Comprehensive evaluation of resistance effects of pyramiding lines with different broad-spectrum resistance genes against Magnaporthe oryzae in rice (Oryza sativa L.)

ABSTRACT Corynebacterium jeikeium is an opportunistic pathogen primarily of immunocompromised (neutropenic) patients. Broad-spectrum resistance to antimicrobial agents is a common feature of C. jeikeium clinical isolates. We studied the profiles of susceptibility of 20 clinical strains of C. jeikeium to a range of antimicrobial agents. The strains were separated into two groups depending on the susceptibility to erythromycin (ERY), with one group (17 strains) representing resistant organisms (MIC > 128 μg/ml) and the second group (3 strains) representing susceptible organisms (MIC ≤ 0.25 μg/ml). The ERY resistance crossed to other members of the macrolide-lincosamide-streptogramin B (MLSb) group. Furthermore, this resistance was inducible with MLSb agents but not non-MLSb agents. Expression of ERY resistance was linked to the presence of an allele of the class X erm genes,erm(X)cj, with >93% identity to other ermgenes of this class. Our evidence indicates that erm(X)cj is integrated within the chromosome, which contrasts with previous reports for the plasmid-associated erm(X) genes found inC. diphtheriae and C. xerosis. In 40% ofC. jeikeium strains, erm(X)cj is present within the transposon, Tn5432. However, in the remaining strains, the components of Tn5432 (i.e., the erm and transposase genes) have separated within the chromosome. The rearrangement of Tn5432 leads to the possibility that the other drug resistance genes have become included in a new composite transposon bound by the IS1249 elements.

Download Full-text

Genetic diversity analysis in indigenous rice (Oryza sativa L.) germplasm for Bacterial Leaf Blight (Xanthomonas oryzae pv. Oryzae) using resistance genes linked markers

10.21203/rs.3.rs-217763/v1 ◽

2021 ◽

Author(s):

Khannetah K. R . ◽

Ramchander S. ◽

Andrew Peter Leon M. T ◽

Shobha D. ◽

Saravanan S. ◽

...

Keyword(s):

Oryza Sativa ◽

Resistance Genes ◽

Bacterial Blight ◽

Rice Yield ◽

Oryza Sativa L ◽

Molecular Data ◽

Lesion Length ◽

R Genes ◽

Leaf Clipping ◽

Moderately Resistant

Abstract Among rice ( Oryza sativa L.) diseases, bacterial blight (BB), caused by Xanthomonas oryza pv. Oryzae , plays a pivotal role in decreasing rice yield. BB is reported to be the most serious constraint to improving rice yield. The present investigation assessed the potentiality of bacterial blight resistance and molecular characterization of 100 rice accessions for four major BB resistance genes, viz., Xa4, xa5, xa13 and Xa21 . Disease screening was carried out under glasshouse conditions using a BB culture isolated from BB-infected rice fields through the leaf clipping method. Analyses of 13 BB resistance genes linked with polymorphic microsatellites markers indicated the presence of single-, two-, three- and four-gene combinations of xa5, xa13, Xa4 and Xa21 . We found four accessions to be resistant; 34 accessions to be moderately resistant; 49 accessions to be moderately susceptible and 13 accessions to be susceptible. Among the resistant lines, IR12L110, Namcheonbyeo, Dhalaheera and SahbhagiDhan recorded a minimum lesion length of 3.7cm, 4.2cm, 4.67cm and 8.3 cm, respectively. Phylogenetic tree, constructed using molecular data, grouped the rice germplasm into four major clusters. R genes xa 5 and Xa4 contributed 14 positive compatible R genes, each belonging to 28 germplasm for BB resistance. The potential genetic resources identified as resistant to BB can be used as donors for the improvement of rice BB resistance in rice breeding programs.

Download Full-text