| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 107 === Pitayas or dragon fruits are native cacti of South America. They are commercially planted worldwide due to their high productivity, rich nutrients, and long shelf-life. Alternaria fruit rot often occur during storage at 5℃. The disease become the major limiting factor of long-term storage and transportation. This study was focused on identification of the pathogens, determination of disease susceptibility during fruit development, and control methods. We collected 53 Alternaria isolates from pitaya stems and fruits. The 53 isolates were selected to construct a phylogenetic tree based on the sequence gapdh, and clustered in 3 clades, 11 isolates in clade A, 13 isolates in clade B, and 29 isolates in clade C. Among them, 28 isolates were selected for a phylogenetic analysis based on partial sequences of ITS, Alt a 1, gapdh, rpb2, tef1, and endoPG genes. The result displayed that 4 isolates of A clade were A. alternata, 4 isolates of B clade were A. gaisen, and 20 isolates of C clade were closely related A. burnsii and A. tomato. A. burnsii species complex (ABSC). Five isolates, A. alternata (HLF6102), A. gaisen (F211144), ABSC 1 (YPH103 and H16-4), and ABSC 3 (F218004), were selected to determinate temperature effects on mycelium growth and condial germination. All the selected isolates grew mycelium and germinated condia in 5-30℃. Under 5℃, A. alternata HLF6102 has the biggest colony diameter, and ABSC 1 (YPH103 and H16-4) has the highest condial germination rate under 5℃. Scanning electron micrographs of pitaya peel inoculated with YPH103 condia indicate that Alternaria could form appressoria-like structure and attach firmly on the peel surface, and hyphae could penetrate fruit through stomata and wounds. To investigate disease susceptibility of developing fruit, conidia of HLF6102 and YPH103 were inoculated on ‘Da-Hong’ and ‘Mi-Pao’ pitayas during fruit developing period in different trials. Both cultivars were highly susceptible at 7-21 days after full bloom in summer but no distinguishable highly susceptible stage in winter. To develop control methods of Alternaria fruit rot, chemical fungicide sensitivity assays were conducted by using isolate HLF6102 and YPH103. Iminoctadine triacetate, tebuconazole, and cyprodinil + fludioxonil effectively inhibiting Alternaria mycelial growth in vitro, and were applied on field trials. Field trials demonstrated that the application of cyprodinil + fludioxonil two or three times stably decreased the disease severity scale of Alternaria fruit rot on ‘Da-Hong’ and ‘Mi-Pao’ pitaya fruits compared to treatments of the other fungicides. Cinnamon, clove, lemon grass, and thyme essential oil could inhibit HLF6102 and YPH103 mycelial growth by directly contact and vapour. The combination of cinnamon and thyme essential oils show better efficiency than single essential oil. The 6.4% of potassium carbonate and sodium carbonate could inhibit HLF6102 and YPH103 mycelial growth, and 6.4% of potassium carbonate could inhibit HLF6102 conidial germination. Non-chemical control need additional recipe optimization and may be integrated with field control to produce high quality pitayas in the future.
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