4 PNL Volume 16 1984

RESEARCH REPORTS

CULT1VAR DIFFERENCES IN SUSCEPTIBILITY TO ASCOCHYTA STEM BLIGHT, ENATION

MOSAIC, AND RED CLOVER VEIN MOSAIC

Baggett, J. R. Oregon State University

Corvallis, Oregon

Commercial pea cultivars and Oregon State University lines were

field tested for resistance to a complex of Ascochyta and

Mycosphaere11a blights (purple stem), pea enation mosaic (PEM), and red

clover vein mosaic (RCVM) at Corvallis and Brooks, Oregon. Two replica-

tions were included at each location. For each disease, a 0-5 scoring

system, with 5 most severe, was used, except that a few 6 scores were

gned to unusually severe infections of purple stem. RCVM scores

were assigned only at Corvallis. Accurate scoring for RCVM is not

possible when PEM symptoms are strong, so the scores assigned for RCVM

are approximations.

Table 1 gives mean scores for 35 commercial cultivars. With few

exceptions, these were clearly either susceptible or resistant to PEM,

but with a range of reactions to purple stem and RCVM. Mean scores are

also shown for 37 lines, mostly resistant to PEM, derived from crosses

of OSL) lines x 'Lowata' for purple stem resistance. These lines were

survivors of one previous field screening.

There was an apparent general correlation between virus infection

and purple stem severity. Table 2 shows correlation coefficients for

various disease combinations for the 35 cultivars shown in Table 1 and

tor the Lowata derived lines. Correlation coefficients were often non-

significant for the latter which received lower scores in general,

especially for PEM. For the commercial cultivars, only the RCVM vs.

Corvallis purple stem correlation was not significant. Some relation-

ship between virus infection and purple stem severity, perhaps involving

predisposition, is suggested by these data.

Table 2. Correlations (r) between virus infection scores and purple

stem scores, Corvallis and Brooks, Oregon, 1983.