| The corn leaf aphid, Rhopalosiphum maidis (Fitch), an important agricultural piercing-sucking pest oncorn, has caused more and more severe damage to corn production in recent years. For detecting therelationship between the damage of R. maidis to different maize hybrids (inbreds) and the resistance of cornvarieties, we researched the development, population dynamic and feeding behavior of R. maidis on8maize hybrids (inbreds) by using time-specific life table and electrical penetration graph. Meanwhile, thenutrient and secondary substance contents in different corn varieties were analysed, and the relevancebetween secondary substance contents and the population quantity of R. maidis in the field was constructed.Furthermore, the activities of detoxification and protective enzymes of R. maidis on different corn varietieswere measured. At last, the paper discussed the resistance mechanism of different corn hybrids (inbreds)to R. maidis based on the above researches. The main results are shown as follow:(1) The investigating results in corn field showed that the population dynamic of R. maidis on8maizehybrids (inbreds) were consistent. Before the corn tassel sprouting, the aphid population quantity was low,and mainly aggregated in leaf, stem and tassel. After entering tassel stage, the number of corn leaf aphidwere increasing gradually, and reached the first peak when tassel completely sprouted. In addition, theaphid primarily focused on tassel at this stage. At silk stage, the R. maidis transferred from tassel to femaleear, and reached the second peak at pustulation period. Afterwards, the population of R. maidis weredeclined rapidly with the corn plant maturing.(2) By using spectrophotometer, we measured the nutrients and secondary substances contents indifferent development stage of8maize hybrids (inbreds). The results indicated that the reducing sugar,starch and total phenolic contents in corn plants at4testing stages showed no significant relevance with theaphid population on all tested maize hybrids (inbreds), and the tannin contents has very significantlynegative relevance with the aphid population on each corn plant. At the forth measuring stage, the solublesugar and protein contents has significantly positive relevance with the aphid population on investigatingparts. Besides, at the third and forth measuring stage, the tannin contents has significantly negativerelevance with the population of R. maidis on corn leaf or female ear.(3) In laboratory condition, we constructed the time-specific life table of R. maidis on8maize hybrids(inbreds). The results showed that the survival rates, adult longevities, fecundities and innate capacity forincrease (rm) of R. maidis on Zhengdan958and Xundan20were lower than other maize hybrids (inbreds),All these results indicated that Zhengdan958and Xundan20have adverse effects on the development and breeding of R. maidis.(4) The activities of detoxification and protective enzymes in R. maidis population fed on8maizehybrids (inbreds) were different. Among these corn varieties, Zhengdan958and Xundan20’ CarE, AChE,ACP and AKP activities were higher than others, but the GST activities were lower, and the activities ofprotective enzymes in various corn varieties were not consistent. Through analyzing the relevance betweencontents of the secondary substances in maize plants and activities of detoxification and protective enzymesof R. maidis, we found that the tannin contents in female ear bracts has significantly negative relevancewith GST activities in R. maidis, but its tannin and total phenolic contents have significantly positiverelevance with ACP activities.(5) Comparing the EPG parameters of R. maidis on8maize hybrids (inbreds), we found that the totalduration time of np wave of R. maidis on Zhengdan958and Xundan20were significantly longer thanother hybrids (inbreds). Besides, the total time and mean duration time of F wave on these2hybrids alsowere long relatively. However, the total time and mean duration time of phloem ingestion (E2wave) of R.maidis on Qi319was longest, maybe it exists some chemical factors that can stimulate the feedingbehavior of corn leaf aphid.(6) Genes of detoxification enzyme in R. maidis were isolated by using reverse transcriptionpolymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Nucleotide sequenceanalysis revealed that the full length of GST, CYP4, CYP6, AChE and CarE were901bp,1806bp,1865bp,2568bp and1763bp, respectively; the open reading frame (ORF) length of which were651bp,1527bp,1539bp,2226bp and1287bp, encoding217,509,513,742and429amino acid residues respectively. |
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