Viability and germination of the pollen of sorghum [Sorghum bicolor (L.) Moench]

Previous studies have demonstrated that pollen of sorghum [Sorghum bicolor (L.) Moench] loses capacity to both germinate in vitro and to set seed in vivo soon after being shed. The current study evaluates the capacity for dehydrated pollen to effect in vitro germination, reduce tetrazolium chloride, and set seed on cytoplasmic male sterile plants. Morphological changes during pollen germination were examined by scanning electron microscopy (SEM). Close to 70 % of the pollen germinated in 5 min, or less, when collected at 80 % relative humidity (RH) and stored in sealed glass vials. Pollen tubes elongated autotropically with atmospheric humidity apparently being a controlling factor in the process. Pollen dehydrated at 50% RH and 25 degrees C for 15-30 min neither germinated in vitro, reduced tetrazolium chloride, nor set seed on male sterile plants. Rehydrating the pollen did not restore the capacity for germination. SEM micrographs demonstrated that elongating pollen tubes encircled the pollen grain and were contiguous to the surface. A fibrillar-like material existed on the exine of separated pollen grains at the point where the grains had been previously attached.