Author: Customer
Company: ARO

Abstract
The persimmon (Diospyros kaki L.) is a deciduous tree. Its fruits mature
during the fall season. Persimmon cultivars are classified into four types depending
on their fruits response to pollination and the nature of astringency-loss. Almost the
only cultivar that is grown in Israel, 'Triumph', is part of the PVA group (pollination
variant astringent), in which the fruit is affected by pollination and it is astringent.
These fruits must be very soft before becoming edible, or they can undergo a
process to remove this astringency. Persimmon flowers can be male, female or
hermaphrodite. Most cultivars bear only female flowers. In Israel the trees bear only
female flowers thus the fruit is parthenocarpy and has no seeds.
In Israel the majority of the fruits, as much as 40 tons a year, are designated
for marketing. One of the main problems in growing 'Triumph' is deformed fruits, in a
rate that can go up to third of the fruits. These deformed fruits cannot be marked.
The deformation has a few forms: a cracked fruit, a fruit with an asymmetrical shape,
a fruit with a bump and a twin fruit.
There is no report on the exact stage in which the fruit deformation occurs nor
the reason causing it. The result of experiments in some persimmon cultivars and
other deciduous tree species shown that high temperature and drought has a
negative effect on the development of the ovule and on the reproductive process. As
a result of these findings, we decided to examine the hypothesis of the adverse
influence of heat and drought stresses on the rate of fruit deformation in 'Triumph'.
The aim of this work was to find out whether the exposure of persimmon trees
to heat and/or drought would cause an increase in malfunctions fruit. In order to
examine this hypothesis trees were covered with a white shading net (30%) in the
field, under three irrigation regimes: 50%, 100% and 150%. This experiment showed
that the shading net reduced the bud, leaf and branch temperature in about 20C. It
seemed that under irrigation of 50% and 100%, the exposed trees had a rate of
deformed fruits that was significantly higher than the shaded trees. Under irrigation
of 150%, the net didn’t have a significant effect. These results support the
hypothesis that heat stress and drought have a negative effect on the rate of fruit
deformation.
In order to find the specific stage in bud development that is sensitive to fruit
deformation, we exposed trees to controlled environment in the phytotron. The
results of the first experiment indicate that there are two potential sensitive periods
for fruit deformation: July-August and March-May. Therefore, we examined more
carefully three periods: July-August, mid march-mid April and mid April-mid May. We
found out that the most sensitive period, in which we saw the highest fruit
deformation level, was mid March-mid April. At the same time, we led an anatomical
and histological observation which examined the development of the 'Triumphs'
buds. We found out that the Triumph's bud is a mixed bud that is formed in the
spring time and contain leaves and flower buds that will flower on the following year.
From April to June, the flowering buds develop bracts and sepals. The bud stays in
this developmental stage throughout the summer, the fall and the winter. At the end
of March, when the dormancy is broken, the mixed bud opens develops a branch
with leaves and flowering buds. At this point, the development of the flowering buds
continues and they develop petals, stamen and ovary that will be fully developed
only a few days before open flower stage.
Examining the ovule under electron scanning microscope revealed that the
deformation is formed in the early stages of the ovule formation, when the tip of the
stigma can be seen.
These findings agree with the results we have came to from the phytotron, it
seems that indeed, the sensitive period for fruit deformation is mid March-mid April,
the time when the ovule is formed.
Because the fruit deformation is actually develops from a deformation of the
ovule, we wanted to find the gene Agamous that is involved with the determination of
identity of the stamen and ovary. Up to the time of this work, the gene was not
isolated. In addition, the control gene for Agamous levels, Actin, was not found as
well. The attempts to find Actin by primers of different plants did not succeed and
there are no results to this work.
It was found, in this work, that disrupting the development of the ovule will
increase the rate of fruit deformation in 'Triumph'. There are some ways to protect
the ovule in the sensitive period, mid March-mid April. In order to protect the dub it is
possible to use a shading net that reduces the temperature and the radiation around
the bud. In addition, one can use sufficient irrigation, spraying with reflective agents
that will scatter the radiation to the shading areas or covering the ground with plastic,
this will improve the water balance in the ground.