficiency in breeding by making selections in the first two years' growth. Then breeders could mass select over several generations for traits with high heritabilities. This strategy for plant improvement offers a quicker and more efficient alternative to breeding schemes now being practiced and will benefit both public and private researchers developing guayule into a viable commercial latex crop.
Technical Abstract: Plant breeding in guayule, a rubber and latex producing plant, has not been as effective as predicted or desired. This study was designed to calculate the proportion of the total measured variability due to the environment and the proportion due to genetic influences within and between three released germplasm lines. Broad sense heritabilities were estimated for each trait and year by dividing the genotypic by the total variance. To estimate the genetic component of the measured variance for each trait, the environmental effects (variance from clonally propagated plants) were subtracted from the total variance (variance from open-pollinated (OP) seed propagated plants). In general, the variances of the means for the measured traits were lower in the clonally propagated plants compared to the apomictic OP seed propagated plants. Heritability for plant height was estimated in line AZ-2 to be 0.84 at one-year-of-age; 0.47 at two-years-of-age; and 0.0 at three- years-of-age. These values imply that a large portion of the observed variation in this line is attributed to genetic effects in the first two years of growth. As the plant grows over several seasons, the environmental effects compound, masking the genetic effects, making effective selection choices more difficult. Heritability for latex content for the same line was estimated to be 0.97 the second year and 0.55 the third year. Selections in this study appear to be most effective during the first and second years of growth, with effectiveness diminishing during the third year. Most selections previous to this study were performed between three and five years of growth, thus suggesting one reason for the lack of significant progress.