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<pre>NOTE: I think it is because I do not regularly contribute in chatting, that
my messages generally turn out to be long and while there is no supporting
pictures they might be boring for some, but that is life.

This is the completed version.

Before contributing to olive topics, I would like to wish you all a merry
Christmas, many happy returns and a coming year full of olive successes, joy
and satisfaction.

Although, for quite some time, I have not been sharing your most interesting
discussions but have not missed a single posting and there were couple of
subjects that I really wished to have the time to jump into the pool. Leaf
analyses was one for sure.

I could not really miss the current interesting discussion on the subject of
"Poor Fruit Set" so here are my thoughts.

FACORS AFFECTING FRUIT SET:

A. POLLINATION

Ø Most of the poor fruit set in olive groves under dry land farming is
generally attributable to mother-nature and therefore when it is poor, it is
poor everywhere among all groves within the same region or district. In
fully irrigated groves management should receive some of the blame or can
make a difference in avoiding such unpleasant results. Across the road,
there is a bearing grove of the same age, varieties, configuration and the
same background but not the same management. Something over there was done
differently.
Ø Morphologically the olive flowers are in principal PERFECT FLOWERS which
encompass both the male and the female sexual organs:
Male: stamen consisting of the filament and the anther, which contains the
pollen grains in the pollen sac.
Female: Pistil consisting of the stigma which is the part that receives the
pollen grains, the style through which they grow and the ovary which houses
the eggs.
Flowering is a result of multiple successive transition stages that happen
to the auxiliary buds, which starts with induction through initiation and
ends with differentiation. During these stages and as a result of genetic,
environmental, nutritional balance status or faulty cultural practices some
of the flowers become MALE FLOWERS (IMPERFECT) in which the female parts
diminish or completely dissipate. The percentage of such flowers changes
among different varieties and within a single variety from year to year as a
reflection to the prescribed factors. Very rare varieties like the Swan
Hill, which is used as ornamental, produces only male flowers.
Ø The above point brings to the stage the question: are the perfect flowers
“self fertile”? Or in other words are they capable of mating and setting
fruits commercially on their own? To the best of my knowledge and experience
the answer is “YES” for the most of the known commercial varieties and such
are classified as “self-pollinated”. Some varieties are "self sterile" or
“self-incompatible” and must be cross-pollinated. Nowadays growers do not
plant such varieties unless they are of exceptional characteristics like the
Coratina (self sterile) which is favored by many growers (me included) for
the morphological features of the tree, the consistent regular cropping if
properly cross pollinated and for its highly graded oil. Examples of
self-incompatible famous varieties are the Pendollino and Leccino.
Ø The olive flowers are relatively tiny when compared with citrus or many
deciduous species and the two pollen sacs are slightly higher than the
stigma and stride almost on top of it. Therefore within self-fertile
varieties a very high percentage of the fruit set happens from pollens of
the same flower or from pollens of nearby flowers on the same inflorescence.
These varieties set a good crop when their branches shake from a light
breath of 10-15 km/hr causing their flowers to be self pollinated.
Ø For self-fertile varieties it can’t be claimed that cross-pollination
could be responsible for an exceptional good fruit set or that the absence
of additional pollinators would result in complete set failure. On the other
hand for “self-sterile” or “self-incompatible” varieties if the pollinators
are not very carefully selected based on their recorded behavior under local
conditions, the fruit set could be in real jeopardy.
Ø In the remote isolated arid oasis of the Egyptian Western Desert, pockets
of single varieties are reported to have good fruit set without other grown
varieties in the vicinity.
Ø In the old traditional olive growing regions, varieties were chosen, among
other variables, based on the easiness of obtaining their genetic materials
or the availability of expert hands for grafting. With recent improvements
of olive culture, the subject of pollination deserves more attention and
intensive localized researches. It is therefore highly recommended to tend
