Etiology And Management Of The Yellowing And Decline Of Fortunella Japonica In Youxi County,Fujian Province

Kumquat(Fortunella japonica)is one of the characteristic fruit trees in Youxi County,Fujian Province.In recent years the yellowing and decline of Kumquat has been occuring widespread in the producing area and it has become a severe production problem of Kumquat in Youxi County.During Dec.2016 to Dec.2017,the research on the problem of yellowing and decline of kumquat was done,and the results showed the etiology of the disease is slow decline disease caused by citrus nematode(Tylenchulus semipenetrans).Field control tests were implemented.The results would have an important significance for sustainable development of Kumquat industry in Youxi County.1.Tylenchulus semipenetrans was identified as the causal agent of yellowing and decline disease of Kumquat in Youxi County.The results are of vital importance for prevention and control of the diseases.A survey of yellowing and decline of Kumquat was conducted in the producing area in Youxi County.The results show that T.semipenetrans is widely distributed in Kumquat producing regions,and is the causal agent of the disease of Kumquat based on field sample,molecular identification and detection by the specific primer.The symptom of Fortunella slow decline disease is described in details.Manifests yellowing and decline,yellowing beginning at the leaf vein,leaf and fruit becoming smaller,root stunting and decay are the most conspicuous symptoms of slow decline of Kumquat induced by T.semipenetrans infection.The morphology of T.semipenetrans collectd from roots of Kumquat was described.The rDNA-ITS regions,18S,28S-D2D3 of populations of T.semipenetrans collected from Kumquat roots were amplified and sequenced,and Phylogenetic trees derived from Maximum Likelihood and Bayesian analysis were performed,and results showed that the close relation among the populations of T.semipenetrans from the world.By using the specific primer OI1 and OI2 to detect Candidatus Liberibacter spp.in yellowing leave samples,and gave negative results.2.The pathogenic nematodes collected from roots of Kumquat were identified.T.semipenetrans is the dominant population of pathogenic nematodes living around roots of Kumquat,the other six nematode species were identified as follows Xiphinema hunaniense,X.brevicolle,Paratylenchus nanus,Rotylenchulus reniformis,Aphelenchus avenae and Helicotylenchus dihystera.3.The field tests were implemented for controlling Fortunella slow decline disease with fungi-manure of Paecilomyces lilacinus PL89 and 10%Fosthiazate,both achieved the obvious effect.The results of the experiment demonstrated that utilizations of both 10%Fosthiazate or Paecilomyces lilacinus PL89 are able to achieve favorable suppression of second stages juveniles T.semipenetrans.The experiment investigated the colonization of P.lilacinus in the rhizosphere and discovered that P.lilacinus were dominant at rhizosphere after 6 months.It does not exist the obvious antagonism with the common funguses such as Penicillium,Aspergillus and Trichoderma in the soil.