Paper presented at the 52nd CFCS Annual Meeting, Guadeloupe, July 10-16, 2016 PESTS AND DISEASES AND THEIR PERCEPTION IN CROP AND ANIMAL PRODUCTION
DISEASES AND DISORDERS AFFECTING PITAYA IN SOUTH FLORIDA A.J. Palmateer1, G. Sanahuja1 and M. Samuel-Foo2. 1
Department Plant Pathology, IFAS, Tropical Research and Education Center, University of Florida 2IR-4 Southern Region, IFAS, Food and Environmental Toxicology Lab, University of Florida. E-mail: ajp@ufl.edu Keywords: Pitaya, Dragonfruit, Anthracnose, Stem and fruit canker, Stem and fruit rot. Abstract Vine, climbing cacti in the genera Hylocereus and Selenicereus produce fruit known variously as pitaya, pitahaya, dragonfruit or strawberry pear. These fruit are very popular in the specialty tropical fruit market and commercial production of Hylocereus undatus and H. polyrhizus has increased steadily over the past decade, but not without challenges from diseases and disorders. Anthracnose was one of the first major diseases mostly affecting the ribs of vines, but capable of rotting the entire vine column of pitaya. This disease is most important when plants are young and newly established, but has not been an issue on fruit. A newly reported and emerging disease is stem and fruit canker caused by Neoscytalidium dimidiatum. Stem and fruit canker has been reported in most production areas and disease incidence has reached levels as high as 70% on the fruit. Bipolaris cactivora is another fungal pathogen that causes stem and fruit rot and like N. dimidiatum mostly affects the fruit. Cankers and fruit rot have currently been the most economically important diseases, but other recent challenges such as a sooty mold affecting young flowers and developing fruit and the occurrence of Cactus Virus X may become more troublesome for pitaya growers in the future. Introduction Pitaya, commonly known as dragon fruit, is a columnar, climbing cactus species (genus Hylocereus) native to the tropical forest region of Mexico and Central America and widely grown in tropical and subtropical areas (Mizrahi et al., 1997). It is distributed through tropical and subtropical America, south Florida, Caribbean, Hawaii, Asia and Australia, Taiwan, Vietnam, Malaysia and Israel (Crane and Balerdi, 2005). In Florida, in 2006 less than 50 acres were planted but in 2010, production had grown six-fold and it was estimated around 320 acres (Evans et al., 2010). The objective of this report is to present all the diseases affecting pitaya in south Florida. Materials and methods All material used was collected from pitaya samples submitted to the Florida Extension Plant Diagnostic Clinic in Homestead, FL, USA. Symptomatic lesions from fungal diseases were surface-disinfected with 70% ethanol (20 s) followed by 10% bleach (1 min), and distilled sterile water prior to sectioning into 0.5 cm and plated at 25oC for 7 days on acidified potato dextrose agar (APDA) medium (Difco PDA; Becton, Dickson and Company, Sparks, MD). Compound and dissecting microscopes were used for morphological and cultural characteristics. To determine molecular characteristics DNA was extracted from cultures of fungi on APDA using the CTAB method described by Daire et al. (1997) and conventional PCR targeting internal transcribed spacer (ITS) regions using primers ITS 1 and ITS 4 and glyceraldehyde-3-phosphate dehydrogenase (GPD) using gpd1 and gpd2 were performed to accurately identify the isolates to species level. ITS and GPD primers used were described previously by White et al. (1990) and Berbee et al. (1999), respectively. Amplicons were sequenced by Eurofins, Louisville, KY, USA. Sequences obtained were submitted to GenBank database (http://www.ncbi.nlm.nih.gov/genbank/). For new diseases Koch’s postulates was completed as described (Palmateer et al., 2007, Tarnowski et al., 2010, Sanahuja et al., 2016). Virus suspect plants were submitted to Agdia Inc. (Elkhart, IN, USA) for virus detection and identification. Results and discussion Several new and newly emerging diseases have affected pitaya production over the past decade. In December 2004, reddish brown lesions with conspicuous chlorotic haloes developed concentrically on the edges of vine ribs. Lesion centers became white and coalesced to rot much of the vine column, and in severe cases, only the vascular column in the vine center was not diseased (Fig. 1A). Salmon-colored spores and waxy, subepidermal acervuli, typically with setae and simple, short, erect conidiophores, were observed in lesion centers. Colletotrichum gloeosporioides was isolated from all samples. Colonies produced abundant conidia that were hyaline, one celled, straight, cylindrical, and averaged 14.7 (12.5 to 17.5) μm × 5.0 (3.8 to 7.5) μm (Bailey and Jeger, 1992). Cultural and morphological characteristics of isolates matched those for C. gloeosporioides except for appressoria and hyphopodia (Bailey and Jeger, 1992, Du, 2005); pitaya isolates had a spherical rather than lobed hyphopodia reported for C. gloeosporioides and averaged 10.9 (8.5 to 12.7) × 9.1 (7.1 to 10.3) μm. ITS sequences for the pitaya isolates were nearly identical (98% homology) to those for C. gloeosporioides isolates occurring on Euphatorium thymifolia in Thailand (GenBank Accession No. AY266393). Koch’s postulates were completed for two isolates of C. gloeosporioides and inoculated plants developed the same symptoms as samples were submitted (Palmateer et al., 2007; Palmateer and Ploetz, 2006). This disease has been already reported on pitaya in Japan (Taba et al., 2006), Korea (Kim et al., 2000) and Brazil (Takahashi et al., 2008).
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