ITEMS FROM ESTONIA

INSTITUTE OF EXPERIMENTAL BIOLOGY AT THE ESTONIAN AGRICULTURAL UNIVERSITY

Department of Plant Genetics, 76902, Harku, Harjumaa, Estonia.

 

Chromosome location of genes for powdery mildew resistance in the common wheat cultivar Helle. [p. 29-31]

Hilma Peusha, Helle Sadam, and Tamara Enno.

Abstract. Chromosomal localization of a powdery mildew-resistance gene was conducted in the resistant wheat cultivar Helle employing the susceptible set of 21 Chinese Spring monosomic lines. Monosomic F1 plants were allowed to self-pollinate and to produce F2 seeds. Seedlings of F2 and F3 plants, and their parents, were inoculated with isolate number 6 of Blumeria graminis f.sp. tritici. The monosomic analysis results revealed that one dominant gene conferring resistance is located on chromosome 3D.

Introduction. Powdery mildew is an important leaf disease of common wheat in temperate climate of Baltic region. Breeding of resistant cultivars is the most economical and environmentally safe method to eliminate the use of fungicides and to reduce crop losses due to this disease. To date, 32 major gene loci conferring resistance to wheat powdery mildew have been located on specific chromosomes (McIntosh et al. 1998, 2003; Hsam and Zeller 2002; Hsam et al. 2003). Nine resistance genes/alleles, Pm1, Pm2, Pm3c, Pm3d, Pm4b, Pm5, Pm6, Pm8, and Pm9, are currently in use in Europe. In Scandinavian countries and in Estonia, some wheat cultivars possess the resistance gene Pm4b (Peusha et al. 1996; Enno et al. 2002). Because of the coevolution of host and pathogen, race-specific resistance genes can be overcome by new races of the pathogen possessing corresponding virulence genes. Therefore, searching for new sources of powdery mildew resistance in wheat genotypes is a necessity. Our objective was to characterize the resistance genes involved in cultivar Helle and to determine their location on specific chromosomes by monosomic analysis.

Materials and Methods. Seeds of the spring wheat cultivar Helle were obtained from the Jõgeva Plant Breeding Institute, Estonia. The pedigree of Helle is 'WW 24042/Polkka//SV70415/Snabbe//Norröna/KärnII//Bor/Hja 25115'. The Chinese Spring monosomic series used for locating the resistance gene were kindly supplied by F.J. Zeller, Technische Universität München, Institut für Pflanzenbau und Pflanzenzüchtung, Freising-Weihenstephan, Germany. The set of CS monosomic lines was used as female parent in crosses with cv. Helle. Cytologically verified monosomic plants F1 of each cross were grown in greenhouse and selfed to obtain F2 generation. Mitotic chromosome counts of all parental lines and F1 plants of all cross combinations were made from squashes of root-tip cells using Feulgen staining procedures.

B. graminis f.sp. tritici (Bgt) isolate no. 6 was used to test segregation in F2 and F3 populations. Avirulent to Helle, isolate number 6 was kindly provided by F. Felsenstein, Technische Universität München, Freising, Weinstephan, Germany. The test for mildew disease resistance was conducted on primary leaves from 10-day-old seedlings cultured on 6 g/l of agar and 35 mg/l benzimidazole in plastic boxes. The expression of resistance was scored at the 10-day stage. The methods of inoculation and the conditions of incubation and disease assessment were according to the detached leaf segment method described by Hsam and Zeller (1997). Three main classes of host reaction were distinguished: r = resistant (0-20 % infection relative to susceptible cultivar Kanzler); i = intermediate (30-50 % infection); s = susceptible (> 50 % infection). In monosomic analysis, the 0 to 4 infection-type scale of Stakman et al. (1962) also was used to clearly separate the tested individuals into two categories, either resistant or susceptible. Chi-square tests for goodness-of-fit were used to test for deviation of the observed data from the theoretical expected segregation.

Results and Discussion. The F2 populations from crosses of the 21 CS monosomic lines susceptible to powdery mildew and the mildew-resistant Helle were tested with Bgt isolate no. 6. All of the F2 populations, except the crosses involving chromosome 3D, segregated in a ratio of 3 resistant : 1 susceptible, conforming to a dominant monogenic inheritance (Table 1). The F2 hybrids from the crosses 'CS M3D/Helle' were tested against Bgt isolate no. 6 and segregated into 202 resistant : 32 susceptible progenies (X2 = 16, P < 0.01). Such great deviation from Mendelian ratio of segregation with significant decrease of the susceptible plants amount indicates the location of the dominant resistance gene on the critical chromosome 3D.

