Identification And Genetic Analysis Of Wheat Germplasm For Resistance To Black Point Caused By Alternaria Alternata

Black point of wheat is a disease caused by Alternaria alternata,Bipolaris sorokiniana and other pathogenic fungi.In recent years,the disease severity of black point gradually increased,and has a negative effect on wheat production.The wheat with black point disease has lower flour quality,lower seed germination rate and seedling growth.Some of these pathogens produce mycotoxins which may induce cancer.Alternaria alternata is a dominant pathogen of wheat black point disease in Henan province.There aren’t any genetic research about wheat resistance to black point caused by A.alternata has been reported yet untill now.In this study,we isolated some A.alternata strains from susceptible varieties in our laboratory.A rapid and specific nest-PCR method for detection of A.alternata in wheat was established.A number of typical black point resistant and susceptible varieties have been screened.The resistant germplasms can be used in wheat disease resistance breeding program.Segregation analysis mdoel of quantitative trait mixed major gene and polygene inheritance was applied to study genetic characteristics of resistance to black point and this provides a scientific basis for QTL mapping in the later study.The main results are listed below:1.Isolation and identification of the dominant pathogens.The pathogen of wheat black point in Henan province was investigated,one dominant pathogen is A.alternata.Several A.alternata strains were identified by morphological and molecular methods.The most toxic strains(named Ta-Aa-1)was obtained by inoculating with different A.alternata strains on wheat spikes.The colony of Ta-Aa-1 is dark black,and has a large amount spores.This laid a foundation for research about resistance to black point caused by A.alternata in the future.2.Establishment of a rapid detection of A.alternaria in wheat.Compared with the ITS sequences of A.relative fungi in GenBank,a pair of primers,namely Aa1F and Aa1R,were designed.A rapid and specific nest-PCR method for detection of A.alternata in wheat was established with fungal universal primers ITS1/ITS4 as the outer primers and Aa1F/Aa1R as the inner primers.The minimum A.alternata DNA concentration detected was 50 pg/μL.3.Screening of wheat germplasm for resistance to black point caused by A.alternata.Based on the statistical analysis,the broad-sense heritability for black point disease resistance of the 403 wheat genotypes was 65.0%,52.3%and 58.6%in 2010,2011 and 2012,respectively,which showed this disease was stronger affected by genetic factors compared to environmental factors.The results demonstrated that no wheat cultivar was immune to black point disease.All studied wheat genotypes were infected by black point pathogens to a different extent.Among the 403 studied cultivars,8.9%were resistant highly and 1.7%were susceptible highly.Black point incidence of the highly resistant cultivars was significantly lower than for the susceptible ones.4.Preliminary genetic analysis of wheat "Zhengfeng 9962" and "Zhengmai 7698" for resistance to black point caused by A.In this study,the resistant variety"Zhengfeng 9962" was used as male parent,the susceptible variety "Zhengmai 7698" as female parent.Segregation analysis mdoel of quantitative trait mixed major gene and polygene inheritance was applied to make genetic analysis of resistance to black point caused by A.alternata in F2 population of "Zhengfeng 9962 × Zhengmai 7698".The analysis result showed that the resistance to black point was controlled by a pair of major resistant genes and multiple minor genes,and the two major genes have interaction of additive,dominant,epistatic effects.The heritability of the major genes for black point disease resistance was 50.444%.Black point disease resistance was influenced by major genes,but also affected by a number of minor genes and the environment.