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26 RESEARCH REPORTS
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PNL Volume 12
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1980
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LINKAGE OF THE en AND st GENES IN PEAS
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Gritton, E. T. and D. J. Hagedorn Departments OF Agronomy & Plant Pathology
University OF Wisconsin, Madison, WI, U.S.A.
Pea enation mosaic virus (PEMV) is an important virus disease of peas
in the United States. It has also been recorded in the Netherlands, Switzer-
land, West Germany, England, and Czechoslovakia (Hagedorn, Amer. Phytopath.
Soc. Monograph No. 9, 1974). The virus produces characteristic blister-like
ridges or "enations" on the underside of leaflets, stipules, and pods and
causes vein clearing and mottling OF the leaves.
Resistance to PEMV was found in PI 140295 and was introduced into commer-
cial cultivars through backcrossing. Resistance is conditioned by a single
dominant gene, En (Schroeder and Barton, Phytopathology 48:628-632, 1958).
A number of lines carrying resistance to PEMV were crossed with a number
of marker stocks. We scored greenhouse-grown F2 plants for resistance and
susceptibility following inoculation with the virus. These same plants were
scored for a number of marker traits. Among the many traits scored, only st
showed a relationship to reaction with PEMV.
Classification of the plants of the three crosses which segregated for
st and en are given in Table 1. All crosses were made in coupling. Recom-
bination values were similar and were statistically homogeneous. Data combined
over all crosses resulted in a crossover percentage of 31.3 as calculated by
the method of maximum likelihood.
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Table 1. F2 segregation of normal size stipule (St) vs reduced stipule (st)
in relation to susceptibility to pea enation mosaic virus (en) and
_resistance (En)_
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Probability values were based on a 9:3:3:1 ratio.
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PNL Volume 12 1980
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RESEARCH REPORTS 27
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The st gene is located on chromosome 3 so en is also a member of this
linkage group. We detected no linkage with which may indicate that en
lies on the far side of st [M side-- Ed.]. Our data with f is incomplete
but a greater number of parental types than expected was found in the segre-
gation of en and f, thus suggesting that en may lie on the same side of
st as f.
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Editor's Note:
The results reported in the above paper are in accord with
unpublished results secured by I). W. Barton in 1959. Barton
obtained negative evidence for linkage with markers on chromo-
somes 1, 2, 4, 5, 6, and 7 but positive evidence for linkage with
M and st on 3. The CrO estimates between En-M and En-St were
calculated as 33 and 38, respectively. In the case of the En-M
linkage, a combined population of over 2200 plants was involved,
but the population size for the En-st linkage was only 171 plants
The estimate of linkage with b was 45% but the Chi-square was
not significant. He concluded that En probably lies between M
and St.
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