Z.A. Stephan
Introduction
Nematology in Iraq
Nematological problems
Control measures
Infrastructure and training
Support to nematology
Conclusions and recommendations
Bibliography
Iraq is basically an agricultural country in the subtropics with an area of 438 317 km2. Out of about 48 million donum (1 donum = 2 500 m2) of agricultural land, there are 23 million donum in use for agriculture and approximately 81.5 percent of the total area in agricultural use is devoted to cereal production, mainly wheat, barley, rice and maize in that order of importance. In the remaining 18.5 percent of the area, a wide variety of crops are planted, the most important being: date-palm, citrus, vegetables, tobacco, sugar cane, grapes and stone fruits.
The country can be divided into three geographical regions: the northern region, with intermediate and high altitude which has high rainfall, a cold and snowy winter, the summer dry in some areas and cool in others; the central region, where the winter is cool and rainy and the summer is dry, very hot and long; and the southern region, which has a low altitude, cool winter but little rainfall, and a very hot and humid summer; 50 percent of the land is covered by water.
In general, the average production level of all the important crops in Iraq is very low compared with that of developed countries. In the last ten years, programmes have been organized by the Iraqi Government with the cooperation of agricultural scientists to improve both the quality and quantity of crops per caput, using proper machinery, fertilizers, recommended varieties and suitable control measures. Also, the area for agricultural use has been increased. For instance the area of cereals increased from 78 percent in 1980 to 81.5 percent in 1989; and the number of citrus trees increased from 10 million in 1979 to 20 million in 1990. These have also helped develop the prosperity of the farmers.
Plant nematodes are relatively unknown except to professional nematologists and in some areas of agriculture, because of the technical difficulties encountered in isolating and preparing them for detailed microscopic examination. Not until the beginning of the 1970s did they achieve even a small portion of the recognition they deserved among the problems confronting agriculture. Today, nematology occupies just about the same position that entomology did in 1940 and plant pathology in 1950. We must have more trained nematologists for research, services and extension.
Root-knot nematodes (Meloidogyne spp.)
Since observation (by Rao) in 1921 of the seed-gall nematode Anguina tritici on wheat, no additional information on plant-parasitic nematodes was recorded until 1955 (by Al-Adhami) when root-knot nematode, Meloidogyne javanica, was found attacking 42 host plants. Today, this species is considered one of the most important nematodes on vegetables, field crops, fruit-trees, ornamentals and even weeds in all soil types in Iraq.
Five species of Meloidogyne have been identified and reported attacking 120 host plants in Iraq. These species are M. arenaria Race 1; M. hapla; M. incognita Race 1 and 2; M. javanica Race 1 and 2; and M. thamesi. Studies also show that M. javanica Race 1 is the most widely distributed in Iraq.
Between 1970 and 1986, several surveys were made that revealed the presence of root-knot nematodes with large population densities in most fields of tobacco, tomato, suger beet and eggplant, with 100 percent of plants infected in a field causing plant death before harvest. Similar observations were found in some almond and peach nurseries. During the last 15 years, greenhouses and plastic houses have been established to grow vegetables in the central and southern regions of Iraq. Root-knot nematodes were found to be one of the most destructive diseases of tomato, eggplant and cucumber plants.
Citrus root nematode (Tylenchulus semipenetrans)
Citrus production is very important in Iraq. The area under citrus cultivation is about 70 000 donum. Most of the citrus orchards are located in the central region. The citrus root nematode, T. semipenetrans, was first recorded in Iraq in 1965 as a cause of citrus decline. Since then, the nematode has been found in more than 95 percent of the citrus groves and nurseries in the country, with large populations in many areas. In one instance over 250 000 larvae were extracted from 1 kg of roots and soil from a seedling. Heavily infected transplants developed severe decline symptoms after being planted in the grove and after three years had grown only about 10 cm. The roots had developed less than 20 percent of the root systems of non-infected seedlings.
Very infrequent occurrences and low population densities of the nematode were also found in Iraq infecting the feeder roots of olive, lilac, grape and Japanese persimmon.
Seed-gall nematode (Anguina tritici)
Wheat is one of the most important cereal crops in Iraq. There are about 2 million ha planted under wheat and 70 percent of the area is concentrated in the northern region. Yield production per caput is very low for several reasons, such as adverse environmental factors and disease.
Seed-gall nematode, A. tritici, is an important wheat pest in Iraq. In 1974, a general survey showed that A. tritici was found throughout the wheat-growing area. The percentage of infection ranged between 0.03 and 22.9 percent. In 1979 and 1989, the percentage of infection on Mexipak wheat increased to 45 and 75 percent in Nineveh and Duhok provinces, respectively.
In 1985, a barley field in Sheikhan area (40 km north of Mosul) in the northern region of Iraq was found to be heavily infected (90 percent) with the seed-gall nematode. Today, this pest has been found in most barley fields in Nineveh province, and the percentage of infection ranges from 20 to 90 percent. The decrease in yield caused by this nematode was 73 percent on a local black barley variety and 30.2 percent on Mexipak wheat.
