Research On Blast Resistance Genes Utilized In Japonica Rice And Analysis Of Blast Isolates Diversity In Jiangsu Province

Rice is the most important agricultural commodity in Jiangsu Province.The leading rice type that grows in Jiangsu is japonica,contributing to up to 85%of paddy.Rice blast caused by Magnaporthe oryzae is one of the most destructive disease reducing rice yield.The most economic and effective way to constrain rice blast is the introgression of resistant genes into rice varieties.Till now,more than 30 resistance genes and 10 avirulence genes have been cloned worldwide.Markers developed by these genes could be utilized to screen and study the genetic diversity of released rice varieties,facilitating the proper layout of certain varieties in blast prone area.The present study provides an overview of the genetic diversity of the 195 released rice varieties on 14 blast resistant gene loci in Jiangsu Province.Combined with phenotypic evaluation,certain genes and gene pyramids will be selected for future deployment on the basis of prevalence of Magnaporthe oryzae.The main results are as follows:1)Among the 14 blast resistant genes,Pigm was not detected in all tested japonica rice varieties/lines.Pib showed the highest occurrence frequency(72%),followed by Pikh and Pita(both over 45%).The presence of Pi25 and Pit were relatively lower,with a frequency of 3%and 6%,respectively.Most of the varieties contained 2 to 5 resistant genes,while 6 varieties were found to harbor more than 7 genes.Pit and Pi3/5/i appeared to be prevalent in middle-maturing middle-japonica(MMML)than that in late-maturing middle-japonica(LMMJ)and early/middle-maturing late-japaonica(E/MMAJ),whereas the distribution of other blast resistant genes in the three ecological types was generally similar.The frequency of Pid3,Pid2,Pia and Pbl genes in regional test varieties/lines of Jiangsu province in 2019 was significantly higher than that in released varietiesThe results show that the distribution patterns of 14 rice blast resistant genes in regional japonica rice varieties are divergent2)158 of the tested varieties were inoculated with neck blast,and 72%of them were observedfrom susceptible to highly susceptible.There was no significant correlation between the number of resistance genes and neck blast resistance.Through logistic regression analysis,it was found that three genes,Pia,Pi3/5/i and Pita,significantly contributed to neck blast resistance of tested cultivar,with the contribution rates of Pia,Pi3/5/i and Pita from high to low.Further comparison showed that there was a significant positive interaction between Pia or Pi3/5/i and Pita.The disease resistance effect after pyramidnation was significantly higher than when each gene existed alone.Pyramiding of Pia+Pita confers better resistance than other combination.All of the varieties carrying this gene combination exhibited a higher level of resistance against neck blast.Inoculation identification of neck blast in 1 7 high-generation backcrossing lines introduced into Pigm in two different japonica rice varities showed that the resistance level of all backcrossing lines was significantly higher than that of their recurrent parents,and the resistance level all reached.This suggests Pigm gene and "Pia+Pita" gene combination would be the most pivotal resistant donor against neck blast in regional breeding program as for japonica rice.3)48 varieties were chosen to assess their ability against 33 blast isolates during seedling stage.We found that 87.5%of the tested rice varieties were resistant to more than half of the blast strains.Specifically,Sidao785、Baofeng1701、Si15-301 and Taigengnuo109 were found resistant to all tested blast strains.Logistic regression analysis showed that Pia,Pi3/5/i and Pita contributed significantly to seedling blast resistance,similar to the result observed in the case of neck blast resistance.Pyramiding Pita with either Pi3/5/i or Pia resulted in expanded resistant spectrum,exhibiting comparable reactions.This suggests "Pi3/5/i+Pita " and "Pia+Pita" gene combination would be deployed as pivotal resistant donor against seedling blast in regional breeding program as for japonica rice4)We also assessed performance of 23 single resistant gene lines with the same genetic background(Lijiangxintuanheigu)to 16 single-spore isolates.We found that lines with single gene Piz,Pi20,Pi9 and Piz5 developed better performance,resistant to over 80%of the tested isolates,whereas single gene line with Pib conferred resistance to only 6%of those isolates.Therefore,through associate with resistance association coefficient and pathogenicity association coefficient we hypothesize that Pi7+Pi9 and Piz5+Piz/Pi9/Pi20 would be the most effective combinations to the tested isolates5)The genotypes of 321 single spore isolates collected and isolates at 10 sites in different regions of Jiangsu province were analyzed by the specific molecular markers of 10 avirulence genes.These strains were divided into 7 groups via cluster analysis,and there were significant differences among the dominant strains prevalent in different ecological areas,different counties in the same ecological area and different years.It was speculated that the strains in groups 3,4,6 and 7 might become the dominant strains prevalent in the next year.Up to 96%of single spore strains isolated from the same disease stem were divided into two or more clusters,and most of the single spore strains derived from the same disease stem showed obvious differences in growth morphology.The results showed that the dominant small species in different regions had obvious differences,and the reason of the outbreak of disease might be related to multiple small species’ combined infection.Together,our results will shed light on the proper selection of genes and gene combinations for future breeding practice against rice blast in japonica producing area of Jiangsu.