Ecotypic differentiation in guineagrass ( Panicum maximum Jacq.)

Abstract

Six Brazilian populations of guineagrass ( Panicum maximum Jacq.) were studied in order to evaluate their quantitative and allozyme variation and to correlate their ecotypic differences with average monthly temperature and rainfall at the collection sites. All six populations came originally from old pastures in the northern and western regions of the State of Sao Paulo, Brazil. Highly significant between-population differences were found for a majority of the morphological and floral characters scored in greenhouse experiments as well as for two allozyme systems (esterase and alcohol dehydrogenase). A discriminant analysis performed on the quantitative characters yielded a cluster diagram showing marked population differences. Principal component analysis, based on the mean annual and monthly temperatures and total rainfall as independent variables, indicated that temperatures in September and January accounted for almost all the observed quantitative variability. The likely occurrence of distinct guineagrass ecotypes in Brazil as well as the roles of sexuality in the evolution of interpopulation variation and in adaptation to different environmental conditions are briefly discussed.