Presence of the Stb6 gene for resistance to septoria tritici blotch (Mycosphaerella graminicola) in cultivars used in wheat‐breeding programmes worldwide

Abstract

Fifty‐two wheat cultivars and breeding lines, most of which have been used in breeding programmes worldwide, were tested for isolate‐specific resistance to Mycosphaerella graminicola isolate IPO323, which interacts with the Stb6 gene of wheat (first identified in cvs Flame and Hereward) via a gene‐for‐gene relationship. Twenty‐three lines were specifically resistant to this isolate. Sixteen resistant lines were crossed with Flame for a test of allelism. All progeny lines were resistant, suggesting that the 16 parental lines had Stb6, a gene allelic to it or a gene closely linked to it. In 14 lines, resistance to IPO323 was controlled by Stb6 only. An exception was Kavkaz‐K4500 L6.A.4., which has two genes for resistance to IPO323, one of which is Stb6. The microsatellite marker Xgwm369 was used to examine genetic diversity in the region of the genome containing Stb6, to which it is closely linked. Eleven alleles of Xgwm369, with amplified fragments of 10 different sizes, as well as apparent nonamplification of this marker in Bulgaria 88, were detected. Through the use of information about lines’ ancestry, combined with Xgwm369 alleles, it was shown that Stb6 entered world wheat‐breeding programmes on a minimum of six occasions, and possibly from as many as 11 sources. The presence of Stb6 in both European and Chinese landraces suggests that this gene has been present in cultivated wheat since the earliest times of agriculture.

Resistance spectra of wheat genotypes and virulence patterns of Mycosphaerella graminicola isolates in Iran

“…This indicates that most of Stb genes are not effective resistance genes against Iranian isolates and thus their effectiveness should be evaluated before introduction or employment in national or regional breeding programs in Iran. All isolates were virulent to Shafir, Estanzuela Federal, and Courtot which carry Stb6, Stb7 and Stb9 genes, respectively (Brading et al 2002;McCartney et al 2003;Chartrain et al 2005bChartrain et al , 2009. Therefore, these genes may not be effective in controlling the disease in Iran.…”

“…However, virulence of fungal isolates to Stb genes in these genotypes as well as Israel 493 and Synthetic W7984 was observed with high frequency, as 12-13 isolates were virulent to these cultivars and lines. Vernapolis carries Stb2 and Stb6 genes and is one of the resistant cultivars, which confers also a high level of partial resistance under field conditions Adhikari et al 2004c;Chartrain et al 2004aChartrain et al , 2005b. Interestingly, all isolates from Golestan were avirulent to Vernapolis, while all isolates from other provinces were virulent to this cultivar.…”

“…Among differentials, Arina and Flame were the most resistant differential wheat genotypes. Arina has Stb15 gene and both Arina and Flame carry Stb6 (Brading et al 2002;Chartrain et al 2005b;Arraiano et al 2007). Since Stb6 was an ineffective resistance gene against all fungal isolates, it is possible that Stb15 in Arina or other unidentified genes in Flame and Arina conferred resistance to the avirulent isolates from different provinces.…”

“…In this study, a set of differential wheat genotypes representing 13 mapped Stb genes was used to determine virulence patterns of the M. graminicola isolates. Stb6 gene has been originally mapped in cultivar Flame (Brading et al 2002), but it is widely present in many wheat genotypes and differentials including genotypes Shafir, Vernapolis, Israel 493, Kavkaz-K4500, TE 9111, and Arina (Brading et al 2002;Chartrain et al 2005b). In the present study, Flame was resistant to seven isolates, while other wheat genotypes carrying Stb6 gene were susceptible to these isolates.…”

Potential new genes for resistance to Mycosphaerella graminicola identified in Triticum aestivum × Lophopyrum elongatum disomic substitution lines

“…The genes on wheatgrass chromosomes 1E and 6E hopefully can augment the STB resistance identified on the same homoeologous groups in wheat. Interestingly, Chinese Spring is thought to contain gene Stb6 (Chartrain et al 2005), which is located on the short arm of wheat chromosome 3A (Brading et al 2002). The disomic substitution line 3E(3A) had the highest disease severity and was significantly more susceptible than Chinese Spring in Experiment 1, possibly due to deletion of the Stb6 gene on wheat chromosome 3A.…”