Occurrence of citrus nematode (tylenchus semipenetrans)
in Sargodha District
Ijaz Parvez, Tariq Mukhtar and
Muhammad Fiaz
Pest Warning and Quality Control of Pesticides, Department
of Agriculture, Punjab, Sargodha. Pest Warning and Quality
Control of Pesticides, Department of Agriculture, Punjab,
Multan.
Abstract: In a survey during the
year 2002 on the occurrence of citrus nematode, Tylenchus
semipenetrans (Cobb) 57 soil and root samples were collected
from 36 localities of district Sargodha in Pakistan. The
analysis revealed that 54.38% of the samples were infested
with the nematode. Maximum infestation (61.11%) was recorded
in Tehsil Bhalwal followed by Sillanwali, Sargodha, Shahpur
and Sahiwal showing 57.14, 53.33, 50.00 and 44.44%
infestation, respectively.
Keywords: Citrus, infestation, Pakistan, Sargodha,
Tylenchus semipenetrans.
INTRODUCTION
Citrus production is one of the world’s largest agricultural
industries. World trade in citrus is second only to bananas
and more than double the volume of apples. Citrus fruit is
highly nutritive and refreshing being a source of vitamins A
and C, organic acids, amino acids, sugars and carotenoids.
Citrus is sown in more than 125 countries in the belt within
35o latitude north and south of equator [Duncan and Cohn
1990].
Pakistan is one of the top ten citrus producing countries of
the world. The area under citrus cultivation in Pakistan
during 2000-2001 was approximately 198.7 thousand hectares,
which is increasing every year. In Pakistan 1951.5 thousand
tonnes of citrus was produced, earning 720.572 million
rupees, during the year 2000-2001 [Anonymous 2002]. Out of
total produce of citrus in the country, Punjab province
contributes 95%, and of the total citrus production of the
province Sargodha contributes 25%. Citrus is also a source
of foreign exchange earnings for Pakistan. The export of
citrus was 82750.80 tonnes during 1999-2000.
Citrus is attacked by a number of insect pests and diseases
causing heavy losses both in quality and quantity. Among the
nematodes, citrus nematode, Tylenchus semipenetrans (Cobb)
has been recognized as one of the greatest threats
throughout the world. It occurs in all citrus producing
regions of the world and limits production of citrus fruits
under a wide range of environmental and adaphic conditions.
In main citrus producing regions of the United States, the
nematode infests from 50 to 60%of the citrus orchard in
California and Florida to as much as 90% in Texas and
Arizona. Similar statistics have been reported worldwide [Heald
and O’Bannon 1987].
In Pakistan, nematode problem is more serious and complex
than in the developed countries. The reasons for this are
many and varied. Firstly, the country lies in the tropical
and sub-tropical regions where climate.
suitable for the activity and reproduction of the nematode
throughout the year. Secondly, soils are very favorable for
nematode infestation, especially in irrigated areas.
Perennial and other crops grown in the same field year after
year are often heavily attacked by nematodes.
The citrus nematode causes “slow decline” and the affected
trees show reduced terminal growth, chlorosis and shedding
of terminal leaves, dieback of branches and considerable
reduction in number and size of fruit. Roots of infested
trees show brownish discoloration and ultimately decay
resulting in reduced volume. Copper and Zinc deficiency
symptoms are more pronounced in attacked trees [van Gundy
and Martin 1961].
As citrus orchards are declining in District Sargodha,
therefore present survey was conducted to ascertain the
occurrence of citrus nematode in the district.
MATERIALS AND METHODS
Soil and root samples from symptomatic and asymptomatic
plants from 36 localities of district Sargodha were
collected up to 30 cm depth. Samples were taken at a
distance of 60 to 90 cm away from the tree trunk. Upper 15
cm soil was removed and then samples were collected by
digging the soil. The soil along with feeder roots was
collected in polyethylene bags and brought to Nematology
Laboratory, University of Agriculture, Faisalabad for
analysis. Juveniles were extracted from the soil by modified
Whitehead and Hemming tray method [Whitehead and Hemming
1965]. The number of nematodes recovered from the soils of
each sample was counted by using a counting dish.