Research studies confirmed the occurrence of three races of A. tritici in Iraq: barley race, soft wheat and hard wheat races.
Sugar-cane nematodes
The area cultivated under sugar cane is about 30 000 donum and is located in the southern region of Iraq. In 1967, four genera of plant-parasitic nematodes - Helicotylenchus, Longidorus, Pratylenchus and Tylenchorhynchus - were found associated with roots of this crop. In 1978, a general survey revealed that the population density of these four plant-parasitic nematodes had increased and caused severe damage to the crop.
Nematode pests of grapevines
In Iraq, there are about 30 million grapevines yielding 450 000 tonnes of fruit annually. Between 1976 and 1978, 180 vineyards in the northern, central and southern regions of Iraq were surveyed, and this revealed the presence of the following nematodes: root-knot nematodes, M. javanica and M. incognita, were associated with damage to the vines; citrus-root nematode, T. semipenetrans, mostly occurred in central and southern regions and produced extensive bark necrosis, root proliferation and the trees showed symptoms of decline; dagger nematode, Xiphinema index, occurred in 30 percent of the total samples with 90 percent in the samples from the northern region. Symptoms of grapevine fanleaf virus were observed in many of the vineyards. Other Xiphinema species found associated were X. vuittenezi, X. diversicaudatum and X. pachtaichum; spiral nematodes, Helicotylenchus pseudorobustus, occurred mostly in the central region where it was present in 70 percent of the samples. The other seven species of Helicotylenchus generally had a distribution in the northern region; and five species of Pratylenchus, four of Paratylenchus, three each of Criconemella, Hemicriconemoides, Longidorus, Merlinius and Tylenchorhynchus, and Ditylenchus destructor, Hemicycliophora sp., Heterodera sp., Hoplolaimus seinhorsti, Rotylenchulus reniformis and Telotylenchus sp. were recorded from vineyard soils.
Stem nematode, Ditylenchus dipsaci
This species was found in 1989 attacking crops of alfalfa and carnation and gladiolus nursery crops in Baghdad, causing serious yield losses.
Interactions of plant-parasitic nematodes with plant diseases (disease complexes)
Under field conditions plants develop close associations with many soil organisms, especially with fungi and nematodes. The nematode-fungus interrelationships have often involved a nematode pathogen, along with one of the wilt-inducing fungi such as Fusarium, Verticillium, Rhizoctonia and Phytophthora on various crops.
Tylenchulus semipenetrans increases root decay by Fusarium spp., that appeared in all citrus orchards examined in which high populations of the nematode were present. Other fungi, Phytophthora and Rhizoctonia were also found associated with this nematode. Our study showed the presence of A. tritici with Dilophospora alopecuri and A. tritici with the incidence of "tundu" disease Corynebacterium tritici. A mixed inoculum of these organisms in soil increased the severity of the disease on wheat and barley, and caused the symptoms to appear on spikes as well as leaves.
Chemical control
Research studies included chemical control on root-knot nematodes, citrus-root nematodes and sugar-cane nematodes. Results concerning the use of nematicides such as DBCP, fenamiphos, carbofuran (Furadan) and oxamyl (Vydate) were effective against these nematodes on vegetables, citrus and sugar cane.
Investigations demonstrated that all nematodes could be killed in two-year-old sour-orange rootstocks infested with T. semipenetrans if they were treated by dipping the roots and soil for five minutes in an aqueous solution of fenamiphos 1 ml/litre. In greenhouse experiments, fenamiphos applied to soil @ 5 ml/m2 and a foliar application of oxamyl @ 1.5 ml/ litre (three times at three-week intervals) increased the yield of a tomato crop by 89 and 42 percent, respectively.
Carbofuran is another systemic nematicide that was applied under greenhouse conditions and gave satisfactory results when it had been incorporated at the time of transplanting of cucumber and eggplant.
Cultural and biological methods of control Time of planting. Six generations were completed by M. javanica on tomato and eggplant roots over seven months starting from 1 October under greenhouse conditions. However, three generations were completed on both hosts when they were planted on 30 October. Root invasion and the life cycle of M. javanica were strongly affected by low temperatures during November, December and January. Average plant production was significantly greater in plants transplanted at the end of October compared with those of 1 October.
Solar heating. Covering the soil with transparent polyethylene plastic during the months (July and August) after soil preparation and irrigation was very effective against root-knot nematodes.
Crop rotation. Seed-gall nematode, A. tritici, can be easily controlled by planting a non-host crop such as legumes for one year which is sufficient practically to eliminate nematodes remaining in the soil after the wheat harvest.
Resistant varieties. A local wheat variety, Saber beg, was found resistant against wheat seed-gall nematode A. tritici. Two citrus rootstocks. Trifoliate and Troyer Citrange, were found resistant against citrus root nematode, T. semipenetrans.
Plant extracts. Plant extracts of Cleome quinquenervia, Haplophyllum tuberculatum, Hypericum triquetrifolium and Rubia tinctorum at 10 percent concentration killed a significant number of eggs and juveniles of M. javanica. Preplanting application improved the plant height and shoot dry weight of tomato plants compared with those treated at planting or postplanting and the untreated control.
