Comparative Morphological Development of Six Johnsongrass Ecotypes

Abstract

The comparative morphological development of six johnsongrass [Sorghum halepense(L.) Pers.] ecotypes was studied over a 10-week period. Three of the ecotypes were previously shown to be susceptible to dalapon (2,2-dichloropropionic acid) while others were resistant to the herbicide. The production of primary culms varied from 5.0 to 9.3 per plant system, and secondary culms ranged from 7 to 24 per plant system. Plant heights varied nearly two-fold, and the number of individual rhizomes produced by different ecotypes varied three-fold. Susceptible ecotypes from Georgia, Washington, and Illinois produced more rhizome nodes and higher dry and wet weights of culms and rhizomes than resistant ecotypes from Mississippi, Louisiana, and California. Ecotypes most resistant to dalapon had longer rhizome internodes and higher water content in culms and rhizomes than susceptible strains. Differences in anatomy and growth support the hypothesis of the existence of johnsongrass ecotypes, but the results were not consistent with the susceptibility of ecotypes to dalapon.