Etiology of Trichosporium vesiculosum Butl. Causing Blister Bark Disease in Casuarina equisetifolia Forst
Blister bark caused by Trichosporium vesiculosum Butl. is a lethal fungal disease of Casuarina equisetifolia Forst. In plantations, blister bark is more prevalent in trees that are more than two and a half years old. So in this present study, the influence of climatic and edaphic factors on blister bark disease development in C. equisetifolia under controlled conditions were investigated. The pathogen isolated from the disease plant tissues was maintained on Potato Dextrose Agar medium. Conidial suspension of the pathogen was inoculated onto 3 to 6 months old. C. equisetifolia seedlings raised on different soil types (Alfisol, Vertisol and Ultisol). The pathogenecity study indicated that T. vesiculosum attacked C. equisetifolia seedlings as early as 5 months old. A temperature range of 25 to 30°C and a relative humidity (%) range of 45 to 60 favoured the conidial development and fungal spread in the seedlings. Similarly soil pH of 5.5 to 6 favoured the pathogen and disease development whereas soil pH<7.5 deters disease development. It was also found that regular watering prevented disease development. Soil type seems to play a major role in disease development as disease incidence and severity was more in seedlings raised in Vertisol than in other soil types. From this experiment it was understood that the favourable temperature, soil factors and soil type for this pathogen to be taken care at the time of planting of C. equisetifolia seedlings so as to avoid the blister bark disease.
April 19, 2011; Accepted: May 25, 2011;
Published: July 20, 2011
Casuarina equisetifolia Forst. is an important multipurpose tree species
mainly grown for its fuel wood. It plays a major role as windbreak and shelterbelt
along coasts in several tropical countries including India (Nicodemus,
2009). It is also a nitrogen fixing tree and grows up to 50 m in height
and 50 cm dbh. It is widely planted in Andhra Pradesh, Orissa, Tamilnadu and
Pondicherry with an area of 50,000 ha (Murthy et al.,
2006). The average yield of C. equisetifolia in India is about 50
to 60 tonnes per ha, under rainfed and 90 to 100 tonnes under irrigated conditions
(Karthikeyan et al., 2009). It is also
used as agroforestry crop and the uses are scaffolding for building construction,
ornamental and soil improvement (Nicodemus, 2009). After
the devastation of coastal areas by a Tsunami in the year 2004, C. equisetifolia
gained much importance as the matured trees up to 20 m tall successfully reduced
the force of the Tsunami and saved the coastal areas in few parts of Tamilnadu,
India (Karthikeyan et al., 2009). Though this
tree is very strong it is highly susceptible to a destructive fungal pathogen
Trichosporium vesiculosum Butl. This disease was first reported in India
during 1905 and in recent years this disease has been known to cause large-scale
mortalities of C. equisetifolia in India, China, Kenya and Vietnam (Narayanan
et al., 1996). This fungus is able to multiply rapidly and spread
over the main stem of the tree that causing death of the tree. This disease
because of its rapid spread affects many places in Tamil Nadu and Pondicherry.
Though the researchers on management of this have carried out considerable research,
no concrete control measure is available for want of information on etiology
of the disease. Therefore, in this study the mode and spread of infection of
this destructive pathogen on the specific host of C. equisetifolia were
studied under controlled conditions through etiology.
MATERIALS AND METHODS
This study was conducted in Institute of Forest Genetics and Tree Breeding IFGTB), Coimbatore, India from April to October 2008.
Isolation of pathogen: Diseased plantations were identified in Panampally
(Kerala) situated at 11° 7'N and 77° 7' E has typical warm-humid climate
with average annual rainfall of 3,020 mm and mean monthly temperature ranging
from 17.5 to 29.5°C and the mean monthly relative humidity range from 75
to 92%. The total area of the affected C. equisetifolia is 1 ha (Narayanan
et al., 1996).
