Unraveling possible association between quantitative trait loci (QTL) for partial resistance and nonhost resistance in food barley (Hordeum vulgaris L.)
Many quantitative trait loci (QTLs) in different barley populations were discovered for resistance to Puccinia hordei and heterologous rust species. Partial resistance (host basal resistance) and nonhost resistance (nonhost basal resistance) in barley to leaf rusts are based on prehaustorial mechanism of resistance which is associated with papillae formation. They are mainly governed by genes with relatively small, quantitative effects, located on QTL. The genes for host basal resistance seem to play similar roles in basal resistance as those governing nonhost basal resistances. From different studies it was observed that these two resistance types are based on shared principles. Four and two quantitative trait loci-near isogenic lines (QTL-NILs), respectively, were developed for basal resistance and nonhost resistance QTLs using SusPtrit as recurrent parent. SusPtrit is a research line which is exceptionally susceptible to leaf rusts for which normally barley is a nonhost. They were infected with one homologous (P. hordei isolate 1.2.1) and three heterologous (Puccinia triticina isolate ‘Flamingo’, P. hordei-murini and P. hordei-secalini) leaf rusts in three replications at seedling stage to evaluate whether relatively large-effect QTLs show specificity in their reaction to homologous and heterologous rust isolates. The result showed that, the QTLs for host basal resistance and the QTL for nonhost basal resistance have a significant (P<0.05) effect on both homologous and heterologous rusts. Also, higher positive (P<0.05, r = 0.98) correlation was observed between different macroscopic and microscopic parameters measured indicating that there is a possible association between partial resistance quantitative trait loci and nonhost resistance quantitative trait loci. These give an indication that indeed, host and nonhost basal resistance are associated.
Keywords: Partial resistance, nonhost resistance, near isogenic lines, barley