Diversity And Characterization Of Plant-parasitic Nematodes Associated With Cereals And Yam (Dioscorea Spp.)

Cereals and yams are part of the most essential food supply in the developing countries.They have nutritive as well as therapeutic value.Plant-parasitic nematodes(PPN)pose a major threat in the production and economy of these crops in a number of ways,resulting in significant yield losses.The association of these crops with PPN has been recorded in some parts of Nigeria and China.However,little research had been conducted in Nigeria and China on the diversity of PPN associated with these crops.Therefore,the objectives of this study were to identify,determine and characterize morphologically and molecularly the most important species present in the agricultural fields cultivated with cereals crops and yam in Nigeria and China.1.Survey of cereal(maize,rice and wheat)fields was conducted in Kaduna(Northern guinea savannah)and Kano(Sudan savannah)States of Nigeria between February and March 2019.In each State,three Local Government Areas(LGAs)and three farming communities per LGA were visited.A total of 450 composite soils were collected from the rhizosphere of cereal crops.Data pooled across the 18 fileds of both states showed that the species Tylenchorhynchus annulatus was the most prominent in the rhizosphere soil and had the highests prominence value(PV)of 92 individuals/(100 ml),followed by Ditylenchus(represented by D.destructor,D.arachis and D.persicus)(PV = 70)and Pratylenchus(PV = 39).These species occurred in 60,50 and 34% of the fields sampled,respectively.The least occurring species were Litylenchus and Criconemella with PVs of 1.2.The stunt nematodes(Tylenchorhynchus spp.)being the most occurring species from the surveyed cereal samples were characterized using integrative taxonomy and molecular approaches.The molecular and morphological studies identified and confirmed the presence of T.annulatus as the occurring specie in the Nigerian Savannahs.The first molecular characterization and sequences of the ITS and 28 S r DNA gene for T.annulatus and other species from Nigeria(Ditylenchus destructor,D.arachis and D.persicus,Aphenlenchus avenae,Litylenchus crenatae mccannii,and Bursilla)were provided in this research.Also,from our literature search,this is the first report of the species on wheat,maize and rice in the savannahs of Nigeria.Further study to test the pathogenicity of these nematode species found in this survey on cereal crops needs is recommended for the prioritization and development of efficient management strategies.3.Similarly,in China,between 2020 and 2021,baseline surveys of yam fields in China(Jiangxi and Shandong provinces)were conducted to investigate the occurrence,distribution,and abundance of plant-parasitic nematodes in major yam growing regions.In China,a total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were extracted from 7 counties in Jiangxi and Shandong provinces.Standard protocols were used to extract nematodes from both soil and roots/tubers and identify them at the genus level.Pooled data shows that 16 species and 13 nematode genera were recovered respectively.The five most prominent species/genera on yam rhizosphere were Pratylenchus coffeae with frequency of occurrence of 73%,Meloidogyne(65%),Merlinius(74%),Rotylenchulus reniformis(51%),and Helicotylenchus dihystera(43%).In the roots/tubers,in terms of frequency of occurrence and prominence value,the three most prominent species were Pratylenchus coffeae(69% and 344/individuals),Meloidogyne incognita(65% and 266/individuals)and Rotylenchulus reniformis(21% and 52/individuals),respectively.This finding reveals the diversity of plant-parasite nematodes associated with yam in the major yam-growing regions,as well as the fact that P.coffeae,M.incognita and R.reniformis were the major parasitic nematode pests of yam encountered in China.Based on the abundance and occurrence of ectoparasites like Merlinius spp.,Tylenchorhynchus spp.,and Tylenchus spp.in the rhizosphere soil,ectoparasitic nematodes may play a major role on yam than previously believed.Therefore,further study to determine the virulence and damage thresholds of each of these four major species(P.coffeae,Meloidogyne [denoted by M.incognita,M.ethiopica and M.hispanica],R.reniformis and Ditylenchus)is needed,in order to put in place proactive pest control measures.These findings provide baseline information for nematode parasite occurrence on cereals and yam in Nigeria and China.