Periods of Chilling Sensitivity in Germinating Pima Cottonseed1

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Abstract
Seed germination and seedling development are adversely affected in many crops by less than lethal chilling temperatures. Periods of chilling sensitivity have been identified in Upland cotton (Gossypium hirsutum L.) but little work has been reported in Pima cotton (G. barbadense L.). This study was conducted to evaluate the influence of temperature on the degree and timing of chilling susceptibility in germinating Pima cotton and to determine if genetic variability exists. Seed were germinated at 25 or 35 C for 72 hours with one additional 24‐hour chilling exposure of 5, 7, or 10 C at various times during germination. Two periods of chilling sensitivity were noted. The first occurred at the beginning of germination. The second period showed maximum sensitivity between 28 and 32 hours when seed were germinated at 35 C and between 40 and 56 hours when seed were germinated at 25 C. Chilling at 7 C during both sensitive periods delayed emergence from a soil mix. In addition, final emergence was reduced by 26% when seed were chilled at the beginning of germination. Chilling at 5 C caused much more severe damage than chilling at 7 or 10 C. Some experimental lines showed greater resistance to chilling than the commercial cultivar, ‘Pima S‐4.’ Two genetic lines that responded similarly when chilled at 5 C differed significantly when chilled at 7 and 10 C. This suggests that these higher temperatures may be best for evaluating genetic variation and seed treatments to impact chilling resistance.