Abstract
A collection of 20 oat genotypes from different sources were evaluated in small isolated field plots for crown rust severity in natural epidemics with virulent P. coronata isolates and further screened with linked molecular markers. Large variation was observed for disease severity under field conditions in spreader plot. Genotypes with partial resistance due to a reduction of disease severity in spite of a compatible interaction (rust score 3) and moderate susceptibility were identified. The twenty genotypes displaying the variable disease severity with visible necrosis were selected for further studies regarding presence or absence of major genes (Pc91 and Pc68) for resistance to crown rust. In field nurseries, on the basis of latency period and disease severity (DS) none of the twenty genotypes fell into the resistant pool (score 1). Most of them showed a prolonged latency period, reduced infection frequency and colony size, and increased percentage of early aborted colonies not associated with host cell necrosis. Result on screening for crown rust resistance in field screening and by linked markers showed the absence of major resistance gene in the target population, several advance lines were identified as moderately resistant to crown rust reaction.
Highlights
Despite being high fed fodder crop, oat is gaining importance due to its unique and important quality characteristics, lipid and protein
The relative infection frequency (RIF) of these genotypes was significantly lower than the susceptible pool genotypes as visible leaf necrosis in them was less and showed least decrease in biological yield in stressed conditions (Table 3)
The resistance difference among the 20 test genotypes can be generalized by acknowledging the absence of the two major resistance genes among them and other minor resistance genes at play, i.e. for the genotypes showing moderate resistance reaction with rust reaction score 3 it can be generalized that this type of partial resistance could be by virtue of genes with minor effect for crown rust resistance [9] and for genotypes with moderate susceptibility and susceptibility reactions for crown rust it can be generalized that the pathogen has evolved with matching virulent genes
Summary
Despite being high fed fodder crop, oat is gaining importance due to its unique and important quality characteristics, lipid and protein. Crown rust, caused by Puccinia coronata, is one of the most destructive diseases of oat (Avena sativa L.) in major oat growing countries. More than 100 race-specific resistance genes to crown rust have been identified out of which 96 were defined as Pc, with the majority considered to be dominant genes [2]. Pc91 is a major crown rust resistance gene effective at all stages of plant development [4] Pc68, on the other hand, which was introgressed in A. sativa from Avena sterilis L. The objectives of this work were to screen the oat genotypes for crown rust resistance, to deduce the status of major genes for resistance and to identify useful material for resistance breeding programs
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