Genetic Control And Application Of Resistance To Cereal Cyst Nematode In The Wheat Cultivar Madsen

Cereal cyst nematode?CCN?has been detected in 16 provinces in China.In particular,CCN seriously threatens the wheat production in Henan province.The co-existence of both species of Heterodera avenae and H.filipjevi together with multiple pathotypes complicates the control of CCN damages.At present,the majority of the Chinese commercial wheat cultivars are susceptible to CCN,and major problem of breeding for CCN resistance using host resistance is the unavailability of effective resistance resources.The winer wheat cultivar Madsen from the US proved to have broad spectrum of resistance to the CCN populations from China.The present study was initiated to test the resistance of Madsen against different nematode populations occurred in China,to investigate the impact of wheat cultivars with different CCN resistance on the CCN population in the rhizoshperic soil,to discover the genetic control of the CCN resistance and to develop germplasms using Madsen as the source of resistance.The main results are as follows:1.Madsen was resistant against different populations of 6 H.avenae populations and 4 H.filipjevi populations collected from Henan,Shandong,and Anhui provinces in both field tests and inoculation tests.The number of CCN on the roots of Madsen were significant less than Wenmai 19,indicating Madsen had a stable and spectrum of resistance to the CCN populations from China.2.The J2 of H.avenae were found to be attracted to the roots of Madsen and the susceptible control Wenmai 19 in the PF-127 gels.However,the roots of Madsen grew normally in the CCN-infested wheat fields.The resistance of Madsen to the nematode was indicated by the penetration of fewer juvenile nematodes?25 day after inoculation?and the final number of cysts on roots compared to the CCN-susceptible genotypes.Conventional enumeration of white female nematodes on the plant roots,reproductive factor?Rf?and PreDicta B test,a molecular diagnostic approach developed from The South Australian Research and Development Institute,were used to determine the CCN populations in the rhizosphere of seven wheat cultivars with different reactions to CCN in two consecutive years conducted in the fields of H.filipjevi and H.avenae.The three methods consistently demonstrated that the growing of a CCN-resistant cultivar reduced not only the multiplication of the nematode,but also the nematode population density for the infestation of wheat in the next cropping season.3.Using a recombinant inbred line?RIL?population derived from the cross MadsenxLiangxing 99,a high-density genetic linkage map was constructed with the aid of Illumina iSelect 90K SNP assay and SSR marker.The genetic map comprised of 3219 polymorphic markers,covered 4576.11 cM with 2466 loci,and could represented all of the 21 wheat chromosomes.Based on the phenotypic data in the three field assessments from 2013 to 2015 and two greenhouse tests in 2013 and 2014 against H.filipjevi,the QTL,QCre-ma7D,was detected on chromosome 7D,which explains 13.6%?42.0%of the phenotypic variation.Because no gene or QTL for resistance to H.filipjevi is detected on chromosome 7D,QCre-ma 7D was most likely a new QTL against H.filipjevi.Another QTL,QCre-ma2A,for resistance to H.avenae based on the phenotypic result of field test and inoculation test in 2016 was detected on chromosome 2A,which explains 15.4%?19.6%of the phenotypic variation.This QTL is most likely Cre5 fro resistance to H.avenae previously identified on this chromosome.We validated three competitive allele-specific PCR?KASP?assays?Kukri_c45628₈92,BS00021745₅1 and Kukri_rep_c68335₆07?that linked to QCre-ma7D and developed the marker-assisted selection technique for the selection of QCre-ma7D.Based on the phenotypic performances of the wheat cultivars in the pedigree of Madsen to both Heterodera species under field and greenhouse environments,in combination with the results of genotype analysis,both QTL for the CCN resistance of Madsen were most likely derived from Aegilops ventricosa segments via the parent VPM1.4.Madsen was highly resistant to H.filipjevi and H.avenae,however,late heading date and susceptibility to powdery mildew prevent its direct use in breeding.Liangxing 99 carries gene Pm52 for resistance to powdery mildew.With the aid of molecular marker-assisted selection technique,lines ML99-18 and ML99-46 with resistance to both CCN and powdery mildew were developed from the progeny of cross MadsenxLiangxing 99.These lines inherited the CCN resistance QTL loci from Madsen and the resistance gene Pm52 from Liangxing 99.They had the agronomic performances and heading dates that resembled Liangxing 99.These germplasm lines can be used in developing disease resistant wheat cultivars.