Heritability of height, width, resin, rubber, and latex in guayule (Parthenium argentatum)

Plant breeding in guayule, a rubber and latex producing plant, has not been as effective as predicted or desired. A surprisingly large amount of varia bility has been reported in this apomictic crop for traits such as plant he ight, width, resin, rubber, and latex contents. This study was designed to calculate the proportion of the total measured variability due to the envir onment and the proportion due to genetic influences within and between thre e-released germplasm lines. Plant heights were measured at 1, 2 and 3-years -of-age; plant width, and latex contents at 2 and 3-years-of-age; and resin and rubber content at 2-years-of-age. Broad-sense-heritabilities were esti mated for each trait and year by dividing the genotypic by the total varian ce. To estimate the genetic component of the measured variance for each tra it, the environment effects (variance from clonally propagated plants) were subtracted from the total variance (variance from open-pollinated (OP) see d propagated plants). In general, the variances of the means for the measur ed traits were lower in the clonally propagated plants compared with the ap omictic OP seed propagated plants. The heritability estimates calculated fo r each trait differed from year to year. For instance, heritability for pla nt height was estimated in line AZ-2 to be 0.84 at 1 year of age; 0.47 at 2 years of age; and 0.0 at 3 years of age. These values imply that a large p ortion of the observed variation in this line is attributed to genetic effe cts in the first 2 years of growth. As the plant grows over several seasons , the environment effects compound, masking the genetic effects, making eff ective selection choices more difficult. Heritability for latex content for the same line was estimated to be 0.97 for the second year and 0.55 for th e third year. Selections for the measured traits in this study appear to be most effective during the first and second years of growth, with effective ness diminishing during the third year. Most selections previous to this st udy were performed between 3 and 5 years of growth, thus suggesting one rea son for the lack of significant progress in most breeding programs. (C) 200 1 Elsevier Science B.V. All rights reserved.