Influence of temperature on primary and lateral root growth of sunflower seedlings

Abstract

Roots play a major role in maintaining the supply of water and nutrients to plant tissues. There are numerous environmental factors such as temperature that can influence the growth and function of root systems. While we have some information about rooting depth in sunflower, we lack information about early root growth and its response to temperature in diverse genotypes based on wild sunflower species. The wild progenitors of the crop species are potential sources for enhancing the rooting system of cultivated sunflower. Root growth characteristics of seedlings of six genetically diverse sunflower ( Helianthus) genotypes and two cultivated hybrids were evaluated during a 10-day period to determine early chronological root growth as influenced by temperature. Root growth was evaluated at temperatures of 10–40°C in 5°C increments. Primary root length, lateral root length, number of lateral roots, root fresh weight, and hypocotyl length and fresh weight were determined beginning at 3 days after planting (DAP), 7 DAP, and 10 DAP. An analysis of variance indicated that genotypes, temperatures, and days were significant sources of variation for primary and lateral root lengths, number of lateral roots, root branching density, root fresh weight, and hypocotyl length and fresh weight. Averaged over all genotypes, primary and lateral root growth was greatest in the 25–30°C temperature range at 10 DAP. Generally, very little root growth occurs at 10, 15 or 40°C. Semi-dwarf hybrid 471D had the greatest primary and lateral root growth at 30°C with 154 cm, as well as the highest number of lateral roots with 48 roots per plant. Interspecific genotypes had similar total root growth compared to cultivated hybrid 894 at 30°C. Temperature-dependent root growth information will be useful in crop modeling of sunflower. There appears to be a temperature-specific response in laboratory evaluated sunflower genotypes, but further studies are needed to correlate the studies with rooting responses under field conditions.