Differences In Stripe Rust Resistance Of Wheat Varieties With High Or Low Canopy Temperatures In The Field And Virulence Variation Of Puccinia Striiformis Through Somatic Recombination

There is difference of the canopy temperature among different wheat genotypes after anthesis in a same particular microclimate environment.The varieties that have lower canopy temperature is named cold type wheat(CTW)and which have higher canopy temperature is named warm type wheat(WTW)in same ecological environment.There are differences of the characteristics of physiological and bio-chemical,and anatomic structure of leaves between the CTW and WTW varieties.The difference of the canopy temperature of two types was not affected by the draught and rainy conditions.There are rarely reports about the resistance of different temperature typical wheat to stripe rust and analysis under stripe rust infection.There are differences of the characteristics of physiological and bio-chemical,and anatomic structure of leaves between the CTW and WTW varieties.There are rarely reports about the resistance of different temperature typical wheat to stripe rust and application in the field.Puccinia striiformis Westend.is an obligate biotrophic basidiomycte fungus causing stripe rust on wheat.Wheat stripe rust,caused by forma specialis P.striiformis Westend.f.sp.tritici Eriks.(Pst)of the species,is one of the most destructive diseases on wheat in the world.The virulent races evolve rapidly and can render previously resistant varieties susceptible within only a few years.The most economic and effective method to control stripe rust is to grow resistant varieties,but it is being challenged now.Therefore,it is important to mining and utilize the wheat resistance to stripe rust in the field to control the disease effectively.In this study,the breakthrough point that is the relationship between the wheat canopy temperature and field resistance.Different resistance and the mechanism of wheat varieties with lower and higher canopy temperature to strip rust in the field and virulence variation of Puccinia striiformis by somatic recombination in the greenhouse were analyzed,achieved the following results:1.This study is the first to define the field performance and different resistance to stripe rust between the CTW and WTW varieties.Five wheat varieties(NR 9405,9430,Xiaoyan 6,Shaan 229 and RB 6)with different canopy temperatures were investigated for the resistance to stripe rust at the seeding and adult-plant stage in greenhouse.All five tested wheat varieties were exhibited adult-plant resistance to stripe rust in the greenhouse.2.In the field,there were no significant differences in the distribution and disease severity of stripe rust on five different canopy temperatures wheat varieties at the seedling stage.And,the high temperature wheat varieties(NR 9405 and 9430)had a significantly lower disease indexes,with a smaller increase in range,than the control(Xiaoyan 6)and the low temperature wheat varieties(Shaan 229 and RB 6)at the adult plant stage in the field conditions.The difference of canopy temperature in 5 different temperature wheat cultivars during the grain-filling period was very significant.The significant negative correlation between canopy temperature and disease index was shown during the grain-filling stage.There were differences in resistance to stripe rust between the CTW and WTW populations in the same background.3.The results showed that the microorganism species from the high temperature wheat varieties(NR 9405 and 9430)were richer than the control(Xiaoyan 6)and the low temperature wheat varieties(Shaan 229 and RB 6)in the heading and filling stage.The number and diversities of phyllosphere and endophytic microorganisms in the five different canopy-temperature wheat varieties were studied by using the culturable and non-culturable methods.This study provided theoretical basis for the difference of rust resistance between the CTW and WTW genotypes.4.This study is the first to obtain the molecular evidence that somatic recombination is a mechanism by which new variants can be generated in P.striiformis and lead to virulence variation.A total of 9 pairwise combinations involving 7 isolates of P.striiformis f.sp.tritici(the wheat stripe rust pathogen)and 2 isolates of P.striiformis f.sp.hordei(the barley stripe rust pathogen)were selected under controlled greenhouse conditions.“Parental” and selected variant “progeny” isolates were tested for virulence patterns on seedlings of the sets of wheat and barley differential cultivars.A total of 413 progeny isolates were obtained from the nine pairwise combinations of isolates,and 84 progeny isolates with virulence patterns were different from the parental isolates.Therefore,our results preliminary indicate that somatic recombination may occur.Simple sequence repeat(SSR)markers were used to identify somatic recombinant isolates.A total of 28 progeny isolates from the five pairwise combinations were tested by 6 of 11 SSR markers.Three had SSR marker patterns different from their “parental” isolates and the combined bands from both parental isolates,indicating that three isolates were recombinants.The three isolates were also determined as recombinants in the virulence tests.The results demonstrate that there is an effect of canopy microenvironment on the stripe rust resistance of wheat,and there is difference in resistance to stripe rust between the CTW and WTW cultivars.In general,high canopy temperatures are not favorable for strip rust development and may enhance the expression of adult-plant resistance.The present study provides a basis for utilizing the resistant characteristics of wheat to control stripe rust in the field,together with the optimal placement of wheat varieties and the development of ecological approaches for reducing stripe rust damage.On the other hand,it was to detect the direct evidence of somatic recombination of Puccinia striiformis f.sp.tritici through developing and characterizing experimental isolates using virulence tests and molecular markers under controlled greenhouse conditions.The results demonstrate that somatic recombination is a mechanism by which new variants can be generated in P.striiformis and lead to virulence variation.