Background Art Most angiosperms in the form of fruit bearing plants produce crop according to fixed seasons and this is particularly the case with mango and avocado plants in sub-tropical regions. For example, in South Africa mangoes reach picking maturity from December to April (the normal season) and avocados reach picking maturity from March to September (the normal season). It will be appreciated that the normal season changes due to climatic conditions and may be different for different fruit varieties and geographical locations.

In order to provide fruit such as mango and avocado out-of-season, the fruit often has to be imported from other countries where it is in-season at the time.

For example, in the out-of-season period in South Africa, mangoes and avocados are often imported from West Africa or Israel.

It is known that fruit bearing angiosperms such as mango and avocado flower after a season of stress, e. g. a dry and/or cold season. In sub-tropical countries flowering takes place after winter which is a dry and/or cold season. In the tropics the seasons are not always defined as clearly as in the sub-tropics but flowering usually takes place after the dry season. However, it is known to manipulate angiosperms in the tropics in an effort to obtain year round production of fruit.

For example it is known to treat mango trees in the tropics in one or more of the following ways to induce earlier flowering and thereby producing mangoes year round: i) administering paclobutrazol to trees; ii) reducing water supply to trees; iii) administering ethephon to trees; and iv) administering KNO3 to trees.

However, none of the above methods or combinations thereof is suitable to produce out-of-season fruit in sub-tropical regions, especially in the case of mangoes and avocados, as these treatments don't inhibit normal season fruitset, resulting in trees bearing a normal and out-of-season crop. This inevitably leads to complications concerning the manageability and sustainability of the desired out-of-season fruiting concept.

The inventors of the present invention have now developed a new method of treating fruit bearing angiosperms, especially mango trees and avocado trees to manipulate the timing of fruit bearing, especially to produce out-of-season crop.

Disclosure of the Invention According to the present invention a method of treating a fruit bearing angiosperm to manipulate the timing of fruit bearing comprises the steps of: - inhibiting fruit formation during the normal fruit formation period by - inhibiting flowering during the normal flowering period of the angiosperm by enhancing vegetative growth of the angiosperm during said normal flowering period; or -destruction of flowers during the normal flowering period of the angiosperm; and - thereafter treating the angiosperm to obtain flowering and accordingly fruit bearing at a period not normal for the angiosperm.

The method especially relates to a method of treating fruit bearing angiosperms to produce out-of-season crop.

Different methods in respect of different angiosperms are known to those skilled in the art to inhibit or destruct flowering during the normal flowering period and also to obtain flowering of angiosperms during a period which is not normal for

the angiosperms. Up to now, these methods have not been combined and used to manipulate the timing of fruit bearing.

INHIBITION OR DESTRUCTION OF NORMAL PERIOD FLOWERING Inhibition of flowering during the normal flowering period by enhancing vegetative growth of the angiosperm may be achieved by administering a plant growth regulator to the angiosperm. The plant growth regulator may comprise one which enhances vegetative growth by increasing gibberellin levels in the angiosperm. The plant growth regulator may comprise a gibberellin substance or a gibberellin-like substance, including gibberellic acid.

It will be appreciated that the timing, and dosage rate of administration of the plant growth regulator will depend on factors such as the type of plant growth regulator, the method of application, the angiosperm to be treated, the location of the angiosperm and the period for how long flower inhibition is required.

The plant growth regulator will usually be administered in the period prior to flower formation, but how long before flowerformation again depends on factors such as those mentioned above.

For example, in the case of mango trees located in subtropical areas, gibberellic acid may be administered (e. g. by foliar spray) during fall and/or winter to inhibit

flowering during the normal flowering period. If this is followed by the further manipulation treatment, fruit may be produced for picking during late fall, winter, spring and early summer of the following year. In a southern hemisphere country like South Africa this means that gibberellic acid treatment during March/April to July of year 1 can inhibit flowering during the normal flowering period in August/September of year 1, and if followed by the further manipulation treatment, can cause mango trees to produce fruit for picking from May to October/November of year 2.

In the case of avocado trees located in sub-tropical areas, gibberellic acid may be administered (e. g. by injection) during the period late summerto fall to inhibit flowering during the normal flowering period. If this is followed by the further manipulation treatment, fruit may be produced for picking during the summer after the summer following the period late summer to fall when the gibberellic acid was administered. In a southern hemisphere country like South Africa this means that gibberellic acid treatment during January to May of year 1 to inhibit flowering during the normal flowering period of late July to October of year 1, and if followed by the further manipulation treatment can cause avocado trees to produce fruit for picking during November of year 2 to February of year 3.

It will be appreciated that the timing and duration of treatment to enhance vegetative growth may be varied as required to produce fruit for picking at a certain desired time.

The plant growth regulator used to enhance vegetative growth may be administered more than once. The concentration and dosage rate will also depend on the situation.

