Identification And Biology Of The Root-lesion Nematode Causing Chinese Yam Red Spot Disease

The red spot disease caused serious damage to the production of Chinese yam in resent years, and reports on the species of root lesion nematode causing this disease were inconsistency. In this thesis the morphological, morphometrical and molecular characters of the nematodes were systemically studied. Results showed that the morphometrical values were consistent with those of Pratylenchus coffeae described before, the ITS and LSU D2-D3 sequence analysis comfirmedproved that the nematode causing the red spots disease is P. coffeae.Its biological characters were studied. The optimum temperature for P. coffeae embryonic development was 25-28℃, It the temperature does not only affect the hatch rate, but also affect on the hatch time, needed 7~9d for eggs hatching at this temperature. Its hatching was inhibited after stored at 4℃. After 20d stored at 4℃, the hatching rate was only 23.02%.The temperatures influenced the span of nematode life cycle significantly. The life cycle span of the P. coffeae life cycle was 23~28d at 25℃, both the higher or lower temperature could prolong its life cycle, the hatching time were 40.6 d, 35.15 d and 30.5d at 17 ℃, 20℃ and 30℃ respectivly.The nematodes were cultured with on carrot disks at different temperatures and densities. Its reproductive rate was 54.4 at 20℃, 320.1 at 25℃ and 175.3 at 30℃ after 8 weeks;. The nematode final population increased with the initial nematode population, but the nematode had the highest reproductive rate when the nematode initial population was 60, the nematode final population increased with culture time, but its reproductive rate may decrease at the end of the culture because of lacking food.The relationship between nematode survival rate and the storage time at -5 ℃ could be described by liner formula, the mortality was 100% after when be kept at -5℃ for 2.5h, while after 1.5h it would be 39.02% at 40℃. The experiment result showed that P. coffeae could not resistant strong ultraviolet irradiationion;, the survival rate was 42.31% after treated by UV for 6min. The tolerance of P. coffeae to the desiccation was tested. Result showed that 50% nematode died in 5min at the 70% of relative humidity. The water content of soil had less effect on the survival rate of the nematode, 75%~90% nematode survived at 25% to 6.25% of soil water content.The host range test showed that P. coffeae could feed on cucumber, corn, tomato, wheat, eleusine and so on, but the host fitness was significantly different between amongdifferent hosts.According to the potted test, the loss was increasing exponentially when the nematode density was 1 per 1 gram of soil.The population density had little effect on morphological characters, but temperature and hosts could may changed the morphometrical values a lot especially the body length, b, b' and c' value.