Feeder roots were washed under tap water carefully to remove
soil particles and blotted dry. One gram of fresh feeder
roots was placed in a blender and 20 ml of 10% sodium
hypochlorite solution was added. Volume was increased up to
200 ml by adding water and blended for 45 seconds. The
suspension was poured over 100 and 325 mesh sieves and
females were collected in a beaker and their numbers were
counted.
RESULTS AND DISCUSSION
The results of analysis of soil and root samples are
given in Table 1. It is clear from the table that 31 out of
57 samples were infested with citrus nematode showing 54.38%
infestation. Maximum samples (61.11%) were found infested
with the nematode in Tehsil Bhalwal, while minimum
infestation (44.44%) was observed in Tehsil Sahiwal.
Percentage of samples infested in Tehsil Sargodha,
Sillanwali and Shahpur was 53.33, 57.14 and 50.00,
respectively.
Nematode population in soil and number of females in roots
are given in Table 2. In Tehsil Bhalwal nematode in soil
ranged from 2,024 to 21,080 per kg of soil and number of
females ranged from 495 to 1,832 per gram of root.
Similarly, nematode population in one kg of soil ranged from
2,818 to 18,120; 1,078 to 11,758; 3,146 to 14,270 and 1,300
to 9,854 and
female per gram of root ranged from 268 to 1,646; 120 to
990; 312 to 1,384 and 178 to 1,030 in Tehsil Sargodha,
Sahiwal, Sillanwali and Shahpur, respectively.
The present survey confirms the occurrence of citrus
nematode in District Sargodha. Since its first report in
roots of citrus trees in California in 1912 and its
description [Cobb 1913], its occurrence has been reported
from all over the major citrus growing regions of the world.
By 1914, it had been reported parasitizing citrus roots in
Florida, Malta, Spain, Australia and South America [Cobb
1914].
 According to Thorne [1961] 90-95% citrus orchards in south
California were infested by this nematode. Survey of citrus
nurseries in India revealed 75% infestation with citrus
nematode [Mani et al. 1988]. In China (Sichuan) 94.7% of the
orchard were found infested [Zhu et al. 1992]. Likewise the
nematode was found infesting citrus orchards in NWFP [Khan
et al. 1990] and in most of citrus orchards in the Punjab
[Ahmad and Khan 1973]. Similar statistics have been given by
other researchers from different countries [Noling and
Duncan 1988, Robinson et al. 1987]. In the present survey,
nematode population and number of females per gram of root
varied in different localities. This is because many factors
affect citrus nematode population and infestation. These
include host variety, age, soil texture, moisture, pH,
nutrient status, temperature, soil depth etc. Reproductive
rates of different races of nematode obviously vary with
rootstock [O’Bannon and Hutchinson 1974]. Tree age has a
marked effect on population size and distribution of the
nematode [Bellow et al. 1986].
The nematode is sensitive to extreme moisture deficits but
population development occurs across the normal range of
agricultural soils [van Gundy and Martin 1961, van Gundy et
al. 1964]. Similarly population will increase between
temperatures of 20-31°C with maximum development at 25° C
and very slow development at the extremes [O’Bannon et al.
1966]. Davis [1984] reported that nematode population peaked
in April and declined to lowest levels in August and
September. Highest number of nematodes was obtained at 120
cm distance from the tree trunk up to 30 cm depth [Chawla
and Sharma 1984]. T. semipenetrans can be found in any soil
texture, but greatest damage occurs in shallow, poorly
drained soils with organic matter contents from 2-3%
[O’Bannon and Essar 1985].
The present study confirms the presence of citrus nematode
in district Sargodha and suggests further intensive survey
and measures to control the nematode.
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Source: Journal of
Research (Science), Bahauddin Zakariya University, Multan,
Pakistan. Vol.14, No.1, June 2003, pp. 91-95 ISSN 1021-1012 |
