SYLLEPTIC SHOOT FORMATION IN YOUNG APPLE-TREES EXPOSED TO VARIOUS SOIL-TEMPERATURE AND AIR HUMIDITY REGIMES IN 3 SUCCESSIVE PERIODS OF THE GROWING-SEASON
J. Tromp, SYLLEPTIC SHOOT FORMATION IN YOUNG APPLE-TREES EXPOSED TO VARIOUS SOIL-TEMPERATURE AND AIR HUMIDITY REGIMES IN 3 SUCCESSIVE PERIODS OF THE GROWING-SEASON, Annals of botany, 77(1), 1996, pp. 63-70
Under otherwise controlled conditions, the effect of two soil temperat
ures (12 and 22 degrees C) and two air humidities (50 and 90%) applied
during three successive periods of 6 weeks (starting at the beginning
of the growing season) on sylleptic shoot production of young apple t
rees was evaluated during the first year of growth. The treatment effe
cts were mainly reflected on sylleptic growth; the growth of the main
shoot was much less influenced. In Period I sylleptic growth tended to
be reduced at 12 degrees C. In Period II it responded greatly to the
soil temperature in Period I resulting in a much stronger sylleptic gr
owth at 12 than at 22 degrees C. However, the actual soil temperature
in Period II was not of any importance. In Period III growth activity
was low and there were no treatment effects. High humidity favoured sy
lleptic growth in Period I at the soil temperature of 22 degrees C but
not at 12 degrees C, but in Period II the reverse was found. Humidity
did not affect syllepsis in Period III. The various treatments greatl
y affected the distribution of sylleptic shoots along the main shoot.
The ability to grow out into sylleptic shoots was restricted to buds i
n a certain stage of development. The results are discussed in terms o
f a negative feed back mechanism between shoot and root growth which c
ontrols sylleptic growth. (C) 1996 Annals of Botany Company