Ghassan Hassan 
General Commission for Scientific Agricultural Research-
Hassakeh Research Center
Damascus University, Faculty of Agriculture
2008

Abstract

Wheat (Triticum spp.) is considered one of the oldest agricultural crops, and is still the most importance and the widely distributed crop worldwide. In Syria, wheat comes in the first grade in agricultural production, whereas Hassakeh province is the highest in wheat cultivation in Syria. Cereal cyst nematode Heterodera spp. is one of the most important diseases which infest wheat, and causes a great damage to this crop.
This research aimed to species determination, distribution, population density, economic impact and life cycle of this nematode on wheat in Hassakeh province. The study was carried out during the years 2005/2007, and included the following:
First: A field survey of cereal cyst nematodes Heterodera spp. was conducted in 145 wheat (durum and bread) fields, planted under irrigated or non-irrigated conditions in different agro-ecological zones of Hassakeh province during the period 2005/2006, from the end of maturity stage to the end of harvest.
The results showed that 65.52% of the surveyed fields were infested with one or more species of cereal cyst nematodes. Cyst nematodes were found in 63.64 and 67.09% of the total non-irrigated and irrigated fields, respectively. Moreover, 62.65 and 69.35% of the total durum and bread wheat fields, respectively.
The 1st agro-ecological zone of the province had a higher infestation level of about 77.36% of the total surveyed fields in this zone, followed by 3rd agro-ecological zone then second zone which had 67.57 % and 52.73 % of the total surveyed fields in these zones, respectively.
Based on the morphological characteristics of the vulval cone, three species of the cereal cyst nematodes were identified in the infested fields, namely: H. latipons (Franklin, 1969), H. avenae (Wollenweber, 1924) and H. filipjevi (Madzhidov, 1981) Stelter, 1984.
H. latipons was most common and was found singly in 44 fields resembling 46.32% of the total infested fields. The infestation was higher in the first agro-ecological zone in Al-Ganamyia location (99 cysts per   200 g soil, density 15490 eggs and juveniles per 200 g soil). Also, it was found mixed with other cysts nematode species in 11 fields, resembling 11.58% of the total infested fields.
H. avenae was found singly in 37 fields resembling 38.95% of the total infested fields, its higher infestation was in third agro-ecological zone in Tel-Aswad location (53 cysts per 200 g soil, density 17120 eggs and juveniles per 200 g soil). It was found mixed with other cysts nematode species in 12 fields resembling 12.63 %.
H. filipjevi had a limited distribution, and was not found alone, but mixed with one or more of the previously mentioned species. It was found in eight fields resembling 8.42% of the total infested fields, with a density ranged between 462-22733 eggs and juveniles per 200 g soil. Most of these fields were in the first agro-ecological zone near Turkish borders, and the higher infestation was in Tel-Aylule location with an average of 90.38% of the total cyst numbers in the field.
Second: The economic impact of the cyst nematode H. avenae on the productivity of wheat varieties, durum -Sham 3- and bread -Sham 6-was studied in naturally infested fields with different densities of this nematode, under non-irrigated conditions in the third agro-ecological zone in Hassakeh province. Different densities of H. avenae caused significant reductions in yield components of both wheat varieties. A negative correlation relationship was found between initial nematode population (Pi) and yield components, i.e., as the initial nematode densities of H. avenae increased, reduction ratios of yield components of both wheat varieties (durum and bread) increased. At the higher sampled initial population (40.4 eggs and juveniles per 1 g soil), reduction ratios reached 48.15 % and  39.58% in plant height, 56.65% and 49.61% in grain yield, 49.53% and 44.62% in straw yield, and 51.61% and 46.55% in weight of 1000 kernels in durum and bread wheat, respectively.
Moreover, durum wheat showed lower resistance than bread wheat, whereas the average reduction ratios in plant height, grain yield, straw yield and weight of 1000 kernels in durum wheat reached 27.48%, 34.71%, 29.23% and 31.24%, respectively, compared to the reduction ratios in bread wheat which reached 22.17%, 28.99%, 24.68% and 28.17% in the same parameters, respectively.
The final nematode population (Pf), at the end of the experiment, increased with every increase in the initial population (Pi), while the reproduction factor (Rf) decreased with increasing initial population.
Third: Study the life cycle of H. avenae on wheat crop. Pots were filled with a mixture of equal parts of sterilized sand and infested soil with this nematode species only. Seeds of bread wheat (variety Sham 6) were sowed in these pots and placed in a plastic house with conditions mimic the field. Second-stage juveniles of the cyst nematode penetrated the plant roots during the second week of planting, coinciding with plant emergence, their density reached to the peak after about one month of planting, and they lasted in soil and root samples for about two months where soil temperature less than 10 C, while they disappeared when soil temperature rose above 15 C. Second-stage juveniles then passed through three molts and successively gave the third-stage, fourth-stage juveniles, and adult males and females. The duration of each stage was about two weeks. The life cycle of H. avenae was completed (first appearance of white cysts) after 77 days of planting. Only one generation was recorded of this species during growing season.