Des enquêtes réalisées de 1991 à 1996 dans les gouvernorats de Batimah, de Dhabira et du Dhofar et dans les régions de l'Intérieur et de Shargia ont révélé la présence de treize genres de nématodes phytoparasites associés à la luzerne. Les #Pratylenchus$ sont les nématodes les plus communs (61% des échantillons) suivis par #Meloidogyne$ spp., #Tylenchorhynchus$ spp., #Helicotylenchus$ spp. et #Rotylenchulus reniformis$. Les fluctuations de population de #Pratylenchus jordanensis$ ont été suivies sur luzerne, en deux sites à Rumais dans la région de Bathinah en 1994-1995 et 1995-1996, respectivement. Une corrélation positive (P supérieur ou égal à 0,01) a été observée entre les populations du nématode et la température. Les populations endoracinaires sont les plus élevées de juillet à novembre et les plus basses de décembre à juin. (Résumé d'auteur

Al Hinai, M.S.

Mani, A.

Name not available

Plant-parasitic nematodes associated with alfafa and fluctuations of Pratylenchus jordanensis population in the Sultanate of Oman

Horizon / Pleins textes

Fundam. appl. Nematol., 1996, 20 (5), 443-447
Plant-parasitic nematodes associated with alfalfa and fluctuations
of Pratylenchus jordanensis population in the Sultanate of Oman
Annamalai MANI and Muzna S. AL HINAI
Directorate ofAgricultuml Research, Ministry ofAgriculture and Fisheries,
PO. Box. 15, Code-328, Rurnais, Suitanate of Oman.
Accepted for publication 5 November 1996.
Summary - Surveys carried out in the Batinah, Dhahira, Dhofar Governorates, and the Interior and Sharqia regions of the
Sultanate of Oman during 1991-1996 revealed the presence of thirteen genera of plant parasitic nematodes associated with
alfalfa. Prarylenchus spp. were the most common nematodes and were found in 61 % of sampIes, followed by Meloidogyne spp.,
Tylenchorhynchus spp., Helicotylenchus spp., and Rorylenchulus renijormis. The population fluctuations of Pratylenchus jordanensis
were studied on alfalfa at rwo locations at Rumais in the Batinah region during 1994-1995 and 1995-1996, respectively. A posi-
tive correlation (P:::: 0.0 1) berween nematode populations in roots and soil temperature was observed. The nematode popula-
tion in roots was highest from July to November and lowest from December to June.
Résu1né - Né1natodes phytoparasites associés à la luzerne et fluctuations des populations de Pratylenchus jorda-
nensis dans le Sultanat d'Oman - Des enquêtes réalisées de 1991 à 1996 dans les gouvernorats de Batimah, de Dhahira et
du Dhofar et dans les régions de l'Intérieur et de Shargia ont révélé la présence de treize genres de nématodes phytoparasites
associés à la luzerne. Les Prarylenchus sont les nématodes les plus communs (61 % des échantillons) suivis par Meloidodgyne
spp., Tyleru:horhynchus spp., Helicotylenchus spp. et Rotylenchulus reniformis. Les fluctuations de population de Prarylenchus jorda-
nensis ont été suivies sur luzerne en deux sites à Rumais dans la région de Bathinah en 1994-1995 et 1995-1996, respective-
ment. Une corrélation positive (P:::: 0,0 1) a été observée entre les populations du nématode et la température. Les populations
endoracinaires sont les plus élevées de juillet à novembre et les plus basses de décembre à juin.
Key-words: alfalfa, distribution, fluctuation, occurrence, plant nematodes, population, Prarylenchus jordanensis.
Alfalfa (Medicago saliva L.) is the most important
forage legume grown in the Sultanate of Oman. It is
grown on most of the farms under traditional farming
systems either as a sole crop or as an intercrop among
irrigated fruit trees. In recent years, it was observed
that the crop started declining 3 to 4 years after sow-
