Received: 24 April, 2008. Accepted: 23 May, 2008. Original Research Paper International Journal of Plant Breeding ©2008 Global Science Books Genetic Mapping of Stem Rust Resistance in Durum Wheat Cultivar ‘Arrivato’ Sridhar Bhavani 1 • Urmil K. Bansal 1 • Ray A. Hare 2 • Harbans S. Bariana 1* 1 University of Sydney PBI-Cobbitty, Faculty of Agriculture, Food and Natural Resources, PMB 11, Camden, NSW 2570, Australia 2 NSWDPI Tamworth Agricultural Institute, 4 Marsden Park Road, Calala, NSW 2340, Australia Corresponding author: * harbansb@camden.usyd.edu.au ABSTRACT Genetic analysis of seedling stem rust resistance in the durum wheat cultivar ‘Arrivato’ indicated the presence of three independent genes. Replicated tests on F 3 families derived from ‘Arrivato’/‘Bansi Strain 168’, putatively segregating at a single locus, were performed to confirm monogenic segregations. These families represented three distinct infection types, viz., IT;1, IT2= and ITX and the genes conditioning these different phenotypic expressions were temporarily named SrAr1, SrAr2 and SrAr3, respectively. Up to 100 plants from at least one family representing segregation for each distinct infection type were grown and harvested individually. These monogenically segregating populations were progeny tested. Bulked segregant analyses were conducted and SrAr1 was mapped 0.7 cM proximal to Xgwm47 in chromosome 2BL. SrAr2 mapped 5.7 cM distal to Xwmc59 in the long arm of chromosome 6A, whereas SrAr3 showed genetic association (4.6 cM) with Xgwm334 in chromosome 6AS. Based on combinations of infection type with genomic locations and/or pathogenic specificities of previously characterized stem rust resistance genes SrAr1, SrAr2 and SrAr3 were concluded to be Sr9e, Sr13 and Sr8b, respectively. _____________________________________________________________________________________________________________ Keywords: genetic analysis, molecular mapping, Puccinia graminis, Triticum turgidum ssp. durum, Ug99 INTRODUCTION Stem rust of wheat, caused by Puccinia graminis Pers. f. sp. tritici Eriks. & Henn. (Pgt), can infect tetraploid wheat in- cluding Triticum turgidum L., ssp. durum (Desf); durum wheat. Durum wheat is grown on over 20 million ha globally and Australian durum wheat production ranges between 300,000 to 700,000 tons annually, depending on climatic conditions. Stem rust can seriously affect durum wheat pro- duction and sustained control can be achieved through the deployment of diverse effective resistance gene combina- tions. A continuous effort to genetically characterise rust re- sistance in durum breeding materials and commercial culti- vars is necessary to ensure the maintenance of host genetic diversity. Unlike hexaploid wheat (Triticum aestivum L.), few reports on the genetic bases of stem rust resistance in durum wheat genotypes are published (Gough and Williams 1963; Williams et al. 1978; Bechere et al. 1991; Singh et al. 1992; Klindworth et al. 2007). Consequently, very little ef- fort has been expended on the molecular mapping of stem rust resistance at the tetraploid level. Availability of a large number of highly polymorphic and reproducible microsat- ellite (SSR) markers could facilitate identification of geno- mic regions controlling traits of economic importance such as resistance to rust diseases. The durum cultivar ‘Arrivato’ (parentage; ‘Tetrapre- lude’/‘Waitohi’) was released by the Crop and Food Re- search, New Zealand in 1987. It was released in Australia in 1995 by Heritage Seeds. Arrivato (AUS 33332, Australian Winter Cereals Collection accession number) possesses high levels of stem rust resistance in Australia and the gene- tic basis of resistance remained unclear. This study was conducted to assess the inheritance of stem rust resistance in ‘Arrivato’ and to determine the genomic locations of the components of stem rust resistance. MATERIALS AND METHODS Host materials Stem rust resistant durum cultivar ‘Arrivato’ was crossed with the susceptible landrace ‘Bansi Strain 168’ (AUS 1866). F 1 plants were grown in the field and harvested individually. The field grown F 2 plants were harvested and threshed individually to pro- duce F 3 families. Stem rust tests were performed on 198 F 3 fami- lies. Approximately 100 plants from selected F 3 families display- ing monogenic segregations for distinct seedling stem rust reac- tions were grown individually, to develop monogenically segre- gating mapping populations (MSPs). Greenhouse studies F 3 families were tested for stem rust reaction in the seedling stage under temperature-controlled greenhouse conditions. Sixteen to 20 seeds of each family were sown in 9 cm pots and held in a rust- free microclimate room maintained at 20°C prior to inoculation. A rust testing procedure, described by Bariana and McIntosh (1993), including growing and inoculation of seedlings under greenhouse conditions, was followed. Urediniospores of Pgt pathotype (pt) 34- 1,2,3,4,5,6,7 (PBI culture no. 103) suspended in light mineral oil (Shellsol T ® 3 mg spores per 10 ml oil for 200 pots) were sprayed over 10-12 days old seedlings using a hydrocarbon propellant pressure pack. Stem rust inoculated seedlings were incubated under natural light at 18-20°C for 48 hrs on water filled trays covered with polythene hoods. Inoculated seedlings were then transferred to a temperature-controlled microclimate room maintained at 25°C. Stem rust seedling infection types were scored 14-16 days after inoculation according to Stakman et al. (1962) with slight modi- fications proposed by Luig (1983). The symbols ‘+’ and ‘-’ were added to describe variations from the typical expression of a given infection type. Symbols ‘N’ or ’C’ were also used where more than usual necrosis and chlorosis, respectively, were associated with a particular infection type. The Pgt pts 40-1,2,3,4,5,6,7 (PBI culture ®