Abstract:
The expression and inheritance of a leaf distortion of beans was
studied in a group of the Oregon State University breeding lines and a
commercial cultivar. Of seven parents involved, two were without distortion
and classified normal, and the remainder were affected by
various degrees of distortion. The distortion affected only the trifoliolate
leaves and never appeared on the primary leaves. It consisted
in a clearing of the leaf area between the veins. The clear region
appeared to be a zone of slower growth compared to the normal region,,
The veins became distorted and the resulting leaf had an abnormal shape.
Variations of the distortion were observed within and among lines.
Distorted lines were intercrossed and crossed with normal lines.
Genetic data were obtained in the field and greenhouse as scores, using
a 0 - 5 system where 0 indicated no distortion and 5 severe distortion.
The scores of parental lines, the F₁, F₂ and backcross generations provided
the base for interpretation of genetic ratios and calculation of
heritability estimates. Reciprocal differences were observed in a cross
between a severe and a mild parent. This cross could not be used for
inheritance study and estimation of heritability as computations
necessitated pooling of reciprocals. The character appeared to involve
one major locus with three alleles: one, A of 'G50', completely
dominant over a of the distorted lines, and a' of 'Oregon 1604',
recessive to a. Modifying genes acting in an additive manner were
assumed to be responsible for the differences in degree of distortion
found among the distorted lines. Heritability estimates of the distortion,
based on regression of F₂ on F₁ and using three methods were 81,
72 and 85 percent.
Factors affecting the expression of the distortion were studied in
a field experiment involving the effects of temperature, soil fertility
and age of plants. The increase of any of these three factors decreased
the degree of severity of the distortion. However, these effects were
not evident on low-scoring plants.
In the greenhouse, groups of plants were grown in a warm lighted
room, and in a colder room with no additional lighting. The distortion
was most severe in the cold room. Plants grown in the warm room had
low average distortion scores which were not significantly different
from the scores of plants grown in the field.
No differences in endogenous auxin level could be detected between
the normal and the distorted types when callus tissues from each type
were cultured on solid media containing various concentrations of 2,4-D.
