Population Genetics and Differential Pathogenicity of the Soybean Brown Stem Rot Pathogen Phialophora Gregata
Meng, Xiangqi
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https://hdl.handle.net/2142/85066
Description
Title
Population Genetics and Differential Pathogenicity of the Soybean Brown Stem Rot Pathogen Phialophora Gregata
Author(s)
Meng, Xiangqi
Issue Date
2001
Doctoral Committee Chair(s)
Chen, W.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Plant Culture
Language
eng
Abstract
Brown stem rot (BSR) of soybean caused by the soilborne deuteromycete, Phialophora gregata, is of great importance to soybean production of the world. This study was aimed at discovering genetic variation in P. gregata from soybean and the relationship between genetic variation and pathogenicity. AFLP (amplified fragments length polymorphism) and ISSR (inter simple sequence repeat) analyses were used to detect genetic diversity in Phialophora gregata. Various levels of DNA polymorphism were detected among the 45 soybean and mung bean isolates of P. gregata . Generally the estimated average genetic diversity is low for the populations. The technique of ISSR is more effective and economical than that of the AFLP technique used here in detecting genetic variation in P. gregata. Eight polymorphic markers were identified which separated 189 soybean isolates of P. gregata into two distinct genotypes (A and B). The separation of the two genotypes by these eight markers is consistent with that by another marker developed previously based on variations in intergenic spacer of rDNA. There is a correlation between the genotype and the reaction of soybean cultivar to the pathogen. When the two genotypes were mixed in 1:1 ratio, genotype A isolates preferentially infected the susceptible cultivar Sturdy, whereas genotype B isolates preferentially infected the resistant cultivar Bell. The results are consistent with field observations. The inoculation results showed that both genotype A and B isolates can cause brown stem discolorations on both soybean cultivars, but only genotype A isolates caused defoliating symptoms on susceptible cultivar Sturdy. The genotype A isolates were more virulent on susceptible cultivar Sturdy, but the genotype B isolates were more virulent on resistant cultivar Bell. The research showed that P. gregata from soybean exhibited generally low levels of genetic variation. The isolates of P. gregata from soybean can be unambiguously separated into two distinct genotypes (A and B). The two genotypes showed cultivar-preferential infection under both field and greenhouse conditions. Furthermore, the two genotypes caused different disease symptoms on certain cultivars.
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