In Vitro Analysis of Cotton Pollen Germination

Abstract

Crops with economically valuable reproductive structures show the greatest negative discrepancy between average and record yields. To alleviate environmental stress–related yield reductions, a better understanding of the relative sensitivities of pollen development, dehiscence, pollen germination, pollen tube growth, fertilization, and subsequent boll development is needed. Progress in identifying the sensitivities of these developmental stress responses has been hampered in part by the lack of a rapid and reliable method of germinating cotton (Gossypium spp.) pollen in vitro. The present study describes the development of an in vitro cotton pollen germination system that provides improved pollen germination levels and pollen tube growth over existing methods. This procedure was used to evaluate the temperature sensitivity of pollen from greenhouse and field‐grown cotton. The medium comprises 10% (w/v) agarose (pH 7.6), 25% (w/v) sucrose, 0.52 mM KNO3, 3.06 mM MnSO4, 1.66 mM H3BO3, 0.42 mM MgS04·7H20, and 1.0 μM A3 gibberellic acid. The medium is overlayed with a layer of 1.5% agarose before use. Optimum pollen germination and rapid tube elongation occurred between 28 and 31°C under 80% relative humidity. Decreased pollen germination occurred at temperatures above 37°C, and decreased tube elongation occurred at temperatures above 32°C. Evaluation of pollen, taken at 1400 h from field‐grown cotton plants, showed that pollen from flowers exposed to direct sunlight had reduced viability compared with pollen from flowers inside the canopy. This could be attributed to the fact that flowers from field‐grown irrigated cotton plants exposed to full sunlight experienced internal temperatures as high as 39°C, well above the 28 to 31°C optimum for pollen germination.