Abstract
Even though survival rates for mangrove restoration in Vietnam have often been low, there is no information on fungal pathogens associated with mangrove decline in Vietnam. Therefore, this research was undertaken to assess the overall health of mangrove afforestation in Thanh Hoa Province and fungal pathogens associated with tree decline. From a survey of 4800 Sonneratia trees, the incidence of disorders was in the order of pink leaf spot > shoot dieback > black leaf spot for S. caseolaris and black leaf spot > shoot dieback > pink leaf spot for S. apetala. Approximately 12% of S. caseolaris trees had both pink leaf spot and shoot dieback, while only 2% of S. apetala trees had black leaf spot and shoot dieback. Stem and leaf samples were taken from symptomatic trees and fungi were cultured in vitro. From ITS4 and ITS5 analysis, four main fungal genera causing leaf spots and shoot dieback on the two Sonneratia species were identified. The most frequently isolated fungal taxa were Curvularia aff. tsudae (from black leaf spot),Neopestalotiopsis sp.1 (from stem dieback), Pestalotiopsis sp.1 (from pink leaf spot), and Pestalotiopsis sp.4a (from black leaf spot). The pathogenicity of the four isolates was assessed by under-bark inoculation of S. apetala and S. caseolaris seedlings in a nursery in Thai Binh Province. All isolates caused stem lesions, and Neopestalotiopsis sp.1 was the most pathogenic. Thus, investigation of fungal pathogens and their impact on mangrove health should be extended to other afforestation projects in the region, and options for disease management need to be developed for mangrove nurseries.
Highlights
Mangroves provide crucial environmental services including habitat for birds, fish, and invertebrates
The number of S. caseolaris trees with pink leaf spot accounted for 33.3% and 30.7%, while the values for S. apetala were 0.9% in both mixed and single stands
The incidence of shoot dieback and leaf spots observed in young afforestation stands of two Sonneratia species suggests that diseases may be contributing to the poor survival rates in some mangrove restoration projects, in central and north Vietnam where Sonneratia species have been widely planted
Summary
Mangroves provide crucial environmental services including habitat for birds, fish, and invertebrates. They are responsible for coastal protection from hurricanes, floods, sea-level rise, wave action, and erosion [1,2]. Abiotic factors, such as hurricanes, lightning strikes, salinity, and flooding, are reported to be affecting the health of mangroves [2,8]. Extreme weather, such as drought, hot water, hot air, and the temporary drop in sea level, have contributed to mangrove dieback [9]. Given the pantropical distribution of mangroves, the number of investigations into mangrove health remain limited [21]
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