Resistance Of Maize "Jingke 968" To Pest Mite,Tetranychus Urticae And Effect Of Beauveria Bassiana On The Pest Natural Enemy,Orius Sauteri

Damage by spider mites（Acari:Tetranychidae）is one of the important causes of maize yield loss.Tetranychus urticae is one of the main pest mites in maize production in China.The breeding of maize varieties resistant to spider mites is one of the effective methods to reduce the loss.Jingke968（JK968）is a widely cultivated maize hybrid in China and had good resistance to spider mites in the field and attraction to the predatory natural enemy Orius sauteri of spider mite during the floor-feeding period.The six maize hybrids and strains,JK968,Jing724（J724,female parent of JK968）,male parent Jing92（J92,male parent of JK968）,the hybrid Xianyu335（XY335）,PH6WC（female parent of XY335）and PH4CV（male parent of XY335）,were used as materials for evaluating of the mite-resistence.The population dynamics and fertility of T.urticae on different maizes were compared to determine the resistance of JK968 and the correlation between physical traits of maize leaves and T.urticae resistance was furtherly studied.The gene expression differences of JK968 and XY335 after T.urticae feeding were analyzed by RNA-seq.This study would reveal the spider mite resistance mechanism of JK968 from multiple perspectives.Beauveria bassiana is a biocontrol fungus commonly used to control corn pests including the mites.Based on the attraction of JK968 to O.sauteri in the field,the effects of different concentrations and dosage forms of B.bassiana on the predation ability and emergence rate of O.sauteri were studied in order to determine the best application method of B.bassiana when JK968was planted.1.Evaluation of resistance of JK968 and its parents to T.urticaeT.urticae population density of JK968 was significantly lower than that of XY335in the field.The resistance of the six maize lines（two hybrids and their parents）to T.urticae was as follows:J92>J968>PH4CV>J724>XY335>PH6WC according to the daily average amount of T.urticae.The results of greenhouse experiment showed that there was no significant difference in female adult mite population dynamic between JK968 and XY335.However,the total number in the colony of T.urticae on XY335 was significantly higher than that of JK968.The order of fecundity from high to low was PH6WC,XY335,J724,PH4CV,JK968 and J92.JK968 reduced the population density of T.urticae by inhibiting the fecundity of female adult.2.Effects of leaf physical characters of JK968 on the resistance to T.urticaeCorrelation analysis was conducted on leaf trichome density,leaf thickness and daily average amount of T.urticae in maize during tasseling stage,the result showed that daily average amount of T.urticae was positively correlated with trichome density,and negatively correlated with leaf thickness.Regression analyses showed that trichome density played an important role in maize resistance to T.urticae.Correlation analysis was also conducted between the physical characters of maize leaves at 3-leaf stage and the resistance indexes of T.urticae in greenhouse.There was significant positive correlation between daily average amount of female adult mite and abaxial stomatal length;daily average amount of mite and adaxial stomatal width;24 h egg number and adaxial stomatal length;hatching rate and adaxial stomatal length.3.T.urticae resistance of maize JK968 and XY335 based transcriptome analysisTo investigate the molecular mechanisms of defense response that T.urticae infestation trigger in JK968 and XY335,transcriptome sequencing was performed to analyze the maize plants infested with T.urticae female adult.The results showed that2197 transcripts were differentially expressed（log2|treatment/control|>1;FDR<0.05）in T.urticae-infested（24 h）JK968’s leaves compared to the uninfested control plants.Among these differentially expressed genes（DEGs）,1599 were significantly upregulated,and 598 were significantly downregulated.And 3867 transcripts were differentially expressed in T.urticae-infested（24 h）XY335’s leaves compared to the uninfested control plants.Among these differentially expressed genes（DEGs）,2396were significantly upregulated,and 1471 were significantly downregulated.KEGG pathways shared by the two maize species include Starch and sucrose metabolism,Phenylalanine metabolism,Glutathione metabolism,Plant hormone signal transduction,Amino sugar and nucleotide sugar metabolism,Phenylpropanoid biosynthesis.4.Evaluation of the effects of B.bassiana on the predation of T.urticae by O.sauteri using functional response modelThe emergence rate and the predation ability on Tetranychus urticae Koch in different densities of the 5^th instar nymphs of O.sauteri treated with two different concentrations of spore suspension（routine:1×10⁷ conidia/m L and low:5×10³conidia/m L）and spore powder（1×10⁷ conidia/nymph）were measured.The predation of O.sauteri fit with HollingⅡfunctional response models from different treatments,and the searching efficiency reduced with the increasing of host densities.From the low concentration of spore suspension treatment,O.sauteri showed the highest number of preys per day（N_a）and the shortest handling time（T_h）,and the regression of search effect showed the lowest decreasing trend with the increasing of prey density.However,in the spore powder treatment group,O.sauteri had the lowest N_a and the biggest T_h.The results showed that low concentration of B.bassiana spore suspension did not affect the predation ability of O.sauteri,but the routine concentration of spore suspension and spore powder treatments may adversely affect the predation ability of O.sauteri.In addition,the emergence rate of O.sauteri was significantly reduced after treated with B.bassiana spore powder.In general,the resistance of maize variety JK968 to T.urticae was determined and revealed the physical resistance mechanism of maize mite resistance was revealed.The transcriptome expression characteristics of JK968 in response to the damage by T.urticae were preliminarily explained.Elaborating the safety of low concentration of B.bassiana spore suspension to O.sauteri.These results provided a theoretical basis for the breeding of mite resistant maize varieties and provided references for the combined application of B.bassiana and O.sauteri to control T.urticae.