Project Number: 5347-21000-009-02
Project Type: Reimbursable

Start Date: Jan 01, 2006
End Date: Dec 31, 2007

Objective:
Determine nightly respiration rates of documented heat tolerant and sensitive germplasm lines under heat stress and non-stress environments, and determine the daily starch accumulation and depletion in leaves of the same lines.

Approach:
Two well documented heat sensitive and heat tolerant cultivars from Gossypium hirsutum and G. barbadense will be planted in a replicated, randomized block design in the field at Maricopa, AZ. Measurements of dark respiration and leaf starch and soluble sugar levels will be made on upper and mid-canopy fully expanded leaves at intervals during vegetative and reproductive growth stages. Dark respiration will be measured with a LiCor 6400 portable gas exchange system with CO2 and temperature control. Steady state dark respiration will be determined for each sample over a temperature range of 25-40 by increasing the measuring chamber temperature incrementally. Prior to measuring respiration leaves will be sampled for starch and soluble sugar analysis by removing leaf discs, freezing on dry ice, and storaging at -80C prior to analysis. Starch and soluble sugars will be extracted and determined by the enzymatic procedure reported by Hendrix et al. (1987). The heat sensitivity and tolerance of the cultivars used in this study will be further documented by pollen sterility measurements made throughout the fruiting interval of the plants, and by plant mapping for fruit rretention at intervals preceding and after heat stress events. Documents Reimbursable with Cotton Inc. Log 31432. Formerly 5347-21000-008-02R (7/06).