Identification of a Hidden Resistance Gene in Tetraploid Wheat Using Laboratory Strains of Pyricularia oryzae Produced by Backcrossing

Abstract

In the process (BC3F1 generation) of backcrossing an Avena isolate of Pyricularia oryzae with a Triticum isolate, color mutants with white mycelia were obtained. These white mutants lacked virulence on all (31/31) hexaploid and most (28/32) tetraploid wheat lines tested. In a BC4F1 population, white and black cultures segregated in a 1:1 ratio, suggesting that the mutant phenotype is controlled by a single gene. Furthermore, the mycelial color was perfectly linked with avirulence in the BC4F1 population; white cultures were all avirulent on common wheat (Triticum aestivum) 'Norin 4' (N4) whereas black cultures were all virulent. White cultures in the BC3F1 and BC4F1 generations were also avirulent on tetraploid wheat (T. dicoccoides) accession 'KU109' (Tat4), which was susceptible to all cultures derived from the parental wild isolates through the BC2F1 generation. A cross between Tat4 and a susceptible tetraploid (T. paleocolchicum) accession 'KU196' (Tat14) produced resistant and susceptible F2 seedlings in a 3:1 ratio against the white cultures. In the F3 generation homozygous resistant/segregating/homozygous susceptible lines segregated in a 1:2:1 ratio. These results suggest that the resistance of Tat4 to the white cultures is controlled by a single major gene. This gene, tentatively designated as RmgTd(t), is considered to be a hidden resistance gene because it was not detected with the Br58, F1, BC1F1, or BC2F1 cultures. Cytological analysis revealed that the moderate resistance controlled by RmgTd(t) was associated with a hypersensitive reaction of mesophyll cells.

Wheat Blast: A Disease Spreading by Intercontinental Jumps and Its Management Strategies

“…Therefore, MoL population massively built up on the variety and mutations occurred in PWT3, resulting in pwt3-carrying MoL isolates that are virulent even to wheat cultivars with Rmg6, turning MoL into MoT (Inoue et al, 2017). RmgTd(t) was detected by a mutant isolate from a cross between MoA and MoT, which was avirulence to most bread and durum wheat cultivars barring few susceptible tetraploid wheat cultivars (Cumagun et al, 2014).…”

Screening and Mapping for Head Blast Resistance in a Panel of CIMMYT and South Asian Bread Wheat Germplasm

“…Recently, Juliana et al (2019) reported a prominent role of the 2NS/2AS translocation in CIMMYT germplasm, conferring yield advantage, lodging resistance, along with blast and rust resistance. Apart from the 2NS/2AS translocation, there have been very limited blast resistance genes identified for MoT, i.e., Rmg2 , Rmg3 , Rmg7 , Rmg8 , RmgTd(t) , and RmgGR119 ( Zhan et al, 2008 ; Cumagun et al, 2014 ; Tagle et al, 2015 ; Cruz et al, 2016 ; Wang et al, 2018a ). However, most of these genes have been overcome by new MoT isolates and only Rmg8 and RmgGR119 remained to be validated in field experiments with new MoT isolates.…”

QTL mapping for field resistance to wheat blast in the Caninde#1/Alondra population

“…So far, most genetic studies for WB resistance were performed at the seedling stage, where the host–pathogen interaction appeared to follow the gene-for-gene model (Anh et al 2015 ). The resistance genes identified in such experiments are Rmg2 , Rmg3 , Rmg7 , Rmg8 , RmgTd(t) and RmgGR119 (Zhan et al 2008 ; Cumagun et al 2014 ; Tagle et al 2015 ; Cruz et al 2016b ; Wang et al 2018a ) for host resistance against MoT, and Rmg1 , Rmg4 , Rmg5 , Rmg6 (Hau et al 2007 ; Nga et al 2009 ; Vy et al 2014 ) for resistance against non-MoT strains of M. oryzae . Of these genes, Rmg7 , Rmg8 and RmgGR119 also conferred resistance at the adult plant stage against spike infection by MoT, but Cruz and Valent ( 2017 ) pointed out that the resistance conferred by Rmg7 has been overcome by recent MoT isolates, whereas Rmg8 and RmgGR119 remain to be tested with the new MoT isolates.…”