PRIMARY AND LATERAL ROOT ELONGATION OF SUNFLOWER SEEDLINGS

Roots play a major role in maintaining a water supply in plants. Differences in root density and rooting depth exist in many crops. Sunflower is a drought-tolerant crop with limited information about early root growth. The wild progenitors of the crop species are potential sources for enhancing the rooting system of sunflower. Primary and lateral root growth th of 10-day old seedlings of eight genetically diverse sunflower (Helianthus spp.) genotypes was evaluated to determine the early chronological root growth. Seeds were germinated and seedlings grown in polyethylene pouches at 25 degrees C in the dark for 10 days. Primary root length, lateral root length and number of lateral roots were determined beginning at 2 days after planting (DAP) for 6 consecutive days, and at 10 days for early primary root growth. An analysis of variance indicated that genotypes differed significantly in primary and lateral root lengths, total root length, number of lateral roots and mean lateral root length, but not branching density. At 10 DAP, genotype PET had the longest primary roots (9.0 cm), and genotype 471D had the longest lateral roots (20.5 cm). Genotype PET had the greatest number of lateral roots with 14.3 root seedling(-1). The greatest increases in primary and lateral root lengths occurred during the fourth-sixth DAP. A high positive correlation was observed between primary and lateral root lengths, number of lateral roots, with the lowest correlation between primary root length and branching density. There appears to be adequate variability for selection to genetically alter root growth patterns in sunflower using wild species, but further studies are needed to correlate laboratory observations with rooting responses under field conditions.