on planting self-fertile varieties in the new world until the correlation
between the different varieties is well established. There is no doubt that
varieties do change their behavior drastically when grown elsewhere from
their native regions even within the boundary of one country which means
nothing to them.
Ø Like all mating creatures, the female sexual part responsible for
reproduction is by far stronger than the male counter part. They can survive
tough conditions and stay viable for fertilization for a long period and for
these reasons they are produced in fewer numbers while males are produced in
millions and out of this huge number only one is needed to do the
fertilization process like the case of eggs and sperm in mammals. As to
olives, the ovary of a flower contains four eggs in two chambers and only
one is going to be fertilized. Most of the pollen grains carried by the wind
will miss their target and only very few will fall on the stigma, whereby
only one will succeed in germinating and growing its pollen tube inside the
style to fertilize one egg within the ovary.
Ø Like olives at harvesting which do not mature and ripe on the same day but
over a period of time, the flowers on a single tree do not reach sexual
maturity all at the same time but do this successively and consequently
fruit set also happens successively within a period of time. Now if some
abnormal weather conditions result in killing the already matured, by
nature, weak pollen grains so that they can not do their job, the tree would
still have other reserves to mature later and fertilize the eggs which have
a better longevity and are tough enough to stay viable.
Ø Some pollen grains of certain varieties are said to be more active than
others, which means that they germinate and fertilize the egg in shorter
time compared with others. This can happen on their own variety flowers or
on other varieties within reach. Koronieke is said to be one of such
varieties and maybe therefore, it is a consistent cropper under my
conditions.
Ø In view of the above I do not see cross pollination as a vital or a
determining factor for setting a good crop on self fertile varieties in the
open field but I see it as:
a) A defense line or barrier against bad weather conditions that might cause
the complete destruction of the at-the-time-of-incident mature pollen grains
but is not so adverse to cause harmful effects on the feminine parts
(stigma, style and eggs with the ovary). Pollens from a second variety would
assist the reduced remaining numbers of the pollen grains of the next
generation yet to mature on the original variety in fertilizing the viable
eggs. In this case the pollinating variety should be flowering almost at the
same time of the original one with slight lapse (overlap) of just few days
and not only that but more of importance it should be also compatible.
Incompatibility could result in that the pollen grains will not germinate on
the stigma or if it does, the pollen tube might not grow inside the style or
it might grow but yet develop very slowly beyond the viability of the egg
resulting in no set. With the expansion of olive growing in Egypt associated
with the introduction of many imported varieties during the last 25 years it
has been noticed that compatibility between different varieties is
influenced by different environmental conditions.
b) If the foreign pollen grains are more active than the native ones and
they ever posses the chance, somehow, to reach the stigma earlier than the
native grains then this might slightly increase the fruit set as the shorter
the period of germination and fertilization is, the more fertilized flowers
there will be.
c) A thought of a possible way for improving the fruit characteristics but I
have never been able to materialistically verify this, neither have I been
lucky to come across any supporting literature.
Not specifically related to this point, one of our specialized institutions
have been doing a long experiment in collaboration with the IOOC which
started some 8 years ago by isolated cross pollination for the purpose of
crossbreeding in an attempt to come up with new varieties having better
genetic characteristics in respect of high and consistent productivity,
accumulation of oil or better oil characteristics. The seeds of the
cross-pollinated fruits of the first and second seasons have been planted
and they have started to crop last year. Some have turned out to have worst
characteristics than their parents but few are of much better
characteristics. Of the latter group is a Koronieke sub-cultivar, which is
of larger size physically but still has the same features of a typical
Koronieke and has produced excellent oil which is currently under further
