High genetic diversity and limited regional population differentiation in populations of Calonectria pseudoreteaudii from Eucalyptus plantations.

Calonectria pseudoreteaudii causes a serious and widespread disease known as Calonectria leaf blight in Eucalyptus plantations of southern China. Little is known regarding the population biology or reproductive biology of this pathogen in the affected areas. The aims of this study were to investigate the genetic diversity, population structure and the reproductive mode of C. pseudoreteaudii from affected Eucalyptus plantations of southern China. Ten polymorphic SSR markers were developed for the species, and were used to genotype 311 isolates from eight populations. The mating types of all isolates were identified using the MAT gene primers. The results revealed a high level of genetic diversity of the pathogen in all investigated populations. Of the 90 multilocus genotypes detected, ten were shared between at least two populations. With the exception of one population from HuiZhou, GuangDong (7HZ), the most dominant genotype was shared in seven remaining populations. DAPC and population differentiation analyses showed that the 7HZ population was well differentiated from the others and that there was no significant differentiation between the remaining populations. AMOVA suggested that most molecular variation was within populations (86%). Index of association analysis was consistent with a predominantly asexual life cycle for C. pseudoreteaudii in the studied regions. Although both mating types were detected in seven of the eight populations, the MAT1-1/MAT1-2 ratios in these populations deviated significantly from the 1:1 ratio expected in a randomly mating population.