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

摘要

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 x 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.