Sanjiv Gupta

Net type net blotch (NTNB) is a prominent barley disease in Australia and elsewhere, inducing significant yield reduction. Selecting resistant material against this disease is important against different isolates of the pathogen along with other traits of quality and agronomic value. Based on parental resistance and their differential responses, three doubled haploid populations: WPG8412 x Stirling, WPG8412 x Pompadour and Pompadour x Stirling were phenotyped against two Pyrenophora teres f. teres isolates 97NB1 and NB73. Bimodal segregation indicated a major gene for resistance was operative in these populations. This major gene was mapped using simple sequence repeat (SSR) markers on chromosome 6H in the centromeric region in all three populations. Ten SSR markers were found to be linked with the resistance gene covering 30 to 40 cM distance of the 6H region. HVM74 and BmagOl73 were found to be the closest markers in these populations. Allelic tests in all possible combinations were conducted on six F2 resistant x resistant (R x R) crosses. These crosses were developed from lines: Pompadour, WPG8412, WA4794 and Cl9214 carrying 6H locus imparting resistance to four P. teres f. teres isolates 97NB1, 95NB100, NB5O and NB81. A small number of susceptible plants were identified in 18 out of 24 allelic tests. No segregation was detected in the remaining six tests. These studies demonstrated that 6H region controlling net type net blotch resistance is a complex region which can provide suite of 6H alleles or linked genes for resistance breeding.

Australian barley crops are affected by a range of leaf and root diseases. Diseases constitute a significant limitation to sustainable barley production. Reducing impacts from diseases is important for reliable production of high quality barley. Some diseases are prevalent around Australia whereas others are of regional significance (Table 1). The lack of resistance in major varieties grown in Australia to diseases like scald, net blotches, leaf rust and powdery mildew (Table 2) can impact on yield and grain quality mainly through a reduction in grain size. Reduced grain yields and low malting quality reduce returns to growers and affect domestic and export marketability. Improvements are sought through the development of varieties with adequate levels of resistance to the range of important biotic stresses. A major objective in barley breeding programs around Australia is to develop varieties with improved combinations of disease resistances while maintaining or improving yield, quality and other agronomic traits.