Study On Infection Cycle Of Alfalfa Verticillium Wilt (Verticillium Alfalfae) And Breeding Of Resistant Germplasm

Alfalfa verticillium wilt(Verticillium alfalfae)(AVA)is a destructive disease on alfalfa(Medicago sativa).It was firstly found in 2016 in Minle County,Zhangye City,Gansu Province,and subsequently found in Jiuquan City,Wuwei City,and Jinchang City,Gansu Province,in 2022.In order to clarify the infection cycle of alfalfa Verticillium wilt in China so that to effectively manage this disease,and also breed resistant varieties to use in the alfalfa production.the disease,overwintering,transmission,and host range of the pathogen were studied in this thesis.New germplasms of alfalfa resistant to V.alfalfae were bred based on field evaluated for resitance level with 9 alfalfa varieties and let hybridized with amonge of 5varieties.The main results are as follows:1.V.alfalfae overwintered in diseased roots and basal stems with hypae,and on debris of died plants with conidia,which resulted from isolation with diseased plants marked with mood pole at planat crowns The fungus survived for 6 months on died diseased shoots at soil level,and 10 months in 40 cm and 20 cmsoil.The fungus was seedborne,up to 3.78%.The pathogen also transmitted by soil,which proved from an inoculation experiment with alfalfa seed and with soil collected from rhizospheres of diseased plants in greenhouse.Conidia of V.alfalfae observed at the surface ofdead shoots in the field,also in air captured with a device of spore trap at 47 CFU/m~3.Alfalfa seedlings exhibited syptoms of AVA in greenhouse,and the fungus was isolated from diseased seedlings after spraying conidia of this fungus on these plants.2.This thesis found the pathogen only infected alfalfa but not infected other plant species which tested in this study in natural condition during two years.Planted crops such as potato(Solanum tuberosum),cotton(Gossypium arboretum),red clover(Trifolium pretense),white clover(T.repens),sainfoin(Onobrychis viciaefolia),standing milkvetch(Astragalus adsurgens),dogbane(Apocynum venetum),tomato(Lycopersicon esculentum),eggplant(Solanum melongena),sunflower(Helianthus annuus),pea(Pisum sativum),common vetch(Vicia sativa)and alfalfa.3.The high resistant alfalfa varieties were Gannong No.4(incidence rate 1.86%,disease index 0.96),Zhongmu No.1(4.90%,1.12),WL343HQ(2.22%,1.22),MF4030(3.33%,1.37),and Prospect(3.33%,1.51),medium resistant varieties were Dryland(15.22%,7.91)and Magnum No.2(16.30%,8.62),and the susceptible varieties were Xinmu No.1(34.5%,21.22),based on re-evaluation in the field in two years with an evaluation standard of relative disease resistance index..These varieties were planted in 2021,but no syptoms of AVA were found and no hypae was isolated from plants randonly collected from each varieted for 4 times in this year.The disease occurred after regreening in 2022,incidence was 1.86%to 37.33%,and disease index was 0.96 to 24.63 on different vavieties in August,in 2022.4.Twenty one new germplasms were bred from the most resitant to AVA,including WL343HQ,Gannong No.4,Zhongmu No.1,and Prospect,after cuting other 5 susceptible varietis before flowering,and no cuting for the 4 varieties and let hybred in 2022.Selecting each new germplasm to evaluate resistance to AVA,resestance of all tested new gremplasm were increased,close to standard resistant variety Oneida VR.Incidence reduced 45.24%,26.77%,16.67%,and 13.39%,respectively,compared with each original varieties,standard susceptible variety Saranac,and standard resistant variety Oneida VR.