Two New Postharvest Fruit Rot Diseases in Apple Caused by Lambertella corni-maris and Ceuthospora cf. pinastri in Washington State

Michele Sanders Wiseman

During surveys for postharvest diseases of apples in 2003-05 and pears in 2001-02, two fruit rots were observed on stored apples and pears collected from packinghouses. Symptoms of the first disease (caused by a dark yellow fungus) were brown lesions and spongy decayed tissue originating from wound infections. Symptoms of the second disease (caused by a pycnidial fungus) were light brown/brown lesions originating from stem, calyx, or wound infections on the skin of the apple often coupled with light/dark concentric rings and firm to spongy flesh. Both fungi were subjected to thorough morphological examinations, multi-host pathogenicity tests, and multi-locus molecular phylogenetic analyses. The dark yellow fungus isolates had high identity with Lambertella corni-maris GenBank accessions, differing by 1-3 bps in the combined LSU, ITS, and SSU regions. Phylogenetic analysis of the dark yellow fungus confirmed the taxonomic placement of representative isolates into a well-supported Lambertella corni-maris v clade with other taxa forming congeneric clades. The pycnidial fungus had a maximum identity with Ceuthospora pinastri and Phacidium lacerum GenBank accessions, differing by 0-4 bps in the combined LSU, ITS, and SSU regions. The phylogenetic analysis for the pycnidial fungus confirmed the taxonomic placement of the fungus in the genus Ceuthospora with the highest match being C. pinastri and with other taxa forming congeneric clades. Morphological characteristics of the dark yellow and pycnidial fungi overlap with descriptions of L. corni-maris and C. pinastri, respectively. 'Fuji' apple fruit and 'D'Anjou' pear fruit that were wounded, inoculated with representative isolates, and incubated at 0°C yielded the same symptoms as seen in packinghouses, and the fungi were re-isolated from the diseased fruit. A representative isolate of the pycnidial fungus was used in field inoculation experiments and demonstrated the ability of the pathogen to cause latent stem, calyx, and wound infections. This is the first report of a fruit rot in apple caused by L. corni-maris in the USA and the first time Koch's postulates have been fulfilled for L. corni-maris as a storage pathogen. In addition, this is the first report of C. cf. pinastri causing a postharvest fruit rot of apple and pear.

Two New Postharvest Fruit Rot Diseases in Apple Caused by Lambertella corni-maris and Ceuthospora cf. pinastri in Washington State

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