Pruning of Manchurian Crabapple for Management of Speck Rot and Sphaeropsis Rot in Apple

Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens are fungal pathogens that cause postharvest speck rot and Sphaeropsis rot, respectively, in apple. Under quarantine regulations established by the Chinese government, export of apple from Washington State to China was banned between 2012 and 2014 because of detection of these pathogens in apple shipments. Previous studies established that pycnidia of P. washingtonensis and S. pyriputrescens survive in twig cankers on manchurian crabapple which serves as a dominant pollinizer in the Washington State apple industry. These pycnidia serve as a primary source of inoculum for infection of apple fruit in the orchard. The objective of this research was to conduct a study at multiple locations in Washington State to determine the efficacy of implementing manchurian crabapple pruning as a method to control speck rot and Sphaeropsis rot in storage. Four commercial orchards at geographically distant locations in Washington State were selected in 2014 and three in 2015. In 2014, two treatments included preharvest pruning of manchurian crabapple and postharvest application of pyrimethanil and untreated control. In 2015, preharvest pruning alone (PO) of manchurian crabapple was included in addition to the two treatments examined in 2014. Pruning conducted in concert with postharvest fungicide treatment significantly reduced the incidence of speck rot and Sphaeropsis rot in storage during the initial experimental field season. During year 2, both the PO and pruning with postharvest fungicide application controlled fruit rot with no significant difference between the two treatments. Findings from this study will be instrumental for the control of these postharvest diseases and maintenance of international market access for fruit from the Pacific Northwest.

Sources and Availability of Inoculum and Seasonal Survival of Sphaeropsis pyriputrescens in Apple Orchards

Sphaeropsis pyriputrescens is the cause of Sphaeropsis rot, a recently reported postharvest fruit rot disease of apple. Infection of apple fruit by the fungus is believed to occur in the orchard, and symptoms develop during storage or in the market. S. pyriputrescens also is the cause of a twig dieback and canker disease of apple and crabapple trees. To determine sources of pathogen inoculum in the orchard, twigs with dieback and canker symptoms, dead fruit spurs, dead bark, and fruit mummies on the trees were collected and examined for the presence of pycnidia of S. pyriputrescens. To monitor inoculum availability during the growing season from early May to early November, dead fruit spurs or twigs from Fuji trees, and twigs with dieback from crabapple trees (as a source of pollen for apple production) in a Fuji orchard as well as dead fruit spurs and dead bark from Red Delicious trees in a Red Delicious orchard were sampled periodically and examined for the presence and viability of pycnidia of S. pyriputrescens. To determine seasonal survival and production of pycnidia of the fungus on twigs, apple twigs were inoculated in early December, sampled periodically for up to 12 months after inoculation, examined for the presence of pycnidia, and subjected to isolation of the fungus from diseased tissues to determine its survival. Pycnidia of S. pyriputrescens were observed on diseased twigs, dead fruit spurs and bark, and mummified fruit on both apple and crabapple trees, suggesting that these tissues were the sources of inoculum for fruit infection in the orchard. With the combined observations from two orchards during three growing seasons, viable pycnidia of the fungus were present throughout the year and observed in 50 to 100% of the Fuji trees, >90% of crabapple trees, and 0 to 50% of the Red Delicious trees. S. pyriputrescens was recovered from diseased tissues of inoculated twigs at all sampling times up to 12 months after inoculation. The results suggest that S. pyriputrescens can survive as mycelium in diseased twigs in north-central Washington State and that availability of viable S. pyriputrescens pycnidia is unlikely a limiting factor for infection of apple fruit in the orchard leading to Sphaeropsis rot during storage.

First Report of Sphaeropsis Rot of Apple Caused by Sphaeropsis pyriputrescens in New York

In March 2012, decayed ‘Empire’ apple fruit (Malus × domestica Borkh.) were sampled from apples grown in Albion (Orleans County) in New York State and stored in bins for 6 months under controlled atmosphere at a commercial packinghouse. At the packinghouse following storage prior to be packed, the fruit were completely rotten, spongy to firm, and light brown without pycnidia. All fruit rots originated from either stem-end or calyx-end infections but no wound infections were observed. The incidence of fruit with these symptoms in the total decay was relatively low (0.1%). To isolate the causal agent, small fragments of fruit flesh from 12 decayed fruit were cut and placed on potato dextrose agar (PDA) acidified with 0.1% lactic acid. The plates were 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 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 on average. The fungus was identified as Sphaeropsis pyriputrescens Xiao & J.D. Rogers based on the morphology of the fungus (3). 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 in GenBank showed that the sequence had 99% homology to an S. pyriputrescens sequence (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 on 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 reisolating the fungus from the decayed fruit. Sphaeropsis rot is a recently reported postharvest fruit rot disease of apple and pear (1,3). The disease was first observed on ‘d'Anjou’ pears, and later more serious economic losses were observed in apples in Washington State (1). The disease has also since been reported in British Columbia, Canada (2). 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. References: (1) Y. K. Kim and C. L. Xiao. Plant Dis. 92:940, 2008. (2) P. L. Sholberg et al. Plant Dis. 93:843, 2009. (3) C. L. Xiao et al. Plant Dis. 88:223, 2004.

