The Progressive Spread of the Vascular Wilt Like Pathogen of Calophyllum Detected in Ranomafana National Park, Madagascar.

Patricia Chapple Wright,Dina H Andriananoely,Alexandra Shea,Paul Rakotonirina,Jean Claude Razafimahaimodison,Beatriz Otero Jimenez,Baovola Ratalata

doi:10.3389/ffgc.2020.00091

Abstract

Pathogens are threatening crops worldwide, but little attention has been given to the threat to tree species in undisturbed rainforest. This communication reports the first case of a tree die off caused by a “wilt” in Madagascar. In 2016 while monitoring monthly tree phenology of Ranomafana National Park (RNP), the Centre ValBio research station observed that many Calophyllum adult trees had brown wilted leaves. There are three species of Calophyllum in this rainforest, C. paniculatum, C. drouhardii, and C. milvum, and all three have contracted this pathogen. Our goal was to document the spead of this suspected wilt in Calophyllum trees and determine if site, elevation and DBH had an influence on tree mortality. In 2019 we conducted an inventory of all Calophyllum trees in RNP and 42% of the observed trees were dead. The species with the highest mortality was C. paniculatum, with 53% of trees dead, followed by C. milvum with 18%, and C. drouhardii with only 2% of surveyed trees dead. Bark beetle traces were observed in all dead Calophyllum trees. Tree death caused by this suspected fungal pathogen has spread across a major river in the area and has been found at mid and high elevations. Our results show that C. paniculatum trees with a larger DBH have a higher mortality risk. Our report highlights the importance of fighting invasive pathogens that threaten protected ecosystems.

Highlights

Madagascar holds the highest number of endemic families and genera of plants in the world (Myers et al, 2000; Kremen et al, 2008), and based on regional (Ganzhorn et al, 2001) and global estimates (Beech et al, 2017) of tree biodiversity, we estimate that Madagascar holds over 5% of the world’s tree diversity (Dunham et al, 2018)
The dead trees within the forest landscape show the dispersion of the Calophyllum trees (Figure 2A)
1000 m elevation, there were few C. paniculatum trees, and they are replaced by other species in this genus, C. drouhardii and C. milvum (Figure 3)

Summary

Introduction

Madagascar holds the highest number of endemic families and genera of plants in the world (Myers et al, 2000; Kremen et al, 2008), and based on regional (Ganzhorn et al, 2001) and global estimates (Beech et al, 2017) of tree biodiversity, we estimate that Madagascar holds over 5% of the world’s tree diversity (Dunham et al, 2018). As with most other tropical plant species, little is known about the ecology and population status of Malagasy forest tree species. For this reason, the emergence of plant pathogens in Madagascar’s rainforest is of particular significance and can lead to undetected disease-induced population declines or extinctions (Anderson et al, 2004; Fisher et al, 2012). In the southeastern rainforest of Madagascar, up to 85% of tree species support the region’s endemic vertebrate frugivores, including birds, bats, and the region’s diverse endemic primates, the lemurs. Loss or declines in tree species population could lead to greater ecosystem effects

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