evaluation by the IOOC. I helped this season in extracting the oil of the
new varieties on an industrial scale using my Oliomio. By the way and just
for the record, my last pressing day was Sunday 22.12.
Ø Literature tells us that a mature olive tree could produce well above half
a million flowers. These tiny creatures with their huge numbers grow to
either set fruits or abscise and during their very short period of growth,
they become the main nutrients withdrawing sink. The stages of their
differentiation, subsequent development, fruit set or abscission are the
worst exhausting physiological phase on the tree reserves and therefore
these stages are immediately followed by a normal phenomenon whereby
noticeable great numbers of leaves turn to yellowish color on trees 4 years
old and above followed by the most severe wave of leaves fall during the
season. Unfortunately some growers become panicked when they notice this
leaf yellowing and sometimes irrationally react in a way that might do harm
than benefit, like substantially increasing nitrogen fertilization that
could cause a later delay in maturing the crop.
Ø The high tendency of the flowers inflorescences to suck the tree resources
almost dry, reminds me with ants when they carry hundred times their weight.
Ø For years I was very impressed by the sight of olive trees dressed in
white coats during blooming until I was very lucky some 7 years ago to
closely watch for two consecutive seasons the very poor negligible fruit set
of a certain very near by grove. Only then that I started to know what
“sexual expression - SE” really means and started to compare my grove with
others during that period and then was when I established my theory about
the corner stone checking points during the growing season to judge the
efficiency of management practices and other inputs. Heavy bloom does not
simply mean good crop or taken for granted to reveal such and although it
really looks pleasing to the eye but the hidden problem associated with this
scene is that the high percentage of the imperfect flowers generally passes
unnoticed to many growers until there is an incident of poor fruit set of a
non-commercial value and only then it is too late to verify that this was
the actual reason behind it all. It is one of the main responsibilities for
growers managing fully irrigated groves to check the “sexual expression -
SE” all the way through blooming to assess the efficiency of their practices
and the money they have spent during the passing season and to take
necessary correcting actions, whenever needed, in the coming seasons. Aside
from looking inside the flowers, one of my secret methods of inspecting the
SE and at the same time verify the nutritional status of a certain grove
during this period is to look at falling petals underneath the trees. If
there is a large % of male flowers, one will spot huge numbers of calyx
complete with their 4 petals opened but yet connected together (seemingly
looking like a full flower) and they can be either dry having dropped few
days ago or yet whitish and fresh. On the other hand where trees have a good
percentage of perfect flowers, the fallen petals will not be connected but
rather separated in ones and they will be even less in numbers. The
morphological reason behind this is that the petals of the calyx are mounted
on the receptacle (the cup) and in case of perfect flowers they are kept in
place and pressed down onto the receptacle by the ovary and falls separately
in singles much later after the set and initial growth of the tiny drupes
which pushes them when they are dry to the outside. If there is no ovary,
the calyx falls early, shortly after opening and in full by the slightest
wind effect.
Ø Although against other reported observations, I personally have very
rarely spotted honeybees visiting olive flowers. When I established my grove
13 years ago in the middle of nowhere desert it was 10% olives and 90%
citrus and I brought in some beehives to promote pollination and have always
noticed that the bees rarely visited the olives. After one year I started to
remove the citrus and plant olives instead and it took me 3 years to
accomplish the complete transfer. When it was all olives my bees were
starving to death and the guy who was taking care of them told me at that
time that we had to artificially feed them so I moved them to my village in
the country side. It is worth mentioning here that some authors have
indicated that even when bees visit the flowers they do not aid in
pollination, while others have reported the contrary.
Ø I have said it before; native varieties generally flower either before or
after weather abnormalities to efficiently mate. Somewhere else they do
really get confused and it might take them quite some time to adapt.

