Differentiation of Cotton Pollen

            Cotton, Gossypium (Malvaceae) has been spun, woven, and dyed since prehistoric times.  There are four cotton species that are economically important; Gossypium arboreum (tree cotton), G. barbadense (American pima cotton), G. herbaceum (levant cotton) and G. hirsutum (American upland cotton).  Some research had been conducted examining the morphology of Malvaceae pollen grains; however, no research has been conducted that differentiates the four economically important cotton species by their pollen grains.  The objective of this research was to determine if the pollen grains of these four species could be differentiated.  Flowers of the four taxa were collected from USDA-ARS greenhouses and fields in College Station, TX.  The stamens were removed, placed into packets, and dried for at least three days.  Both dry and acetolyzed pollen grains were examined with light and scanning electron microscopy.  The length and width of 300 pollen grains and the length and width of 100 processes of each taxon were measured.  There was no size difference between the acetolyzed and the unacetolyzed grains.  Gossypium barbadense and G. hirsutum had the largest grains (105.48 and 94.59 um, respectively), while G. herbaceum and G. arboreum had the smallest (82.25 and 84.61um, respectively). Gossypium hirsutum and G. barbadense had the widest processes (12 and 11um, respectively), and G. arboreum and G. herbaceum had the narrowest (9.21 and 9.27um).  Using micro-morphometrics of the pollen grains, it is possible to differentiate different these four taxa.  Differentiation of these taxa can be useful in the determination of the origin of boll weevils that feed on cotton.  However, additional research is needed to examine the pollen grains of the cotton varieties and cultivars.