Introduction

Favret (1949) investigated the resistance of 'Engledow India'. He pointed out that this resistance is inherited dominantly and is located at the Mla locus of chromosome 5. Furthermore, he compared the resistance spectra of Engledow India and 'Monte Cristo' and concluded that these two accessions possess the same resistance gene. On this basis, he proposed to designate this resistance gene as Mlm. These results and the nomenclature (Mlm) were supported by Hiura (1960) and Wiberg (1974a, b).

However, Koltin et al. (1964) were able to distinguish the resistance gene of Engledow India from Monte Cristo with the help of seven Israeli powdery mildew isolates. Later on Giese (1981) observed that reaction of Engledow India is similar to 'Rupee' which was designated Mla₁₃.

Material and Methods

For the test of allelism, a cross between Engledow India and 'Rupal' was carried out. Furthermore, Monte Cristo, Rupal, and Engledow India were included to compare the resistance spectra.

Mildew tests were conducted in seedling stages as described by Jahoor and Fischbeck (1987). Infection types were scored 9 to 11 days after inoculation according to 0-IV scale (Nover, 1972; Torp et al., 1978).

Results and Discussion

Out of 397 tested F₂ plants, no recombinants were found in the test cross between Rupal and Engledow India which confirms that the Engledow India resistance belongs to the Mla locus as reported by Favret (1949), Hiura (1960), and Wiberg (1974a).

For the comparison in resistance spectra among the varieties 'Welam' and Rupal possessing Monte Cristo and Rupee resistance, respectively, and Engledow India, seventy European and Israeli isolates were included. Table 1 summarizes the distinct reaction patterns obtained with 4 isolates which differentiate Engledow India from Rupal (Mla₁₃) as well as from Welam (Mla₉).

Twenty-one alleles of the Mla locus have already been identified and localized (see Jahoor and Fischbeck, 1987). In addition, Mla₂₂ and Mla₂₃ are proposed for the barley accessions 'HOR1657' and 'HOR1402', respectively (Jorgensen, pers. comm.). Since the resistance gene in Engledow India is distinct from the Mla₉ and Mla₁₃, the designation Mla₂₄ is suggested.

Acknowledgement: Thanks are due to Mrs. A. Viethen for technical assistance in this research.

References:

Favret, E. A. 1949. On the genetic of resistance to mildew in barley. Phytopathology 39:6.

Giese, H. 1981. Powdery mildew resistance genes in the Ml-a and Ml-k regions on barley chromosome 5. Hereditas 95:51-62.

Jahoor, A., and G. Fischbeck. 1987. Genetical studies of resistance of powdery mildew in barley lines derived from Hordeum spontaneum from Israel. Plant Breeding 99:265-273.

Koltin, Y., R. Kenneth, and I. Wahl. 1964. Powdery mildew disease of barley in Israel and physiologic specialization of the pathogen Proc. 1st Int. Barley Genet. Symp., Wageninqen 228-235.

Nover, I. 1972. Untersuchungen mit einer für den Resistenztrager 'Lyallpur 3654' virulenten Rasse von Erysiphe graminis DC. f. sp. hordei Marchal. Archiv für Pflanzenschutz 8:435-445.

Torp, J., H. P. Jensen, and J. H. Jorgensen. 1978. Powdery mildew resistance in 106 Northwest European spring barley varieties. Kgl. Vet.- Og Landbohojsk. Arsskr. 75-102.

Wiberg, A. 1974a. Genetical studies of spontaneous sources of resistance to powdery mildew in barley. Hereditas 77:89-148.

Wiberg, A. 1974b. Sources of resistance to powdery mildew in barley. Hereditas 78:1-40.