The oil palm tree (Elaeis guineensis Jacq.) is an important estate crop
in southern Thailand. Oil palm production areas in Thailand total approximately
625,600 ha and of these about 528,400 ha are in the south (Chavananand,
2011). Like most other crops, oil palm is infected by several pathogens.
The main diseases are caused by fungi, inhibiting the growth and reducing the
yield (Turner, 1981; Tengoua and
Bakoume, 2005; Flood, 2006). Several diseases of
oil palm trees have been reported from many oil palm producing countries.
The basal stem rot or Ganoderma butt rot disease, caused by Ganoderma
boninense, is the most severe oil palm disease in Indonesia and Malaysia
(Susanto et al., 2005). It has also destroyed
oil palms in Africa, Papua New Guinea (Turner, 1981),
Colombia (Nieto, 1995) and Thailand.
Seed rot and brown germ caused by S. commune have been severe in Malaysia
(Dikin et al., 2003). The causal agent S.
commune causes up to 65% loss of germination rate to oil palm. Dikin
et al. (2003) reported on a number of fungi found during plant quarantine
investigations in seeds from Costa Rica and Papua New Guinea: Aspergillus
spp., Colletotrichum gloeosporioides, Fusarium moniliforme, F.
solani, Penicillium spp. (Zubir et al.,
Some nutrient deficiencies can also severely damage the yield, such as nitrogen,
phosphorus, potassium, boron and magnesium deficiency (Von
Uexkull and Fairhurst, 1999). Nitrogen deficiency is the most significant
nutritional problem in young oil palm. Boron and copper deficiencies of oil
palm have been severe in Sumatra (Purba and Turner, 1973;
Turner (1981) documented over sixty diseases and disorders
of oil palm, from around the world. Only few studies of oil palm diseases in
Thailand exist at present, the main one being a survey from 1976-1980 by Limsriwilai
et al. (1984). They categorized the diseases by effects in the different
growth stages: Germination (with brown germ diseases); nursery stage and field
In nursery stage the diseases were Curvularia seedling blight, Helminthosporium
leaf spot, anthracnose, chlorotic streak and nursery spear rot. In field planting
stage they were seedling blight, algal disease, crown disease, frond rot, bud
rot, little leaf disease, Marasmius bunch rot, fruit rot, Ganoderma trunk
rot, charcoal base rot and sudden wilt.
The objective of this study was to assess the geographical distribution of
oil palm diseases in the southern regions of Thailand and to provide updated
information on the most important diseases that affect oil palm in this region.
MATERIALS AND METHODS
Field inspection and collection of samples: During the period of June
2010 to June 2012, on-site surveys were conducted to diagnose oil palm diseases
and disorders in eleven provinces of southern Thailand. At first the location
of observed symptom was noted. The typical symptoms of disease or signs of pathogen
were observed to determine that the disease was caused by a pathogen or an environmental
factor. Both un-germinated and germinating seeds that showed brown germ symptoms
were collected from the oil palm seed production companies in Nakon Sri Thammarat
and Songkhla provinces. Oil palm trees were surveyed in several nurseries and
private oil palm plantations, in eleven provinces of Southern Thailand. Seeds
and affected tissue samples of infected trees were collected, kept in plastic
bags and transferred to laboratory. In the laboratory, the causal agents of
diseases were I solated and identified. Disease diagnosis used diagnostic keys
for identifying nutrient deficiencies, diseases and disorders (Fairhurst
et al., 2005; Turner, 1981; Von
Uexkull and Fairhurst, 1999; FLREC, 2012).
Data analysis: The disease incidence for each farm was determined as
percentage of infection, by counting the number of visibly infected trees and
expressing it as fraction of all trees, following Farrag
and Abo-Elyousr (2011).
The main diseases noticed in seeds during germinating process were brown germ
and seed rot. Losses were variable, in some cases up to 40%. Curvularia
leaf spot had the highest incidence in the nursery stage. The basal stem rot
was found to be the most destructive disease at the fruiting stage, causing
decline and death of oil palm trees. Summaries of the diseases found in oil
palms, from seed, nursery and field stages, are shown in Fig.
1 and Table 1. The incidence rates of diseases and disorders
are located in Table 2.
||Survey sites of oil palm nurseries and private plantations
in southern Thailand
|| List the pathogens isolated from symptomatic plant parts
|No. count of isolates with the pathogen is given in parentheses
Diseases associated with oil palm in south Thailand Seed diseases
Brown germ: The symptoms become apparent as the seed germinates.
Typically, light brown spots develop on the elongating radical as it emerges
through the micropyle and these lesions merge to produce a solid discoloration
of its tip. Seeds affected by the brown germ normally have a stubby radical
with brown lesions mostly midway on the plumule and radical (Fig.
2a). Seed rot: Several fungi can kill an embryo and its surrounding kernel
tissues before the seed germinates, causing seed rot disease. This disease becomes
evident when the seeds are cracked: It cannot be detected without breaking the
seeds open (Fig. 2b).
