Studies On The Use Of Wheat Cultivar Mixtures For The Control Of Stripe Rust

Wheat stripe rust (yellow rust) is one of the most seriously diseases of wheat nationwidein China. Presently, There is no essentially change of the single resistant source though a largeamount of cultivars are growing in China. It is the key point that develop the reasonable,economic and effective approach of the use of cultivars and resistant sources. However, therapid development of the virulent races often circumvents the resistance in cultivars after theirrelease, which make the use of resistant cultivars a outstanding problem. Wheat resistancebreeding and cultivars alternation significantly follow behind the variation of races. Moreover,The excessive use of fungicide make the cost continuously increasing. And the environment isbadly damaged. It is very important subject that how to solve the problem of rapid breakdownof resistance and race variation.Recently, the use of clutivars mextures has made fruitful progress in wheat stripe rustmanagement, because cultivar mixtures require low technology and reduce the dependence onpesticides to increase or stabilize grain yields. Cultivars, with different resistance to pucciniastriiformis f. sp. tritici, are designed (5cultivar in Ankang area and6cultivars in Baoji area)for mono-cultivar treatments and multi-cultivars treatments while disease incidence, focinumbers and yield per plot were investigated. TP-M13-SSR technique was used to detectpopulation genetic diversity of P. striiformis f. sp. tritici in natural infested wheat inmono-cultivar and multi-cultivars plots. Thus, our objective of this research is to find aneconomic, sustainable measure for stripe rust control and achieve high stable yields. The mainresults are summarized as following:1) Occurrence of wheat stripe rust and developing process of stripe rust in differentcultivars mixture are studied, the results show that diseased leaf rate and disease index ofcultivar mictures are lower than the mean value of the pure stannd. Daily multiplication rateof wheat stripe rust is significantly decreased in cultivar mixtures; Disease foci of cultivarmixtures is less than those of the susceptible pure stand and expanding rate is also inhibited incultivar mixtures. Disease index is decreased in cultivar mixtures in spring. The cultivarmixtures, comprising Mianyang31(R), Mianyang35(R), Mianyang98-351-15(S) andMiannong6(MR),have beter mixture effect on disease control. 2) Control effect and yields of cultivar mixtures are studied, the results show that diseaseincidence and the area under the disease progress curve (AUDPC) of the cultivar mixtures aresignificantly lower than those of the susceptible pure stands. The relative efficacy of cultivarmixtures range from14.29%to86.38%during2007, among them relative efficacy of theresistant and susceptible mixtures(R and S mixtures) is72.60%, and the relative yield increaseis13.26%. The relative efficacy of the R and S mixtures is31.22%during2008, and therelative yield increase is8.21%. Two treatments of cultivar mixtures (mixed with equal ratioof each component) had the best efficacy, one is that of comprising culitvars of Xiaoyan22(S), Shan138(R) and Xinong889(R), another is that of comprising culitvars of Xiaoyan22(S), Wunong148(S), Qinnong142(R) and Xinong889(R).3) Population genetic diversity is investigated for the P. striiformis f. sp. tritici populationfrom different plots with TP-M13-SSR technique. The important conclusion is that P.striiformis f. sp. tritici populations are considerably diversity in plots of cultivar mixtures,while there are different between plots. Genetic diversity for the pathogen population from thesusceptable pure stand and the cultivar mixtures are much higher than that from the resistanpure stand. The polymorphic from cultivar mixtures, such as enetic diversity The percentage ofpolymorphic loci, the Nei's gene diversity (H) and Shannon's information index (I), are91.30%,0.2860and0.4260respectively. Those of the above are possibly genetic mechanism thatcultivar mixtures sustainably control stripe rust.4) The resistance mechanisms of cultivar mixtures is studied, results show that thedensity effect, as one of three effects, played the most important role. The density effectplayed a larger role from the beginning in disease process, Strengthen in the mid-up, andshowed the downtrend in the latter stage. Blocking effect is not obvious in the early stage ofdisease process, and it demonstrat in the late stage. Blocking effect is significantly less thandensity effect during the whole disease process. Induced resistance effects took the effectfrom the second generation of pathogens, but it didn't play a greater role until medium-latestage of disease process.The diversifying cultivars in mixed-planting had good control effect to the wheat striperust, and the diversifying cultivars could maintain population stability of P. striiformis f. sp.Tritici, Which make cultivar mixtures is to be used as one of an ecological measures toprevent and control disease.