Marker-assisted pyramiding of two major, broad-spectrum bacterial blight resistance genes, Xa21 and Xa33 into an elite maintainer line of rice, DRR17B.

C H Balachiranjeevi ,Hajira Sk,Jauhar Ali,B C Viraktamath ,G Rekha ,K Suneetha ,G Harika ,B P Mallikarjuna Swamy ,V P Bhadana ,S M Balachandran ,Abhilash Kumar ,G S Laha ,Abdul R Fiyaz ,Yugender A,Archana Giri ,K Pranathi ,P Senguttuvel ,Bhaskar Naik S,M S Madhav ,M Anila ,Ravindra Ramrao Kale ,A S Hariprasad ,Koushik M B V N,Dilip Kumar T,Mahadev Swamy H K,R M Sundaram

doi:10.1371/journal.pone.0201271

Abstract

Bacterial blight (BB) disease reduces the yield of rice varieties and hybrids considerably in many tropical rice growing countries like India. The present study highlights the development of durable BB resistance into the background of an elite maintainer of rice, DRR17B, by incorporating two major dominant genes, Xa21 and Xa33 through marker-assisted backcross breeding (MABB). Through two sets of backcrosses, the two BB resistance genes were transferred separately to DRR17B. In this process, at each stage of backcrossing, foreground selection was carried out for the target resistance genes and for non-fertility restorer alleles concerning the major fertility restorer genes Rf3 and Rf4, using gene-specific PCR-based markers, while background selection was done using a set of 61 and 64 parental polymorphic SSR markers respectively. Backcross derived lines possessing either Xa21 or Xa33 along with maximum genome recovery of DRR17B were identified at BC3F1 generation and selfed to develop BC3F2s. Plants harboring Xa21 or Xa33 in homozygous condition were identified among BC3F2s and were intercrossed with each other to combine both the genes. The intercross F1 plants (ICF1) were selfed and the intercross F2(ICF2) plants possessing both Xa21 and Xa33 in homozygous condition were identified with the help of markers. They were then advanced further by selfing until ICF4 generation. Selected ICF4 lines were evaluated for their resistance against BB with eight virulent isolates and for key agro-morphological traits. Six promising two-gene pyramiding lines of DRR17B with high level of BB resistance and agro-morphological attributes similar or superior to DRR17B with complete maintenance ability have been identified. These lines with elevated level of durable resistance may be handy tool for BB resistance breeding.

Highlights

Rice production needed to be increased 42% by 2050to feed the demands of an ever-increasing human population globally [1, 2]
The true F1s derived by crossing DRR17B with ‘ISM’ (i.e., Cross I) and FBR1-15 (i.e., Cross II) were backcrossed with DRR17B to obtain BC1F1s, which were screened with the genespecific markers
In addition to improving bacterial blight (BB) resistance of DRR17B, The current study focused on the identification of Improved lines (ILs) of DRR17B possessing plant height which is significantly shorter than DRR17B, as shorter plant is preferred for deployment as good maintainers [23]

Summary

Introduction

Rice production needed to be increased 42% by 2050to feed the demands of an ever-increasing human population globally [1, 2]. One of the principal reasons for slow adoption of rice hybrids in India is their susceptibility to major rice diseases like bacterial blight (BB) and blast [4]. Most of the commercial rice hybrids that have been released and cultivated in India do not possess broad spectrum resistance for BB disease [5]. It is one of the most devastating diseases in rice [6]. Breeding BB resistant rice varieties and hybrids is the best strategy for managing the BB disease in rice [10]. Large scale and long-term cultivation of varieties and hybrids with a single gene results in the breakdown of resistance due to a high degree of pathogenic variation [12, 16, 17]. Pyramiding of two or three Xa genes can enhance the durability and spectrum of resistance against BB [18, 19]

Methods

Results

Discussion

Conclusion