Culture of pathogen: Culture of T. vesiculosum was developed
by plating the spores collected from the disease trees on to Potato Dextrose
Agar (PDA) Medium (potato extract 200 g, Dextrose 20 g and Agar 20 g in 1000
mL of sterile distilled water). Fungal colonies developed after seven days under
normal room temperature conditions (21 to 24°C). To identify the influence
of temperature on the mycelial growth of T. vesiculosum the pathogen
was placed under seven temperature conditions (10, 15, 20, 25, 30, 35 and 40°C)
in the laboratory using growth gradient chamber. Each treatment was replicated
at five times. The colony development was measured after 72 h. The growth incidence
was calculated according to the methods of Karthikeyan et
Inoculation of pathogen in C. equisetifolia seedlings under different
environmental conditions: Five millilitre of T. vesiculosum spores
(106 spores mL-1) was inoculated to three months old C.
equisetifolia according to Davison (1994) and kept
under different temperatures (10-40°C) in an environmental chamber (NK system,
Nippon chemicals and Laboratory Co. Ltd. Japan). Seedlings inoculated with T.
vesiculosum were regularly observed for the presence of disease symptoms.
Similarly, a second set of inoculated seedlings were kept under different humidity
levels (30 to 60°C) in a growth chamber. These seedlings were also periodically
observed for the development of blister bark disease.
Influence of irrigation frequency: Seedlings inoculated with T. vesiculosum were watered at different intervals (Daily, once in two days, once in 4 days and once in a week) and monitored up to 6 months. The influence of water in development of disease symptoms were also noticed and recorded.
Influence of soil type, moisture and pH: C. equisetifolia seedlings
were planted and inoculated with T. vesiculosum in three different soil
types. Vertisol soil was collected from Panampally (Kerala), Alfisol was collected
from Sadivayal (Coimbatore, T.N) and Ultisol was collected from Coimbatore (T.N).
The plants were monitored for 6 months and the soil moisture and soil pH of
each soil type was calculated according to Jackson (1973).
Statistical analysis: All the data were statistically analysed by using
the software SPSS (ver.10). The data were presented as means and their standard
errors. The data were subjected to Critical difference and Pearsons coefficient
correlation was used to determine the degree of association between soil characteristics,
growth and disease incidence of T. vesiculosum (Zar,
Growth incidence (%): The growth incidence (%) was higher under temperature of ranged from 25 to 40°C. A significant positive correlation (p<0.01) was also occurred between Temperature and growth of T. vesiculosum (Table 1).
Disease symptoms under different environmental conditions: Under temperature
above 25°C the conidial formation was occurred in the seedlings. Similarly
the relative humidity between 40 to 60% was influenced the disease as the diseases
symptoms occurred (Table 2). Influence of water was also noticed
that caused disease in T. vesiculosum inoculated C. equisetifolia
seedlings daily watered seedlings did not exhibit any disease symptoms. Significant
positive (p<0.01) correlations were established among Temperature, RH (%),
percentage of infection and disease incidence (Table 3).
||Growth of T. vesiculosum under different temperature
conditions (mean of 5 replicates)
|*Values significant at 5% of C.D; ** Correlations are significant
at p = 0.01
|| Influence of temperature and humidity on T. vesiculosum
inoculated seedlings of C. equisetifolia (mean of 5 replicates)
|DSI = 0: No symptoms; 1: Yellowing of needles; 2: Wilting
and withering of needles, 3: Drying and dead of seedlings, *±SE of
||Correlation co-efficient (r) for Temperature, RH (%), Percentage
of infection and disease incidence (n = 5)
|Correlations are significant at p = 0.01
|| Influence of soil pH and soil moisture of different soil
types on disease severity of T. vesiculosum inoculated seeding of
Influence of soil moisture and pH: Soil moisture and pH are greatly influence the disease as showed disease symptoms in seedlings of C. equisetifolia. Soil pH ranges between 5.5 to 6 highly favours the disease and soil moisture <40% showed the symptoms (Fig. 1).
