Registration of Powdery Mildew Resistant Barley Composite Cross XLII Germplasm

A SIX-ROWED spring barley (Hordeum vulgare L.) (Reg. no. GP64) male sterile-facilitated recurrent selection population, (MSFRSP) designated Composite Cross (CC) XLII, was developed cooperatively by the Montana Agricultural Experiment Station and USDA-ARS. This population contains numerous sources of resistance to Erysiphe graminis DC. ex Merat f. sp. hordei Em. Marchal, the causal organism of powdery mildew, in a background of diverse agronomic types. CC XLII originated as a bulk of RSP-5C (50%), CC XXXVI that was selected for powdery mildew resistance in Morocco in 1979 (10%), CC XXXVIII that was selected for powdery mildew resistance in Morocco in 1979 (10%), Ramage MSFRS 499-unselected (20%), and Ramage MSFRS 499-selected (10%). RSP-5C and Ramage MSFRS 499 are described below. CC XXXVI and CC XXXVIII have been described previously (1,2). RSP-5C is a MSFRSP consisting of bulked F2 seed of crosses between Manchuria (CI 2330) msg 10 and 'Beecher' (CI 6566), 'Gem' (CI 7243), 'Unitan' (CI 10421), 'Gait' (CI 11770), 'CM 67' (CI 13782), 'Atlas 68' (CI 13824), 'Hullless Glacier' (CI 13831), 'Nordic' (CI 15216), 'Steptoe' (CI 15229), M21 (CI 15481), 'Arimont' (CI 15509), 'Atsel' (CI 6250), 'Waxy Titan', and 'Hull-less Vantage*. Ramage MSFRS 499 was assembled by crossing elite F3 to F7 2-rowed breeding materials from Nickerson RPB Ltd. (Rothwell, England) onto male sterile plants in CC XXXE (3). Male sterile plants in the ¥3's of these crosses were used as females in crosses with 177 lines chosen for their reported resistance to E. graminis f. sp. hordei at some time or location. F2 seed of these crosses was bulked and identified as Ramage MSFRS 499-unselected. A small number of powdery mildew resistant plants in Ramage MSFRS 499unselected were harvested from disease nurseries in England, France, and Sweden in 1977 and intercrossed in Arizona in 1977-1978. The progeny of the intercrosses was identified as Ramage MSFRS 499-selected. After assembly, CC XLII was planted in isolation at El Centre, Calif, during the winter, 1979-1980, and allowed to randomly outcross. Seeds on male sterile plants were then harvested to form the zero cycle. Two cycles of recurrent selection have since been completed. Each cycle consisted of two generations: 1) selection for resistance and 2) recombination. Selection for resistance was conducted yearly at Bozeman, Mont, and several other barley-growing regions of the world. Selection was based on natural infection of E. graminis f. sp. hordei. Seed harvested from the various nurseries was bulked proportionally based on selection intensity for powdery mildew resistance and number of plants harvested. This bulked seed was grown in isolation in recombination nurseries at El Centro and Scottsdale, Ariz. Seeds set on male sterile plants were harvested to continue the next cycle. Population sizes above 10 000 plants were maintained in each generation. CC XLII presently consists of components selected for resistance in Montana, Mexico, France, Morocco, Egypt, and Syria. CC XLII contains a broad range of agronomic types. It performs best under conditions of moderate rainfall and should be a good source of multigenic resistance to powdery mildew. About 50% of the plants in CC XLII are resistant to powdery mildew under Montana conditions. A list of the resistance sources in CC XLII is available upon request from the authors. Seed of the latest available generation can be obtained in 500 g quantities from the authors or from the Curator, World Collection of Small Grains, USDA-ARS, Beltsville, Agric. Res. Ctr., Beltsville, MD 20705.