The effect of different temperatures under both in vitro and in vivo conditions on the hatching behaviour of second-stage juveniles (J2) of the cereal cyst nematode, Heterodera filipjevi, was studied. Cumulative percent hatching was affected significantly by temperature after 290 days of incubation. Hatching was significantly greater at lower temperatures (5, 10 and 15°C) compared with that at the higher temperatures of 20 and 25°C, ranging between 75 and 94% vs 19 and 22%, respectively. The highest cumulative hatch of 94% was obtained at a constant temperature of 15°C at 290 days. However, the lowest cumulative hatch of 33% was obtained after initial exposure to 5°C followed by transfer to 25°C at day 290. In general, incubating the cysts at lower initial temperatures of 10 or 15°C for 58 days gave the highest initial hatching rates 1 week after exposure to the final temperatures. Under natural temperature conditions in the field, J2 emergence started at 17°C in October and continued until the end of April in the temperature range of 2-17°C. A total hatch of 94% was recorded under field temperature conditions over the course of 1 year. Hatch of most J2 occurred in two peaks; the first in October and the second in February, and, accordingly, the greatest invasion by H. filipjevi is most likely to occur just after these two peaks. Heterodera filipjevi does not seem to have a diapause and could hatch anytime when wheat plants are available.
The distribution of important plant-parasitic and free-living nematodes in the cereal production areas of the Central Anatolian Plateau (CAP) of Turkey was investigated with systematic surveys. Two important plant-parasitic nematode groups were found widely distributed; cereal-cyst nematodes (78.3%) and root-lesion nematodes (42.6%). Cereal cyst nematodes (CCN) were identified as Heterodera filipjevi in 18 provinces. Heterodera latipons was found in only one province. Pratylenchus thornei and P. neglectus were the most widely distributed species of root-lesion nematodes. Other frequently recorded plant-parasitic nematodes belonged to the genera Geocenamus (52.4%), Pratylenchoides (35.6%), Helicotylenchus (29.7%) and Paratylenchus (19.2%). Konya on the southern CAP had a significantly high incidence of P. neglectus as well as free-living nematodes. The incidence of CCN was greatest in areas of sandy soils on the CAP, with densities of up to 95 cysts (100 g soil)−1. Population densities of Geocenamus, Pratylenchus and Pratylenchoides were high in some locations. Soil physicochemical properties were investigated for their relationship to nematode distribution. There was a slight positive correlation of P. thornei and clay content; conversely, there was a significant negative correlation of P. neglectus with clay and a positive correlation with sand. Electrical conductivity (EC) was positively correlated with P. neglectus. Nematodes in the genera Helicotylenchus, Paratylenchus, Trophurus and Tylenchorhynchus were only recorded at low population densities in the sampled area. By contrast, nematodes in the genera Aphelenchus, Aphelenchoides, Ditylenchus, Dorylaimus, Tylenchus and bacterivorous genera had relatively high populations. Total free-living nematodes were positively correlated with EC and zinc (Zn) concentration. The Zn content of soil was generally at a level deficient for plant growth.
The distribution of plant-feeding and free-living nematodes in large scale onion production areas in five geographical regions in Turkey was investigated in 2016 and 2017. Ditylenchus spp. and Tylenchus spp. were widely distributed. The stem and bulb nematode, Ditylenchus dipsaci, was found in 48 locations from 13 provinces. Other plant-feeding nematode genera were Pratylenchus, Paratylenchus and Pratylenchoides. Pratylenchus thornei was the most widely distributed root-lesion nematode species in onion fields in 11 locations from seven provinces. Pratylenchus neglectus was present in three locations and P. vulnus was in four locations. Aphelenchus spp. and Aphelenchoides spp. were the principal fungal-feeding nematodes in onion-growing areas. The most abundant bacterial-feeding nematode genera were Acrobeloides, Cephalobus, Eucephalobus and Rhabditis. Acrobeles and Wilsonema genera were low in occurrence and abundance. Nematodes from Dorylaimida and predator nematodes, Mononchus spp., were also found. The numbers of Ditylenchus from plant samples were significantly correlated positively to silt content, and significantly correlated negatively to organic matter and calcium content.