Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2008
Publication Date: 9/30/2008
Citation: Seiler, G.J. 2008. Root Growth of Interspecific Sunflower Seedlings Derived from Wild Perennial Sunflower Species. Canadian Journal of Plant Science. 88:705-712. Interpretive Summary: Plants require a root system that delivers adequate water and nutrients for shoot growth, and to anchor them in the soil. The optimum distribution of root length depends mainly on the distribution of water and nutrients in the soil. In dry seasons plants may require long main root axes to access water stored deep in the soil profile, while if abundant water and nutrients are available, only a small fraction of the root length may suffice. The number of roots, rooting patterns, and rooting depth are important characteristics needed for sunflower to survive. The problem is that we do not know what variability in rooting characteristics is available from the wild ancestors of the cultivated sunflower. Several perennial wild species are adapted for survival under limited water conditions. Six interspecific sunflower genotypes based on perennial wild sunflower species and two cultivated hybrids were evaluated for early primary and lateral root length, number of lateral roots, mean lateral root length, and hypocotyl length. Considerable variability for rooting characteristics was observed in the interspecific genotypes. Variability for specific characters is necessary to make progress in a breeding and selection program aimed at improving cultivated sunflower. The next step will be to evaluate the interspecific genotypes under field conditions to correlate the responses in the laboratory and under field conditions.
Technical Abstract: Roots play a major role in maintaining an adequate water supply for plant growth and development. Since sunflower is a tap root plant and because the major limitation to yield in semiarid and arid regions is the availability of water, differences in the characteristics of the lateral root system affect the plant's ability to explore the available soil for water and nutrients. The wild progenitors of the crop species are potential sources for enhancing the rooting system of cultivated sunflower (Helianthus annuus L.). The objectives of this study were to determine the early primary and lateral root growth, branching density, number of lateral roots, hypocotyl length, and hypocotyl and root fresh weights, and the interrelationships among these characteristics for five genetically diverse interspecific sunflower hybrids derived from wild perennial Helianthus species and two cultivated hybrids. Seedlings were germinated and grown in polyethylene pouches at 25 C in the dark for 10 days. An analysis of variance indicated that hybrids and days after planting (DAP) were significant sources of variation for primary and lateral root length, number of lateral roots, root branching density, root fresh weight, and hypocotyl length and fresh weight. Primary root growth begins at 4 DAP, while lateral root development begins by 7 DAP. At 10 DAP, 23% of the total root length was primary and 77% were lateral roots in the present study. At 10 DAP, cultivated semidwarf hybrid 471D had the longest average primary root length at 13.9 cm and also the longest lateral root length at 118 cm, and the highest number of lateral roots with 38. A high significant positive correlation was observed between primary and lateral root lengths and number of lateral roots, with the lowest correlation between primary and lateral root lengths and branching density. The high positive correlation between the root growth characteristics should be helpful in selecting adapted sunflower genotypes. The correlations indicate that selection for one trait, for example, primary root length, would not be detrimental to other important factors. The wild interspecific sunflower hybrids derived from wild perennial species did not possess as much variability for early root growth as expected. Nevertheless, there appears to be adequate genetic variability for further selection and genetic improvement. This information will be useful when attempting to alter rooting patterns in sunflower. However, studies on heritability and response to selection will be required before determining the likelihood of successfully breeding for these traits. Further studies will also be needed to correlate laboratory observations with response under field conditions.