Infection Process And Seed Transmission Of Verticillium Dahliae On Sunflower And Cross-pathogenicity Of Verticillium Spp.Isolated From Different Hosts

Sunflower Verticillium wilt is a widespread and destructive vascular disease.It is caused by the soil-borae fungal pathogen Verticillium dahliae Kleb.which affects seed quality and leads to significant losses in sunflower yield.In this study,one transformant of V.dahliae which contains green fluorescent protein(GFP)was used to study its colonization process on sunflower;it was confirmed that the sunflower testa is an important tissue for colonization and seed transmission of V,dahliae;an MNP-10-based assay was developed to detect V.dahliae on sunflower seeds and studied the genetic diversity of V.dahliae isolated from sunflower seeds.Finally,we also clarified the biological morphology and the cross pathogenicity of Verticillium spp.isolated fromdifferent hosts.The results we obtained are as follows:1.A total of 120 V.dahliae transformants were obtained and labelled with GFP by ATMT.Ten of the transformants were selected based on their phenotypic similarity to the wild-type strain,they were then compared with the wild type strain for growth rate,fecundity,total crude toxin production,and virulence.The transformant VdBM9-6 was chosen for subsequent studies,since its morphology,biological properties,and virulence were indistinguishable from the wild type strain.2.It was observed that conidia could germinate and develop into mycelia on sunflower root caps,hairs and elongation zones of lateral roots hence producing more elaborate networks of hyphae along the root surface and also exhibiting growth within the grooves between epidermal cells.After successful colonization of the taproot of sunflower,V.dahliae quickly expanded up via vascular system to the plant parts above ground,such as stem,petiole,leaf vein,corolla,hull and testa.3.MNP-10 selective media was used to detect V.dahliae on sunflower seeds,which were collected from inflorescences harvested from sunflower plants inoculated with V.dahliae and symptomatic plants in the field,respectively.The results indicated that MNP-10 medium could be used to quickly and accurately identify the infection rate of V dahliae on sunflower seeds.4.The infection rate of V.dahliae on sunflower seeds of 105 sunflower varieties(19 oil varieties and 86 confectionery varieties)was detected by using MNP-10 plating.The results showed that 2 of 19 oil varieties('KY2' and 'KY3')carried V.dahliae with an infection rate of 1%,the seeds of remaining 17 oil varieties were uninfected,and 43 of 86 confectionery varieties were infected with V.dahliae at a percentage rate ranged from 1 to 5%.Among them,only 'Gankui 2' had an infection rate of 5%,'H16-22','H16-24'and other fifteen varieties were with a rate of 1%,the seeds of remaining 43 confectionery varieties did not carry V.dahliae.5.A total of 89 strains were isolated from sunflower seed,and all of them were identified as V.dahliae.The race and mating type of the 89 isolates were identified by using specific primers.All isolates were characterized as race 2,indicating that race 2 was the only race type of V.dahliae on sunflower seed.Of the total 89 isolates tested,62(69.66%)were of MAT1-1-1 idiomorph and 27(30.34%)were of MAT1-2-1 idiomorph,indicating that MAT1-1-1 is much more predominant on sunflower seed.6.A total of ten of Verticillium spp.were isolated from different hosts,which were sunflower,cotton,eggplant,lettuce and potato.Variable colony morphology and growth speed were observed among the ten tested isolates and the pathogenicity of each isolates always showed the highest virulence on its own hosts.The race and mating type of the ten isolates were identified by using specific primers,and the results indicated that except Ls 16-1 isolated from lettuce was race 1,all the other tested isolates were characterized as race 2 and the mating type of the ten tested strains were all MAT1-2-1.