Infection Dynamics And Economic Thresholds Of Cereal Cyst Nematodes

Cereal cyst nematodes(CCN)are important parasitic nematodes on cereal crops and cause serious damage to wheat yield in worldwide.Heterodera avenae and H.filipjevi are the CCN species mainly infecting wheat in China.Up to now,H.avenae has been widely distributed in 16 provinces,and H.filipjevi distributed in Henan,Anhui,Shandong Province as well as in Xinjiang Autonomous Region.In this study,the infection dynamics of H.avenae in wheat field from Peixian,Jiangsu Province,was investigated systematically,and the effects of initial population densities of H.avenae,H.filipjevi or their combined infection on nematode reproduction and wheat growth were evaluated.Understanding the infection dynamics and economic thresholds of CCN can be beneficial to making integrated control strategy.The main results are as following:During the growth season of winter wheat,from October 2016 to June 2017,the infection dynamics of H.avenae in wheat field from Peixian,Jiangsu Province was investigated systematically.The results showed that a few second-stage juveniles(J2)of H.avenae hatched from cysts before wheat over wintering,and the number of J2s in rhizosphere soil of wheat is limited.Only few J2s invaded into roots and none of them developed into next stage.During the re-greening period,the hatching peak of J2s appeared in rhizosphere soil and the invasion peak of J2s into root was appeared as well.During the tassel and earing stage,white females on wheat roots were visible with naked eyes,several males were detected from root and rhizosphere soil.During the maturation period,the white females matured gradually and changed into brown cysts,and finally fell into soil for over-summering.The Peixian population of H.avenae finished one life cycle during the whole growth season of winter wheat.During the growing season of winter wheat in year 2016-2017,the effects of initial population densities(Pi)of H.avenae and H.filipjevi on nematode reproduction and wheat growth were evaluated in PVC tube experiments under natural conditions.The results showed that the reproduction factor(Rf)of H.avenae,H.filipjevi or their combined inoculation on wheat cultivar 'Zhengmai 9023' were all decreased with the increasing population densities.The reproduction factor was 8.8 when Pi was 0.5 egg/mL soil,while Rf was 2.3 when Pi was 64 eggs/mL soil.The plant height,aerial shoot dry weight,root dry weight and grain yield were also decreased with the increasing of Pi,indicating the negative relationships between them.The growth of wheat and grain yield decreased significantly when Pi was higher than 8 eggs/mL soil.Using the Seinhorst model,the tolerance limit value(T)was calculated based on the wheat grain yield.The T values of 'Zhengmai 9023'to H.avenae,H.filipjevi and their combined infection were determined as 8.7,9.3 and 11.3 eggs/mL soil,respectively.The integrated control strategies for cereal cyst nematodes in wheat field should be taken when the population densities are higher than these economic limit values.