| Wheat stripe rust,caused by an biotrophic fungus Puccinia striiformis f.sp.tritici(Pst),causing frequently significant wheat yield losses resulting from the disease epidemics.Pst is macrocyclic rust with five spore stages,and has asexual and sexual cycles.At the asexual cycle,Pst mainly infect wheat(Triticum aestivum L.),and also infect barley(Hordeum vulgare L.)and other gramineous grasses.At the sexual stage,it attacks alternate(aecial)host(Berberis spp.and Mahonia spp.).So far,we isolated some Pst samples from diseased barberry in three single year in China and demonstrated that in China Pst completes its sexual cycle under natural conditions and indicated indirectly that in spring basidiospores produced by germination of viable teliospores infect young leaves of barberry.However,recently domestic and foreign studies suggested that under natural conditions teliospores bearing on infected wheat tissue lost their viability after summer,autumn and winter due to complete degradation of the teliospores.In the next spring,there were no viable teliospores resulted in mismatch with growth of barberry in phenology and in not infect barberry after emergency of new leaves of barberry.Whereas,the question is where the viable teliospores come from? In recent years,we conducted field investigations in Gansu where it is an important oversummering area for Pst,and found that some gramineous grasses were infected by stripe rust and formed teliospores in autumn.Whether the grasses can be infected by Pst? How about viability of teliospores after overwintering? Whether the teliospores can germinate to produce basidiospores infecting barberry? Therefore,we carried out a series of experiments and reported that the results were as follows.1.In Gansu,in which Leymus secalinus,Elymus cylindricus,and Poa pratensis were major grass species and distributed widely.The three grass species were infected by stripe rust and formed teliospores in autumn.2.In autumn and after overwintering,teliospore produced on the three grasses can germinate.Teliospores from 47 leaf segments of the three grass species collected in theautumn of 2014 and the spring of 2015 successfully infected barberry B.shensiana producing aecia.Of the 47 leaf segments bearing teliospores for inoculation,26,9,and 12 were derived from Leymus secalinus,Elymus cylindricus,and Poa pratensis,respectively.Totally,of 92 Pst isolates produced from 2744 single-aecial cups derived from 584 aecidia,63 were highly virulent(infection type,IT 3-4),and 29 were lowly virulent(IT 1-2),respectively.3.Of 63 Pst isolates from 92 isolates,48 were derived from Elymus cylindricus and accounted for 76.2%,4 were derived from Leymus secalinus,accounting for 6.3%,and 11 were derived from Poa pratensis,accounting for 17.5%.Twenty six of the 63 Pst isolates matched with known Pst races,and other 37 were new races(14 were virulent to Hybrid 46,Suwon 11,and Guinong 22;16 were completely or nearly immune to all of the differentials except for Mingxian 169;3 isolates can only be infected by one or a few of certain differential and Mingxian 169,other 4 had mixed reactions with high and low infection types on some certain Chinese differential hosts).4.Molecular detection showed that DNA of the tested 63 Pst isolates were amplified specific fragment with Pst–specific primers,indicating that sexual progeny population isolated from the three grass species were Pst.5.The results based on traditional and molecular biology showed that the gramineous grasses play an important role in survive of Pst teliospores for overwintering and infecting barberry to complete its sexual cycle.These results suggested that under natural conditions the gramineous grasses can harbor viability of Pst teliospores infecting barberry to complete its sexual reproduction and generating new diverse races in spring in China.It also improves epidemic system of wheat stripe rust and provides scientific basis for making integrated strategy for control of the disease in China. |
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