GRASS AEROPOLLEN OF THE WESTERN UNITED-STATES GULF-COAST

Volumetric air sampling was performed at Corpus Christi, Tex., September 1987 to August 1989. Grass aeropollen during all of 1988 accounted for 15.3% of total pollen captured during two major peaks, one in May and another during September and October. The remaining grass pollen, about one-quarter of the total, was found throughout the year with low levels in the winter and mid-summer. This bimodal pollen release corresponds to the flowering of two major types of grasses occurring in the western Gulf Coast region, the cool temperate species which are predominantly spring flowering in response to long-day photoperiodicity, and the more common warm temperate and subtropical species flowering by and large in the fall as short-day plants. Supplementing the already rich grass flora and adding to the high proportion of total aeropollen was the long distance dispersal of grass pollen found perhaps in sufficiently high quantities to trigger allergic symptoms and to cause grass pollinosis out of season, at least in acutely sensitive individuals. This occurred in late March, well before the spring peak in May. Correlations existed between near-drought conditions and reduced pollen shed in 1988, and normal precipitation and much higher pollen shed during parts of 1987 and 1989, illustrating the importance of environmental factors such as moisture on annual pollen frequency and level of pollinosis which can be variable and annually unpredictable. What is predictable is the genetically controlled timing of pollen maturation and release which will be generally the same year by year. Even though grass species may have unique diurnal shedding of pollen, at localities like Corpus Christi, where frequency and diversity of species are great, sufficient overlaps of anthesis allow a constant rain of ambient grass pollen over a 24-hour period. Thus the potential for day-long exposure to grass allergens during the two annual peak periods of pollen emission and at other times is great.