Preharvest Applications of Fungicides for Control of Sphaeropsis Rot in Stored Apples

Sphaeropsis rot caused by Sphaeropsis pyriputrescens is a recently reported postharvest fruit rot disease of apple in Washington State and causes significant economic losses. Infection of apple fruit by the fungus occurs in the orchard, but decay symptoms develop during storage or in the market. The objective of this study was to evaluate preharvest fungicide applications to control Sphaeropsis rot. Thirty isolates of the fungus collected from various sources were tested for sensitivity to the registered fungicides Pristine, Topsin M, and Ziram using an in vitro mycelial growth assay. In the orchard, ‘Golden Delicious' apple fruit were inoculated with the conidial suspension of the fungus at 2 or 5 weeks before harvest, sprayed with fungicides within 2 weeks before harvest, and harvested and stored at 0°C for disease evaluation. All three fungicides effectively inhibited mycelial growth of the fungus in the in vitro tests. On apple fruit in four seasons, Pristine applied 1 week and Ziram applied 2 weeks before harvest significantly reduced incidence of Sphaeropsis rot compared to the nontreated control by 43 to 80% and 42 to 83%, respectively. In 4 years of testing, the performance of Topsin M was less consistent than that of Pristine and Ziram. Accepted for publication 18 July 2013. Published 19 September 2013.

Control of Sphaeropsis Rot in Stored Apple Fruit Caused by Sphaeropsis pyriputrescens with Postharvest Fungicides

Sphaeropsis rot caused by Sphaeropsis pyriputrescens is a recently reported postharvest fruit rot disease of apple grown in Washington State. The objective of this study was to develop chemical-based mitigation measures for Sphaeropsis rot in stored apple fruit. To determine in vitro sensitivity of S. pyriputrescens to the three registered postharvest fungicides thiabendazole, fludioxonil, and pyrimethanil, 30 isolates of S. pyriputrescens obtained from various sources were tested for mycelial growth and conidial germination on fungicide-amended media. Golden Delicious apple fruit were inoculated with the pathogen in the orchard at 2 or 5 weeks before harvest. After harvest, fruit were either nontreated or dipped in thiabendazole, fludioxonil, or pyrimethanil solutions, stored at 0°C, and monitored for decay development for up to 9 months after harvest. The mean effective concentration of a fungicide that inhibits mycelial growth or spore germination by 50% relative to the nonamended control (EC50) values of thiabendazole, fludioxonil, and pyrimethanil on mycelial growth were 0.791, 0.0005, and 2.829 μg/ml, respectively. Fludioxonil and pyrimethanil also were effective in inhibiting conidial germination of the fungus with EC50 values of 0.02 μg/ml for fludioxonil and 5.626 μg/ml for pyrimethanil. All three postharvest fungicides applied at label rates immediately after harvest were equally effective in controlling Sphaeropsis rot in stored apple fruit, reducing disease incidence by 92 to 100% compared with the nontreated control. The results indicated that Sphaeropsis rot may be effectively controlled by the currently registered postharvest fungicides thiabendazole, fludioxonil, and pyrimethanil.

First Report of a New Postharvest Disease of Pear Fruit Caused by Sphaeropsis pyriputrescens in Canada