The above mentioned plant growth regulator may be administered in any suitable manner e. g. by spraying, injecting, stem painting, ç drenching, and combinations thereof.

Alternatively, but preferably additionally, enhancement of vegetative growth during the normal flowering period may be achieved by pruning the angiosperm.

Preferably the angiosperm is pruned prior to administration of the plant growth regulator used to enhance vegetative growth. In cases of angiosperms where pruning of previously fruiting shoots is normally required to improve vegetative growth after harvest, the step of pruning will usually be carried out. In the case of mango trees, the trees are preferably pruned prior to administering the plant growth regulator used to enhance vegetative growth. Pruning is preferably done by the selective removal of the apical bud and/or fruiting shoot from the previous fruiting season. This results in the development of vegetative flushes from the normally inhibited axillary buds adjacent to the point of cutting. The type of pruning described above for mango trees is usually not required in the case of avocado trees.

Destruction of flowers during the normal flowering period can be done mechanically or by hand.

Alternatively the angiosperm may be chemically treated to destruct flowers during the normal flowering period. The angiosperm may be chemically treated by administering a substance which prevents fruit set and/or administering an abscission-enhancing agent. The plant may be chemically treated by a source of ethylene, such as ethephon. Treatment to destruct flowering during the normal flowering period is especially suitable in the case of avocado trees and may be carried out instead of vegetative growth enhancement. Treatment to remove flowers during the normal flowering period may, but will usually not be considered in the case of mango trees.

In the case of avocado trees removal or destruction of flowers during the normal flowering period is preferably carried out at full bloom during the normal flowering period. In South Africa this will be during late July to October.

OBTAINING OUT-OF-SEASON FLOWERING Out-of-season flowering that is flowering at a period not normal for the angiosperm may be obtained by administering a plant growth regulator which inhibits vegetative growth and/or enhances reproductive development.

Preferably the plant growth regulator inhibits biosynthesis of gibberellin. The

plant growth regulator may comprise a triazole compound (e. g. paclobutrazol or uniconazole).

The above mentioned plant growth regulator may be administered in any suitable manner e. g. by spraying, injecting, stem painting, drenching, and combinations thereof. In the case of mango trees paclobutrazol may be administered as a soil drench.

Out-of-season flowering may also be obtained by reducing water supply to the angiosperm, especially in the case of mango trees. In the case of mango trees reduction of water supply will usually take place after administration of the plant growth regulator which inhibits vegetative growth and/or enhances reproductive development. The reduction of water supply may include stopping irrigation for a certain period.

Out-of-season flowering may also be obtained by administering a senescence enhancing agent to the angiosperm. The agent may comprise a source of ethylene, and preferably it comprises ethephon. In the case of mango trees this method of obtaining flowering may be used in combination with one or more of the preceding methods (preferably both) to obtain out-of-season flowering. The agent may be applied after water reduction treatment. Ethephon may be administered in any suitable manner e. g. by spraying.

Out-of-season flowering may also be obtained by administering a source of fertilizer to the angiosperm, especially in the case of mango trees. Preferably the fertilizer comprises a source of nitrogen, preferably a source of nitrate e. g.

KNO3 and/or NH4NO3. In one embodiment the source of fertilizer may comprise KNO3, preferably at a high concentration, and preferably it is administered by foliar spray. The source of fertilizer may be administered more than once, depending on the situation. The fertilizer treatment may be used in combination with one or more of the preceding methods (preferably all of them) to obtain out- of-season flowering. Preferably the source of fertilizer is administered after administering the senescence enhancing agent.

Out-of-season flowering may also be obtained by a method which temporarily disrupts and/or alters the angiosperm's normal transport system for growth regulators and assimilates in the bark (more specifically in the phloem).

Preferably this can be achieved by girdling. A girdled tree is one in which the phloem is completely severed, either by a narrow incision (cincture) or by the removal from the trunk of a more or less wide cylinder of bark (girdle). This method is especially applicable in the case of avocado trees, and multiple girdling may enhance the effectiveness of the treatment.

Subsequent to out-of-season flowering the plants may be treated in the normal manner, including treatment to enhance fruit retention. For example, in the case of avocado trees uniconazole or paclobutrazol may be applied to the out-

of-season flowers to enhance fruit retention.

TREATMENT OF MANGO TREES According to one aspect of the present invention a method of treating mango trees to manipulate the timing of fruit bearing comprises the steps of: - inhibiting fruit formation during the normal fruit formation period by inhibiting flowering during the normal flowering period for the mango trees by administering a plant growth regulator to the trees to enhance vegetative growth of the trees during said normal period; and - thereafter treating the trees to obtain flowering and accordingly fruit bearing during a period not normal for the trees by administering to the trees a plant growth regulator which inhibits vegetative growth, and by administering a fertilizer to the trees.

Preferably the trees are pruned prior to administering the plant growth regulator to the plant to cause vegetative growth.

