The occurrence of gummosis on invasive Acacia decurrens after
Mount Merapi eruption in Yogyakarta, Indonesia
Sri Rahayu1*, Rahman Gilang
Pratama1, Muhammad Ali Imron1,
Januar Mahmud1, Widyanto Dwi
Nugroho1
1Fakultas Kehutanan, Universitas Gadjah Mada,
Jl. Agro No. 1 Bulaksumur Yogyakarta 55281, Indonesia ,* Corresponding author’s email: tatarahayu@yahoo.com
Introduction
Large, but infrequent, volcanic eruptions, such as the 2010 eruption of
Mount (Gunung ) Merapi in Yogyakarta, Indonesia, caused
significant changes in ecosystem composition and vegetation structure in
surrounding areas of the volcano (Anon 2012, unpublished data). Similar
ecological impacts were observed in Washington, USA when Mount St.
Helens erupted in 1980. The eruption of Mount St. Helens produced a
complex of disturbance agents, such as pyroclastic flow, debris
avalanche, mud flow, ash deposits, blow down, and several other agents
which interacted at specific sites exacerbating the degree of damage and
delay in recovery (Adams et al., 1980; Dale et al., 1998; Franklin et
al., 1985; del Moral 1993). Moreover, combinations of post-disturbance
site characteristics influenced the composition of the biota. The
pyroclastic flow from Mount Merapi apparently destroyed all flora and
fauna that it contacted in the surrounding area of the volcano.
In a period of 2 yrs following the eruption, Acacia decurrens(Wendl.) Willd. (green wattle) was the first tree species to appear,
establish, and dominate large areas impacted by the pyroclastic flow.
Data collected by Merapi Volcano National Park (MVNP) in 2012 showed
that the density of A. decurrens averaged 16167 seedlings
ha-1 and 11814 saplings ha-1 (Anon
2012, unpublished data). Native to Australia, A. decurrens is
introduced and grown in plantations in several countries in the tropics
and subtropics. It is an important invasive species especially in Africa
and Oceania where it spreads rapidly via seed and root suckers (CABI,
2018). The tree can invade grass lands, roadsides, savannah and riverine
habitats developing dense thickets impacting on native biodiversity and
obstructing water flow (Boucher 1978). The rapid establishment ofA. decurrens in the MVNP area poses a serious threat since it
will affect the recuperation of ecosystems and regeneration of native
flora impacted by the volcanic eruption.
A preliminary survey conducted in 2014 by MVNP on the health of A.
decurrens stands showed that the ambrosia beetle, bagworm,Ceratocystis sp., Uromycladium falcatarium , andGanoderma sp. occur in the stands. Rahayu et al. (2015) have
reported that over 50% of A. decurrens stands in the region
showed gummosis and symptoms of stem canker associated withCeratocystis sp. However, these symptoms were not visible on
trees within the area around Mount Merapi before eruption. Gummosis ofA. decurrens and Acacia mearnisii caused byCeratocystis fimbriata Ellis and Halsted was recorded from Brazil
and South Africa, respectively by
Ribeiro
et al. (1988) and Morris et al. (1993). The symptoms described onA. mearnsii were similar to those observed on A. decurrensin MVNP. The genus Certocystis includes some well-known pathogens
of trees responsible for a wide range of diseases including stem
cankers, vascular wilts and root diseases (Kile, 1993) For e.g.,C. fimbriata is known to cause diseases of several vegetable
crops, fruit trees and forest trees (CABI, 2014). Another species ofCeratocystis, C. albifundus occur on Acacia
mearnsii plantations in southern and eastern Africa causing gum
exudation, wood-discoloration, stem cankers, rapid wilting and tree
death (Morris et al., 1993; Roux et al. 1999). It is also reported that
wounds on trees are a predisposing factor for C . fimbriatasensu lato (s.l .) to cause infection. These wounds can result
from wind and hail damage, growth cracks, insect and animal damage as
well as activities such as grafting and pruning.
Recent studies have shown that artificially induced wounds on trees are
infected by Ceratocystis spp. (Barnes et al, 2003; Roux et al,
2004; Rodas et al, 2008). Success of infection is dependent on a number
of physical and environmental factors. For e.g., C. fimbriataspecies complex are able to infect their hosts when viable fungal
propagules are deposited onto bark wounds (DeVay et al., 1968). OtherCeratocystis spp., such as C. fagacearum (Bretz) Hunt, can
only infect if viable fungal propagules are deposited onto freshly
exposed wood of the host (Kuntz and Drake 1957). Temporal factors also
affect the success of infection by Ceratocystis spp. For example,
Kuntz and Drake (1957) showed that C. fagacearum could not cause
infection when wounds were older than 24 h. Climatic factors such as
temperature and relative humidity have also been shown to influence
germination of spores and infection by Ceratocystis spp. (Cole
and Fergus 1956). So, it needs to be examined whether tree wounds caused
by insects was one of the reasons for the occurrence of gummosis onA. decurrens in the Mount Merapi region and whether the spread of
the disease was assisted by the dominance (monoculture) of A.
decurrens trees in the MVNP area.
Against this background, the present study aims to i) identify the
causal organism associated with the disease, ii) analyze the disease
symptoms and predisposing factors for infection, iii) understand the
spatio-temporal distribution of gummosis in the tree population and iv)
examine the anatomy of the infected wood. This information would help
developing methods to manage A.decurrens and control the spread
of the gummosis pathogen to native plants.
Materials and Methods