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With 2 figures and 4 tables Abstract Net type net blotch (NTNB) is an important barley disease in Australia and elsewhere, inducing significant yield reduction. 'WPG8412' was resistant against Australian NTNB isolates 97NB1 and NB73, whereas 'Pompadour' and 'Stirling' showed differential responses to these isolates. Using these lines, three F1-derived double haploid populations that comprised 194 double haploid lines (DHLs) of 'WPG8412' ×'Stirling', 116 DHLs of 'WPG8412' × 'Pompadour' and 206 DHLs of 'Pompadour' × 'Stirling' were tested against these two isolates. Bimodal segregation indicated a major gene for resistance was operative: in 'WPG8412' × 'Stirling' against 97NB1; in 'WPG8412'×'Pompadour' against NB73; and in 'Pompadour' × 'Stirling' against either of the isolate. This major gene was mapped using simple sequence repeat (SSR) markers on chromosome 6H in the centromeric region in all three populations. This work demonstrated that 6H region controlling NTNB is a complex locus, where at least three alleles or closely linked genes are possible in these parents against these isolates. This is a first report of 6H complexity for NTNB resistance against Australian isolates. [ABSTRACT FROM AUTHOR]

With 2 figures and 5 tables Net type net blotch (NTNB) is an important barley disease in Australia and elsewhere, with significant yield reduction. This trait is important in selection along with other traits of quality and agronomic value. Two-hundred doubled-haploid lines were generated through anther culture from a cross between ‘Pompadour’ and ‘Stirling’. Quantitative trait loci (QTL) were identified against five isolates of Pyrenophora teres f. teres, which represent virulences across Australia. QTL were mapped on chromosomes 3H and 6H using simple sequence repeat (SSR) markers. The resistance locus on 6H was detected with all isolates while the 3H locus was detected with two isolates. The 6H QTL from ‘Pompadour’ contributed resistance to isolates 97NB1, 95NB100 and NB81, whereas 6H QTL from ‘Stirling’ contributed resistance to isolates NB50 and NB52B. The 3H QTL from ‘Pompadour’ contributed resistance to NB50 and NB52B. Significant epistatic interactions were detected between QTL on 3H and 6H. These resistance QTL are a useful resource and identifying closely linked SSR markers with allelic combinations will facilitate in marker-assisted selection to develop NTNB resistant breeding lines. [ABSTRACT FROM AUTHOR]

Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape ( Brassica napus), worldwide, including Australia and France. The aims of these studies were first, to determine if higher levels of resistance to L. maculans could be generated in double haploid (DH) lines derived from spring-type B. napus cv. Grouse, which has a good level of field resistance to blackleg; and second, to determine whether the resistance to blackleg disease of individual DH lines responds differentially to different L. maculans field populations within and between the two countries. DH lines were extracted from cv. Grouse and tested in field experiments carried out in both France and Australia against natural L. maculans populations. Extracting and screening DH lines were an effective means to select individual lines with greatly improved expression of resistance to blackleg crown canker disease in comparison with the original parental population. However, relative disease resistance rankings for DH lines were not always consistent between sites. The higher level of resistance in France was shown to be because of a high expression level of quantitative resistance in the French growing conditions. Big differences were observed for some DH lines between the 2004 and the 2005 field sites in Australia where the L. maculans populations differed by their virulence on single dominant gene-based resistant lines derived from Brassica rapa ssp. sylvestris. This differential behaviour could not be clearly explained by the specific resistance genes until now identified in these DH lines. This investigation highlights the potential to derive DH lines with superior levels of resistance to L. maculans compared with parental populations. However, in locations with particularly high pathogen diversity, such as in southern Australia, multiyear and multisite evaluations should be performed to screen for the most efficient material in different situations. [ABSTRACT FROM AUTHOR]