Out-of-season flowering may be obtained by one, but preferably all of the following additional methods : - reducing water supply to the trees; and - administering a senescence enhancing agent to the trees.

TREATMENT OF AVOCADO TREES According to one aspect of the present invention a method of treating avocado trees to manipulate the timing of fruit bearing comprises the steps of: - inhibiting fruit formation during the normal fruit formation period by - inhibiting flowering during the normal flowering period of the trees by enhancing vegetative growth of the trees during said normal period by administration of a plant growth regulator to the trees; or - by destruction of flowers during normal flowering period; and - thereafter treating the trees to obtain flowering and accordingly fruit bearing during a period not normal for the trees by girdling the trees.

The invention also relates to fruit yielded by angiosperms treated according to the method set out above.

The invention will now be further described by means of the following non- limiting examples.

Example 1 <BR> <BR> Treatment of mango trees (Mangifera indica L. ) to disrupt the normal phenological cycle thereby to produce an out-of-season crop under sub-tropical conditions (the months mentioned relate to the southern hemisphere).

(a) Enhancing vegetative growth to inhibit flowering during the normal flowering period.

Mango trees located in the district Hoedspruit at Mariepskop Estate in the Limpopo Province, a sub-tropical region in South Africa, were pruned during the period April to May by selectively removing 1 to 3 terminal flushes and any remaining flower panicles from the previous fruiting season.

After pruning gibberellic acid foliar spray was sprayed on to emerging soft flushes of the plants at weekly intervals using a 3D nozzle size. The gibberellic acid foliar spray comprised ProGibb°4% (32g/I gibberellic acid) and had an active ingredient concentration of 250 ppm at a spray volume of 2t per tree. Trees had a canopy diameter of 2.5m and a height of 2m.

This was carried out for 3 weeks and ensured the production of an appropriate bearing shoot on most of the branches consisting of at least two vegetative flushes. This treatment was discontinued in mid June when sufficient vegetative growth was achieved on trees.

(b) Obtaining out-of-season flowering Cultar @ (250glui paclobutrazol) was administered to the trees as a soil drench 10 weeks after the last gibberellic acid treatment, that is the paclobutrazol was administered during the last part of August. The Cultar

was applied at a rate of 1 g active ingredient/meter canopy diameter. The paclobutrazol suppressed vegetative growth resulting in shortened internodes.

Eight weeks after the paclobutrazol application, irrigation was suspended for a period of 5 to 8 weeks until the trees were in full flower (out-of- season flowering).

Ethrel@ (480girl ethephon) at a concentration of 400 ppm active ingredient was applied as a foliar spray one week after suspension of irrigation at a frequency of once a week for three consecutive weeks at a spray volume of 2 to 3/tree (canopy diameter: 2.5m ; tree height: 2m). Drooping of leaves was an indication that sufficient Ethrelo had been applied.

A week after the last application of Three, KNO3 (380g/kgK, 130g/kgN) at a concentration of 1 5. 2g/lK and 5. 2g/l N was applied once a week as a foliar spray for three consecutive weeks at a spray volume of 2 to 3t/tree (canopy diameter: 2.5m ; tree height: 2m). Swollen out-of-season flower buds were present during the last application and full bloom occurred about fourteen days later.

The fruit reached picking maturity from June to October as opposed to December to April which is the normal season.

Example 2 Treatment of avocado trees (Persea americana Mill.) to disrupt the normal phenological cycle thereby to produce an out-of-season crop under sub-tropical conditions (the months mentioned relate to the southern hemisphere).

(a) Destruction of flowers during the normal flowering period.

Avocado trees located in the district of Letaba at Westfalia Estate in the Limpopo Province, a sub-tropical region in South Africa were treated with a de-flowering spray during the normal flowering period (late July to October), using Ethrelo (480g/l ethephon) at a concentration of 1g active ingredienVE. A light canopy spray was applied to inflorescences when individual flowers were open, at a spray volume of 6t/tree. Flowers died and dropped within four weeks after the Ethrelo application.

(b) Obtaining out-of-season flowering The trees were girdled during late October/early November by using a girdling tool or pruning saw forming cuts which vary between 0,5 and 2cm wide. All main branches were girdled leaving one smaller branch as a breather branch. This ensures the continuation of some phloem-transport to the roots of the plant, thereby reducing stress caused by girdling. The first swollen out-of-season flower buds were observed in mid December

and out-of-season flowering commenced in late January and February.

(c) Enhancement of out-of-season fruit retention and yield Sunnas (50g/l uniconazole) at a concentration of 0.5g active ingredient/t was applied once as a light canopy spray when trees were in full bloom (individual flowers were open). This treatment caused enhanced fruit retention (i. e. reduced fruit drop) and subsequently improved yield.

The fruit reached picking maturity from November to February as opposed to the normal season March to September.

It will be appreciated that many variations in detail are possible without thereby departing from the scope of the invention.