Nursery diseases and disorders
Anthracnose: The disease caused by this disease first appears as
small brown spots between the veins and these spots will expand to elongated
streaks. Typically, these are brown or black in color and are bordered by a
pale yellow halo. Acervuli are produced on the dead tissues and when mature
they exude a pink spore mass (Fig. 3a).
||Severity and incidence of diseases in different growth stages
of oil palm
|| Seed diseases of oil palm, (a) Brown germ and (b) Seed rot
||Nursery diseases and disorders of oil palm, (a) Anthracnose,
(b) Cercospora leaf spot, (c) Curvularia leaf spot, (d) Pestalotiopsis
leaf blight, (e-h) Genetically abnormal seedlings, (e) Bifurcate, (f) Fertilizer
burn at leaf tips, (g) Narrow leaf (grass leaf) and (h) White stripe
Cercospora leaf spot: Cercospora leaf spot of the oil palm is
caused by Cercospora elaeidis. The disease on the leaves initially presents
small yellow spots with a brown point in the middle and purple in the margins.
The spots spread and merge. At a later stage of the disease, the leaves become
brownish-gray and brittle (Fig. 3b).
Curvularia leaf blight: Leaf blight caused by Curvularia oryzae
is the most important disease of oil palm during nursery stage. The first symptom
is spots on the inner whirl and young leaves. The fungal spots grow with yellowing
around them. During moist weather, these lesions expand rapidly into large,
dark brown or black lesions (Fig. 3c). Damage to foliage in
advanced stages includes necrotic lesions that kill leaflets and eventually
the entire frond.
Pestalotiopsis leaf blight: Lesions associated with this disease are
large, irregularly shaped and orange-red in colour (Fig. 3d).
Genetically abnormal seedlings: These can be classified into two groups,
those showing leaf abnormalities and those showing abnormalities of form (Fig.
Bifurcate: The pinnate of older seedlings remain fused; the general
morphology of the leaf remains juvenile. In such instances, leaf laminae are
either late in dividing into their component pinnate or remain entire (Fig.
Field diseases and disorders
Algal disease: The algae, Cephaleuros sp., usually attack
leaves on low-hanging pinnate and can also be found on the rachis. Colonies
have the appearance of a flat spot, burnt-orange to brown or rust-colored (Fig.
Basal stem rot: This disease is caused by Ganoderma mushroom
that attacks the palm at the stem base. The fungus may be observed as a whitish
skin-like layer on the inner surfaces of the exodermises; cortical tissue becomes
brown. The disease causes dry rot of internal tissues that severely restricts
the supply of water and nutrients to the palm.
||Field diseases of oil palm, (a) Algal leaf spot, (b) Basal
stem rot (1) The oldest fronds have died and collapsed, (2) Fruiting body
of Ganoderma boninense, (3) The beginning of infected tissues, (4)
Mycelia of Ganoderma boninense in diseased tissues, (c) Spear rot
of oil palm (1,2) The spear leaf and next youngest leaves discolored or
collapsed, (3) Yellowing and rotting of spear leaf, (d) Bunch end rot and
(e) Sooty mold on the pinnate
The earliest visible symptoms occur on the foliage with the accumulation of
unexpanded spear leaves. The foliage generally is much paler green in color
than that of a healthy palm (Fig. 4b).
Spear rot: The first symptoms of spear rot are seen in the unexpanded
spear leaf. The entire spear is quickly killed once basal rotting begins. Such
decaying spears can beeasily pulled out. When this is done, the basal tissues
are found to be affected by a dark brown, wet rot. Given some time, the rotting
spear collapses and dies and then is often seen hanging down among the outer
healthy fronds (Fig. 4c).
Boron: Boron deficiency results in a wide array of symptoms. These
symptoms always occur on newly emerging leaves but remain visible as they are
mature and are replaced by younger leaves. Mild boron deficiency can be manifested
as sharply bent leaflet tips, commonly called wrinkled leaf. One
of the most common symptoms of boron deficiency is the failure of newly emerging
spear leaves to open normally. They may tightly fuse throughout their entire
length, or the fusion can be restricted to basal parts of the spear leaf (Fig.
Nitrogen: Symptoms may appear on either young or old fronds, with the
entire plant often affected. Deficient fronds first become pale green in color,
changing to pale or bright yellow as the chlorosis becomes more severe. In advanced
cases of deficiency, the apocone also becomes deep orange in color and ultimately
the entire petiole and rachis become bright orange in appearance (Fig.
||Mineral deficiencies of oil palm, (a) Boron deficiency; wrinkled
leaf, (b) Nitrogen deficiency, (c) Potassium deficiency, (1) Confluent orange
spotting, (2) Chlorotic or necrotic spots on older fronds and (d) Magnesium
Potassium: The first symptom of potassium deficiency is pale green spotting
on the pinnae of older fronds. The spots expand and either become round or develop
an irregular outline, with the color changing to bright orange or red-orange.
In a severe deficiency, the number of lesions is greater and the older leaves
can be entirely covered by a reticulate mass of orange spots. In these severe
cases, entire older fronds may dry up (Fig. 5c).
