Seedling Root Growth Response to Cool Environmental Conditions for Diverse Cotton Cultivars

Cotton (Gossypium hirsutum L.) grown in the Mississippi River Delta is generally planted in cool conditions that can lead to slow germination, uneven emergence, and poor root growth. A study was conducted to determine the effects of low temperature on four genetic and geographically diverse cotton genotypes. The cultivars chosen were: Acala Maxxa, grown primarily in California; Stoneville 4892BR, grown primarily in the Mississippi River Delta; Tamcot Sphinx, from the plains of Texas; and FiberMax 966, with a genetic makeup from Australia. The cultivars were grown for 10 days in six temperature regimes: 15/20°C, 15/25°C, 15/30°C, 15/35°C, 15/40°C, and 15/45°C (night/day). The temperature regimes resulted in different root growth patterns for each cultivar. Tamcot Sphinx was statistically greater than all other cultivars in root dry matter, while the statistical least amount of cotyledon dry matter was produced in the 15/20°C temperature regime. The highest lateral root length, lateral root numbers, and root branch intensity were produced at 15/35°C. Tamcot Sphinx was numerically higher than all other cultivars in mean taproot length and total lateral root number over all temperature regimes. In the cool temperature regime of 15/20°C, Stoneville 4892BR had the greatest taproot length, showing tolerance for cooler temperatures. The results from the study on taproot and lateral root growth showed the existence of genetic diversity for root growth among cotton genotypes which can be exploited to find a cultivar able to tolerate cool temperatures and produce a more vigorous cotton seedling.