Pollen Germination of Diverse Cotton Cultivars.

High temperatures during cotton (Gossypium hirsutum L.) flowering and early boll development can detrimentally affect cotton yield. Current commercial cultivars do not have pronounced tolerance to elevated temperatures, and improved methods of screening for thermo-tolerance are needed. Pollen germination is a potential method for screening for heat tolerance.   The overall objectives of this study were to determine the best growth medium and optimal conditions for cotton pollen germination, and to use pollen germination percentages to evaluate the effect of high temperature stress on cotton cultivars in a controlled environment.  Four cultivars representing variable tolerance to high temperatures were evaluated in controlled conditions.  Cultivars planted were one heat tolerant cultivar (VH260), one with moderate heat tolerance (Arkot 9704), one intermediate (DP393) and a cultivar of unknown heat tolerance (DP210).  Treatments consisted of a normal temperature regime 30/20°C (day/night) and a heat-stressed treatment (40/20°C) applied at first flower for one week. A modified growth medium of Burke et al., (2004) was used.  MnSO4 was replaced with CaNO3.  Then 3.5g agar, 18 g sucrose, 0.03 g CaNO3, 0.052 g KNO3 and 0.01026 g H3BO3 were made up to 100 ml deionized water.  The growth medium (pH 7.6) were heated slowly after including the agar and then poured into petri dishes. Pollen of a single flower was gently tapped into the middle of a petri dish. Total pollen germination percentages ranged from 11% for cultivar VH260 that received heat stress (40°C) compared to 40% for DP210 in the control chamber (30°C). At normal temperatures (30°C) cultivar DP393 had higher pollen germination percentages (29.6%) than after a week of high temperature (40°C) with germination percentage of 20%.  These results showed that heat stressed cotton had lower pollen germination percentages and also that pollen germination can be used as a screening method for heat tolerance.