RHS Level 2 Certificate Year 1 Week 8 – pollination, fertilization and plant breeding
Learning outcomes <ul><li>Pollination and fertilization </li></ul><ul><li>10.1 Define the term: ‘pollination’. </li></ul><...
Pollination  <ul><li>The transfer of pollen from the anther to the stigma.. </li></ul><ul><li>Carried out by insects, wind...
Compatibility <ul><li>Not all pollen will be able to fertilize a flower – it must be compatible.  Chemicals on the stigma ...
Double Fertilization – stage 1  <ul><li>Two cells in the pollen grain (each with one set of chromosomes). </li></ul><ul><l...
Double Fertilization – stage 2 <ul><li>Within the ovule is an egg cell and another cell .One of the two sperm cells unites...
A bit of genetics -1 <ul><li>Chromosomes – occur in pairs, made up of genes.  The ‘code’ for the plant – species, height, ...
A bit of genetics - 2 <ul><li>Cell division to produce gametes is different.  Only one chromosome per cell.  Four cells ar...
Why does the genetics matter? Part 1 <ul><li>Plants evolved to maximise genetic mixing – but plant breeders want consisten...
Why does the genetics matter? Part 2. <ul><li>Each gene = one of four combinations (because there are two pairs of genes f...
F 1  Hybrids <ul><li>Give predictable outcomes – one parent line has two dominant genes, the other two recessive.  Crossin...
Hybrid vigour <ul><li>The genetic mixing in F1 hybrids often leads to the offspring being stronger or more disease resista...
Triploids <ul><li>More than two sets of chromosomes in a cell. </li></ul><ul><li>Such plants are often more vigorous and p...
Parthenocarpy (literal meaning ‘virgin fruit’) <ul><li>This means a fruit that has formed without fertilization. </li></ul...
Learning outcomes <ul><li>Pollination and fertilization </li></ul><ul><li>10.1 Define the term: ‘pollination’. </li></ul><...
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RHS Year 1 week 7 overview 2011

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RHS Year 1 week 7 overview 2011

