The 2009 Late Blight Pandemic in the Eastern United States - Causes and Results.

The tomato late blight pandemic of 2009 made late blight into a household term in much of the eastern United States. Many home gardeners and many organic producers lost most if not all of their tomato crop, and their experiences were reported in the mainstream press. Some CSAs (Community Supported Agriculture) could not provide tomatoes to their members. In response, many questions emerged: How did it happen? What was unusual about this event compared to previous late blight epidemics? What is the current situation in 2012 and what can be done? It's easiest to answer these questions, and to understand the recent epidemics of late blight, if one knows a bit of the history of the disease and the biology of the causal agent, Phytophthora infestans.

First Report of the Pear Trellis Rust Fungus, Gymnosporangium sabinae, on Pyrus calleryana ('Bradford' and 'Chanticleer') and P. communis in New York State.

Owing to their relative disease resistance and showy spring flowers, cultivars of Callery pear (Pyrus calleryana) are commonly planted ornamental and streetside trees in New York state and elsewhere in the U.S. Over the past 2 years, we collected a leaf rust on P. calleryana 'Bradford' or 'Chanticleer' (also known as 'Cleveland Select') from Hempstead (Nassau County), East Moriches and Riverhead (Suffolk Co.), Rochester (Monroe Co.), and Staten Island (Richmond Co.), NY. Leaf samples were collected in June and August 2010 and 2011; adaxial surface lesions resembled infection by fungi in the genus Gymnosporangium (Pucciniales). Lesions were yellow- to red-orange with irregular red to purple margins, 1 to 3.5 cm in any one dimension, and contained 20 to 45 black, subepidermal spermogonia. Hypertrophied plant tissue was evident on the abaxial surface below the spermagonia, but aecia were absent. Genomic DNA was extracted from rust-infected tissue on P. calleryana 'Bradford' (East Moriches, Hempstead, Rochester, and Staten Island) and 'Chanticleer' (Riverhead), and the D1/D2 domain of the 28s ribosomal DNA was PCR-amplified using primers 4 and 11 (3) and sequenced. Partial 28s rDNA sequences (GenBank Accession Nos. JN969962 to JN969966) were either identical or nearly so (99%) to that of the trellis rust fungus, G. sabinae (AF426209 and AY512845). G. sabinae produces aecia with conspicuous balanoid peridia from August to November or until leaf drop; both characteristics are unique to the genus (1). We therefore monitored rust-infected Callery pears in Riverhead as well as a common pear (P. communis) in Ithaca, NY, for the appearance of aecia in 2011. The telial state of G. sabinae on taxa in the genus Juniperus sect. Sabina (e.g., J. sabina and J. virginiana) was not observed within the vicinity of affected pears. In late September, aecia of G. sabinae with morphological features identical to those described by Kerns (1) and Yun et al. (4) were collected from a P. calleryana in Riverhead (Cornell Plant Pathology Herbarium; CUP-067943) and a P. communis in Ithaca (CUP-067943): aecia roestelioid, hypophyllous; periderium balanoid, apex intact and conic, cancellate along the sides; aeciospores brown, globoid to broadly ellipsoid, 22.5 to 28.2 × 25.1 to 32.4 µm, walls 3.3 to 4.7 µm thick. A native of Eurasia and North Africa, G. sabinae was first identified in North America on common pear in 1960 in British Columbia and California (2). Thereafter, the fungus was collected on Callery pear in northern Washington in 1988 and recently, in Michigan in 2009 (4). To our knowledge, this is the first report of G. sabinae on P. calleryana 'Bradford' and 'Chanticleer' as well as P. communis in New York and the new records represent a large (>800 km) eastward expansion of the distribution of the pathogen in the U.S. The geographic locations of affected trees described herein suggest that the trellis rust fungus is well-established across New York, and has spread undetected since its introduction. Given the widespread planting of Callery pear and occurrence of susceptible Juniperus spp. in urban landscapes of New York, G. sabinae has the potential to become a perennial problem where epidemiological conditions permit host alternation. References: (2) F. Kerns. A revised taxonomic account of Gymnosporangium, 1973. (4) A. McCain. Plant Dis. Rep. 45:151, 1961. (1) G. Van der Auwera et al. FEBS Lett. 338:133, 1994. (3) H. Yun et al. Plant Dis. 93:841, 2009.

First Report of Plum pox virus on Plum in New York State.

Plum pox, also known as Sharka, is one of the more significant viral diseases of stone fruit trees such as plum, peach, and apricot. It was first reported in Europe in the early 1900s and more recently in Chile in 1992, the United States (Pennsylvania) in 1999, Canada (Ontario and Nova Scotia) in 2000, China in 2001, and Argentina in 2004. Plum pox virus (PPV) was recently detected in two plum (Prunus domestica) trees in an orchard in Niagara County, NY, located within 5 miles from a Canadian plum pox eradication zone. Typical symptoms of chlorotic rings and spots were observed on some of the leaves from these trees. No symptoms were reported prior to the survey collection in July 2006. Survey samples were screened for the presence of PPV by ELISA using the Agdia PPV (Agdia, Elkhart, IN) specific kit that recognizes all strains but C of PPV. Approximately 5% of the survey samples were additionally analyzed by a validated immunocapture reverse transcription (IC-RT)-PCR TaqMan assay in a Cepheid SmartCycler (Cepheid, Sunnyvale, CA). Both replicates of the two New York plum trees produced a positive ELISA reaction in two consecutive tests. The ELISA-positive samples also produced positive results when subjected to the real-time IC-RT-PCR test. The PPV-positive trees were sampled again and an additional 53 samples were collected from trees in the surrounding area. Suspect trees again tested positive, while all the trees in the surrounding area tested negative. The methods used for confirmation included two ELISA tests (Durviz [Valencia, Spain] DAS indirect monoclonal ELISA and Agdia DAS polyclonal ELISA). Confirmatory real-time IC-RT-PCR was performed using universal 3' nontranslated region (NTR) primers (2,3) in a SYBR Green assay format and a coat protein (CP) primers/probe TaqMan assay (3,4). Further, the New York PPV isolate was identified as PPV D group using a subgroup specific conventional IC-RT-PCR (1). A 1.4-kb sequence fragment from the 3' end of the New York PPV was sequenced (GenBank Accession No. DG 883816). Comparison of the sequence with the database confirmed this isolate as subgroup D and exhibited a high degree of identity with other PPV D accessions (PPV D Teycheney [Accession No. X16415]; Penn4 [Accession No. DQ465243] Cnd 123-1 [Accession No. AY9553267]; and Cnd 3 [Accession No. AY953262]). To our knowledge, this is the first report of PPV in New York. References: (1) T. Candresse et al. Phytopathology. 88:198, 1998. (2) L. Levy et al. J. Virol. Methods. 49:295, 1994. (3) V. Mavrodieva and L. Levy. Acta Hortic. 657:141, 2004. (4) T. Wetzel et al. J.Virol. Methods 33:355, 1991.