A Peep At Pollination & Apples.

Pollination.

Pollination is all about plant sex; ooh err! Or, is it? Read on for the full story. Flowering plants and honey bees are inextricably linked in a close symbiotic relationship which means that both species benefit from plant reproduction. Plants always produce much more pollen than they need for fertilisation and so the honey bee gets a good share whilst the plant usually reproduces successfully.

Protein Source.

Honey bees must have pollen which is their only source of protein, and they need large amounts. Bees need pollen for bee-growth, tissue repair and brood development. It is essential for the development of the hypopharyngeal glands which are the food producing glands in a nurse bee’s head. Without adequate pollen, brood food cannot be produced.   A colony of around 20,000 bees might collect around 57kg pollen in a year. Pollen also provides minerals, lipids, vitamins and essential amino acids, and if there is not enough pollen, or it is of insufficient quality, then brood rearing decreases and workers live shorter lives. Inadequate pollen income can the herald the death knell for a colony.

Since plants are firmly rooted to the ground, they require a courier to transfer pollen from the male part of the flower (anther) to the female part (stigma). For some plants like grasses and grain, the wind obliges, (anemophilous) and in other situations transfer is by insects (entomophilous). The latter is the means by which our honey bees assist plants in reproduction.

Around 15% of honey bees from a colony will collect pollen only. Nectar alone is collected by 60%, and 15% collect both. However, during nectar collection the bee has to push past the anthers to reach the nectaries which are often at the petal base and so pollen that adheres to the bee lands on the surface of the receptive stigma during this process. This is pollination. The branched feathery plumose bee-hairs have a small positive electromagnetic charge, whilst the flower has a small negative electromagnetic charge and so the passing bee inadvertently attracts pollen.

Fertilisation.

For fertilisation to occur there must be an exchange of genetic material. Plants have varying numbers of chromosomes unlike humans who have 23 pairs, and female honey bees who have 16 pairs. Plants have no such set numbers with hawkweed having 8 chromosomes and black mulberry trees 308. Plants also have the largest genomes amongst all organisms with wheat having 94,000 genes which is five times more than our own compliment of genes.

If the female stigma, situated on top of the style, is receptive and ready for reproduction then a pollen grain, from the male anthers, landing on it will absorb moisture and germinate. During this process, a tube bursts out of the pollen grain’s pore and through its outer wall known at the exine. It grows outwards and down through the style towards the ovary which contains the ovules or eggs to be fertilised.

In a clever reproductive strategy, unique to angiosperms or flowering plants, ensuring a food supply for the developing plant embryo, each pollen tube advancing towards the ovary carries two sex cells or male gametes. When eventually the pollen tube arrives at the ovary, one of these gametes will fuse with an ovule (egg) to produce an offspring, whilst the other will amalgamate with another type of plant cell to become an endosperm which produces the necessary food source and thus the offspring arrives with its own food parcel. Once fertilised, the ovules become seeds and the ovary swells to evolve into the fruit.

Apples.

Apples are interesting fruit to study. Cut one open and notice that the ovaries are divided into 5 chambers each containing 2 available ovules for pollination. Count the seeds and if you find 10 then your apple has been fully pollinated. One that contains 6-7 seeds has not been fully pollinated but still gives good fruit development.

Let’s focus on apples, but firstly consider general fruit production in the UK. Apples, cherries, pears, plums and apricots are the main top fruits grown mostly in the south commercially, though Northern Ireland produces great cooking apples.

Over the years, due to changes in land management and consumer demand, the total UK orchard areas have been reduced to 17,500 hectares/43,000 acres, and apple orchards to 14, 468 hectares/35,750 acres, which is about the size of Liverpool or Aberdeen.

Given the need for good weather at apple pollination time, it is no wonder that the orchards are mainly concentrated in the following southern areas of Kent, East Sussex, Gloucestershire, Worcestershire, and Herefordshire. Some top fruits can be grown in Scotland but not on a large commercial scale. Ferocious winds on the west coast preclude such activities. The island of Tiree, devoid of trees, bears testimony to this fact.

Honey bees are used to pollinate apple orchards because they are available in large numbers when most insects are not yet out and about in full force. In early spring, bumble bee queen are the only member of their species to be seen foraging for food to raise the current year’s brood. However, red mason bees Osmia spp are being increasingly used in British orchards because they are around 100 times more efficient than honey bees and better adapted to the working environment.

https://glosorchards.org

Large numbers of well managed honey bee colonies are needed at just the right time and it is a carefully coordinated process. Insect pollination gives a higher crop yield and fruit quality. There are more seeds in insect pollinated apples, and the calcium level of the fruit is higher which slows ageing and gives a longer shelf-life. The vitamin C level is also higher and the fruit better shaped.

Bee farmers manage their colonies in certain ways to have them ready at short notice for migration to the orchards when the fruit farmer considers the blossom ready. Bees are usually taken to the orchards when apple is around 5% in bloom. Bear in mind that unpredictable weather and seasonal changes make this migration a flexible one. The Bee Farmer’s Association (BFA) Pollination Officer arranges with the orchard growers and receives payment from them. Individual bee farmers are given contracts by the BFA and receive around £75 per hive for a 4- week period. There may be a very small amount of apple blossom honey for the bee farmer but it is the pollination contract that drives the hard work in preparing and transporting honey bee colonies to the orchards.

Apple pollination relies on biology and climate. The pollen grains may not germinate if the temperature is below 5˚C, and pollen tube growth will be slow below 10˚C. Compounding this, apple ovaries are only receptive for 2-4 days after the flower opens, and so pollination must occur within this time otherwise the embryo sac in the ovary degenerates before fertilisation takes place. Now you realise just how important a reasonable climate is for apple growing, and how carefully the fruit grower and beekeeper must plan for successful commercial pollination. Next time you bite into a juicy apple you can enjoy it even more knowing the process of its production.

Health Benefits.

Have you ever wondered about the old adage ” An apple a day keeps the doctor away”? It seems that it isn’t just an old wive’s tale and the research scientists have proof that eating apples is good for us. This popular phrase was coined in 1913 but based on a proverb that originated in Wales in 1866. Back then in Pembrokeshire, they were told to “Eat an apple on going to bed, and you’ll keep the doctor from earning his bread”.

Professor Jonathan Hodgson and colleagues at the University of Western Australia have found that flavonoids found in apples, and especially in the skin, have positive effects on cardiac function. Flavenoids are antioxidants and they naturally protect plants from stress. Hodgson says, “We found that flavonoid-rich apples improve blood vessel relaxation and enhance nitric oxide status–the molecule that causes blood vessel relaxation. A reduced ability of of the blood vessels to relax may cause high blood pressure and heart disease”.

Flavonoids and fibre have a great effect on our gut biomes too increasing the good bacteria and reducing the bad. Apples contain tri-terpenoids which are involved with anti- inflamatory responses. They can reduce cholesterol and have a postive effect on our brains. The good news is that cooking apples will not cause degradation of these properties though some apples contain more flavonoids than others. The Western Australian study reports the highest flavonoid levels in “pink lady” apples.