ing as compared with 8 to 10 years of healthy crops in
the past. Results of a preliminary survey revealed that
Pratylenchus spp. were associated with alfalfa in cer-
tain parts of Oman (Waller & Bridge, 1978). Other
surveys carried out in parts of Oman revealed the
occurrence of P. jordanensis and this nematode was
considered to have a negative effect on the production
of alfalfa (Anon., 1993; Mani, 1993, 1996). There-
fore, it was considered necessary to identify the plant-
parasitic nematodes associated with alfalfa in ail
regions and to study the population fluctuations of
P. jordanensis to understand its behaviour. Surveys
were carried out in ail alfalfa growing regions of
Oman and the fluctuations of P. jordanensis population
at Rumais in the Batinah region were monitored dur-
ing the present investigations.
ISSN 1164-5571197/05 $ 7.00 / © Gauthier- Villars - ORSTOM
Materials and methods
OCCURRENCE AND DISTRIBUTION OF PLANT-
PARASITIC NEMATODES
Surveys were carried out for two consecutive crop-
ping seasons during 1990-1992 in the Batinah Gover-
norate, 1992-1994 in the Interior region and the
Dhahira Governorate, and 1994-1996 in the Sharqia
region in northern Oman, and for a single season
(1995) in Dhofar Governorate (Salalah) in southern
Oman. Twelve wilayats (divisions) in Batinah, twelve
in Interior, six in Dhahira, six in Sharqia, and five in
Dhofar were surveyed (Fig. 1). Five farms were ran-
domly selected in each wilayat with the help of exten-
sion personnel. Three to five samples were collected
from each farm using a trowel, then pooled together.
Soil and root samples were collected from the rhizo-
sphere region up to 20 cm from the base of alfalfa
plants and at a depth down to 15 cm. One sample
from each farm and a total of 169 soil samples were
collected from five regions. A composite sampie of
250 cm3 of soil was processed by Cobb's sieving and
443
A. Mani & M.S. Al Hinai
Results and discussion
OCCURRENCE AND DISTRIBUTION OF PLANT-
PARASITIC NEMATODES:
Thirteen genera of plant-parasitic nematodes were
identified from the 169 soil samples collected
(Table 1). Pralylenchus spp. were the most commonly
occurring nematodes with a frequency of occurrence
of 61 %. Meloidogyne spp., Tylenchorhynchus spp., Heli-
cOlylenchus spp. and ROlylenchulus sp. occurred in 33.1,
32, 24.9, and 16% of the samples, respectively, and
these five nematode genera were found widely distrib-
uted in ail the regions. Among the various species of
nematodes, P jordanensis was the most frequently
recorded, with a frequency of 38.5%, followed by
R. reniformis and M. javanica with, 16 and 11.8%,
respectively. R. reniformis was recorded with the maxi-
mum mean population of522 nematodes per 250 cm3
of soil, followed by M. javanica) M. incognita and
P jordanensis with means of 424, 335, and 155 nema-
todes, respectively. Pralyleru:hus spp. were recognized
as the major plant-parasites of alfalfa in Australia
(Georgaras el al., 1992) and USA (Griffin, 1984).
Thus, considering the widespread distribution, fre-
quency of occurrence and population density, the
present results suggested that Pralylenchus spp., and
particularly P jordanensis) were potentially important
parasites in alfalfa-production systems in Oman.
R. reniformis and Meloidogyne spp. were the other
nematode parasites which might have an impact on
crop health and longevity.
FLUCTUATIONS OF PRA TYLENCHUS ]ORDANENSfS
POPULATIONS
Weather data recorded at the Agricultural Research
Centre, Rumais during 1994-96 revealed that the
monthly mean of the daily maximum air temperature
increased from February and reached a peak of
