Recent pathotype development of New Zealand cereal rust populations

Abstract

Rust diseases are serious threats to New Zealand cereal crops. Beside the use of fungicides, resistant varieties are an important option for managing these diseases. Changes in rust pathotypes commonly occur due to mutations in existing populations or exotic incursions. Information on these changes is the basis of gene-based disease management. Rust-infected leaves were collected from cereal crops from 2012 to 2015. The pathotypes of these and some historic samples were determined in glasshouse studies, using specific differential host sets. Eight pathotypes of Puccinia triticina (Pt, causal agent of wheat leaf rust), five of P. striiformis f. sp. tritici (Pst, causal agent of wheat stripe rust) and two of P. hordei (Ph, causal agent of barley leaf rust) were identified. The Pst ‘WA’ pathotype was most frequently found. Wheat varieties ‘Empress’ and ‘Torch’, previously resistant to Pt, were found to be susceptible to leaf rust for the first time. The ‘WA’ pathotype of Pst is likely to have arrived in New Zealand from Australia, and is now widespread. The two Pt pathotypes could have overcome resistance gene Lr24 in ‘Empress’ and ‘Torch’.

Extensive somatic nuclear exchanges shape global populations of the wheat leaf rust pathogenPuccinia triticina

“…Both of these are identical to pathotypes found in the lineage derived from pathotype 76-3,5,7,9,10+Lr37, first detected in Australia in 2005 (Huerta-Espino et al ., 2011; Park, 2015). The 20QLD87 isolate has the same pathotype (104-1,3,4,6,7,8,9,10,12+Lr37) as the lineage first detected in 2014 as an apparent exotic incursion into Australia via New Zealand (Warren et al ., 2018). The 20ACT90 isolate has the same pathotype as the currently predominant pathotype in Australia, which was first detected in 2016 (Bariana et al ., 2022), while 19NSW04, 19ACT07 and 20QLD91 share the same pathotype but with additional virulence for Lr27 / Lr31 (104-1,3,4,5,6,7,9,10,12+Lr37).…”

“…In 2005, a Pt isolate with a novel pathotype (76-3,5,7,9,10) was first detected in Australia as a postulated exotic incursion (Huerta-Espino et al ., 2011; Park, 2015) and several isolates derived by single-step mutations were subsequently detected (Bariana et al ., 2022), including isolates with pathotypes matching isolates 19ACT06 and 19QLD08 (AU1 lineage, AB genotype). Similarly, an exotic incursion with pathotype 104-1,3,4,6,7,9,10,12 was first detected in New Zealand in 2012, followed by a mutational derivative with virulence to Lr28 (pathotype 104-1,3,4,6,7,8,9,10,12) in 2014 in both New Zealand and Australia (Warren et al ., 2018). This pathotype matches the 20QLD87 isolate (AU3 lineage, CD genotype).…”

“…These lineages have apparently evolved clonally through stepwise mutations to virulence on single leaf rust resistance genes in wheat to give rise to numerous derived pathotypes (Park, 2015). A further exotic incursion of a lineage with pathotype 104-1,3,4,6,7,9,10,12+Lr37 was detected first in New Zealand in 2012 and subsequently mutated to acquire virulence on Lr28 (pathotype 104-1,3,4,6,7,9,10,12+Lr37) with the latter pathotype first detected in Australia in 2014 (Warren et al ., 2018).…”

Effectiveness of Leaf Rust Resistance Genes in the Adult and Juvenile Stages in Southern Russia in 2011–2020

“…A significant number of cultivars possess Lr34 as well [ 33 ]. Recently, pathotypes virulent to Lr24 have also been found in New Zealand [ 12 ]. In Israel, Lr24 still retains its effectiveness [ 34 ].…”

“…Such resistance is not “durable” because it’s controlled by one or more genes [ 9 , 10 ]. The evolving nature of plant pathogens results in new virulent races that rapidly overcome ASR genes [ 11 , 12 ]. Race non-specific resistance genes (APR genes)— Lr34 , Lr46 , Lr67 and Lr68 —are usually susceptible at the stage of seedlings.…”