Path analysis of growth differences between weed and nonweed populations of poorjoe (Diodia teres) in competition with soybean (Glycine max).
Growth of an agricultural weed population and a coastal nonweed population of poorjoe (D. teres) was compared in a competition experiment with soyabeans and when grown alone. Mean aboveground biomass production of the weed population was roughly twice that of the nonweed population, whether grown alone or with soyabeans. A path-coefficient model of growth was fitted to the data in order to compare the populations with respect to 5 independent measurements of weed growth: establishment rate, early and later growth rates, growth form and final growth rate. These measurements indicated plant growth over successive intervals of the growing season by statistically equating the size of all plants at the beginning of an interval of growth using analysis of covariance. In general, growth measurements were positively associated with aboveground biomass production. The weed population of poorjoe had a greater establishment rate and a greater early aboveground growth rate compared to the nonweed population; however, the final growth rates of the two populations were similar whether soyabean was present or absent. Genetic changes leading to earlier establishment and faster early growth, but not increasing tolerance of soyabean and intraspecific competition, may have occurred in the adaptation of poorjoe to an agricultural ecosystem.