The disease blister bark affects C. equisetifolia trees of different
ages causing large scale mortalities as high as 90% (Sharma,
1994). Few chemical control measures were developed to control the disease
(Narayanan et al., 1996; Narayanan,
2000). However; these were not successful in curing the disease in the field
(Narayanan and Sharma, 1996). So, to control this disease
in field it is essential to understand the edapho climatic factors which may
help to prevent the disease in field. Generally the symptoms of the disease
include yellowing of the needles (cladophylls) and wilting of the needles. In
advanced stage of the disease, small blister appear on the stem and roots. The
black spores are exposed when the bark split bursting open blisters. The symptoms
of yellowing and wilting of needles were evident at the temperature range of
25°C and above which indicates that the optimum temperature for the pathogen
is 25°C and above. It also reflects the water stress which showed chlorotic
appearance (Dell and Malajczuk, 1989). Jabnoun-Khiareddine
et al. (2006) found similar results with Verticillium wilt of tomato
under 30 °C temperature conditions. Pensuk et al.
(2010) supported these results from their experiment stating that peanut
bud necrosis virus inoculated pea nut plant to low temperature did not increase
the infection. Further, in an earlier study it was showed that the incubation
condition of 25°C induced the optimal growth of Fusarium solani,
F. oxysporum, Verticillium thalia and Rhizoctonia solani (Fayzalla
et al., 2008). These all fungi are soil pathogens and belong to fungi
imperfecti category. T. vesiculosum also falls under the fungi imperfecti
category hence the similar results were found in this study. The positive correlation
between edapho climatic factors and disease severity showed that favorable environmental
conditions activate the growth and disease severity of pathogen on seedlings
of C. equisetifolia. Similar results were found by Chang
et al. (2006) in root rot severity at 5-15°C in Cone flowers.
Hiber et al. (2006) also stated that optimum
temperature was more favorable to disease development by fungal pathogens. However,
seedlings watered daily failed to exhibit any symptoms in spite of T. vesiculosum
inoculation. Routine watering may help to prevent the disease development through
control of plant temperature. This effect was also observed in plantations of
Tamilnadu and Pondicherry where there is a good irrigation. Less soil moisture
of vertisol soils are also indicated the results of severe yellowing, drying
of needles and formation of black conidial spores. It showed the impact of environment
and soil influence the disease (Shearer and Tippett, 1989).
The acidic pH causes the disease whereas the pH<7.5 did not show any symptoms.
These results supported by Fayzalla et al. (2008)
as F. solani, F. oxysporum, V. thalia and R. solani
found grown well under pH 9. Similar results also found in earlier study on
impact of soil pH on Phytophthora cinnamomi in Cedrus deodara
(Karthikeyan et al., 2000). In this present study,
vertisol type soils favours suitable for the pathogen to proliferate and survive.
Similarly, Nerey et al. (2010) found calcisol
soil type is the most suitable soil for Rhizoctonia solani causing hypocotyl
rot in Phaseolous vulgaris which proved that certain soil types are more
favourable to particular pathogen than any other soil types. The Temperature,
humidity, soil factors and soil types definitely influences the pathogen development
which may also cause sever damage in field conditions according to Aigbe
and Remison (2010). Hence, it was understood that to prevent this blister
bark disease in C. equiestifolia seedlings necessary steps have to be
undertaken while planting viz., (1) adjusting soil pH to an alkaline range,
(2) providing good irrigation system and (3) avoidance of planting sites at
vertisol type soils.
T. vesiculosum is a severe pathogen which causing blister bark disease in C. equisetifolia trees. To control this disease understanding the etiology of the pathogen is very much essential. From this experiment it was understood that the favourable climatic conditions soil factors, soil type for this pathogen to be avoided while planting so as to control the blister bark disease in C. equisetifolia trees.
The author (A.K) thanked Indian Council of Forestry Research and Education, Govt. of India for financial support in form of a research project.
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