  1. 1. RHS Level 2 Certificate Year 1 Week 8 – pollination, fertilization and plant breeding
  2. 2. Learning outcomes <ul><li>Pollination and fertilization </li></ul><ul><li>10.1 Define the term: ‘pollination’. </li></ul><ul><li>10.2 Define the terms: ‘cross-pollination’ and ‘self-pollination’. </li></ul><ul><li>10.3 State two characteristics of wind pollinated plants and two characteristics of insect pollinated plants including the exposure of reproductive structures, pollen surface roughness, and quantity of pollen produced.. </li></ul><ul><li>10.4 Describe the process of fertilisation, including the meaning of the terms ‘gametes’, ‘zygote’, ‘incompatible’, and ‘compatible’. </li></ul><ul><li>10.5 - State the significance of F1 seeds and explain the term ‘hybrid vigour’ </li></ul><ul><li>10.6 Define the term ‘parthenocarpy’ and state its horticultural significance </li></ul><ul><li>10.7 State the horticultural significance of triploid cultivars. </li></ul>
  3. 3. Pollination <ul><li>The transfer of pollen from the anther to the stigma.. </li></ul><ul><li>Carried out by insects, wind, water, animals </li></ul><ul><li>Flowers show particular adaptations for their particular mode of pollination. </li></ul><ul><li>Role in sexual reproduction – hybridization. </li></ul><ul><li>Cross and self- pollination. </li></ul><ul><li>Compatibility – mechanisms to ensure that only compatible DNA reaches the ovule. </li></ul>
  4. 4. Compatibility <ul><li>Not all pollen will be able to fertilize a flower – it must be compatible. Chemicals on the stigma control this. So Beech pollen will not fertilize a Lily – even if pollination occurs. </li></ul><ul><li>Flowering plants evolved to cross pollinate – genetic mixing. So self-pollination is less desirable. </li></ul><ul><li>Strategies include – self-incompatibility, dioecious plants, different maturity times for anthers and stigma on same plant . </li></ul>
  5. 5. Double Fertilization – stage 1 <ul><li>Two cells in the pollen grain (each with one set of chromosomes). </li></ul><ul><li>If pollen compatible, then one cell from the pollen grain divides and forms a pollen tube. The pollen tube grows down the style. </li></ul><ul><li>The second cell divides into two identical cells– one new cell becomes the tube nucleus which moves to the tip of the pollen tube. The other new cell divides again to produce two sperm cells containing the male parent’s DNA </li></ul><ul><li>The pollen tube finds a tiny opening in the ovule and enters it, guided by the tube nucleus. The sperm cells enter the ovule. </li></ul>
  6. 6. Double Fertilization – stage 2 <ul><li>Within the ovule is an egg cell and another cell .One of the two sperm cells unites with the egg cell to produce a zygote or fertilized egg. This will develop to produce the plant embryo within the seed. </li></ul><ul><li>The other sperm cell unites with the other ovule cell to form the endosperm. The endosperm provides food for the development of the embryo and for germination. </li></ul>
  7. 7. A bit of genetics -1 <ul><li>Chromosomes – occur in pairs, made up of genes. The ‘code’ for the plant – species, height, flower colour etc. Each characteristic is carried by a pair of genes, one on each chromosome of a pair. </li></ul><ul><li>We know that in cell division for growth identical daughter cells are produced. Each of these has it’s own nucleus which contains an exact replica of both sets of chromosomes from the original cell. </li></ul><ul><li>Cell division for growth is called mitosis. </li></ul>
  8. 8. A bit of genetics - 2 <ul><li>Cell division to produce gametes is different. Only one chromosome per cell. Four cells are produced by each dividing parent cell – each are genetically from the other. </li></ul><ul><li>Fertilization – the egg and sperm cells fuse and the embryo has diploid cells again. </li></ul><ul><li>However the resulting embryo has a random mix of genetic characteristics from each parent plant. New varieties arise in this way. </li></ul>
  9. 9. Why does the genetics matter? Part 1 <ul><li>Plants evolved to maximise genetic mixing – but plant breeders want consistent, predictable outcomes (dwarf blue lupins should not be 1m tall and pink!) </li></ul><ul><li>Each characteristic is the result of a pair of genes. The two genes are not necessarily the same though. </li></ul><ul><li>Some genes are dominant –if they are present then the physical appearance of the plant is determined by the dominant gene for that characteristic. So if the red colour gene is dominant the flower will be red, even if the other gene of the pair (called th recessive) carries the white flower information. </li></ul>
  10. 10. Why does the genetics matter? Part 2. <ul><li>Each gene = one of four combinations (because there are two pairs of genes for each characteristic – one pair in the mother and one in the father – which are split when the egg or sperm cell is produced.) </li></ul><ul><li>Each parent = dominant red flower and a recessive white flower gene. Three of the resulting combinations will include the dominant gene and one will have a pair of recessive white flower genes. Three of the offspring will have red flowers and one white. </li></ul><ul><li>This three : one ratio tells the plant breeder that both parents have dominant red flower genes. If the offspring were half white flowered and half red then only one parent has the dominant red gene. </li></ul>
  11. 11. F 1 Hybrids <ul><li>Give predictable outcomes – one parent line has two dominant genes, the other two recessive. Crossing them means that each offspring carries the dominant gene. </li></ul><ul><li>If the dominant gene is for, say, red flowers the breeder can be certain they will be the same in this respect. The offspring are called F 1 hybrids – F 1 means ‘first filial generation’. </li></ul><ul><li>However if F1 plants cross then their offspring (F 2 ) will not necessarily all have red flowers. If the other parent plant has one dominant (red) and one recessive gene (white) then the offspring will be three to one red to white. This is why it is said that F 1 hybrids do not ‘come true from seed’. </li></ul>
  12. 12. Hybrid vigour <ul><li>The genetic mixing in F1 hybrids often leads to the offspring being stronger or more disease resistant than the parents. This may be due to the distribution of such dominant genetic characteristics in the offspring or as a result of the particular interactions between the gene pairs. F1 hybrids often have larger flowers or fruit than their parents which is why they are desirable, despite being difficult and expensive to produce. </li></ul>
  13. 13. Triploids <ul><li>More than two sets of chromosomes in a cell. </li></ul><ul><li>Such plants are often more vigorous and produce larger flowers and fruit than their parents. However they are often difficult to fertilize or may be sterile. The apple M. domestica ‘Bramley’s Seedling’ is a triploid plant and does not produce fertile pollen. It is therefore a poor pollinator (self or cross) which is why another pollinator is required in orchards which have Bramley’s in them. </li></ul>
  14. 14. Parthenocarpy (literal meaning ‘virgin fruit’) <ul><li>This means a fruit that has formed without fertilization. </li></ul><ul><li>Encouraged as a trait in some varieties of fruit and breeding produces varieties that are solely parthenocarpic – for example Musa acuminata (dessert banana) as the seeds are large and hard in fertile varieties. Cucumbers are often all female clones that produce unfertilized fruit. </li></ul><ul><li>However parthenocarpy = the variety can only be propagated vegetatively. Makes these clones vulnerable to disease. </li></ul>
  15. 15. Learning outcomes <ul><li>Pollination and fertilization </li></ul><ul><li>10.1 Define the term: ‘pollination’. </li></ul><ul><li>10.2 Define the terms: ‘cross-pollination’ and ‘self-pollination’. </li></ul><ul><li>10.3 State two characteristics of wind pollinated plants and two characteristics of insect pollinated plants including the exposure of reproductive structures, pollen surface roughness, and quantity of pollen produced.. </li></ul><ul><li>10.4 Describe the process of fertilisation, including the meaning of the terms ‘gametes’, ‘zygote’, ‘incompatible’, and ‘compatible’. </li></ul><ul><li>10.5 - State the significance of F1 seeds and explain the term ‘hybrid vigour’ </li></ul><ul><li>10.6 Define the term ‘parthenocarpy’ and state its horticultural significance </li></ul><ul><li>10.7 State the horticultural significance of triploid cultivars. </li></ul>

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