Inoculum dynamics and infection of citrus fruit by Phyllosticta citricarpa

• Published in: Phytopathology Vol. 110; no. 10; pp. 1680 - 1692
• Main Authors: Tran, Nga Thi, Miles, Andrew, Dietzgen, Ralf Georg, Shuey, Tim Andrew, Mudge, Stephen R, Papacek, Dan, Chandra, Kerri A, Drenth, Andre
• Format: Journal Article
• Language: English
• Published: United States 01.10.2020
• Subjects: Ecology and epidemiology
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO-02-20-0047-R

Citrus black spot caused by is characterized by fruit blemishes and premature fruit drop, resulting in significant economic losses in summer rainfall areas. The pathogen forms both conidia and ascospores during its life cycle. However, the occurrence of these spores and their contributions to infection of fruit in field conditions are not well-understood. Our research using direct leaf litter monitoring and volumetric spore trapping in Queensland orchards revealed that pseudothecia and ascospores in leaf litter, as well as trapped ascospores had low abundance, while pycnidia and conidia were highly abundant. Both and endophytic spp. were identified, with being dominant. In replicated field trials we determined that infection of 'Imperial' mandarin fruit by occurred from fruit set until week 20 of fruit development, with the key infection events taking place between weeks 4 and 16 in Queensland subtropical conditions. These results demonstrate that protecting fruit during weeks 4 to 16 significantly reduced infection. We found no significant correlation between the disease incidence in fruit and conidial abundance in leaf litter, or ascospore abundance measured by volumetric spore trapping. It is therefore suggested that inoculum sources in the tree canopy other than those detected by spore trapping and direct leaf litter monitoring may play a major role in the epidemiology of citrus black spot. The improved knowledge on epidemiology of and an understanding of propagules causing infection may aid in development of more effective disease management strategies.