FACTORS OTHER THAN POLLINATION:

Ø After genetic characteristics, the % of perfect flowers is a direct
outcome of the stored carbohydrates and the nutritional balance of
assimilates, something which is highly controllable in fully irrigated
farming. When the buds satisfy their chilling requirements, the prime mover
for them to reach the swelling stage with a good SE, is the tree reserves of
carbohydrates and if these are not at the adequate level, the percentage of
imperfect flowers will increase proportionally causing a reduction of the
fruit set. Once the buds reach this stage they demand, in addition to the
carbohydrates, readily available nitrogen to grow and reach maturity
promptly in the shortest time possible. Securing the right levels of
carbohydrates at this very specific period which coincides generally with
late winter/early spring can be through different approaches on top of which
is adequate feeding and compensation of the trees reserves during the
preceding season, a practice which could be efficiently performed in fully
irrigated groves. Other methods involve some mechanical work especially when
reserves are low and in an attempt to dedicate their withdrawal at this very
specific physiological stage to the floral buds, timely girdling, pinching
of apical tips of bearing shoots or root pruning could be very effective.
I tried girdling and although successful, I found that it has lot of
disadvantages and therefore it would not be recommended for use on
commercial scale.
Pinching has proven to be effective but apart from being very laborious and
thus expensive it will slow down the first flush of vegetation growth and
cause broom branching all with too much consequential negative effects on
the coming season crop. I only exercise pinching as a part of integrated
training process of juvenile trees and it really helps in getting early
commercial crops. My Tafahi (UC13A6) trees planted August 1998 have produced
6.7 kg on average in September 2000 while they are only 25 months old,
although climatic conditions were totally unfavorable as shall be discussed
later. This contradicts in part with Steve Sibbett’s message of 18.12.
Proper and promptly root pruning has lot of advantages and that is what I
regularly practice from year to year and my staff became experts in doing
it.
Ø Properly managed fully irrigated groves use fertigation frequently in
small doses to satisfy the nitrogen nutritional needs of the swelled floral
buds to assist them in performing their tasks efficiently, while in dry land
farming it is a common practice to apply the spring full nitrogen quantity
in a single large dose during the early stages of flowering. Rain in dry
farming or rain and excess irrigation in irrigated farming can cause
leaching of the nitrate nitrogen beyond the reach of the root system. On the
other hand water shortage at this stage can cause growth retardation and
consequent reduced set. Feeding or irrigation mismanagement in irrigated
groves can lead to catastrophic results.
Ø In relation to the above points, when the trees are subjected to water
stress during the previous growing season they lack good levels of
assimilated nutrients and when it comes to flowering, the majority are
imperfect ones.
Ø Weakening of leaves by pests or reducing to their total surface area due
to any reason can lead to the same result above. Such reasons could be, but
not only limited to:
v Attack by pests or diseases.
v Suffering from draught (water mismanagement in fully irrigated farming).
v Very cold temperatures during winter, which causes damage to the leaf
petiole followed within 48 hours with color fading and abscission.
v Abscission due to spraying with higher concentration of winter oil or
application at high temperature.
Ø Obstruction to the sap movement caused by sucking insects will result in
noticeable reduction of perfect flowers and flowering in general.
Ø Literature indicates some pests, which directly attack the flowers during
different growing phases such as olive leaf midge, olive weevil, olive
kernel borer, olive psylla and olive moth. In Egypt, the later two exist and
the olive psylla, if not properly treated, could be very detrimental in
setting a crop.
Ø Temperatures after floral bud swelling are as important as those during
the winter preceding the flowering season.
In the event winter chilling temperatures are satisfactory but not followed
by adequate warm spring temperatures, a case that I have personally
experienced for the first time this passing season, flowers would fall to
set fruits due to the following which we have recently observed:
1. Continuing cold weather delays the sexual maturity and opening of the
flowers by few days up to 2 weeks.
2. The pollen grains were presumably not active enough to germinate and
fertilize the egg.
3. The slow rate of growth caused lot of miscarriages resulting in large
numbers of shot berries.
4. In spite of the excellent chilling during winter and the good nutritional
balance of the trees verified by leaf analyses, the % of imperfect flowers
was enormous and the fruit set was in fact the worst in 10 years since my
trees started cropping. Surprisingly the only exception came from the
juvenile ones at the time of flowering.
Ø Under my semi-arid conditions and apart from the Khamaseen Winds which is
very hot, dry with blowing sand, I have found that the most favorable
temperatures for a good fruit set range from 22 C to 29 C. At higher
temperatures and up to 36 C flowers would still give a crop but of reduced
volume and the higher the temperatures get the less crop there is. With the
help of irrigation, the situation could be corrected to some extent.
Typically under my conditions such high temperatures are not prevalent
