Latent entry and spread of <i> <scp>C</scp> olletotrichum acutatum </i> (species complex) in strawberry fields

Abstract

Anthracnose, caused by C olletotrichum acutatum (species complex), has become a troublesome problem in strawberry production worldwide. This paper reports (i) an optimized sampling method combined with a real‐time PCR technique to detect the latent presence of C . acutatum in cold‐stored strawberry plants used as planting material in several European countries, and (ii) a study of the spread of C . acutatum following a point inoculation under field conditions. Screening of different parts of planting material suggested that C . acutatum is most likely to be present on runners and old petioles. In addition, in seven out of nine batches of planting material from different nurseries, latent infection by C . acutatum was detected in at least one of five replicate samples. Field experiments in 2009 and 2010 showed extensive latent within‐field spread of the pathogen on strawberry leaves, with a within‐row dispersal distance up to at least 1·75 m in 1 week. A straw ground cover between the rows did not decrease C . acutatum spread, probably because introduced (and/or subsequent) inoculum was confined to the plant bed (within the row) and was not present between the beds. Moreover, the number of C . acutatum spores on the symptomless leaves, as estimated using a real‐time PCR method, was significantly ( P &lt; 0·05) correlated with the incidence of fruit rot at harvest and post‐harvest ( r = 0·56–0·66). These results illustrate the importance of detecting latent infections in planting material and strawberry leaves in the field.