Tuesday, June 14, 2011

The avocado, female today, male tomorrow

The Avocado, Persea gratissima or Persea americana, is a Central American fruit tree of the Lauraceae family of grown three races: Mexican, Guatemalan and Antillean, with many natural hybrids between them have led multiple varieties. Mexican cultivars generally resist the cold better than the Guatemalan and Antillean. Under optimum growing avocado tree born of seed can exceed 20 meters, being a wild specimen reaches 30 meters. The grafted samples are much lower, which facilitates the collection of fruit. In recent decades, the cultivation of varieties of Mexican race has spread to many countries with subtropical and Mediterranean climate without frost, especially in coastal areas.

The avocado has hermaphrodite flowers that prevent selfing of a very clever way. The flowers open in two phases well separated in time. In the first phase all flowers of same tree open as female pistil receptive to pollen from other trees, but with undeveloped six stamens to pollen can not fertilize at the same pistil. These details are clearly visible in this and the following images. Recommend expanding the photos with a double click.

Avocado flowers are inconspicuous. Lack petals. The sexual organs are surrounded by six sepals yellow-green to a yarn in each of them. To attract pollinating insects have three orange nectaries situated between the stamens and ovary. With the nectar the bees produce a dark honey with a characteristic taste. In plantations of Malaga, Granada and the Canary Islands produce large amounts of avocado honey protected designation of origin.

In this other flower in female phase is clearly visible all the details. In the center is the swollen ovary of the white pistil leaving just the stigma receiving pollen. Surrounding the ovary are the three nectar of a vivid orange, followed by the six stamens in which extreme are full of pollen anthers still immature.

Finishing the day of the first stage of flowering the female stigma is sealed and the male anthers of the stamens begin to mature, so that at sunrise the next day all flowers of same tree enter the male phase of flowering and anther open for insect pollinators are impregnated with the pollen and bring it to the flower of another avocado that day is in female phase. Thus it is almost impossible for the own pollen fertilizes the stigma, thus avoiding inbreeding would lead to the degeneration of the species perpetuating regressive genes.

Here we see three flowers in male phase with mature stamens that have been stretched and lifted so that the insects gluttonous of the nectar are impregnated with the pollen from the anthers.

In some mysterious way which has not yet been explained all individuals of the same cultivar agree to bloom at the same level on alternate days. In large plantations of avocados grow different cultivars are often intermingled, as if they were planted all of the same cultivar bloom all at the same level and no flowers would be pollinated so they would not give any fruit.

In avocado plantations of a single cultivar, to get to fruition, the agriculturists use the random planting of some individuals born seed edges, ie mongrel hybrid, each of which blooms in a different phase, so that ensure good pollination, and that whatever the stage of flowering of avocado plantation edges will always be several avocados flourish in a different phase, bringing the precious pollen by bees and other insects.

In this type of fruit is well understood the importance of bees as pollinators, without which very few flowers would be pollinated and the fruits would be very rare. Pesticide spraying in full bloom would be catastrophic for the bees and productivity of avocados.

Avocado flower in the male phase. The sepals are bent down to make it exposed the stamens and facilitate impregnation with pollen from insects. In this second phase the three nectaries still produce abundant nectar to attract pollinators to flowers.

Another flower of Persea gratissima in male phase. If the ovary is fertilized with pollen from another avocado in a few days begin to grow larger and change its color from white to green. With the passage of the days its weight will double the long petiole downwards and the fruit will acquire the aspect of a testicle. Just the name of avocado, ahuacatl, comes from the ancient Aztec language Nahuatl and means testicle. The word guacamole, ahuacamolli, also comes from the Nahuatl language and means avocado salsa. During the Inca empire avocado cultivation spread south and in Quechua-speaking Incas gave the name of Palta, which is why in South America they call the fruit Palta and the tree Palto.

And here is the result of this curious flowering in two phases, a beautiful ahuacatl or palta seed always a hybrid, which if planted will result in a massive tree that will take about 12 years to give their first flower and 15 years to produce the first fruits, as during the early flowers tend to fall without reaching fruition.

The fruits may be round or oblong, with green or purple skin, smooth or rough and weight can range from about 50 grams in dwarf avocados without seed to more than one kilogram in some varieties of Puerto Rico.

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