II. 2 Genetic relationships between several net blotch resistance cultivars.
M. E. Bjarko, E. L. Sharp, and H. E. Bockelman, Dept. of Plant Pathology, Montana State Univ., Bozeman, MT 59717, USA.
Three barley cultivars, C. I. 7584, C. I. 9776 and C. I. 9819, each carrying resistance to net blotch, incited by Pyrenophora teres, were used in crosses for the purpose of studying the relationship of the resistance genes in these cultivars. Two crosses, C.I. 7584 x C.I. 9776 and C.I.7584 x C.I.9819 were tested.
F2 seed and parental material were planted in flats in the greenhouse and inoculated with several different isolates of P. teres. The results of these tests are shown in tables #1 and #2. The different isolates were chosen in order to obtain differential reaction types from the respective parents in each cross. The isolates Mor 1, Mor 15 and Mor 18 were collected in Morocco. Pt S-2 and Mt 77-l are from Sidney, Mt., and Fairfield, Mt., respectively.
From the results shown in table #1, it appears as though genes for resistance to Mor 1 in C.I.9776 and to Pt S-2 in both C.I.9776 and C.I.7584 may occur at more than one locus. Resistance to Mor 18 in C.I.7584 may be controlled by one recessive or perhaps one incompletely dominant gene.
The results in table #2 indicate that the genes for resistance to Mt 77-1 and Pt S-2 in C.I.7584 and C.I.9819 may also occur at more than one locus. The resistance to Mor 15 in C.I.9819 may possibly be controlled by one dominant gene. Khan and Boyd (1969) reported that resistance to an Australian isolate of net blotch in C.I.9819 is controlled by duplicate genes.
In addition to the above two crosses, F2 plants of five other crosses of net blotch resistant cultivars were tested in the greenhouse to a single isolate, Pt S-2, of P. teres. The results of these tests are shown in table #3.
Table 1: Reactions of parents and F2 progeny of the
cross C.I.7584 x C.I.9776 to three isolates of P. teres.
Table 2, Reactions of parents and F2 progeny of
the cross C.I.7584 x C.I.9819 to three isolates of P. teres.
Table 3: Reactions of F2 progeny and parents from
five different crosses to a single isolate+ of P. teres.
The results in table #3 suggest that Tifang and C.I.2330 may have a common gene for resistance to Pt S-2. The same appears true in the cross Tifang x C.I.7584. Resistance to Pt S-2 in Tifang and C.I.9776 appears to be controlled by genes at more than one locus. This may also be true in the cross Tifang x C.I.5791. Resistance to Pt S-2 in C.I.1197 and C.I.9819 does not seem to be controlled by the same gene. It is suggested that the lack of type 4 reaction types in the F2 generations of the crosses in table #3 may be due to the effect of minor genes.
Interpretation of these results depends a great deal on how the F2 class frequencies are grouped. In this case, if the resistant parent or parents exhibited only a type 1 reaction, then only type 1 reactions in the F2 generation were considered to be parental types. If the resistant parents showed both type 1 and type 2 reactions, then these two reaction types were grouped when interpreting the F2 data.
Reference:
Khan, T.N. and W. J. R. Boyd, 1969. Inheritance of resistance to net blotch in barley. II. Genes conditioning resistance against race W. A.-2. Can. J. Genet. Cytol. 11:592-597.
