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24
7 月
First Report of Postharvest Fruit Rot on Passion Fruit ( Passiflora edulis ) Caused by Lasiodiplodia theobromae in the U.S.A
| 作者： Weber, Shelby ; Lugo-Duque, Maria A. ; Gazis, Romina |
| 刊名： Plant disease |
| 期刊所屬國別： |
| 出版年： 202503 |
| 關鍵字： Agar ; Australia ; Bermuda ; California ; Chile ; China ; Conidia ; Education ; Florida ; Fungi ; Hawaii ; Industries ; Mycelium ; New Zealand ; Passion fruit ; Peptide Elongation Factors ; Phylogeny ; Taiwan ; Virulence (Microbiology) |
| 摘要： The commercial production of passion fruit is geographically limited (California, Florida, and Hawaii), but the development of cold-tolerant varieties could expand it beyond warm-climate states (Stafne et al. 2023). With only few countries allowed to export fresh fruits to the United States (i.e., Australia, Bermuda, Chile, and New Zealand; USDA-APHIS 2024) and its high retail value ($3 to $5 per fruit), domestic production of passion fruit has awakened the interest of producers. During 2019 to 2022, fruit samples showing rot symptoms were received at the Plant Diagnostic Clinic of the Tropical Research and Education Center (TREC) and diagnosed as affected by Lasiodiplodia theobromae based on symptomatology and on the morphology of the isolated fungus. In July 2023, similar symptoms were observed at TREC's experimental plot and at two local commercial farms (Homestead, Florida). Incidence in these locations was about 10 to 15% of the harvested fruits. Initial lesions were irregular in shape with a water-soaked greasy appearance. After 3 days of incubation, lesions enlarged into dark sunken blotches and were covered by globular pycnidia and greenish-gray hyphae. A cross section of the fruit revealed fungal colonization of the locular cavity and softening of the mesocarp. Infected tissue was plated (six pieces per fruit, total of six fruits), and isolates which morphology matched that described for L. theobromae (Alves et al. 2008) were recovered consistently. Conidia were initially hyaline, unicellular, apex rounded, thick-walled, and ellipsoid, becoming dark brown, bicellular with longitudinal striations at maturity, 25 ± 4 × 14 ± 2 μm (n = 50). Two isolates (TREC-L-1 and DAK-L-2A) were selected for identification through the sequencing of the partial regions of the internal transcribed spacer (ITS), translational elongation factor 1α (TEF1α), β-tubulin (Bt), and RNA polymerase II second largest subunit (RPB2) genes (Glass and Donaldson 1995). The ITS (PP806573 and PP806574), TEF1-α (PP812413 and PP812414), Bt (PP812415 and PP812416), and RPB2 (PQ807646 and PQ807647) sequences, of both isolates, had the highest similarity with those generated from the type material of L. theobromae (CBS 164.96), and the concatenated phylogenetic analysis confirmed the identification of the isolates. For the pathogenicity test, disinfested fruits that were either punctured with a sterile needle or nonwounded, were inoculated with an agar plug excised from the growing edge of a 5-day-old potato dextrose agar (PDA) colony of the TREC-L-1 isolate or with 100 μl of a 10³ conidia suspension collected from pycnidia produced in 4-week-old cultures of the same isolate. Negative controls consisted of wounded and nonwounded fruits inoculated with sterile PDA plugs or sprayed with water. Each treatment consisted of 10 fruits. The fruits were kept inside plastic boxes at 25°C, under darkness, and with >80% relative humidity. After 8 days, black sunken rot symptoms, pycnidia production, and external and internal mycelial growth were observed on the inoculated and wounded fruits, whereas no symptoms were observed on the nonwounded plug-inoculated and on the mock-inoculated fruits. Severity and fungal colonization were higher in wounded fruits. In the spore suspension inoculation experiment, all wounded fruits showed symptoms, while in the nonwounded fruits, 8/10 showed symptoms. The fungi recovered from the fruit lesions were confirmed as L. theobromae by morphological characteristics. This disease has been reported in Taiwan and China (Zhang et al. 2021). To our knowledge, this is the first formal report of this disease in the United States. As the industry grows, management strategies to control this disease need to be explored. |
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