ABSTRACT Visible and nonvisible quiescent
infections of immature and mature fruit are an integral component of the disease cycle of brown rot of sweet cherry in California. Detection of these
infections is critical for developing efficient and efficacious fungicide management programs. The previously published
DNA amplification primers mfs3 and NS5 for the identification of Monilinia fructicola were very specific in amplifying
DNA of M. fructicola only and not M. laxa. This primer set, however, only detected
DNA from some of the California isolates of M. fructicola. This genetic diversity was supported by random amplified polymorphic
DNA (RAPD) analysis. Using eight 10-mer primers, seven M. fructicola isolates from California were all identified as genetically distinct. Using the same primers, only one polymorphism was detected among seven isolates of M. laxa. The multiple genotypes identified within the small population sample of M. fructicola, but not of M. laxa, using RAPD analysis could be indicative of genetic recombination within M. fructicola but not within M. laxa. To detect early brown rot
infections in fruit, two primer sets that were developed from DNA sequences of either
ribosomal DNA (MF5/ITS4/ITS3) or a RAPD
fragment (X-09intF3/X-09R) specifically amplified
DNA from isolates of M. fructicola and Monilinia species, respectively. No amplification products were present when using
DNA from Botrytis cinerea or from other fungi commonly found on sweet cherry fruit. Primers X-09intF3 and X-09R were more sensitive and reliable for detecting small amounts of target
DNA either extracted from conidia or from laboratory-inoculated cherry fruit with early brown rot
infections that showed no visual symptoms or with visible quiescent
infections. Furthermore, these primers also were effective for detecting visible quiescent
infections in cherry fruit that were collected in the field.