A Postharvest Fruit Rot of Apple Caused by Lambertella corni-maris in Washington State

During surveys for postharvest diseases of apple conducted in Washington State, an unknown fruit rot was observed on stored apple fruit collected from commercial fruit packinghouses. This disease was present in 66 of the 179 grower lots sampled, accounting for an average 1 to 3% of the total decayed fruit sampled. The disease appeared to originate from infection of wounds on the fruit skin. Lesions were brown and decayed tissues were spongy. A Lambertella sp. was consistently isolated from the decayed fruit. Sequences of the fungus and those of Lambertella corni-maris in GenBank differed by 0 to 4 bp across the combined small ribosomal subunit + internal transcribed spacer + large ribosomal subunit regions with a maximum identity ranging from 99 to 100%. The fungus grew at 0 to 20°C and formed apothecia on artificial media after 8 to 24 weeks. On potato dextrose agar under a 12-h photoperiod, apothecial dimensions were variable, ranging from 1 to 6 mm in diameter with stipes of 1 to 4 by 0.5 mm. Asci were 76 to 125 by 3.5 to 5.5 μm, inoperculate, eight-spored, clavate, and narrowed at the base. Ascospores were aseptate, 7 to 10 by 2.5 to 4.5 μm, uniseriate to biseriate, and orange-brown at maturity in the ascus. Colony characteristics included little or no aerial mycelium, dark-yellow to gray-black mycelium, gray-black pseudosclerotia, and yellow pigmentation in the agar. Morphological characteristics of the fungus overlapped with the description of L. corni-maris. 'Fuji' apple fruit that were wounded, inoculated with representative isolates, and incubated at 0°C yielded the same symptoms as seen in packinghouses, and the fungus was reisolated from the diseased fruit. This is the first report of a fruit rot in stored apple caused by L. corni-maris in the United States. We propose Lambertella rot as the name of this disease.