A Database for Triticeae and Avena
II. 23. Attempts to locate powdery mildew resistance gene Ml-(La)
to a barley chromosome.
H. P. Jensen, J. Helms Jørgensen, and Jens Jensen, Agricultural
Research Department, Risø National Laboratory, DK-4000 Roskilde,
One of the important donors of powdery mildew resistance for northwest
European spring barley (Jørgensen 1982) is the so-called Laevigatum-resistance.
The resistance is conditioned by one apparently dominant gene tentatively
designated Ml-(La) conferring an infection type 2-3nc
or 3nc (moderately susceptible) on seedlings (Torp et al. 1978). In the
present report we describe our attempts to locate gene Ml-(La)
to chromosome using five high-lysine genes and several translocations as
The five high-lysine mutants, Risø Nos. 13, 16, 17, 527, and
1508, induced in the variety 'Bomi' that has gene Ml-(La)
were crossed with translocation lines induced in the variety 'Bonus'. The
crosses were made for locating the high-lysine genes in the five mutants.
In order to make the linkage tests efficient, only shrivelled F2 seeds
(seeds homozygous for a high-lysine gene are shrivelled) were sown in the
field. All the high-lysine mutants have each one recessive high-lysine
gene; the genes in mutants 13 and 527 are on chromosome 6, those in mutant
16 and 17 are on chromosome 1, and that in mutant 1508 is on chromosome
7 (Jensen 1979).
A number of cross combinations from the above F2 material were used
for locating gene Ml-(La). The F2 plants were progeny tested
as F3 seedlings with powdery mildew culture CR3 that is avirulent on the
'Bomi' mutants and virulent on the 'Bonus' translocation lines.
Some of the F2 plants listed in Table 1 were used to check the inheritance
of the resistance. Those underlined were not used because a possible linkage
between Ml-(La) and one of the high-lysine genes, either
directly or indirectly via a translocation, may cause a deviation from
a Mendelian segregation for Ml-(La). Therefore, only the
not-underlined 1225 F2 plants in Table 1 were used. Assuming that the resistance
is conferred by one gene these F2 plants will segregate in a 1:2:1 ratio
of homozygous resistant, heterozygotes, and homozygous susceptible, respectively.
the observed segregation was 347:595:283. A X2 of 7.69
significant at the 5 per cent level indicated some deviation from the expected
ratio. The deviation is probably caused by difficulties in scoring the
F seedlings because the two infection types, 2-3 or 3 and 4, are fairly
close to each other, and because gene Ml-(La) may be incompletely
dominant. However, considering this, we regard the observed segregation
as a strong indication for the 'Laevigatum'-resistance in 'Bomi'
to be conferred by a single gene.
Table 1. The cross combinations and the number of
F2 plants analyzed for reaction to powdery mildew.
X2 tests for independent inheritance of gene Ml-(La)
and the five high-lysine genes on chromosomes 1, 6, and 7, respectively,
did not suggest any linkage.
The joint F2 segregation for gene Ml-(La) and for partial
sterility vs. fertility due to the translocations are shown in Table 2.
The data do not suggest any linkage between Ml-(La) and the
13 translocation breakpoints, not even when the data per chromosome are
Table 2. The joint F2 segregation for partial sterility
vs. fertility and for powdery mildew resistance gene Ml-(La)
(A vs. a).
If the translocation breakpoints are in or near a centromere, and when
the actual number of F2 plants is considered, it can be estimated that
gene Ml-(La) probably is located more than about 30 centimorgans
from a centromere. However, 1) all the translocation breakpoints are not
at or near a centromere, and 2) the underlined numbers of F2 plants in
Table 1 showed linkage between the breakpoints and the high-lysine genes.
Both these factors contribute to increasing the length on the linkage map
on which gene Ml-(La) is probably not located. A conservative
estimate suggests that gene Ml-(La) is probably located more
than about 50 centimorgans away on either side of the centromere.
Jensen, J. 1979. Chromosomal location of one dominant and four recessive
high-lysine genes in barley mutants. In: Seed Protein Improvement in Cereals
and Grain Legumes. I. IAEA, Vienna, 1979, p. 89-96.
Jørgensen, J. Helms. Durability of barley powdery mildew resistance
genes in Denmark 1963-1980. In: "Durable Resistance in Crops". Proc. NAT0
Symp., Italy, 30 Sept. - 11 Oct. 1981 (in press).
Torp, J., H. P. Jensen and J. Helms Jørgensen. 1978. Powdery
mildew resistance genes in 106 northwest European spring barley varieties.
Kgl. Vet. - og Landbohøhsk. Arsskrift 1978, 75-102.
BGN 12 toc
BGN Main Index