A Moroccan Pyrenophora teres f. teres population defeats the Rpt5 broad-spectrum resistance on barley chromosome 6H

Authors: RICHARDS, JONATHAN - Louisiana State University; LI, JINLING - North Dakota State University; KOLADIA, VAIDEHI - North Dakota State University; Wyatt, Nathan; REHAM, SAJID - The International Center For Agricultural Research In The Dry Areas(ICARDA); BRUEGGEMANN, ROBERT - Washington State University; Friesen, Timothy

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2023
Publication Date: 6/29/2023
Citation: Richards, J., Li, J., Koladia, V., Wyatt, N.A., Reham, S., Brueggemann, R., Friesen, T.L. 2023. A Moroccan Pyrenophora teres f. teres population defeats the Rpt5 broad-spectrum resistance on barley chromosome 6H. Phytopathology. https://doi.org/10.1094/PHYTO-04-23-0117-R.
DOI: https://doi.org/10.1094/PHYTO-04-23-0117-R

Interpretive Summary: Net form net blotch caused by the fungal pathogen Pyrenophora teres f. teres causes economic losses globally wherever barley is grown. Several resistance sources have been identified that are effective globally. CI5791 harbors the resistance gene Rpt5, a gene that has been used in several breeding programs in North America. Here we show that highly effective Rpt5 was overcome by a P. teres f. teres pathogen population in Morocco. This discovery highlights the ability of the pathogen population to overcome single sources of resistance. This information will be used by breeders trying to introgress resistance to control net form net blotch in barley.

Technical Abstract: Net form net blotch (NFNB), caused by Pyrenophora teres f. teres, is an important barley disease. The centromeric region of barley chromosome 6H has often been associated with resistance or susceptibility to NFNB, including the broad-spectrum dominant resistance gene Rpt5 derived from barley line CIho 5791. We characterized a population of Moroccan P. teres f. teres isolates that had overcome Rpt5 resistance and identified QTL that are effective against these isolates. Eight Moroccan P. teres f. teres isolates were phenotyped on barley lines CIho 5791 and Tifang. Six isolates were virulent on CIho 5791 and two were avirulent. A CIho 5791 × Tifang recombinant inbred line (RIL) population was phenotyped with all eight isolates and confirmed the defeat of the 6H resistance locus formerly mapped as Rpt5 (Manninen et al. 2006) in barley line CI9819. A major QTL on chromosome 3H, as well as several minor QTL, were identified and provided resistance against these isolates. F2 segregation ratios supported dominant inheritance for both the 3H and 6H resistance genes. Furthermore, inoculation of progeny isolates derived from a cross of P. teres f. teres isolates 0-1 (virulent on Tifang / avirulent on CIho 5791) and MorSM 40-3 (avirulent on Tifang / virulent on CIho 5791) onto the RIL and F2 populations determined that recombination between isolates can generate novel genotypes that overcome both resistance genes. Markers linked to the QTL identified in this study can be used to incorporate both resistance loci into elite barley cultivars for durable resistance.