Identification of novel sources of resistance against bacterial blight disease through intensive screening of wild rice introgression lines

Abstract

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a serious threat to rice production in many rice growing regions of the world. Deployment of host plant resistance is the most feasible strategy for managing the disease. The present study was carried out with an objective to identify
novel sources of resistance against BB among introgression lines derived from wild rice. Forty-four wild rice introgression lines in the genetic background of IR54, IR72 and a new plant type rice breeding line possessing introgressions from different wild rice accessions were screened for their resistance against BB disease using a local, virulent strain of Xoo (strain IX-020). The selected resistant lines which showed very high level of resistance were further screened with multiple hyper-virulent isolates of Xoo collected from different geographically distinct hotspot regions of India along with susceptible and resistant checks.
Three lines carrying genomic introgression from Oryza officinalis and O. longistaminata displayed broad spectrum resistance against multiple isolates of Xoo. These lines were also analysed with a set of functional markers specific for known BB resistance genes such as Xa21, xa13, xa5 and none of the selected introgression lines, viz., IR 75084-15-3-B-B, IR 75083-49-25-9-5-B-B-B and IR 75085-35-5-2-B harboured the resistance specific allele with respect to these gene specific markers. Based on resistance spectrum of these introgression lines and absence of some of the known major BB resistance genes, it can be speculated that the resistance in these accessions may be novel. These introgression lines can be an important source for identification and marker-assisted transfer of novel BB resistance gene(s).