Mycorrhizal fungi. Infection by Glomus mossae, the mycorrhizal fungus increased seedling growth in rough lemon (Citrus limon) compared with non-mycorrhizal seedlings.
Biological control agents. The fungus Paecilomyces lilacinus and the bacterium Pasteuria penetrans are considered promising biological control agents of the root-knot and citrus-root nematodes.
The laboratory of nematology at the Plant Protection Research Centre, Abu-Ghraib, Baghdad, is the only laboratory for research studies on nematodes in Iraq. There are few other research stations and universities in Iraq with equipment for nematode extraction from soil. There are a few trained nematologists (six Ph.D. and five M.Sc.) in the scientific research centres and the universities, and several research studies have been achieved between them. Facilities for training are not available and it is very difficult to improve the expertise and skills of current personnel.
Unfortunately Iraq does not receive any foreign aid programmes. There are difficulties in obtaining the journals of nematology and staff are unable to attend any international nematological meetings, scientific conferences or symposia because of financial constraints.
· Root-knot nematode, M. javanica; citrus-root nematode, T. semipenetrans; seed-gall nematode, A. tritici and species of Xiphinema and Pratylenchus are of great economic importance to vegetables, citrus and cereals in Iraq.· Surveys should be made for these nematodes to determine their distribution.
· The presence of races of important nematode species should be studied to avoid problems of crop rotation and host-resistance breakdown.
· Crop-loss assessment trials should be done for those important nematode species which cause economic damage.
· Integrated control should be developed by research studies on the effect of cultural and biological factors on nematode populations.
· Personnel training programmes at various levels, especially for technical staff, are necessary.
· Collaboration with international nematological research centres should be developed.
Al-Askari, A.A., Stephan, Z.A., Antoon, B.G. & Obaedi, J.F.W. 1990. Effect of plant extracts on the control of the root-knot nematode Meloidogyne javanica. Iraq. J. Agric. Sci., 21: 1-12.
Al-Beldawi, A.S., Stephan, Z.A., Alwan, A.H., Antoon, B.G. & Ismail, A.K. 1985. Susceptibility of some wheat cutivars to wheat-gall nematode and the effect of level of inoculum, time and method of inoculation on infection. J. Agric. Water Resour. Res., 4: 201-210.
El-Behadli, A.H., Stephan, Z.A., Al-Zahroon, H.H. & Antoon, B.G. 1991. Effects of chemical control on the Fusarium-Meloidogyne disease complex of eggplant. Iraq. J. Agric. Sci., 22: 40-46.
Fattah, F.A. 1988. Effects of inoculation methods on the incidence of ear-cockle and "tundu" on wheat under field conditions. Plant & Soil, 109: 195-198.
Fattah, F.A., Saleh, H.M. & Aboud, H.M. 1989. Parasitism of the citrus nematode, Tylenchulus semipenetrans, by Pasteuria penetrans in Iraq. J. Nematology, 21: 431-433.
Stephan, Z.A. 1988. New race of Meloidogyne javanica from Iraq. Int. Nematol. Network Newsl., 5:21.
Stephan, Z.A. & Antoon, B.A. 1991. Races of earcockle nematode, Anguina tritici in Iraq. Basrah J. Agric. Sci., 4: 95-99.
Stephan, Z.A. & Estey, R.H. 1982. Effect of soil texture, moisture and temperature on the migration of Meloidogyne hapla larvae and their invasion of tomato roots. Phytoprotection, 63: 6-9.
Stephan, Z.A. & Trudgill, D.L. 1983. Effect of time of application on the action of foliar sprays of oxamyl on Meloidogyne hapla in tomato. J. Nematol., 15: 96-101.
Stephan, Z.A., Awan, A.H. & Antoon, B.G. 1988. Effect of planting date on development of root-knot nematode (Meloidogyne javanica), plant production and percentage of infection of tomato, eggplant and cucumber. Zanco, 6: 59-68.
Stephan, Z.A., Hassan, M.S. & Antoon, B.G. 1990. Seasonal population changes of the citrus nematode and some fungi on different citrus trees in Iraq. Basrah J. Agric. Sci., 3: 47-64.
Stephan, Z.A., Yousef, A.N. & Antoon, B.G. 1989. Interactive effect of root-knot nematode, nematicide (Nemacur) and root-nodule bacteria on nodulation and growth of faba bean and bean plants. J. Agric. Water Resour. Res., 8: 319-328.
Stephan, Z.A., El-Behadli, A.H., Antoon, B.G. & Al-Zahroon, H. 1989. Effect of Glomus mosae on citrus rootstock growth and its interaction with Tylenchulus semipenetrans infecting citrus roots. Iraq. J. Agric. Sci., 20:191-200.
Stephan, Z.A., Al-Taae, A.K.M., Al-Talib, N.Y, Shams Al-Din, S., Ayoub, M. & Antoon, B.G. 1992. Studies on barley seed gall nematode, Anguina tritici.
