| dc.description.abstract | Under the supervision of Professor Malcolm N. Dana
The effect of low temperature in flowering of red
raspberry (Rubus idaeus L.) and also the possible involvement
of endogenous gibberellins and cytokinins in flower
induction were studied.
For studying the effect of 10\'1 temperature in f'Lowe rinduction
and flower bud development in mature or overwintering
canes of red raspberry, 'Heritage', fall-bearing,
and 'Latham', June-bearing,cultivars were used. Flower
induction occurred in warm ·t;emperaturesbut 10\'J temperatures
hastened not only flower induction but also flower
bud development. In non-cold treated plants no development
beyond the stage of initiation was observed. In cold
treated plants a gradual degree of flower bud development,
basipetally expressed, occurred.
For studying the effect of low temperature on the
time of flowering in fall-bearing red raspberries, 'Heritage'
plants gr-own under controlled environmental conditions
were used. Plants at any stage of growth, even at the
stage of preformed buds on the roots, responded to cold,
the response being expressed as shortening of the vegetative
plant-life. ~The older the shoots were at time of
cold treatment, the earlier the flower induction occurred.
Shoots never flowered at less chan 20 visible nodes of
growth. The flowering response to cold was not transmissible
by grafting. 'Heritage' plants responded to vernalization
in a way similar to that of most annuals and
biennials.
Removal of the developing inflorescences did not
alter the total number of inflorescences produced. The
more the number of inflorescences removed, the greater
the number of suckers produced.
The possible involvement of plant hormones in flower
induction was studied by comparing changes (qualitative
and auantitative) that occurred in endogenous gibberellinlike
substances and cytokinins when plants were shifting
from the vegetative to the reproductive phase. Coldtreated
and non-cold treated fall-bearing cultivars, and
cold treated June-bearing cultivars as well, were involved
in the analyses. Samples were taken at two stages of
growth, 10 and 20 visible nodes. At 10 node stage of
growth all plants were vegetative, at 20 nodes only
cold-treated fall-bearing cultivars were at or before the
beginning of rLowez- induction.
Qualitative differences in endogenous gibberellinlike
substances were observed between 10 and 20 node
stage of growth in cold treated and f'Lower- induced plants
of fall-bearing cultivars and between cold treated and
non-cold treated 'Heritage' at the 20 node stage of growth.
Major quantitative changes from 10 to 20 node stage
of growth occurred only in cold treated fall-bearing cultivars.
Sixty percent greater activity of gibberellinlike
substances was observed at 20 node stage of growth
than'at 10 nodes and 100% greater activity at 20 node
stage of growth in cold-treated and flower-induced than in
non-cold treated and non-flower-induced fall-bearing
cultivars.
In all cultivars and treatments cytokinin activity was
always greater at the 20 than at the 10 node stage of
growth. However, greater cytokinin activity was observed
at both stages of growth in cold treated than non-cold
treated fall-bearing cultivars.
It was concluded that both gibberellins and cytokinins
may be involved in the production of the floral stimulus in
this species | en |