A survey of stored d'Anjou pears was conducted in British Columbia (BC), Canada in January 2006 to determine if Sphaeropsis rot was present in BC as had been reported previously for apples and pears in Washington (1,2). Sphaeropsis pyriputrescens Xiao & J.D. Rogers produces decay similar to Botrytis cinerea that originates from the stem or calyx end. Of 3,614 pears sampled, 55 (1.5%) had symptoms similar to those described for Sphaeropsis rot. Isolations were made from each infected pear onto acidified potato dextrose agar (APDA) dishes and incubated at 20°C for 5 to 7 days. Twenty-seven cultures resembling S. pyriputrescens were induced to produce pycnidia by exposing them to 12-h cycles of alternating light and dark periods at 20°C (1). Conidia extracted from pycnidia were then streaked onto PDA dishes and incubated at 20°C for 12 to 24 h from which single-spore cultures were made. These isolates developed a dense, white-to-cream mycelium that turned yellow over time; black pycnidia were formed on the culture dishes after 4 weeks. Conidia were brown, clavate to subglobose to irregular, and similar in size (16 × 10 μm) to previous descriptions (1). Identification of S. pyriputrescens was confirmed by using DNA sequence data from the β-tubulin and ribosomal genes. Sequences from S. pyriputrescens from Washington (1) were compared with those from BC, Canada. Isolates from Canada shared 99 to 100% sequence homology with those from Washington. Two of the BC isolates (DAOM 238917 and 238918) were deposited in the Canadian Culture Collection, Ottawa, ON and their corresponding sequences were placed in the GenBank database (NCBI, Bethesda, MD) with accession nos. EU156037 and EU156040 (ribosomal gene) and EU156048 and EU 156050 (β-tubulin gene), respectively. Five isolates from different locations in BC and two isolates from Washington were tested for pathogenicity on d'Anjou pears and four apple cultivars (Ambrosia, Fuji, Gala, and Granny Smith). Plugs (3 mm in diameter) removed from 2-week-old cultures were placed into two corresponding wounds on each of five fruit per cultivar. The fruit were then placed at 1 or 20°C for 22 or 7 days, respectively, when the diameters of the decay areas were recorded. All isolates were pathogenic on pears (P = <0.05). Decay lesion diameter was greater at 1°C, ranging from 46.8 to 57.9 mm, than at 20°C, ranging from 32.6 to 44.2 mm. All BC isolates were also pathogenic on the fruit of each apple cultivar (P = <0.05), although at 20°C, decay areas were smaller than on pears, and at 1°C, very little rot developed. Koch's postulates were completed by reisolating S. pyriputrescens from the inoculated pears and apples and identifying the isolates as above. Although S. pyriputrescens was only observed on pears in BC, research in Washington indicates that it is a more serious problem on apples (2). To our knowledge, this is the first documented report of the occurrence of S. pyriputrescens in Canada. References: (1) C. L. Xiao and J. D. Rogers. Plant Dis. 88:114, 2004. (2) C. L. Xiao et al. Plant Dis. 88:223, 2004.

Distribution and Incidence of Sphaeropsis Rot in Apple in Washington State

Sphaeropsis rot, caused by Sphaeropsis pyriputrescens, is a recently recognized postharvest disease of apple in Washington State. To determine the distribution and incidence of this disease as well as other postharvest diseases, decayed fruit were sampled during packing or pre-sizing operations in commercial fruit packinghouses from 26, 72, and 81 grower lots in 2003, 2004, and 2005, respectively. Fungi associated with decayed fruit were isolated and identified. The most common postharvest diseases of apple in the region were blue mold caused by Penicillium spp., primarily P. expansum, gray mold caused by Botrytis cinerea, and Sphaeropsis rot, accounting for 32, 28, and 17% of the decayed fruit, respectively. Percentages of these diseases in the total decayed fruit varied from lot to lot. Bull's eye rot caused by Neofabraea spp. was responsible for 13.4% of the total decay and was most prevalent on Golden Delicious. Other minor diseases included speck rot caused by Phacidiopycnis washingtonensis, Alternaria rot caused by Alternaria spp., Mucor rot caused by Mucor piriformis, and core rot caused by a group of fungi, primarily Alternaria spp. Sphaeropsis stem-end rot was more common than calyx-end rot on Golden Delicious, whereas Sphaeropsis calyx-end rot was more common than stem-end rot on Fuji. On Red Delicious, both stem-end rot and calyx-end rot were common. Sphaeropsis rot resulting from infections through the fruit peel was more commonly seen on Golden Delicious and Fuji than on Red Delicious. The percentage of gray mold was higher on nondrenched fruit than on fruit drenched with thiabendazole (TBZ), whereas blue mold was more prevalent on TBZ-drenched fruit. Our results indicate that Sphaeropsis rot is an important component of storage rots of apples in Washington State.

Postharvest Fruit Rots in Apples Caused by Botrytis cinerea, Phacidiopycnis washingtonensis, and Sphaeropsis pyriputrescens

Postharvest fruit rot diseases can be a limiting factor for storage of apples, and identifying target pathogens is the first necessary step for development and implementation of relevant measures for disease control. However, the symptoms of two new diseases, Sphaeropsis rot and speck rot, are similar to those of gray mold, and the two newly recognized diseases are often misdiagnosed as gray mold. The objective of this article is to provide a practical guide to diagnosis of these three diseases in apples. Accepted for publication 14 July 2008. Published 19 September 2008.

Postharvest Fruit Rots in d'Anjou Pears Caused by Botrytis cinerea, Potebniamyces pyri, and Sphaeropsis pyriputrescens

The ‘d'Anjou’ pear is the major winter pear variety in the US Pacific Northwest, and postharvest fruit rot diseases are a limiting factor for their long-term storage. The symptoms of the newly recognized diseases Phacidiopycnis rot and Sphaeropsis rot are similar to gray mold, and in fact, the new diseases are often misdiagnosed as gray mold. The objective of this article is to provide a practical guide to diagnosis of these three diseases. Accepted for publication 30 May 2006. Published 5 September 2006.