Population Adaptability And Control Effect Of Metarhizium Anisopliae In Peanut Root Environment

The survival adaptability of Metarhizium anisopliae in soil critically related to its effect againstwhite grubs in peanut field. In the dissertation, we determined the specific primers and Real-Time PCRconditions for M. anisopliae quantization, evaluated the fungal persistent ability when applied atdifferent stages, and investigated its influence to soil microbial communities. The results of the researchwill offer theory support to the control effect and ecology of M.anisopliae. The results are as follows.1. Survival ability of M.anisopliae in the peanut field was evaluated by Real-Time PCR.1) Atfirst, specific primers for M.anisopliae were designed after comparing the internal transcribed spacer(ITS) sequences of fungi, and an optimal reaction system for Real-Time PCR was established. Theresults showed that the copy number of standard had a good linear relationship. The linear equation wasy=-3.257x+6.969, the PCR amplification efficiency was E=102.8%. The detection of trace was low to20spores/g soil. Two testing methods, Real-Time PCR for DNA content and classic dilution plates forCFU, were used to analyze the survival quantitaties of M.anisopliae applied in peanut field. The resultsindicated that the tendency of the fungal population detected by the two methods was similar duringpeanut development. It proved that the Real-Time PCR system can be used for the quantitative detectionof M. anisopliae persistence in soil, even more suitable for the detection of low level.2) Thepopulation of M.anisopliae applied when peanut sowing would decline rapidly at early stage, followedby a gradual recovery, either in rhizosphere soil or in bulk soil of the root. Relatively, the fungalquantity in rhizosphere soil dropped slower and recovered faster than that in bulk soil. For90d, thefungal number was1817CFU/g and5850CFU/g in rhizosphere soil and bulk soil, dropped to5.80%and4.83%of the initial level and rebound after. For120d, the CFU in rhizosphere could recover to theinitial38.65%, significantly higher than16.98%, the recovery in bulk.2. Optimal applying time of M.anisoplae and the control effect were determined.1) We appliedM.anisopliae at the stages of sowing (0d), seedling emergence (15d), seedling (30d), flowering (45d),pod-bearing (60d) and pod-filling (75d) respectively. The results showed that M.anisopliae populationapplied at the stages of sowing, seedling emergence and seedling could increase61.51%-203.23%after30-60days. Especially applied at seedling stage, the population could reach the highest,3.03times ofthe initial level. When applied at sowing time, the fungal population would decrease rapidly to21.65%in the first15d then fluctuated. The population would constantly decline when applied at pod-fillingstage. The latter declined faster with only9.00%survivals after applying30days. The efficiency of thegrub control with different treatments indicated that seedling stage was best for M.anisopliaeapplication, which could increase189.25%of peanut pod number and161.96%of peanut pod weight,and decrease50.54%of damaged pod number comparing to control treatment. The effect was notsignificant applying the fungus after pod-bearing stage.2) Adding M.anisopliae application atseedling stage after first applying at sowing, the fungal population presented a similar dynamics to oneof only applying at seedling stage. The CFU at the pod-filling stage became the highest with1.55-2.41 times of the adding amount. The rate of damaged peanut decreased47.00%, lowest among varioustreatments. Adding third application of M.anisopliae with4.67times amount of second time applicationat pod-bearing stage, the rate of final damaged peanut was44.40%, having no significant differencecompared with only adding second application. So it inferred that additional M.anisopliae atpod-bearing stage have no effect on grub control. The experiment proved that seedling stage is theoptimized time to control white grubs in peanut field.3. Influence of M.anisopliae to the soil microbial eclology was investigated. The quantities of fungi,bacteria and actinomycetes as well M.anisopliae in rhizosphere and bulk soil was monitered afterM.anisoplae application at sowing time. The results showed that the effect arranged as in rhizosphere>in bulk, and as on actinomycetes> on fungi> on bacteria.1) M.anisopliae had no significant effect onbacteria in root bulk or rhizophere and on fungi in root bulk.2) Compared to control treatment, totalamount of fungi in rhizophere declined slower in the initial stage after M.anisopliae application,delaying the time of lowest amount from15d to30d and advancing the time of higher amount from60dto45d. The peak value was only one-third of one by control.3) Compared to control treatment，theamount of actinomycetes in bulk became lower drop, delaying the time of lowest amount from30d to45d and recovering smaller amplitude. In the rhizosphere, applying M. anisopliae inhibited obviouslythe actinomycetes populations, the dynamics of actinomycete rise and fall was opposite to controltreatment. It did not rebound when dropped to low site after45d.