Development of chloroplast DNA markers in Japanese Imperata cylindrica

Abstract

Imperata cylindrica (cogongrass) is one of the most invasive grass weeds found worldwide. In Japan, this grass grows as three climate types: cool temperate (CT), common (CM) and subtropical (ST). An early flowering (E) type has been also reported. Among them, the CM type is large and most invasive. Recent global warming may cause the extension of distribution of the CM type to northern parts of Japan and may allow hybrids to form between the CM and CT or E types. The hybrids sometimes show heterosis and this leads to new weed problems. Distinguishing between the hybrids and parents on a morphological basis is difficult. We investigated polymorphisms of eight cpDNAs to enable distinction between the ecotypes and the hybrids. Fourteen haplotypes were detected in 33 Japanese clones, based on variations in eight cpDNA regions. Based on three substitutions in the psbA-matK spacer, the ORF170 intron1, the trnL(UAA) intron-trnF(GAA) spacer and indels in the trnL(UAA) intron-trnF(GAA) spacer, the haplotypes were clustered into three phylogenetic groups: I, IIa and IIb, which corresponded with the CM and ST, E and CT types, respectively. The polymorphism in the cpDNA therefore enables us to distinguish among the ecotypes and is useful for prediction of the range expansion of the CM type.