Twenty four near-isogenic barley lines were developed in 'Pallas' barley (Kølster et al. 1986) and 17 lines in 'Siri' barley (Kølster and Stølen 1987). They can be expected to possess Mla8 in all the case where the near-isogenic lines have resistance genes not present near or at locus Mla because the backcross parents 'Pallas' and 'Siri' possess Mla8 (Jørgensen and Jensen 1983). This may also be the case with the about 35 near-isogenic lines backcrossed to 'Ingrid' barley by James Mac Key (pers.com.). The near-isogenic lines with and without the mlo5 resistance gene with 'Carlsberg II' as the backcross parent also possess Mla8. This has sometimes caused difficulties in our own experiments. The 10 near-isogenic lines with powdery mildew resistance genes developed by Moseman (1972) using 'Manchuria' barley as a backcross parent are less difficult to work with because no well-defined racespecific resistance genes has never been detected in 'Manchuria'.

In the present test, (Table 1) the backcross parent 'Pallas' and the cultivar 'Herta', which both have Mla8 (Jørgensen and Jensen 1983) were included. From the 'Pallas' near-isogenic lines we examined six lines P14, P18, P20, P21, P23 and P24 with resistance genes not located near or at the Mla locus and on which the two isolates, Race I (RI) and HL 3/5, produce different infection types. Further, we included two lines, 2R and 3R, from the 'Manchuria' set of near-isogenic lines with genes Mlg and Mlh, respectively. The infection types on these 10 barley lines produced by mildew isolates RI and HL 3/5 are listed in Table 1.

Isolate RI is avirulent on barley with the Mla8 resistance gene (infection type 0). It also has avirulence corresponding to the other resistant lines except line 3R with Mlh. Isolate HL 3/5 is virulent on Mla8, Mlra, Mlnn, Mlg, Mlh, and avirulent on Mlat and MlLa with infection types 2 and 3, as with HL 3/5, respectively (Table 1). The resistant infection type 0 produced by RI on 'P20' and 'P23' with Mlat and MlLa compared with the 'normal' infection types 2 and 3, as with HL 3/5 indicate the presence of an additional resistance gene with infection type 0. Comparison of the infection types produced by RI on lines P24 and 3R (respectively 0 and 4), both known to possess Mlh, shows an additional resistance gene to be present in line P24.

The presence or absence gene Mla8 was detected with progeny isolates from the cross between isolates RI and HL 3/5. The 42 progeny isolates segregated 17 avirulent and 25 virulent isolates on 'Pallas' and 'Herta'. (Table 1.) This fits a 1:1 segregation ratio for Mla8. The segregation of the isolates on P14, P18, P21, and P24 gave the same progeny segregation with the same isolates avirulent and virulent as on Mla8. It will say that the 42 isolates singly yield exactly the same infection type on e.g. P14 as on 'Pallas' with Mla8. On P21 only 20 isolates, which are virulent on Mlg (infectiontype 4, see segreation on Iso 2R) and avirulent on Ml(CP) (infectiontype 1-2) could be taken into account. They segregated in 6 isolates with infection type 0 and 14 with higher infection types, indicating Mla8 to be present, because the 6 and 14 isolates were avirulent vs. virulent as on Mla8 in 'Pallas'. On P18 there is one deviation which may be ascribe to a wrong plant.

On P20 only 31 of the isolates were tested, and the same isolates yield infection type 0 as on 'Pallas', while the other gave infectiontype 2. Also on P23 the same 17 isolates yield infection 0 as on 'Pallas', the other 25 segregate in both infection type 3 and 4 showing RI must be virulent on lines with resistance gene MlLa alone.

This shows that gene Mla8 is present in these six 'Pallas' near-isogenic lines P14, P18, P20, P21, P23 and P24. In all the above cases the segregations did not deviate statistically from a 1:1 ratio.

The presence of resistance gene Mla8 in several 'Pallas' near-isogenic lines was expected, but was actually verified in the present study by the progeny isolates from RI crossed with HL 3/5. The results further indicate that RI may possess virulence genes corresponding to resistance genes Mlra, and Mlnn, as on Mlh, and MlLa, but not on Mlat.

References:

Jørgensen, J.H. and H.P. Jensen 1983. Powdery mildew resistance gene Mla8 (Reg 1h8) in northwest European spring barley varieties. Barley Genetic Newsletter 13: 51-53.

Kølster, P., L. Munk, O. Stølen and J. Løhde 1986. Near-isogenic barley lines with genes for resistance to powdery mildew. Crop Science 26: 903-907.

Kølster, P. and O. Stølen 1987. Barley isolines with genes for resistance to Erysiphe graminis f.sp. hordei in the recurrent parent 'Siri'. Plant Breeding 98:79-82.

Moseman, J.G. 1972. Isogenic barley lines for reaction to Erysiphe graminis f.sp. hordei. Crop Science 12:681-682.

Table 1 Test of 'Pallas' near-isogenic barley lines for the presence of powdery mildew resistance gene Mla8

Barleyı    Ml alleles           Infection      Segregation in

line    known to   found in     type with      avirulent:virulent 

        be present the present  RI   HL 3/5    of the progeny 

                   study                       isolates
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Pallas    a8                    0       4         17:25

Herta     a8                    0       4         17:25

P14       ra          +a8       0       4         17:25

P18       nn          +a8       0       4         18:24

P20       at          +a8       0       2         12:19

P21       g, (CP)     +a8       0       4          6:14

P23       La          +a8       0       3         17:25

P24       h           +a8       0       4         17:25

2R        g                     0       4         22:20

3R        h                     4       4          0:42



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1) P= 'Pallas' near-isogenic lines
R= 'Manchuria' near-isogenic lines