Magnesium: Mg deficiency results in the development of bright orange
color in older fronds. The orange discoloration is very pronounced on the upper
rank pinnate exposed to sunlight (Fig. 5d).
A global review of literature, up to 1981, on oil palm diseases and disorders
is available. Later on, the diseases of oil palm in various growth stages in
Thailand were reported by Limsriwilai et al. (1984).
In this study, the incidence in southern Thailand of oil palm diseases in seed,
nursery and field stages were determined. The inspection was conducted and samples
were collected to identify the causal agents found in oil palm production areas,
within southern Thailand. During the seed stage brown germ (13.12%) and seed
rot (4.2%) had the highest incidence rates. During the nursery stage, the disease
incidences in decreasing order were leaf spot (11.26%) and genetic disorder
(6.85%), while during the field stage similarly sooty mold (51.30%) was followed
by algae (24.92%), Boron micronutrient deficiency (19.15%), Nitrogen deficiency
(13.46%) and Magnesium deficiency (9.54%).
Aspergillus flavus and A. parasiticus were the fungi most often
detected in oil palm seeds showing brown germ, while Schizophyllum commune
was rarely found. This deviates from a report on Malaysia, where S. commune
was the most important pathogen causing brown germ and seed rot (Dikin
et al., 2003). According to Turner (1981),
brown germ is also caused by Aspergillus spp., Mucor spp. and
Fusarium spp.; however, S. commune was recorded as a causal agent.
There is no epidemic of S. commune in southern Thailand; its incidence
rate is probably due to low humidity storage of seeds.
Leaf spots caused by Curvularia oryzae were quite widespread in nurseries,
with moderate to severe infection levels. The disease was of a mild form in
nurseries with good sanitation. High incidence of the disease may be due to
the absence of control management system. In Malaysia, C. lunata and
C. maculans have been reported as causal agents of leaf spots in oil
palm (Englert et al., 1999).
The sooty mold and algae occurred widely at oil palm plantations in the south,
where the climate is tropical. While severe levels of infection were recorded,
the diseases occurred on the surface of the oil palm tree and did not attack
the inner tissues of the plant.
Basal stem rot also occurred widely and as a lethal disease for palm trees.
This appears the most serious of all diseases affecting the oil palm in southern
Thailand. Basal and stem rot are the main factors accountable for the low yields
of oil palm in Cameroon, Malaysia (Kinge and Mih, 2011).
The disease has been recorded in Malaysia and Indonesia, Angola, Ghana, Nigeria,
North Mozambique, Zaire and Tanzania (Turner, 1981). Several
species of Ganoderma are reportedly pathogenic on oil palm, in various
countries. In Malaysia and Indonesia the causal agents identified include
G. boninense Pat., G. chalceum (Cooke) Steyaert, G. miniatocinctum
Steyaert, G. tornatum (Pers.) Bers., G. xylonoides Steyaert
and G. zonatum Murill (Turner, 1981; Pilotti,
2005; Utomo et al., 2005). The most serious
fungal pathogen in Malaysia and Indonesia has been identified as G. boninense
(Al-Obaidi et al., 2010; Susanto
et al., 2005). The current observations agree, with G. boninense
occurring widely at oil palm plantations in southern Thailand; particularly
on older plants.
During the seed stage, oil palms are faced with several diseases including
seed rot and brown germ (Fig. 2). In order to reduce the severity
of these diseases, the seeds should be cleaned before planting. The most effective
way is to remove the pericarp of oil palm seed, with sanitation in seed germinator.
The major diseases in nursery stage include leaf spot, genetic disorders and
nutrient deficiency. The best way to control leaf diseases is to reduce excessive
shade and ensure adequate air movement. Preventive fungicide applications can
be repeated at fifteen day intervals. A balanced fertilizing program would remedy
nutrient deficiencies, both in the nursery and field stages of oil palm. Avoiding
damage to oil palm stem, caused by man or insects, may reduce the penetration
of most oil palm pathogens. In the field stage, the basal stem rot is the most
destructive disease for oil palm plantations. It can lead up to 80% losses with
repeated planting cycles. There is no effective method to cure this disease
because the mycelia have penetrated and reside within the palm tree. Chemical
application is useless against basal stem rot, while the use of antagonistic
microorganisms has no quick effects. Infected oil palms have to be eliminated
and removed from the planting field, to prevent further spreading of the disease.
This study was conducted to survey the diseases and disorders of oil palm.
The reporting has been structured by the seed, nursery and field stages. Numerous
diseases were found in each stage. The observed incidence rates encourage pursuing
effective disease management of oil palm diseases in southern Thailand. This
study on the incidence rates of diseases and disorders of oil palm has also
listed some valuable appropriate control measures and can guide the development
of further measures. These will help farm advisors guide farmers in effective
This study was supported by the Higher Education Research Promotion and National
Research University Project of Thailand, Office of the Higher Education Commission.
The copy-editing service of Research and Development Office (RDO) of Prince
of Songkla University (PSU), especially the comments and suggestions of Assoc.
Prof. Seppo Karrila, are gratefully acknowledged.