| Spot blotch is a foliar disease of barley caused by the fungal pathogen Bipolaris sorokiniana(Sacc.) Shoemaker(abbreviated as Bs), resulting in remarkable reduction in barley grain yield and its quality. It has been threatening seriously the barley production in Northeast of China in recent two decades. In this study, a set of barley differential hosts has been established with cultivars of different resistance levels to spot blotch through selecting commercial barley cultivars and important resistance lines; and analyses has been conducted on virulence variation among the pathogen population, major pathotypes and their distribution areas with the differentials. Genetic diversity of the strains collected from different regions has been characterized with AFLP molecular markers to find out the relationship between pathogen virulence variation and its distribution area, and the genetic difference between the pathogen strains isolated from hosts of barley and wheat. Using the typically high virulence strains we have screened the barley germplasm collection for the resistance accessions. In addition, the host specificity of B. sorokiniana for barley and wheat was explored. The results in this study could technically benefit the control of barley spot blotch.Based on the stability of resistance level and infection types, big difference in genetic backgrounds between barley cultivars, a set of differential hosts which was suitable for testing the pathotypes of spot blotch pathogen population derived from China was established. The candidate barley differentials for spot blotch pathogen were selected from 78 representative major cultivars and backbone parent lines used widely in China by inoculating with 21 strains of Bs. Finally, twenty one candidates were obtained, of which twelve cultivars or lines with a different resistance level to spot blotch were chosen as differential hosts of Bs, including highly resistant cultivars such as ND B112, Kenpimai 11, 10PJ-24; moderately resistant ones such as Kenpimai 9, Mengpimai 3, Tradition, Bowman; moderately susceptible ones such as Kenpimai 7, Vorunda, Morex; and highly susceptible ones such as Zaoshu 3 and ND 5883. According to the virulence test results with this set of differentials, 71 stains isolated from barley host were classed into 18 pathotypes, of which 83.1% of the tested strains belong to 11 pathotypes. The most predominant race is C0466, whose appearance frequency is 12.7%, and the second potential dominant races are C0027, C0067 and C0267, all of whose frequency is 9.9%.In this study the genetic diversity of 45 Bs strains isolated from host barley and 27 strains from wheat was characterized with AFLP molecular markers. 261 polymorphic AFLP DNA bands were detected using 23 AFLP primer combinations. Cluster analysis results with the UPGMA(Unweighted Pair-Group Mean Average) method of software NTSYSpc2.2 showed that 72 strains were clustered into group A and group B. 91.5% of the members in group A are the strains isolated from barley, and 92.0% of of the merbers in group B are those from wheat, indicating that significant difference in DNA polymorphism exists between the spot blotch pathogen populations isolated from hosts barley and wheat respectively. Furthermore, the 45 Bs strains from host barley were clustered into 5 groups. The results showed that there is genetic diversity even among the strains originating from the same sampling location.And we found that there is difference between the cluster results with DNA polymorphism and pathotypes of the strains, but obvious correlation was observed between DNA polymorphism of the pathogen strains and their geological distribution areas.Through inoculating two barley lines ND B112(highly resistant), ND 5883(highly susceptible), and two wheat cultivars Yangmai 6(moderately resistant) and Longmai 15(highly susceptible) with highly virulent strains ZBTX14479 and ZBTX14594(collected from barley and wheat respectively) and low virulent strains BTX14474 and 13YJ1-46(collected from barley and wheat respectively) at seeding stage, significant difference was observed in the infection types of pathogen strains used on hosts barley and wheat. In the histopathological microscope observation, there are differences in the rate of aspersorium formation, and the formation of intracellular epidermal hyphae(IEH) and intercellular mesophyll hyphae(IMH) of the strains tested on leaf surface of barley and wheat seedlings respectively. Therefore, the difference is apparently present in host specificity of B. sorokiniana infection on barley and wheat.Using highly virulent strains ZBTX14479, ZBTX12014 and ZBTX13027 to inoculate 369 barley accessions for spot blotch resistance identification at adult-plant stage in field, we found that most of the tested accessions were susceptible to spot blotch. The percentage of the susceptible ones to the strains used above was 84.43%, 91.48% and 87.50% respectively. Among the 369 barley accessions, 16, 15 and 38 accessions were resistant to all three strains, two and only one of the three strains respectively. So, the resistance analysis results would accelerate the exploitation and utilization progress of new spot blotch resistance genes of barley. |
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