Population Differentiation Of Sitobion Avenae In China

The English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is a major wheat, Triticum aestivum (L), insect pest, responsible for frequent and extensive damage in wheat-growing areas worldwide. In China, S. avenae is one of primary cereal aphid species, sucking nutrients from a sieve tube inserted into wheat phloem and transmitting barley yellow dwarf virus (BYDV). S. avenae damage affects approximately 13 million hm2/yr and causes wheat yield loss up to 40%.Insecticides are the major methods used to control the grain aphid, but the excessive and improper use of pesticides can seriously impact the local economy, environment and food safety. Plant resistance is the most effective and environmentally friendly pest control measure. Grain aphid biotypes are necessary to breed aphid-resistant wheat varieties; however, none have currently been identified. Here we describe a method to identify grain aphid biotypes and survey the aphid biotype variation in the wheat growth area of China. Clones of S. avenae were collected from 14 locations in China and used to establish culture populations. These populations were then utilized to assess the resistance of 12 wheat varieties. Based on resistance responses, seven differential hosts were selected to identify the biotype of S. avenae: Amigo, cv. Fengchan No.3, Zhong 4 wumang, JP1, L1, 885479-2 and cv. Xiaobaidongmai. S. avenae was ultimately classified into five biotypes: EGA I, EGA II, EGA III, EGA IV and EGA V. These methods provide a mechanism to detect the variation and evolution of grain aphids in different wheat-growing locations and also allow for selection of appropriate aphid-resistant germplasm for wheat breeding of commercial wheat cultivars.Fourteen populations of S. avenae originating from China were tested for their ability to transmit Barley yellow dwarf virus-PAV (BYDV-PAV, Belgium isolate) using wheat cv. TOISON d'OR as test plant. By sequence analysis, the coat protein gene was showed closed to other European BYDV-PAV isolates and distinguishable from BYDV-PAV-CN isolate. All aphid populations could transmit the isolate and variation in transmission rates ranged from 24.42±2.21% to 66.67±3.84%. A one-way variance analysis of percentages of transmission showed a significant differences between the populations (df = 13, MS= 0.02, F = 9.81, P < 0.0001). Tukey's Studentized Range (HSD) test indicated that transmission efficiency of the populations from the middle-lower reaches of Yangtze River (AH, HD, HDE, HZ, JZ, JY and SJ) and Yunnan province (YH) were not different in terms of transmission efficiency; they were nevertheless different of the populations from the northern (ST and STA) and northwestern (QX, SB and XS). Transmission efficiency of S. avenae from northern and northwestern, where BYDV impact is more important, was higher than that from the middle-lower reaches of Yangtze River and Yunnan province. The results emphasize the efficient transmission of BYDV and aphid vectors from different world areas.In this study, partial sequences of the mitochondrial cytochrome oxidase subunit I (mtDNA-COI) gene of S. avenae, collected from 17 localities in China, was sequenced and compared, to analyze their genetic variation and population structure. Sequence analysis of the 588bp mtDNA-COI gene from 269 individuals resulted in 16 haplotypes, ranging in sequence divergence from 0.2% (one nucleotide) to 1.7% (10 nucleotides). Of 15 variable sites, 12 were transitional substitutions, two were transversional substitutions and one was transitional and transversional substitution. Phylogenetic analysis showed that all haplotypes were highly interconnected with each other. From a geographical perspective, eight haplotypes were found singly at one locality, with other haplotypes distributed different localities. The genetic diversity of S. avenae from northern areas is higher than that from southern areas of China. The little genetic differentiation (Fst = -0.06945-0.69857) and high migration rate (Nm = 0.21575-infinite) of Chinese populations suggest that over long-distances dispersal is a major factor for the demography of S. avenae. Mismatch distribution analysis showed bimodal in S. avenae populations. In addition, results of Tajima's D and Fu's Fs neutrality tests (not significant, p>0.05) implied that there might not be a population expansion in recent time and the English grain aphid populations was at demographic equilibrium.