Phenotyping Kariega × Avocet S doubled haploid lines containing individual and combined adult plant stripe rust resistance loci

Abstract

The bread wheat cultivar Kariega has maintained its stripe rust resistance since the first detection of Puccinia striiformis f. sp. tritici (Pst) in South Africa during 1996. Doubled haploid mapping population (MP) lines derived from a Kariega 9 Avocet S cross, carrying consistently detected adult plant resistance (APR) quantitative trait loci (QTLs)/gene combinations, were phenotyped at macroscopic and microscopic levels. Field data obtained over four seasons revealed that MP lines carrying a combination of any two of the APR loci QYr.sgi-2B.1, QYr.sgi-4A.1 or Yr18 displayed low coefficients of infection. Lines MP 45 and MP 65, carrying all three gene regions, showed leaf area infected and host reaction type ratings similar to Kariega. The microphenotype of lines was studied in flag leaves sampled from field plots during two seasons using fluorescence microscopy. Pst colony length, number of haustorial mother cells per colony and hypersensitivity index supported the phenotypic data. All three microscopy variables attested to low levels of disease in lines containing multiple stripe rust resistance loci. Lines MP 51 and MP 223 with a single QYr.sgi-2B.1 and Yr18, respectively, also showed adequate resistance, in contrast to lines carrying only QYr.sgi-4A.1 which showed significantly more disease symptoms. Host cell necrosis and lignification were revealed as mechanisms of resistance in some lines.

Assessing the Individual and Combined Effects of QTL for Adult Plant Stripe Rust Resistance Derived from Cappelle-Desprez

“…Despite the many reports proposing gene combinations as a resistance breeding strategy, few studies have actually investigated complementary effects of gene combinations at the histological level. In an analysis of stripe rust histopathology in the spring, wheat cultivar Kariega, Maree et al [46] have shown that colony length, number of haustorial mother cells and HI all verified high levels of resistance in lines with three resistance QTL. Although most lines with two QTL showed acceptable levels of resistance, the stripe rust phenotype seemed to be influenced by the particular QTL combination [46].…”

Molecular and phenotypic evaluation of wheat (Triticum aestivum) containing different combinations of rust resistance genes

“…The variety Kariega reportedly contains three Yr APR genes/QTL that in combination provide complete resistance (Maree et al. 2019).…”

Long-read genome sequencing of bread wheat facilitates disease resistance gene cloning

“…Stripe rust inoculations at seedling and adult plant stages were performed with urediniospores of the South African Pst pathotype 6E22A+ (virulent to Yr2 , Yr6 , Yr7 , Yr8 , Yr17 , Yr25 and YrA ; avirulent to Yr1 , Yr3a , Yr4a , Yr4b , Yr5 , Yr9 , Yr10 , Yr15 and Yr27 ) 56 and pathotype 30E142A+ 16 (virulent to Yr2 , Yr3a , Yr4a , Yr6 , Yr7 , Yr8 , Yr9 , Yr19 , Yr25 , Yr27 and YrA; avirulent to Yr1 , Yr4b , Yr5 , Yr10 , Yr15 , Yr24 , Yr32 , YrCle , YrMor , YrSd , YrSp , YrSu and YrHVII) . In brief, freshly propagated urediniospores were suspended in FC-43 oil (3M Fluorinert FC-43) and then sprayed onto the leaves using a high-pressure air sprayer.…”