Research On Genetic Differentiation Of Chilo Suppressalis Populations

Chilo suppressalis Walker （Lepidoptera:Pyralidae）, commonly known as the stripped stem borer boring into rice sheath and heart, is one of the important and destructive borer pests to rice widely distributed in China’s rice production areas. Its hosts include rice, water bamboo, corn, sugarcane, barnyard grass, oil rape and etc. In recent years, C. suppressalis populations have significantly risen to a serious threat to rice production in the extensive host plant areas of China. The genetic diversity within an insect species is one of the core issues of biodiversity and evolution, which commonly derives from geographic isolation, host isolation and distinct environmental stress of the species populations and promotes intraspecific differentiation and new species formation. This study is designed to aim at genetic differences between and within the populations in C. suppressalis to benefit insight of the native insect polymorphism and regional management for the borer populations. The main results in this study are as follows.DNA molecular markers by amplified fragment length polymorphism （AFLP） were applied to detect the genetic variation of13geographical populations of C. suppressalis collected from11provinces of China. A toltal of445distinct DNA fragment bands were amplified by three AFLP primer pairs from C. suppressalis genomic DNA, of which386bands （86.75%） were found to be polymorphic. The coefficient of gene differentiation between the populations was0.74. There was high genetic identity between the13populations with the value greater than0.67. Cluster analysis showed that all the tested populations could be grouped into4clades based on polymorphism of AFLP markers, of which the northern Huai river plain clade including GY, FN and FNing populations, the east-south region clade including YX, MH and YS populations, and the Jing-Xiang-Chuang plain clade including JZ, SY and DY populations are credible in that the populations within each of the clades are consistently subject to similar geographic climate and near distance. However, the lone population with longer genetic distance to all other tested populations was probably clustered into a random clade. So the sampled populations for genetic polymorphism clustering should be as many as possible and dispersed.By the field survey it was found that the development of C. suppressalis was much inconsistent in a paddy with a difference of four stages at the same time before overwintering. And just after overwintering, the moth occurring duration for a generation of C. suppressalis always last more than30days with the earliest （E） and latest （L） emerging individuals separated by time. This study is designed to analyze genetical background of the asynchronous development in a generation of C. suppressalis by using genetic markers.In order to explore the genetic diversity of C. suppressalis with different development rate, the specific DNA band was first selected from337random primers by random amplified polymorphic DNA （RAPD）, then transformed to sequence characterized amplified regions （SCAR） markers to identify the different development rates of pupae randomly from FuNing （FNing） and ShangRao （SR） populations. The results showed that, by RAPD with the primer S117, the specific DNA fragment band L820was amplified stably from the L type of the pupae. There are66%and68%identity respectively between the sequences of this fragment and transcription initiation factor IIF auxiliary subunit （Eint₀31520） mRNA, and those of this fragment and Encephalitozoon intestinalis queuine tRNA-ribosyltransferase （Eint₀60220） mRNA which generally results in transglycosylase activity in vitro and mitochondrial localization in vivo. Furthermore, the L820was transformed to specific SCAR marker, which was used to identify the L type of pupae in two consecutive generations of FNing and SR populations. With the more specific S117S1primer, the L820was identified in only4%the E type and up to67.39%the L type of pupae, and had nothing to do with the pupa sex.By using AFLP technology, the study of asynchronous development in C. suppressalis showed that distinct sequences can be amplified between the E and L types by only one pair of primers （P1T1） with Pst I and Taq I combination out of36pairs. The specific fragment L130was detected only in the L type of pupae in FNing population, but this specificity was not obvious in the L type of SR population. Another specific fragment E300was more consistently found in the E types of both FNing and SR pupae, which was identified up to94%in the E pupae and21.74%in the L pupae in two consecutive generations of FNing and SR populations. The E300showed to be responsible for an unknown protein after cloned and sequenced. Both the E300and L130sequences were found69.3%of identity. It’s resonably inferred that L130and E300might belong to the same family, while L130and Balsam poplar protein tyrosine phosphatase had similarity of72%which acts in the cell growth, differentiation and transformation.