Cotton genotype response to early-season cold temperatures

Identifying cotton (Gossypium hirsutum L.) genotypes that are less sensitive to cool temperatures may improve productivity in areas where late-spring cold fronts are common. Our objectives were to compare commercially available genotypes for relative cold tolerance and to determine whether seedling growth response to cool temperature in a controlled environment was a valid predictor of held performance. Four genotypes, 'DPL 20' (early maturity), 'DPL 50' (mid), 'DPL 5690' (late), and 'DPL Acala 90' (late), were studied. Cotyledon area, root and shoot length, and root and shoot fresh weight were measured after 4-d-old seedlings were exposed to temperatures of 15, 20, 25, and 30 degrees C for 6 d. The four genotypes were also evaluated in the field in 1991 and 1992 by planting in mid-April, early-May, and mid-May near Florence, SC. Root length was the only seedling trait for which the temperature response was genotype dependent. Root length of DPL 5690 and DPL Acala 90 was the same at all assay temperatures (mean = 4.3 cm). For DPL 20, root length aas 9.3 cm at 15 and 20 degrees C, 11.8 cm at 25 degrees C, and 14.3 cm at 30 degrees C. DPL 50 root length was 8.7 cm at 30 degrees C and averaged 6.4 cm at the other three temperature treatments. In the field, when DPL 20 emerged faster than the two late-maturity genotypes at planting dates that were followed by cold temperatures, it had lower lint yield. The results suggest that measuring the amount of seedling root length inhibition (rather than relative growth differences) caused by suboptimal temperatures may be useful for determining cold sensitivity in cotton.