The Emergence of New Aggressive Leaf Rust Races with the Potential to Supplant the Resistance of Wheat Cultivars

Abstract

Characterization of the genetic structure and the physiological races of Puccinia triticina is a growing necessity to apply host genetic resistance against wheat leaf rust as a successful control strategy. Herein, we collected and identified about 130 isolates of P. triticina from 16 Egyptian commercial wheat cultivars grown at different locations, over two seasons (2019/2020 and 2020/2021). The 130 isolates of P. triticina were segregated into 17 different physiological races. TTTST and TTTKS were the most common virulent races, whereas TTTST and MTTGT were the most frequent races. The races were classified into three groups, based on their distinct DNA band sizes (150 bp, 200 bp, and 300 bp) after RAPD analysis. The new wheat cultivars (Sakha-94, Sakha-95, and Shandweel-1) infected with the most virulent race (TTTST), Gemmeiza-12, and Misr-3 were resistant to all physiological races. The resistance of these cultivars was mostly due to the presence of Lr19- and Lr28-resistant genes. Our results serve as a warning about emerging aggressive races capable of supplanting resistance to leaf rust, and help in the understanding of the pathotype–cultivar–location association and its role in the susceptibility/resistance of new wheat cultivars to P. triticina.

Mechanism of Wheat Leaf Rust Control Using Chitosan Nanoparticles and Salicylic Acid

“…This can also be achieved by developing rust resistant genotypes or by successful varietal manipulation of the available genotypes throughout the country to avoid heavy infection to the susceptible genotypes [ 1 ]. The emergence of new races capable of breaking the resistance in the new varieties, such as the emergence of the TTTST race on Shandweel-1, Sakha-94 and Sakha-95 varieties was reported [ 5 ]. Therefore, the second line of control methods should be used, which is chemical fungicides.…”

“…In recent years, the cultivation of more than one resistant variety was utilized [ 1 ]. The emergence of new disease races and the breaking of resistance in the varieties increase disease losses [ 5 ]. Therefore, the second line of disease control is to rely on chemical control.…”

Genome-Wide Screening of Broad-Spectrum Resistance to Leaf Rust (Puccinia triticina Eriks) in Spring Wheat (Triticum aestivum L.)

“…The main defect in this type of resistance is that, due to the race adaptation ability, the disease could overcome the resistant genes and produce new virulent races that cause epidemics situation in single gene wheat cultivars (Folr, 1956;Flor, 1971). This is the recent situation in the Egyptian fields where different Pt races among the Egyptian governorates and growing seasons have been reported that resulted in a breakdown of the resistance in some important Egyptian cultivars (Omara et al, 2021). To date, more than 80 leaf rust resistance genes (Lr) have been identified and formally cataloged in wheat, most of them confer race specific resistance (McIntosh et al, 1995(McIntosh et al, , 2008(McIntosh et al, , 2013Gill et al, 2019;Bhavani et al, 2021).…”

The Impact of Wheat Yellow Rust on Quantitative and Qualitative Grain Yield Losses under Egyptian Field Conditions.

“…The difference in the genetic background of resistance reflects the difference between the type of infection and the disease. This is due to the appearance of new virulent race in pathogen populations therefore, the type of infection of some varieties may change over time (Omara et al, 2021). Some varieties can maintain resistance for many years but become susceptible after a period of time (Al-Maaroof, 1997).…”