A comparison of twenty-six baits for isolating Calonectria species illustrates differences in their efficacy and relevance.

Calonectria is a genus of plant-pathogenic fungi that are soil-borne and widely distributed globally. Baiting with plant tissues is commonly used to isolate these Calonectria spp. from soils, but the choice of effective baits is typically not based on experimental evidence. In this study, samples of forest soil were collected from five provinces in southeastern, southern, northeastern, central, and southwestern China. A total of 1,040 soil samples were exposed to 26 different baits, resulting in 1,282 Calonectria isolates. Based on DNA sequence analyses of the tef1, tub2, cmdA, and his3 gene regions, the isolates were identified as eight Calonectria spp. The number of species, tef1-tub2 genotypes, and isolates obtained from each of the 26 baits was compared. The efficacies and diversities of the baits for detecting Calonectria were evaluated for the genus as a whole and for each of the eight Calonectria spp. At both the genus and species levels, leaf baits performed better than seed baits, and several baits had consistently higher efficacy. Germinating Medicago sativa (alfalfa) seed baits, commonly used in previous studies, were not the most efficient means of isolating Calonectria from the soil, and seeds of Lythrum salicaria provided comparable results. Eucalyptus urophylla leaves were most effective in isolating Calonectria pseudoreteaudii, which is an important Eucalyptus leaf blight pathogen. This suggests that baiting with leaves of the target host plant could produce optimum results when considering a particular pathogen. Based on the overall results, combined baiting with seeds of M. sativa or L. salicaria and leaves of a variety of plants, including, where possible, the target host plant, is recommended to obtain Calonectria from soil samples in China and other regions of the world.