Differential Interference Between Soybean (Glycine max) Varieties and Common Cocklebur (Xanthium strumarium):a Path Analysis

Abstract

Soybean varieties ‘Ripley’ (semidwarf determinate group IV) and ‘Douglas' (indeterminate group IV) were compared in an interference experiment with common cocklebur. A path analysis model was used to independently estimate interference effects of soybean density on common cocklebur growth and stem diameter, and interference responses of soybean density and seed production to common cocklebur size. Path analysis identified an early period of interference between soybean and common cocklebur, from 40 to 62 d after planting, and a late period, from 63 to 145 d after planting. Late interference measures were independent of early measures, since effects of early interference were statistically removed from estimates of late interference. The semidwarf determinate variety Ripley had early interference effects on common cocklebur 5.3 and 9.5 times greater than those of Douglas in 1987 and 1988, respectively. The Douglas variety had a stronger late interference effect on common cocklebur than Ripley. Soybean varieties were similar in response to common cocklebur interference. Path analysis of crop-weed interference may be useful in breeding crop varieties that suppress weed growth and thus require fewer weed control inputs.