Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/22/2013
Publication Date: 8/8/2013
Publication URL: http://dx.doi.org/10.1094/PDIS-03-13-0320-PDN
Citation: Kim, Y.K., Caiazzo, R., Sikdar, P., Xiao, C. 2013. First report of Sphaeropsis rot of apple caused by Sphaeropsis pyriputrescens in New York. Plant Disease. 97:9. Interpretive Summary: Sphaeropsis rot caused by the fungus S. pyriputrescens is a recently reported postharvest fruit rot disease of apple and pear. The disease was first observed on ‘d’Anjou’ pears, and later more serious economic losses were observed in apples in Washington State. The disease has also since been reported in British Columbia, Canada. In this study, we reported the occurrence of Sphaeropsis rot on apple in New York State. This is the first report of this disease in any region outside of the Pacific Northwest in North America.
Technical Abstract: In March 2012, decayed ‘Empire’ apple fruit (Malus × domestica Borkh.) were sampled from apples stored in bins for 6 months under controlled atmosphere at a commercial packinghouse in Orleans County in New York State. The fruit were completely rotten, spongy to firm, and light brown. The incidence of fruit with these symptoms in the total decay was relatively low (0.1%). To isolate the causal agent, small fragments of decayed fruit flesh were cut and placed on potato dextrose agar (PDA) acidified with 0.1% lactic acid. The plate was incubated at 20°C for 4 days and sub-cultured on PDA to obtain a pure culture. The colonies initially appeared with dense hyaline mycelium and later turned to light yellow to yellow, and black pycnidia formed after about 2 weeks of incubation under a 24-h fluorescent light at 20°C. Conidia were light brown to brown, clavate to subglobose to irregular, and 15×8 µm in average. The fungus was identified as Sphaeropsis pyriputrescens Xiao & J.D. Rogers based on the morphology of the fungus (1). The identity of a representative isolate was further confirmed by analysis of nucleotide sequences of the internal transcribed spacer (ITS) regions amplified using the primers ITS1/ITS4. A BLAST search showed that the sequence was 99% homology with that of S. pyriputrescens deposited at GenBank (Accession No. GQ374241). One representative isolate was tested for pathogenicity on apple fruit. Organic ‘Red Delicious’ apple fruit were surface-disinfected in 0.6% sodium hypochlorite solution for 5 min, rinsed twice with deionized water, and air-dried. Each fruit was wounded with a sterilized finish-nail head (3 mm in depth and 4 mm in diameter) and inoculated by placing a 4-mm-diameter plug from the leading edge of a 4-day-old PDA culture at the wound. Control fruit were treated with sterile PDA plugs. The inoculation site was covered with two layers of moist cheesecloth to avoid dehydration. There were four 10-fruit replicates for each treatment, and fruit were placed in plastic crispers and stored at 4°C for 4 weeks. The experiments were conducted twice. Sphaeropsis rot developed on all inoculated fruit, while no decays appeared on the control fruit. Koch’s postulates were fulfilled by re-isolating the fungus from the decayed fruit. Sphaeropsis rot is a recently reported postharvest fruit rot disease of apple and pear (1,2). The disease was first observed on ‘d’Anjou’ pears, and later more serious economic losses were observed in apples in Washington State (2). The disease has also since been reported in British Columbia, Canada (3). To the best of our knowledge, this is the first report of the occurrence of Sphaeropsis rot caused by S. pyriputrescens on apple in New York or in any region outside of the Pacific Northwest in North America.