Introduction. During an initial seed increase of the Harrington/TR306 population in 1993, it was noted that the progeny segregated for reaction to the powdery mildew (Blumeria graminis f. sp. hordei) population present in the greenhouse. An additional powdery mildew evaluation revealed that Harrington was resistant and TR306 susceptible. To determine the genetics of resistance to powdery mildew in Harrington, the North American Barley Genome Mapping Project (NABGMP) (Kleinhofs et al. 1993) populations of Harrington/TR306 (H/T) and Harrington/Morex (H/M) were evaluated to a single pustule isolate of B. g. f. sp. hordei. Additionally, the disease reaction data of progeny from the two doubled haploid populations were merged with the molecular marker data generated by the NABGMP to map the resistance locus.

Materials and Methods. A single pustule isolate of B. g. f. sp. hordei (ND92GH) was made from an infected progeny and increased in isolation on a vegetative dwarf mutant of barley (Falk and Kasha 1982) until needed for inoculation. This isolate exhibits a low virulence/high virulence pattern of P01, P03, P04A, P04B, P06, P07, P08A, P08B, P09, P10, P11, P13, P14, P17, P21, P22/P02, P12, P15, P18, P19, P20, P23, P24 on the Pallas differential genotypes of Kølster et al. (1986). Parents and doubled haploid progeny (5 seeds each) of the two populations were sown in plastic cones filled with a peat moss:perlite (3:1 ratio) potting mixture and grown at 22-25(C in a greenhouse where supplemental lighting was provided for 13 hr/day. Fertilizer was applied at planting with water soluble (N15-P0-K15) and controlled release (N14-P14-K14) formulations. When the first leaves of plants were fully expanded (seven days after planting), inoculations were made by shaking conidia from the infected dwarf barley plants onto the parents and doubled haploid progeny. These plants were then incubated under ambient greenhouse conditions (22-25(C). Twelve to fourteen days after inoculation, the infection types of plants were assessed using a 0-4 rating scale (Mains and Dietz 1930). Infection types 0, 1, and 2 were considered indicative of host resistance (low infection type), whereas infection types 3 and 4 were considered indicative of host susceptibility (high infection type). The experiments were conducted in a randomized complete block design with two replicates and were repeated.
 
 

Results and Discussion. The infection types observed on the parents of the two populations were very distinct: Harrington exhibited infection type 0, whereas TR306 and Morex exhibited infection type 4 (occasionally type 3). Reactions of the progeny were equally distinct; this allowed for the unequivocal classification of progeny into resistant and susceptible groups. The H/T and H/M populations segregated approximately 1:1 for resistance:susceptibility to isolate ND92GH of B. g. f. sp. hordei (Table 1), indicating the involvement of a single gene for resistance. This gene was mapped to chromosome 4. The closest molecular markers identified to the gene were CDO650 (at 0.7 cM) in the H/T population and MWG058 (at 2.9 cM) in the H/M population. This resistance gene is presumed to be Mlg based on its reaction to tester isolates of B. g. f. sp. hordei (J. H. Jørgensen, personal communication) and its mapping location near the centromeric region of chromosome 4 (Wiberg 1974).

References.

Falk, D.E., and Kasha, K.J. 1982. Barley Gen. Newsl. 12:69-72.

Kølster, P. L., et al. 1986. Crop Sci. 26:903-907.

Kleinhofs, A., et al. 1993. Theor. Appl. Genet. 86:705-712.

Mains, E.B., and Dietz, S.M. 1930. Phytopathology 20:229-239.

Wiberg, A. 1974. Hereditas. 77:89-148.

Table 1. Segregation of the Harrington/TR306 and Harrington/Morex doubled haploid populations to isolate ND92GH of Blumeria graminis f. sp. hordei.

	Number of Progeny		Prob.
Population	Resistant : Susceptible	Chi2	>Chi2
Harr./TR306	85 : 65	2.67	0.103
Harr./Morex	80 : 70	0.67	0.414

 

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