Field Production And Viablility Of Puccinia Striiformis F.sp.tritici Teliospores And Occurrence Of Its Sexual Reproduction In Qinghai,Yunnan And Guizhou Provinces

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is heteroecious and macrocyclic rust.The fungus is biotrophic rust,depending on living host.The pathogen depends on wheat as the primary(telial and uredinial)host and barberry as the main alternate(pycnial and aecial)host to complete the complete life cycle.Viable teliospores are essential for the initiation of sexual reproduction of Pst.Studies showed that the teliospores were unable to infect barberry because teliospores are degraded under the fluctuating moisture and temperature conditions in the U.S.Pacific Northwest.However,in China existence of natural infection of Pst on susceptible barberry bushes under field conditions has been demonstrated in some province including Gansu,Shaanxi,Sichuan and Tibet.Those results indicate that in those regions viable Pst teliospores could spread to barberry in which teliospores cause infection.However,little is known about origin of viable teliospores resulting in Pst infection on susceptible barberry in spring.Further study is needed.Qinghai,Yunnan and Guizhou are considered as important epidemiological regions of wheat stripe rust in China.Wide distribution of a great number of susceptible barberry were observed in these regions,where the barberry rust infection occurs all year round were common in spring.Up to now,studies on Pst infection on barberry in the spring in these areas has not been reported.In this study,field investigations were performed to observe production,germinability of Pst teliospores produced on growing wheat plants at different growth stages in fields in epidemiological regions of west China in 2018 and 2019 cropping seasons,and to check viability of Pst teliospores inside wheat straw stacks.A combined method of biological and molecular technique was used to detect Pst infecting barberry in spring,and to evaluate availability of Pst-specific markers for detecting the rust fungus infecting barberry bushes.Population structure of Yunnan and Guizhou Pst isolates were also analyzed,which could provide a basis for making strategy for management of wheat stripe rust in China.Main results were as follows:1.Pst teliospores are produced at all growth stages of wheat under field conditions,and teliospores harbored inside wheat straw stacks after wheat harvest are able to survive through winter to following spring for potential infection on barberry.Studies have shown that telial formation of Pst were observed at various locations throughout the surveyed winter/spring wheat regions.Wheat straw stacks keep teliospores viability to next spring,overlapping with re-growth of barberry in spring.These observations indicated that initial formation of Pst telia in the southern winter wheat region(December of last year at Yunnan,from January to February at Sichuan and Guizhou,and March at the southern of Shaanxi)was earlier than those in the northern winter wheat region(March to April at Gansu and the middle of Shaanxi,June at Qinghai)as long as wheat plants were infected.The production rate ranging from 1.0-88.9% and being 7.3% at tillering stage,9.3% at early booting stage.The telia samples existed in 37.5% wheat straw stacks in 2018 and 21.4% in 2019.In general,teliospores from most telial samples were capable of germinability,although the overall germination rate was low from 0 to 28.7%.The percentage of leaves bearing viable teliospores and germination rate of Pst teliospores were averaged 78.5% and 5.1% at tillering stage,83.2% and 9.4% at early jointing stage,and 91.8% and 4.9% after booting stage in 2018 and 2019,respectively.Among wheat straw samples bearing telia collected from Qinghai,the number of samples with germinable teliospores ranged from 23.9% in January to 4.4% in June in 2018 and from10.3% in January to 6.0% in May in 2019.2.Sexual reproduction of Pst on barberry was determined to occur in the eastern of Qinghai,providing direct evidence for the variation of the rust pathogen and occurrence of wheat stripe rust.In2018,7 Pst(3.45%)samples were isolated from barberry in eastern of Qinghai in spring.Two to five phenotypes were detected from one of the 7 Pst samples.Nineteen phenotypes among 28 single uredinium strains deriving from those samples showed a high Kosman diversity index(K=0.652).Twelve SSR markers were detected 24 MLGs among 28 Pst single uredinium isolates,representing a high Shannon diversity index(I=0.701)and expected heterozygosity(He= 0.368),respectively.All results indicated that the Pst on Berberis species produced from sexual reproduction.At the same time,detection for the above samples by Pst-specific markers of YR(F)/YR(r1)and EF-1-F/EF-1-R showed that the two pairs of markers could be used to detect Pst infecting barberry.Additionally,besides Pst,other rust including P.poae-nemoralis could infect barberry based on ITS and EF-? gene sequence analysis.3.Sexual reproduction of Pst in Nayong,Hezhang counties of Guizhou and Fuyuan county of Yunnan might have little effect on the occurrence of wheat stripe rust in fields.No Pst on barberry was detected by inoculation on wheat,phylogenetic analysis of conserved gene and markers of YR(F)/YR(r1)and EF-1-F/EF-1-R in aecial collections from Nayong,Hezhang of Guizhou and Fuyuan county of Yunnan in which genetic diversity of Pst populations in these regions were low(Expected heterozygosity(He)ranging from 0.213 to 0.306).Pst populations from Shilin and Mile in southeastern Yunnan was unique,and a sexual Pst population from Mile could be potentially existed(rBarD=-0.03924,P=0.824).In summary,Pst teliospores are produced at all growth stages of wheat under field conditions.Viable teliospores on wheat plants at all growth stage or inside wheat straw stacks can be maintain their viability to shooting of the barberry and potentially infect the barberry in spring.The results showed that teliospores are a key factor affecting occurrence of the sexual reproduction of Pst.The combination of Pst-specific markers YR(F)/YR(r1)and EF-1-F/EF-1-R may be used for the detection of Pst infecting barberry,which provide a technical support for rapid detection of Pst infecting barberry.Sexual reproduction cycle of the rust pathogen exists in eastern Qinghai,but not in northwestern Guizhou and Fuyuan of Yunan due to quietly low frequency.A unique group of Pst populations was found in southeastern Yunnan,including Shilin and Mile,and Pst from Mile was possibly produced sexually.The results will provide a theoretical basis for making strategy for the management of wheat stripe rust.