Asteraceae aeropollen of the western United States Gulf Coast

Volumetric air sampling was performed near Corpus Christi, Texas during 1988 and supplemented with data from 1987 and 1989. Frequencies of captured pollen grains of Parthenium hysterophorus, Ambrosia and allied genera, Helianthus, and other Asteraceae were examined. Asteraceous aerospora in 1988 accounted for 22.1% of all pollen found, of which 83.4% were pollen of Ambrosia, 12.4% of Parthenium, and the remainder (4.1%) representative of other genera. Capture of native Ambrosia species and P. hysterophorus peaked in September and October in 1987 and 1988, but Parthenium pollen was also found year round with a smaller secondary peak during May, 1988 and 1989. In the winter a different Ambrosia pollen was captured which compared with A. hispida found in the Yucatan Peninsula and southern Florida at a time when no ragweed was flowering in the vicinity of Corpus Christi. Such a pollen capture probably represents long distance dispersal (ca. 600 miles, 965 km) on strong easterly to southerly prevailing winds. Pollen capture occurred most frequently during daylight hours when percent relative humidity was lower and near midnight when inversions occur. Comparison of pollen capture with meteorologic data demonstrated that photoperiodic responses probably account for the initiation and termination of Ambrosia flowering, and to some extent that of Parthenium, and not sharply lowered temperatures or frost for ending pollen release. Previous plant surveys have shown that P. hysterophorus is more common in the Corpus Christi area than species of Ambrosia, or any other Asteraceae, even though ragweed pollen capture proved 6.9 times greater. This disparity is most likely due to limited long distance dispersal of Parthenium pollen, less pollen produced per anther, and a less developed mechanism of wind pollination (passive dispersal or amphiphilous). Since both Parthenium and Ambrosia are significant allergenic plants, correlations between airborne pollen of Parthenium and allergic potential suggest that a prolonged pollination season and perhaps increased allergenicity of unique Parthenium pollen proteins allow Parthenium to be a major allergen despite significantly less ambient pollen.