Effects of seed size and a fungal pathogen, Colletotrichum coccodes, on population dynamics of velvetleaf (Abutilon theophrasti Medic.)

Experiments were conducted in controlled and field conditions to determine the effect of seed size, a fungal pathogen (Colletotrichum coccodes), and soybean interspecific competition on the population dynamics of Abutilon theophrasti (velvetleaf). Seed size differences among ten individual A. theophrasti plants significantly (P < 0.001) affected seed germination and dormancy. Higher seed viability (98%) was observed among seeds having a weight above 6.0 mg. The response of A. theophrasti plants that originated from two extreme seed size groups (small <7mg and large >12mg) to the pathogen, C. coccodes, did not change over generations, and the most vigorous plants produced heavier seeds regardless of the initial seed size or infection with C. coccodes. Under field conditions, the application of C. coccodes and the herbicide, bentazon, did not affect the vegetative and reproductive biomass of A. theophrasti plants when grown in monospecific stands. However, a split application of C. coccodes and bentazon significantly reduced the aboveground biomass and reproductive output of A. theophrasti plants when grown in competition with soybean. The frequency distributions of A. theophrasti plant height, aboveground biomass, and stem diameter were positively skewed (L-shaped) when competing with soybean. However, A. theophrasti plant height and stem diameters were negatively skewed (J-shaped) and the aboveground biomass was positively skewed (L-shaped) in monospecific stands. The allometric relationships of A. theophrasti aboveground biomass and stem diameter in comparison with plant height were curvilinear when grown alone and when in the presence of soybean. However, aboveground biomass and stem diameter showed a simple linear relationship on a log-log scale in both monospecific stands and in competition with soybean.