MIKESELL, JAN E. Department of Biology, Gettysburg College, Gettysburg, PA 17325. - Correlation of overcompensation and the breaking of apical dominance in Phaseolus aureus .
Growth promotion induced by herbivory has been frequently reported and
termed overcompensation. Overcompensation in browsed plants
ultimately results in enhanced development as compared to intact
plants. This promotion of growth can suspiciously resemble the
breaking of apical dominance. A complicating factor in the activation
of axillary shoots following decapitation is nutrition. To
investigate influences of decapitation, terminal stem apices were
excised from plants in one of three ways: 1) at the middle of the
first or basal internode, 2) at the middle of the second internode,
and 3) immediately subjacent to the apex itself. Nutritional
influences were examined by removing one of the two basal unifoliate
leaves from one-half of the plants. Stem apex and leaf removal
occurred when Phaseolus aureus plants were thirty days old.
Plants were monitored for vegetative and reproductive development for
the next two months. Axillary shoot formation was negligible in
intact plants. Most axillary shoot elongation took place early in
treated plants during the sixty day monitoring period. Treatment
plants exhibited differences in: 1) axillary shoot number, 2)
individual length of axillary shoots, 3) combined axillary shoot
length per plant, and 4) the length of fruit-bearing axillaries.
Intact and experimental plants revealed differences in above-ground
height as well as pod length. However, pod mass was similar in
control and treatment plant groups. Stem apex removal was considered
more influential than leaf excision in the promotion of axillary shoot
development.
Key words: Phaseolus aureus , apical dominance, axillary shoots, decapitation, overcompensation