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.

The identification and deployment of disease resistance genes are key objectives of Australian barley breeding programs. A doubled haploid (DH) population derived from the cross VB9104 × Dash was used to identify markers for resistance to scald (Rhynchosporium secalis). The map comprised of 205 markers including SSRs and AFLPs. The population was assessed for severity of scald during grain fill in a field trial in South Australia. Marker analysis was performed using the software packages Mapmanager and Qgene. QTL analysis identified a region on chromosome 3H, associated with scald resistance in a number of studies, and a region on 4H which has not previously been associated with scald resistance. R2 values for the 3H and 4H chromosome regions were 29% and 22%, respectively. Multiple regression analysis of these two QTLs explained 42% of the variation. There are a number of markers showing strong associations with the resistance in these regions. These markers present an opportunity for marker assisted selection of lines with resistance to scald in barley breeding programs.

Net type net blotch caused by Pyrenophora teres f. teres is a major disease in Western Australia which reduces significant barley production around the world. Studies were focussed on four resistant lines to identify microsatellites linked with the resistance. The four lines, WA 4794 (103 IBON 91) (Pedigree: Arupo S × 2/3/PI 2325/Maf 102//Cossack), Pompadour (Pedigree: FDO192/Patty), CI 9214 (Pedigree: Collected from South Korea) and WPG 8412-9-2-1 (Pedigree: Bowman//Ellice/TR451) were crossed with Stirling (Pedigree: Dampier//Prior/Ymer/3/Piroline), a susceptible but well adapted cultivar in Western Australia. Doubled haploid (DH) populations were generated through another culture. In case of WA4794, two genes were mapped on 4H and 6H using the microsatellite markers GMS089, Bmag0384 for 4H, and Ebmac0874 for 6H. In Pompadour population, two NNB resistance genes were mapped on 3H and 6H using the microsatellites Bmac0209 and Bmag0173 respectively. In CI 9214, Bmac0218 was linked with the resistance for 2H, Ebmac0871 with 3H, suite of microsatellites Ebmac0635, Ebmac0701 and Ebmac0788 with 4H, and similarly Bmag0173, Bmgtttttt1, Ebmac0874 and HVM74 with 6H. In case of WPG 8412/Stirling, single gene was mapped on 6H using the microsatellite Bmag0173. The R2 value ranged up to 0.80 for the linked microsatellites and some are closely mapped to the resistance genes.

Studies on variation, occurrence and distribution of virulence in Pyrenophora teres f. teres are essential to identify effective sources of resistance for net type net blotch. Disease surveys suggested two different stains are prevalent in Western Australia and 13 in all around Australia. Sixty nine barley lines from different breeding groups in Australia and elsewhere were tested against most prevalent pathotypes. Majority of lines have partial to complete resistance while some have elite resistances to net type net blotch. Four lines out of 69 were chosen for further studies. These four lines: WA 4794 (103 IBON 91), Pompadour, CI 9214, and WPG 8412-9-2-1 were highly diverse and resistant to most of the isolates, and were crossed with Stirling-a highly adaptive but susceptible cultivar. Doubled haploids, F2s, and resistant x resistant crosses were studied against five prevalent isolates. Four genes from WA 4794 (all dominant), three (two dominant and one recessive) from Pompadour, five (two dominant and three recessive) from CI 9214, and two (one dominant and one recessive) from WPG 8412-9-2-1 were identified. In total, 11 different genes were operative against P. teres f. teres isolates. Molecular work is initiated to develop markers which would aid screening of the breeding populations for these resistances.