Dissertation
Dissertation > Agricultural Sciences > Plant Protection > Pest and Disease Control > Crop pests and diseases and their prevention > Cereal crop pests and diseases > Corn pests and diseases > Maize Disease > Transgression ( pass ) an infectious agent harmful

Genetic Diversity and Ultrastructural Studies of Southern Corn Rust in China

Author XingGuoZhen
Tutor ZhengWenMing
School Henan Agricultural University
Course Cell Biology
Keywords Corn Southern rust Common rust of corn Genetic diversity Molecular Evolution Molecular detection of Ultrastructure
CLC S435.131.4
Type Master's thesis
Year 2011
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Corn is one of important cereal crops, also is important industrial raw material.The corn rust occurs increasingly and seriously influences the yield and quality ofcorn. The use of corn rust resistance is the basic way to control the disease. It isimportant to understand the molecular genetic diversity and the ultrastructure of cornrust fungus for the application of resistance breeding and the resistant varietiesdeployment of corn. In this research the molecular genetic diversity of southern cornrust fungal collected from Hainan province and Henan province was analysed. Theultrastructure of rust from infected corn leaves was also distected using electronicmicroscope. Main results as follows:1. Conserved primers based on rDNA+ITS andβ-tubulin gene of fungi weredeveloped for the amplification of the genomic DNA from rust isolates collectedfrom Hainan(11), Henan(13), Chongqing(1) and from Jilin (1) . The obtainedspecific fragments were then cloned and sequenced for the genetic diversityanalyse and molecular detection of corn southern rust (Puccinia polysoraUnderw.)and common rust (Puccniia sorghi Schw.).(GeneBank number:HM452902,HQ154021~HQ154038;HM452903,HM452904,HQ162104~HQ162124).2. The evolutionary tree was constructed Separately used the rDNA+ITS and betatubulin sequences, results showed: the isolates that collected from Hainan,Henanand Chongqing are belonged to southern corn rust, while the isolates collectedfrom Jilin province are belonged to the common corn rust. The similarity of therDNA+ITS sequences in different isolates of southern corn rust is between99.12%-100%, while compared with common corn rust is between56.32%-63.96%; The similarity of the beta tubulin gene fragment sequences indifferent isolates of southern corn rust is between 98.97%-99.91%, while compared with common corn rust is between 80.90%-81.25%. The DNAmolecular diversity of the southern rust isolates by genetic sequences shows nothigh, isolates were not separated between the areas, it means there is no apparentsubgroups between genetic differentiation, and probably exist frequent rustpathogens communication between different regions.3. Genome-specific primers for molecular rapid detection of two corn rust fungiwere developed (patent application number: 201010606982.0; 201010606639.6).According to the rDNA+ITS sequence of two rust fungi, we designed specificprimers which were identified by using the DNA sample controls fromExserohilum turcicum,Bipolaris maydis,Curvularia lunata and corn. Then wedetected the rusts genomic DNA at a series of concentrations. The results showthat the minimum concentration is 10pg and 1pg respectively. The sensitivity canmeet the requirement of detecting two rust fungi in incubation period.The established primers can be used for the eraly warning of corn rust.4. Use the Scanning Electron Microscope (SEM), the form of the fungi wasobserved, urediospore are sphere or oval,(10~20)μm×(25~35)μm, theurediospore covered with thick and irreqular spines, a concave around each spine;the uredinia were scattered, long ovoid, broken the skin of leaf and outstanding,they can contact with each other, mature urediospores were scattered aroundthem.5. Take advantage of the Transmission Electron Microscope (STM), theorganization structure of rusts in the host cell was observed for the first time,results showed: the intercellular hyphal cells like the classics silk shape,developed and branched all along the cell wall; haustorial mother cell (HMC)cangrow up to a penetration peg, then the peg get through to the inner cell, at thehead it can be expanded to a haustorial body, so the mature haustorium isconsisting of a neck and haustorial body.6. There are different numbers of nucleus in different varieties of corn were seenVia STM, there is no more than two nucleus in the southern corn rust, that isdifferent from the Puccinia striiformis f.sp.tritici. In zhengdan 958 there are twonucleus, while in xianyu 335 there is only one nucleus in most of cells. So weinferred that there maybe a relationship between the varieties of infected corn andthe number of nucleus in cell, so it is still need to make more evidence to supportthis hypothesis.

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