during blooming but hit and run in short waves and during the years we have
markedly noted the following between 30 C up to 36 C:
1. When the inflorescences have elongated to their final length and the
flowers clusters are still small in size, greenish in color and closed, then
with irrigation no serious harm would be experienced, but maybe to the
contrary as the opening of the flowers will happen quicker compensating for
any other damage as fruit set will proceed then much quicker provided that
temperatures would go back to normal. Without irrigation and when the wave
prevails for 4-5 days at this stage, a complete loss would be experienced
and all inflorescences will completely dry and stay closed on their shoots
until maybe mid summer.
2. Same case above but the clusters have already swelled and changed color
to creamy yellow. In this case serious damage will happen causing remarkable
reduction to the fruit set especially if the temperature is up the scale and
the hit goes for 2-3 days roasting the calyx. This will happen because the
more developed the sexual parts are, the more sensitive they become to
severe weather conditions, I think it is something like becoming aged within
the specific physiological stage. Irrigation alone will not help reducing
the losses but we have tried water spraying in some blocks in some years and
it set by weight 36% more. In practice, such a method would be recommended
if overhead sprinklers or foggers were installed. Surprisingly enough we
have marked inflorescences with roasted flowers clusters both in and out of
the sprayed blocks and have found that quite good numbers have set fruits
and I do not have any rational explanation other than it is a result of self
pollination at higher temperature from the same flower while the petals are
still closed because in such case the roasted calyx stays sticking for quite
some time covering the stigma until it falls as a result of the fruit
development. It would be also concluded that the sexual parts on some
flowers stay viable and active during the severe wave under such conditions
for some unknown reasons at least for me.
3. When the flowers are fully opened which is a worse case than the above
two cases, especially if no advanced set has already taken place to secure
some crop and the wave lasts for 3-4 days, the following would progressively
happen from temperatures down the scale to those up the scale: first roasted
part would be the anthers followed by the stigma, the petals and then
finally the ovary which does not show signs of roasting immediately but can
take days. Unlike petals of flowers which set fruits, roasted petals stick
onto the receptacle and take relatively long time until they fall.
4. The higher the temperatures are during blooming, the more shot berries
are born on the trees and some of these berries are developed from ovary
with roasted stigma which means that the fertilization took place prior to
the hot wave but was aborted (miscarriage).
Ø Adequate levels of Boron is said to have a profound effect on increasing
the activity of the pollen grain or in other words on reducing the
germination period. Successfully for 8 years I have been applying Boron
spray mixed with Urea at the time of bud swelling. For effectiveness, Urea
is used basically to aid in opening the leaves stomata. During the first 3
years I had unsprayed controls to verify the efficiency of this practice and
have verified the following on the treated trees:
1. Better fruit set.
2. More uniform set, which makes the grower life easier in respect of
irrigation, feeding and most importantly harvesting.
3. Less falling fruits during the three natural waves of fruit fall during
the season.
4. The shorter period of germination and fertilization results in saving
much of the crop against un-favored weather conditions.
Ø Under irrigation farming, excess unnecessary winter pruning not only
result in removing considerable carbohydrates, but also push the trees
prolifically into irrational vegetative growth. Such trees normally carry
very low % of perfect flowers resulting in very poor fruit set.
Ø Many authors have reported that a fruit set of only three% under dry
farming condition will result in a good crop. Under well-managed fully
irrigated condition it can well reach 5 times that figure. Although not in
line with available literature in principle, but it worth mentioning here
that in my FULLY IRRIGATED* grove we have ascertained that new vegetation
twigs emerging laterally on shoots late summer till mid autumn (September to
mid November Northern Hemisphere) will carry flowers and set fruits the
following spring while they are 12 to 15 cm long and less than 6 months old.
As a result of their tiny size and the load they are carrying their apical
tips dominancy diminishes and they do not grow vegetatively and sometimes
they start to die back at the time of harvesting. Such die back would be
stopped when the substitution buds are triggered either naturally or
artificially.

* Not supplementary. Irrigation is totally managed and under control. During
the last 6 years rain was never more than 50 mm per annum.

To Garth Renowden,

Could the insects that you have seen in your flowers be olive leaf midge
(dasyneura oleae)? I have never seen it in reality. The mature insect is a
small fly 2.2 to 2.5 mm. Yellowish black in color. The mature female flies
lay their eggs on the floral buds or leaves during springs. Eggs hatches in
two weeks and the tiny larvae hides inside the leaves or flowers tissues to
feed and this causes swelled spots on the leaves like knots. It can cause
destruction to between 30 – 70 % of the flowers.
Or was it the olive weevil.

Kindest Regards to all,
Mohamed


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