Page 448 - Biosystems Engineering

424 Cha pte r F i f tee n

shoots (the fruits being protected by a cover of aluminum foil,
removed after the liquid had been dried).
The auxin used was IAA. Auxin treatment was started 3 days after
the retardant was applied (term 1) or 2 weeks later (term 2). In both
terms, the fruits were treated with IAA for 3 consecutive days: on the
first and second days by immersion in a solution containing 50 mg/L
IAA plus 0.1 percent Tween 20, and on the third day by injecting a 0.1-mL
50 mg/L of IAA solution without Tween 20 into the core of the fruit.
The control trees were not treated with growth regulators. Two
other treatments were introduced in both years: some trees were
treated only with retardant and others only with auxin.
In 1988, two additional treatments were introduced. In the first,
the apices of current-year shoots including the youngest leaves were
pinched on the day when the retardants were applied in other combi-
nations. This was the treatment in which the optimum suppression of
growth was expected. In the second treatment, the current-year
shoots on the branches were sprayed once with 500 mg/L GA
3
(Gibrescol), using glicerol (5 mg/L) as a surfactant. Gibberellin was
applied to stimulate growth to obtain the greatest contrast with the
effect of the retardant.
Five uniform branches with approximately 100 clusters of flow-
ers were selected for each combination of treatments. Just after petal
fall, the fruitlets were hand thinned in such a way that only one
central fruitlet remained in every cluster. The treatments with retar-
dant only and with retardant plus auxin in two terms were carried
out on different branches of the same tree. One branch comprised
one repetition.
The influence of the treatments on the uptake and distribution of
45 Ca was investigated. Plant material for a radioactive tracer study
was taken 2 days after the second treatment with auxin (approxi-
mately 4 weeks after bloom). The fragments of branches with a single
short shoot and with a fruit and a single long shoot were excised and
their cut ends immersed in water. Five such branches were taken after
every treatment. After being transported to the laboratory, the excised
shoots were immersed in Hoagland’s solution labeled with 20 MBq
37
of CaCl (O.P.I.D.I., Swierk, Poland, specific activity 230 GBq/g Ca)
45
2
per 100 mL of solution. Then they were placed in the greenhouse in
conditions of high air humidity. After 3 days, the branches were
removed from the solution and divided into short shoots, fruits, and
long shoots. Each part was separately weighed and ashed. The result-
ing ash was suspended in a scintillation cocktail (7 g/L butyl-PBD in
dioxane) and radioactivity was determined on a liquid scintillation
counter (Beckman LS-1701, Beckman Instruments, Inc., Fullerton,
California).
The results of radioactivity measurements of the analyzed plant
parts, expressed in the fresh mass, were worked out statistically after