Submitted to: Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2007
Publication Date: 3/1/2008
Citation: Jaradat, A.A., Rinke, J.L. 2008. Phenotypic divergence and population variation in cuphea. Journal of Agronomy. 7(1):25-32. Interpretive Summary: The objectives of this study were to quantify the level of variation in a cuphea selection (PSR23) as a potential oilseed crop and its divergence from its wild parents based on seed, capsule and plant traits, and to identify which agronomic traits in PSR23 are impacting its seed weight and seed yield, two of the most important determinants of oil yield. Several cycles of sowing and harvesting of PSR23 significantly influenced morphological divergence of PSR23 from its wild parents and generated a large within population variation at the plant, capsule, and seed levels. A plant ideotype with short (<100 cm), sparsely branched (3-4 branches per plant) stature, small (4-5 m2m-2) leaf area index, a maximum of 40-50 mature capsules per plant, 10-15 seeds per capsule, and a seed weight of 2.8-3.0 mg is proposed and would maximize seed yield if planted at a density of ~320-350 plants m-2. This information is of value for cuphea breeders and agronomists in their quest to fully domesticate this potential oilseed crop.
Technical Abstract: Morphological and seed-related traits in populations of a semi-domesticated, potential oilseed crop (PSR23), selected from an inter-specific Cuphea spp. cross, were used in quantifying levels of divergence from its wild parents and levels of variation among and within its populations. Multivariate analyses suggest that PSR23, in response to directional selection during several cycles of sowing and harvesting, significantly diverged from its wild parents in plant height, plant dry weight, branch density, leaf dimensions, 1000-seed weight and seeds per capsule. Among-population variation was dominated by plant dry weight, leaf area index (LAI), main branches per plant, capsule's major axis and seeds per capsule; however, large within population variation for flowers per plant, branching pattern (expressed as a fractal dimension), 1000-seed weight, seed area (mm2) and seed yield g m-2 could be attributed to the low impact of directional selection for these traits in a predominantly cross-pollinated plant, grown at high density. Sensitivity analyses indicated that 1000-seed weight and seed yield m-2, considered as the main determinants of oil yield, can be optimized by maximizing biomass m-2 and its proper partitioning among a number of inter-related yield components. A plant ideotype is proposed with short (<100 cm), sparsely branched stature (3-4 branches per plant), small (4-5 m2m-2) LAI, a maximum of 40-50 mature capsules per plant, 10-15 seeds per capsule, and a seed weight of 2.8-3.0 mg, would maximize seed yield if planted at a density of ~320-350 plants m-2.