Abstract
Partial resistance is generally considered to be a durable form of resistance. In barley,
Rphq2
,
Rphq3
and
Rphq4
have been identified as consistent quantitative trait loci (QTLs) for partial resistance to the barley leaf rust pathogen
Puccinia hordei.
These QTLs have been incorporated separately into the susceptible L94 and the partially resistant Vada barley genetic backgrounds to obtain two sets of near isogenic lines (NILs). Previous studies have shown that these QTLs are not effective at conferring disease resistance in all stages of plant development. In the present study, the two sets of QTL–NILs and the two recurrent parents, L94 and Vada, were evaluated for resistance to
P. hordei
isolate 1.2.1 simultaneously under greenhouse conditions from the first leaf to the flag leaf stage. Effect of the QTLs on resistance was measured by development rate of the pathogen, expressed as latency period (LP). The data show that
Rphq2
prolongs LP at the seedling stage (the first and second leaf stages) but has almost no effect on disease resistance in adult plants.
Rphq4
showed no effect on LP until the third leaf stage, whereas
Rphq3
is consistently effective at prolonging LP from the first leaf to the flag leaf. The changes in the effectiveness of
Rphq2
and
Rphq4
happen at the barley tillering stage (the third to fourth leaf stages). These results indicate that multiple disease evaluations of a single plant by repeated inoculations of the fourth leaf to the flag leaf should be conducted to precisely estimate the effect of
Rphq4
. The present study confirms and describes in detail the plant development-dependent effectiveness of partial resistance genes and, consequently, will enable a more precise evaluation of partial resistance regulation during barley development.