Genetic Diversity Of Avirulence Gene Avr1b In Phytophthora Sojae

Phytophthora root rot of soybean caused by Phytophthora sojae Kaufmann & Gerdemann) is the worldwild distructive disease..Avr1b gene is an avirulence gene cloned by map-based approach from P.sojae.In addition to being recognized by cognate resistance gene Rps1b in soybean,it may play important role in plant infection.Using PCR-SSCP,174 isolates from Chinese major soybean area were examined for variation in Avr1b.Compared to reference strains representing four major genotypes,135 isolates showed identical genotype to P7064,35 to P6497,and 3 to P7076.The P7074 genotype was not detected..One isolate from Hei longjiang showed different conformation from 4 genotypes.Selected isolates were subjected to virulence test and Avr1b sequencing.The results indicated that simple genotype structure for Avr1b,suggesting low levels of selection pressureand and the cognate resistance gene Rps1b is still efficient in the field.Bioinformatic analysis predicted that the Avr1b protein contains likely five kinase phosphrylation sites and one N-glycosylation site.Amino acid changes occurred in some isolates which may lead to virulence towards resistance gene Rps1b.One base deletion in Avr1b was identified in one avirulent and causes changes in amino acid sequence.This rare mutation may be related to virulence changes,bur it may also be another copy of Avr1b in the genome.An understanding of genetic diversity and dynamiss of Avr1b gene in P.sojae populations will be important for soybean breeding program and rational deployment of resistance genes.The identification of amino acid residues in Avr1b protein that are important for Avr1b function will aid further investigation on molecular recognition between P.sojae and soybean.