41.2°C and 40.4°C in June of 1994 and 1995, respec-
tively (Fig. 2 A). The temperature declined gradually
from July on and reached a low of 26.2°C and 24.5°C
in January of 1995 and 1996, respectively. The mois-
May digital soil thermometer. The mean soil tempera-
ture recorded at 5 and 15 cm depth was calculated
and used for statistical analysis and graphical repre-
sentation. Nematodes were extracted from 250 cm3 of
soil. One gram of roots was washed free of soil, cut
into pieces and macerated in a waring blender for
1 min. The root suspensions were incubated in modi-
fied Baermann funnels filled with water for 36-48 h.
Nematode populations were counted in 1 ml aliquots
using a stereo-binocular microscope. Moisture con-
tent of soil samples was estimated by an oyen-dry
method. Data on maximum and minimum tempera-
tures and rainfall were recorded.
s'"'
'\,
GULF OF OMAN
o REGIONS SURVEYED
li SITES SAMPLED
• IMPORTANT TOVVNS
REP. OF
YEMEN
DHOFAR
IBo Hf.-+---------::vc-f -------------1
~\
1~~
AL WUSTA
SAUDI ARABIA
decanting technique and modified Baermann funnel
method. Nematodes were identified by morphological
and morphometric analysis of semi-permanent and
permanent mounts of the specimens. Meloidogyne spp.
were identified based on perineal patterns of adult
females as weil as characters of the second-stage juve-
niles Gepson, 1987). Nematode populations were esti-
mated from 1 ml aliquots under a binocular micro-
scope.
FLUCTUATIONS OF PRA TYLENCHUS ]ORDANENSfS
POPULATIONS
II HI- -----;f-_+-__--Ir-SHAR--'-"'Q""IA'--;I-l
Fig. 1. Map of che Suüanale of Oman showing che regions sur-
veyed and [he sùes sampled
UNITED ARAB EMIRATES
The study was carried out in 3-year old alfalfa
fields, at two locations in the Batinah region from
February 1994 to January 1995 and February, 1995
to January, 1996. The fields were flood-irrigated twice
a week. Farmyard manure was applied at 2 tlha once
every 6 months. Soil and root samples were collected
from ten randomly selected plots on the 14/15th of
every inonth. The samples were collected from three
plants in each plot, down to 15 cm depth around the
plant. Soil temperature was recorded in the rhizo-
sphere region at 5 and 15 cm depths using a Kane-
( IRAN
1ft Hf-----------n~1"<!'1D*=_----___,
444 Fundam. appl. NemaLOI.
Nematodes associated with alfalfa
Table J. Occurrence. population densiry and distribution of phytonematodes in association with alfalfa
Nematode species Frequency of Population
. Distribution
..
occurrence(%)
(n=169)
Aphelemhoides sp. 1.78 28 D, I, S
(20-40)
Cnconemella sp. 0.59 20 S
(20)
Ditylenchus sp. 4.14 44 B, D, I
(20-70)
HelicOlylemhus mulcicimtus 2.96 66 B, D, I, S
(40-100)
Helicotylenchus spp. 21.89 142 B, D, DG, I, S
(15-960)
Hemicriconemoides spp. 2.37 37 B, D, I
(20-65)
Hoplolaimus sp. l.18 16 B,S
(12-20)
Longidortls spp. 5.92 26 B, D, DG, I, S
(10-60)
Meloidogyne incognita 7.1 335 B, D, I
(44-2080)
M. javanica 11.83 424 B, D, I, S
(20-1320)
Meloidogyne spp. 14.2 153 D, DG, 1, S
(20-550)
Pratylemhus brachyurus 4.14 III B,D, S
(20-300)
P. delaurei 8.88 109 B, I
(25-300)
P. jordanensis 38.46 154 B, D, DG, I, S
(20-1254)
P. neglec/Us 1.18 50 DG
(40-60)
Pratylemhus spp. 8.28 32 B, DG, I, S
(15-120)
Rotylenchulus reniformis 15.98 522 B, D, DG, I, S
(20-4820)
TelOlylemhus indicus 6.5 40 B, D, I
(30-110)
1Ylenchorhynchus spp. 31.95 140 B, D, DG, I, S
(T. annulatus, T. goffam) (15-500)
Xiphinema amen'canum 8.88 28 B, D, DG, I, S
(15-80)
* Mean and range of number of nematodes in 250 cm3 of soil.
** B=Batinah; D=Dhahira; DG=Dhofar Gov.; I=Interior; S=-Sharqia
ture content of soil samples ranged from 9.S to Il %.
The physical and chemical charaeteristics of the field
