In Planta And In Vitro Effects Of Major QTL Fhb1 On Wheat Resistance To Fusarium Head Blight

Fusarium head blight(FHB)of wheat,caused mainly by Fusarium species complex,is a globally important disease.It not only leads to yield reduction,but also produces mycotoxins in the infected grains,threatening human and animal health.Fhb1 is a well-known locus with major effects on reducing FHB severity for its large and stable effects in different genetic backgrounds;but our understanding on its resistance mechanism is still very limited.In this paper,the resistance mechanism of Fhb1 was analyzed in planta and in vitro,using near isogenic lines(NILs)contrasting in Fhb1 alleles.In planta,11 pairs of Fhb1 resistant and sensitive NILs were used for comparisons of disease severity and the content of DON accumulated in the grains after harvest under UBFI,BBFI and BRII to analyze the advantages and disadvantages of these methods and to provide reference for the accurate evaluation of resistance phenotype of FHB.In vitro,three types of wheat tissues(rachis internode(RI),grain and palea and lemma(PL))at three developmental stages(5,15 and 25 days post anthesis,DPA)from a pair of near isogenic lines(NILs)contrasting in Fhb1 alleles were co-cultured with F.graminearum on water agar(WA)medium and on trichothecene biosynthesis induction(TBI)medium,and the tissular effects of the NILs on fungal growth and toxin production were compared to uncover the resistance mechanism of Fhb1.The main results are as follows:We compared proportion of symptomatic spikelets(PSS)and DON content in grains in Fhb1 NILs among the three inoculation methods,upper bilateral floret injection(UBFI),basal bilateral floret injection(BBFI)and basal rachis internode injection(BRII),The results showed that there was a significant(P<0.01)difference in PSS between the NILs contrasting in Fhb1 alleles.For the susceptible lines,BBFI frequently caused early withering of spikelets at the upper part of inoculation point;Although UBFI did not cause early withering of spikelets,it reduced the difference in PSS between the resistant and the susceptible lines.Unexpectely,under BBFI method,there was no significant(P>0.05)difference in DON content of the grains between the resistant and susceptible lines;Under BRII method,there was a significant difference(P<0.05)in DON content of more than 100 PPB between between the NILs contrasting in Fhb1 alleles;Surprisingly,UBFI method maximized(P<0.01)the difference in DON content of more than 1000 PPB between the NILs contrasting in Fhb1 alleles,indicating that DON content was subject to inoculation methods or infection point.In the study of the effect of Fhb1 in vitro,we found that on WA medium,all tissues promoted funga1 growth,but none induced DON accumulation,suggesting tissues per se are not able to incite DON production.On TBI medium,exogenous toxin-inducing substances stimulated F.graminearum to produce DON and the inhibitory effects of Fhb1 on both funga1 growth and DON accumulation were heavily dependent on the tissue type and development stage,and the inhibition of F.graminearum depends on the accumulation of DON to a large extent.PL might play a decisive role in inhibiting the growth of the pathogen and DON production.