First report of brown rot caused by Monilia mumecola on Chinese plum (Prunus salicina) in Fujian, China.

Abstract

Brown rot caused by Monilinia spp. (anamorph Monilia) is a common disease in stone fruits worldwide, but the species in different hosts or regions may vary. Monilia mumecola is a recently identified species, only reported in some regions. Although the pathogen has been found on plum in Yunnan, Hubei, and Zhejiang provinces, and Chongqing municipality in China (Yin et al. 2015), it has not been reported in southeast coast of China. In May 2022, brown rot with grey spores on fruit was observed in a plum orchard with 15% disease incidence in Sanming City, Fujian Province, located in southeast coast of China. Four single-spored isolates were obtained from germinating conidia on the water agar for further investigation. The colonies on potato dextrose agar (PDA) were initially white, gradually turned gray to brown, with lobbed margins and rare sporulation. Average mycelial growth rate ranged from 0.74 to 1.08 cm/day at 25 oC. Conidia were lemon-shaped or subglobose, hyaline, with an average size of 17.64 to 19.35×11.14 to 14.44 μm (n=30). Each isolate produced one to three or four germ tubes. Such characteristics are similar to M. mumecola (Yin et al. 2015). To confirm the identity of the isolates, genomic DNA was extracted and species-specific primers of Hu et al. (2011) were used to amplify the 712 bp sequence. In addition, the ITS region, partial genes of glyceraldehyde-3- phosphate dehydrogenase (GAPDH) and beta-tubulin (TUB2) were also amplified using primers sets ITS1/ITS4 (Glass and Donaldson 1995), Mon-G3pdhF/Mon-G3pdhR and Mon-TubF1/ Mon-TubR1, respectively (Hu et al. 2011). Sequences obtained for those three regions were 478, 762 and 1527 bp, respectively. Each region of all four isolates was identical, so one sequence for each region was submitted to GenBank with accession numbers OQ207672, OQ225251 and OQ225252, respectively, which had 100% identity with M. mumecola HQ908786 (ITS), HQ908784 (GAPDH), and HQ908775 (TUB2) using BLAST analysis in NCBI database, respectively. Pathogenicity was conducted with mycelium plugs from the edge of 7-day-old colony on three mature 'Angeleno' plums fruit (Prunus salicina) creating nine inoculations with three wounds per fruit, and each wound was 5 mm in diameter and 2 mm in depth. The same amount fruit and wounds inoculated with PDA plugs without fungi were used as a control. Brown rot symptoms were observed on all inoculated plums 4 days post-inoculation under room temperature with 100% humidity, whereas control plums remained symptomless. Fungal colonies re-isolated from the lesions showed the same morphological features as the original isolate , thus fulfilling Koch's postulates. To our knowledge, this is the first report of M. mumecola on plum in Fujian Province of China. The findings in this studies have important management implications for local plum growers because more than one Monilia species have been reported, where only M. fructicola was present in this region.