soil and irrigation water are given in Table 2. The
population of P. jordanensis in soil did not vary signifi-
Vol. 20, n° 5 - 1997
cantly and was high throughout the year (Fig. 2 B).
However, the population was lowest in May and
August at the first and second site, respectively. The
correlation between nematode soil populations and
445
A. Mani & M.S. Al Hinai
Parameters Site 1 Site 2
Sail
Coarse sand (%) 16.2 9.8
Fine sand (%) 68.2 70.9
Silt (%) 11.9 11.6
Clay (%) 3.7 7.7
CaC03 (%) 26.8 24.0
pH 8.2 8.1
Electrical conductivity 600 460
(~Q/cm-1.5)
Irrigation waler
pH 7.5 7.2
Electrical conductivity 4600 5200
(~Q/cm-1.5)
Table 2. Physical and chemical charaClerisrics of field soil and
irrigation waler al rwo e.xperimental siles in the Baliruzh region
of Oman
perature. Similar observations have been made wim
those species of Pratylenchus which are usually present
in warmer regions. P brachyurus was found to repro-
duce on soyabean in large numbers at 29°C when
compared with low temperature levels (Lindsey &
Cairns, 1971). Similarly, P negleetus, observed on
many field crops in Interior region of Oman (Anon.,
1993), also penetrated maize roots in high numbers at
30°C (Townshend, 1972) and the rate of reproduc-
tion was higher at 38°C than at omer temperarures
(Mountain, 1954). Besides soil temperature, me phe-
nology of the crop also might have played a major role
in determining the population fluctuations of me
nematode as suggested by Ferris and McKenry
(1976). The significantly high populations of P jorda-
nensis in roots indicates mat mis nematode needs to be
controlled to improve the healm of the crop.
45
Q 35
<>
'-<El
~ 25<>
a.
E
~
;j 15
<>
~
5
0 ----;
F M A M J J A S 0 N 0 J
0
2
bO 3 B
~
'-'
"'"
<'lE
u 2
0
V") \C:'CD0d-U><>"0
0
<;j
E
<>
Z 0
F M A M J J A S 0 N 0 J
Fig. 2. A: Nfonrhly mean of lhe daily maximum and minimum
air œmperacure and mean sail œmperacure recorded during
1994-96; mean of IWO years daca (.: Maximum œmperacure;
.: Minimum œmperalure; .À.: Mean soillemperalUre); B: Pop-
ulation fluclUations of Pratylenchus jordanensis in rhizosphere
sail and raolS of alfalfa during 1994-96 (mean of IWO years daca;
(.: Sail population; .: RaO! population).
soil temperature was not significant (P ~ 0.05). In
contrast with me soil population, nematode popula-
tions in roots flucruated greatly with a distinct high
from July to November at both locations, which coin-
cided wim higher soil temperatures. In spite of me
presence of a high nematode population in the soil,
the population in roots was very low from December
to June, coinciding with lower soil temperarures.
These findings were confirmed by me positive corre-
lations between the populations in roots and the soil
temperature (r = 0.433 and 0.324; P ~ 0.01), repre-
sented by me linear regression equations,
Y=78.45+29.43x and Y=76.11+3.38x. The high nem-
atode population in roots from July to November sug-
gested that the penetration and/or reproduction of P
jordanensis into roots was favoured by high soil tem-
Acknowledgements
We are grateful to the Director General of Agriculrural
Research and Director of Plant Protection, Directorate of
Agricultural Research, Rumais for providing necessary facil-
ities; Dr. Z. A. Handoo, Nematology Laboratory, USDA,
MD, USA, for identifying certain nematode specimens and
Dr. R. McSor1ey, University of Florida, Gainesville for criti-
cally reviewing the manuscript.
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447


Plant-parasitic nematodes associated with alfafa and fluctuations of Pratylenchus jordanensis population in the Sultanate of Oman

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