First Report of Anthracnose Caused by Colletotrichum fioriniae and C. karstii in California Pistachio Orchards

In 2010 and 2016, pistachios (Pistacia vera) cvs. Kerman and Red Aleppo showing severe anthracnose symptoms (black, sunken, and circular lesions) in fruit, leaves, and rachises were observed in Tulare and Glenn counties, California. By harvest time in September, lesions on fruit and rachises became pink due to mature conidia oozing from the acervuli of the pathogen. In 2016, two isolates from Tulare Co. and five isolates from Glenn Co. were morphologically identified as C. acutatum and C. boninense complexes (†,†). Multilocus approach was used to confirm pathogen identity (†). For that, the ITS1-5.8S-ITS2 and beta-tubulin (BT) regions were amplified with primers ITS1/ITS4 and BT2-A/BT2-B and sequenced. BLAST and phylogenetic analysis of the amplified fragments showed that the two isolates from Tulare Co. were identified as C. karstii (accessions KY498481, TUB-2; and KY498482, ITS), while the five isolates from Glenn Co. were identified as C. fioriniae (KY498479, TUB-2; and KY498480, ITS). To test Koch’s postulates, 60 mature pistachio fruits (with intact hulls) of the cvs. Joley, Red Aleppo, Sirora, and Kerman wounded with a nail tip (2 × 2 mm), and 20 pistachio leaflets of the cvs. Red Aleppo, Golden Hills, and Kerman wounded with syringe needle, were inoculated with a drop of 10 µl of 5 × 10-4 conidia/ml suspension of C. fioriniae isolate (11K01). Pistachio fruits and leaflets were placed in moist chambers at 25 ± 1°C and incubated for 6 and 15 days, respectively. Fruit disease incidence accounted for 100, 97, 93, and 73% of Joley, Red Aleppo, Sirora, and Kerman fruits. Disease incidence in leaflets accounted for 90% on Kerman and Red Aleppo and 77.5% on Golden Hill. After symptom appearance, which were similar to symptoms observed in the field, small pieces (3 × 3 mm) of tissues from the lesion margins were cultured, and identified based on morphology as Colletotrichum species. The experiment was conducted twice. The anthracnose of pistachio has been reported to cause significant yield losses in years with a wet summer in Australia and China (†;†). In California, during the wet spring of 1998, anthracnose was first found in Tulare Co. but the Colletotrichum species was not identified at that time (†). In the meantime, Colletotrichum spp. have been isolated during the plating of dormant buds of pistachio to check for infection by Botryosphaeria species, causing panicle and shoot blight of pistachio. To our knowledge, this is the first report of C. fioriniae and C. karstii causing anthracnose in pistachio. The correct identification of the pathogens causing anthracnose of pistachio in California will facilitate epidemiological studies and the development of appropriate control strategies of this disease. © 2017, American Phytopathological Society. All rights reserved.