Table 1. F2 segregation for seedling reaction to Blumeria graminis f.sp. tritici isolate number 6 in progenies of monosomic F1 plants from crosses of 21 Chinese Spring monosomic lines with the cultivar Helle (* P < 0.01).

Chromosome	# of plants	Observed segregation to isolate no. 6		X2 < 3:1
		Resistant	Susceptible
1A	142	105	37	0.08
2A	120	96	24	1.60
3A	132	102	30	0.36
4A	89	68	21	0.09
5A	150	114	36	0.08
6A	147	112	35	0.10
7A	107	79	28	0.07
1B	157	117	40	0.01
2B	146	112	34	0.22
3B	57	44	13	0.14
4B	103	78	25	0.06
5B	120	92	28	0.17
6B	142	107	35	0.01
7B	89	66	23	0.002
1D	109	79	30	0.27
2D	119	88	31	0.07
3D	234	202	32	16.00*
4D	138	100	38	0.47
5D	133	103	30	0.52
6D	150	118	32	1.03
7D	91	68	23	0.002
CS/Helle	165	120	45	0.45
Total without CS M3D/Helle	2,441	1,848	593	0.65

Additional tests with Bgt isolate no. 6 involving six F3 families of resistant F2 plants from the critical crosses of 'CS M3D/Hell'e was also made to confirm results of the F2 monosomic analysis. No susceptible plants was observed in the five families of F3 'CS M3D/Helle' after inoculation with the Bgt isolate, confirming the location of the resistance gene on chromosome 3D. Very few susceptible plants were found in only one F3 family of the respective crosses. These plants were expected to be nullisomic (2n = 40) derived from monosomics F2 plants. Thus, the available evidence obtained from disease reaction assessment of the F2 and F3 populations indicated that cultivar Helle possessed the dominant powdery mildew resistance gene located on chromosome 3D. Because no wheat mildew resistance gene is known on chromosome 3D, we propose that this new resistance gene in cultivar Helle be designated Mlhl.

References.

• Enno T, Peusha H, and Priilinn O. 2002. Monosomic analysis of powdery mildew resistance in common wheat cultivar Sunnan. Ann Wheat Newslet 48:49-51.
• Hsam SLK and Zeller FJ. 1997. Evidence of allelism between genes Pm8 and Pm17 and chromosomal location of powdery mildew and leaf rust resistance genes in the common wheat cultivar Amigo. Plant Breed 116:119-122.
• Hsam SLK and Zeller FJ. 2002. Breeding for powdery mildew resistance in common wheat (Triticum aestivum L.) In: The powdery mildews. A comprehensive treatise (Belanger RR et al., Eds.). APS Press, St Paul, Minnesota, USA. Pp. 219-238.
• Hsam SLK, Lapochkina IF, and Zeller FJ. 2003. Chromosomal location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L. em Thell.). 8. Gene Pm32 in a wheat-Aegilops speltoides translocation line. Euphytica 133: 367-370.
• McIntosh RA, Hart GE, Devos KM, Gale MD, and Rogers WJ. 1998. Catalogue of gene symbols for wheat. In: Proc 9th Internat Wheat Genet Symp (Slinkard AE Ed). University Extension Press, Saskatoon, Saskatchewan, Canada. 5:1-236.
• McIntosh RA, Devos KM, Dubcovsky J, and Rogers WJ. 2002. Catalogue of gene symbols for wheat: 2002 Supplement. Ann Wheat Newslett 48:287-321. http://wheat.pw.usda.gov/ggpages/wgc/2002 upd.htm.
• Peusha H, Hsam SLK, Enno T, and Zeller FJ. 1996. Identification of powdery mildew resistance genes in common wheat (Triticum aestivum L. em Thell.). VIII. Cultivars and advances breeding lines grown in Finland. Hereditas 124: 91-93.
• Stakman EC, Stewart DM, and Loegering WQ. 1962. Identification of physiological races of Puccinia graminis var. tritici. US Dep Agric ARS E617: 1-53.