Research Of Biological Control Against Tomato Yellow Leaf Curl Virus

Tomato yellow leaf curl virus disease is a devastating disease caused by tomato yellow leaf curl virus(TYLCV),transmitted by Bemisiatabaci.The disease was first discovered in Israel in 1964,and then quickly spread to the Middle East,the Mediterranean coast,Africa,Europe,and Australia and other regions.Especially since the 1990s,as global warming and whitefly outbreak,the disease rapidly in the global spread of the disease in over 40 countries and regions,becoming one of the important diseases on tomato production.Currently,the disease prevention and control measures are mainly dependent on breeding for disease resistance and chemical control.But the results are not satisfactory,and pesticide residue problems have become increasingly prominent,it is proposed to adopt the strategy of biological control of tomato yellow leaf curl virus disease.In this study,857 bacterial isolates were obtained from the rhizosphere,endorhiza,surface and interior of stems,phyllosphere,and endosphere of field-grown tomato plants and bulk soil.To effectively screen potential BCAs against TYLCD from them,an assessment system was established to evaluate their biocontrol potential according to in vitro activities of their extracellular metabolites(protease,chitinase,cellulase,glucanase,and siderophores).Amplified ribosomal DNA restriction analysis and BOX-PCR analysis were performed to examine the genetic diversity of 165 isolates with at least three points of assessed biocontrol potential,of which 60 exhibiting relatively abundant genetic diversity were investigated for their biocontrol efficacy against TYLCD under greenhouse conditions.Forty-nine isolates achieved positive biocontrol efficacy ranging from 20.49%to 55.88%at 35 days post pathogen inoculation(dpi),with 11 accomplishing the biocontrol efficacy over 40%even at 45 dpi.The conventional correlation coefficient was 0.85 between the biocontrol efficacy of 60 isolates at 45 dpi and their assessed biocontrol potential,indicating that the established assessment system was effective.This study is the first to screen tomato-associated bacteria as potential BCAs against TYLCD by developing an assessment system to evaluate their biocontrol potential according to in vitro activities of their extracellular metabolites.In the fall of 2012,biocontrol in greenhouse and field experiments and to explore the mechanism of 12 biological control agents which selected in pre-trial on resistance to tomato yellow leaf curl virus disease were studied.All of them have a preventive effect of TYLCV,with rate of 28.22%-49.77%at 35d and the rate of 18.24%?57.62%at 50d under field conditions.Which,Lgb-7,Lgn-4 and Lgn-3 in the greenhouse and in the field have better control effect.Plant viral proliferation can be delayed about 2d or more in the greenhouse,4d in the field.The root colonization and leaf colonization of 6 biological agents could still reach 104 CFU/g or more after treated 30 days.Among them,Lgb-7 had the best colonization ability.5 biological agents can also promote plant growth effectively,with 15.48?74.15%biomass increase.Lgn-3 with irrigating treatment alone or Lgn-6 with irrigating/spray treatment alone have better control effect.In addition,in the fall of 2013,the paper picked five biocontrol which on resistance to tomato yellow leaf curl virus disease were studied.Ljb-10(Bacillus pumilus)?Ljn-9(Cellulosimicrobium cellulans)?Lgn-6(Enterobacter sp.)?Lgn-3(Bacillus sp.)?Ljb-2(Pantoe agglomerans)were originally isolated from the tomato environment.field control combined with a certain resistance to the strains of resistant varieties Difenni.The results show that biocontrol efficacy reached 22.26%?57.89%against TYLCD after 50d,Lgn-6?Ljb-2 can reached 57.89%and 45.26%respectively.Defenni showed the biocontrol efficacy of 31.93%compared with Geruisi,and the combination of BCAs and Difenni accomplished the biocontrol efficacy of 47.09%-71.34%as compared with Geruisi.Additionally,BCAs significant increased the contents of leaf chlorophylls a,b,and a+b in the field;Elevated tomato yield by 2.31%-20.05%,leading to rises in the contents of vitamin C,soluble sugar,titratable acid,and sugar-acid ratio in tomato fruit in the field in fall 2012.This study is the first report that application of an Pantoea agglomerans to a moderately resistant tomato variety effectively suppressed TYLCD;this approach can promote the application of BCAs against this disease.