The Control of the Root to Shoot Ratio of Radish (Raphanus sativus L.)

The regulation of the root to shoot ratio of radish was studied with emphasis on the factors controlling assimilate distribution. Analysis of indol-3yl-acetic acid (lAA) and gibberellin levels in radish through its vegetative cycle revealed that shoot hormone levels, initially high, declined with time to become lower than the levels in the root. Thus, the ratio of shoot to root hormone content changed from a high to a low value. This change in the balance of hormones occurred prior to the increase in the ratio of root to shoot weights and is considered to be instrumental in bringing about this change. Daminozide treatment, which produced an increase in the ratio of root to shoot weights, caused a transient decrease in gibberellin levels but had very little effect on lAA levels. It did, however, bring forward, in time, the change in hormone balance compared with the controls. An attempt was made to shorten the growing period for radish under winter conditions. An increase in air temperature gave differing results depending upon the radish variety grown. Varieties Robino and Cherrybelle both showed an increased dry matter production but only Robino had an increased root/shoot ratio. Saxa, Serra, Istar and Saxerre showed no increase in dry matter production and a decrease in root/shoot ratio. Daminozide treatment and soil heating increased the root/shoot ratio of Cherrybelle and Robino. Daminozide was more effective at 7°C than 12°C but both daminozide and soil heating decreased the time to harvest by approximately ten days. The results are discussed with reference to the relative importance of sink and source strength in controlling the growth of radish. Under winter conditions the varieties Cherrybelle and Robino are considered to be sink limited. The mode of action of daminozide was studied. An indication was found that daminozide caused an increase in the rate of photosynthesis. The age of the plant to which daminozide was applied was found to be critical. The earliest application only decreased shoot growth. Later application decreased shoot growth and increased root growth, but the latest application decreased both root and shoot growth. In these experiments there was no correlation between the sensitivity to daminozide and any morphological parameter. Three possible modes of action of daminozide are discussed. The favoured interpretation is that it reduced shoot sink strength and increased root sink strength, with the latter indirectly increasing the rate of photosynthesis.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1981

Author dc:creator

• Thompson, Julie Anne

Licence

• https://dora.dmu.ac.uk/bitstreams/03d3c730-5c09-4f95-9bd6-349f90f56f0a/download