Methods to improve cropsMethods to improve crops• Enhancing the vitamin A content of rice Enhancing the vitamin A content of rice

through genetic manipulationthrough genetic manipulation– Green parts of rice plants contain beta-carotene – vital Green parts of rice plants contain beta-carotene – vital

precursor of vitamin A – No beta-carotene in grainsprecursor of vitamin A – No beta-carotene in grains– Vitamin A essential for operation of body’s immune Vitamin A essential for operation of body’s immune

system. Deficiency causes increased risk of infection, system. Deficiency causes increased risk of infection, night-blindness and total blindness.night-blindness and total blindness.

– Genetically-modified strain of rice has been produced Genetically-modified strain of rice has been produced which stores significant levels of beta-carotene in the which stores significant levels of beta-carotene in the grains (grains (golden ricegolden rice) – contains genes from daffodil and ) – contains genes from daffodil and a bacteriuma bacterium

– General method used: incorporate genes into a bacterial General method used: incorporate genes into a bacterial plasmid and use bacteria (plasmid and use bacteria (Agrobacterium tumefaciensAgrobacterium tumefaciens) ) to carry genes into the plant cellsto carry genes into the plant cells

– Method used for rice: genes are delivered directly into Method used for rice: genes are delivered directly into the cells using small the cells using small μμm-sized tungsten or gold bullets m-sized tungsten or gold bullets coated with DNA. The bullets are fired from a device that coated with DNA. The bullets are fired from a device that works similar to a shotgun (works similar to a shotgun (gene gungene gun))

ALBIO9700/2006JK

ALBIO9700/2006JK

White rice and golden riceWhite rice and golden rice

Gene gun (Courtesy of Bio-Rad Gene gun (Courtesy of Bio-Rad Laboratories)Laboratories)

ALBIO9700/2006JK

ALBIO9700/2006JK

Producing polyploids in wheat Producing polyploids in wheat through hybridisationthrough hybridisation

• Modern bread wheat (Modern bread wheat (Triticum aestivumTriticum aestivum) is a ) is a hexaploidhexaploid plant (6n) – result of hybridisation of plant (6n) – result of hybridisation of several wild species of grasses (such sterile several wild species of grasses (such sterile hybrids can only reproduce asexually)hybrids can only reproduce asexually)

• Doubling of chromosome number appears to have Doubling of chromosome number appears to have occurred twice during the evolution of modern occurred twice during the evolution of modern wheat – resulting in the formation of fertile wheat – resulting in the formation of fertile polyploids from previously sterile hybridspolyploids from previously sterile hybrids

• Formation of polyploids important in plants – Formation of polyploids important in plants – animal polyploids are often not viableanimal polyploids are often not viable

• Now it’s possible to induce the formation of Now it’s possible to induce the formation of polyploids by preventing spindle formation, using polyploids by preventing spindle formation, using chemicals (e.g. chemicals (e.g. colchicinecolchicine))

• Polyploids are generally more hardy and higher Polyploids are generally more hardy and higher yielding than their parent speciesyielding than their parent species

• Ancestors of wheat are small, not very robust and Ancestors of wheat are small, not very robust and produce small ears of small seedsproduce small ears of small seeds

ALBIO9700/2006JK

ALBIO9700/2006JK

PlantPlant

Probable Probable ancestral ancestral haploid haploid numbernumber

ChromosomChromosomee

numbernumber

Ploidy Ploidy levellevel

domestic oatdomestic oat 77 4242 6n6n

peanutpeanut 1010 4040 4n4n

sugar canesugar cane 1010 8080 8n8n

bananabanana 1111 22, 3322, 33 2n, 3n2n, 3n

white potatowhite potato 1212 4848 4n4n

tobaccotobacco 1212 4848 4n4n

cottoncotton 1313 5252 4n4n

appleapple 1717 34, 5134, 51 2n, 3n2n, 3n

ALBIO9700/2006JK

Evolution of modern bread Evolution of modern bread wheatwheat

ALBIO9700/2006JK

Producing vigorous, uniform maize Producing vigorous, uniform maize through inbreeding and through inbreeding and

hybridisationhybridisation• Through selection, inbreeding and hybridisation, Through selection, inbreeding and hybridisation,

growers have been able to produce varieties of growers have been able to produce varieties of maize that grow vigorously (therefore high maize that grow vigorously (therefore high yielding) and uniformly under the prevailing yielding) and uniformly under the prevailing conditions (soil type, prevailing temperatures, conditions (soil type, prevailing temperatures, rainfall, etc)rainfall, etc)

• Assuming conditions remain similar year after Assuming conditions remain similar year after year, farmers can continue to grow the same year, farmers can continue to grow the same variety and expect to obtain a similar cropvariety and expect to obtain a similar crop

• Desirable characteristics:Desirable characteristics:– High yieldingHigh yielding– Disease resistantDisease resistant– Good quality in terms of market desirabilityGood quality in terms of market desirability– Vigorous growth under the prevailing conditionsVigorous growth under the prevailing conditions– Plants all grow to a similar height (easy harvesting)Plants all grow to a similar height (easy harvesting)– Crops are all ready to harvest at the same timeCrops are all ready to harvest at the same time

ALBIO9700/2006JK

• Plants that show desirable characteristics would be Plants that show desirable characteristics would be selected and self pollinated – pollen transferred to selected and self pollinated – pollen transferred to stigma – muslin bag placed around flower (ensure stigma – muslin bag placed around flower (ensure pollen from other plants does not reach stigma) – pollen from other plants does not reach stigma) – homozygous plants for desired characteristics will be homozygous plants for desired characteristics will be produced if repeated for many generationsproduced if repeated for many generations

• Inbreeding depressionInbreeding depression: loss of vigour and fertility, : loss of vigour and fertility, as well as a reduction in size and yield due to as well as a reduction in size and yield due to inbreedinginbreeding

• Inbred maize has very little variation (every plant Inbred maize has very little variation (every plant having the same allele of every gene)having the same allele of every gene)

• However, if 2 inbred lines are crossed, it will produce However, if 2 inbred lines are crossed, it will produce a hybrid that has a greater yield and is more vigorous a hybrid that has a greater yield and is more vigorous than either of the parental lines (than either of the parental lines (hybrid vigourhybrid vigour))

• This hybrid heterozygous for most genes, so This hybrid heterozygous for most genes, so deleterious recessive alleles are hidden – at the same deleterious recessive alleles are hidden – at the same time, it inherits the lack of variability from its parentstime, it inherits the lack of variability from its parents

• Such single cross hybridisation has been used for Such single cross hybridisation has been used for selective breeding since the early 1960’s to double selective breeding since the early 1960’s to double the yield and to breed uniform, high yielding maizethe yield and to breed uniform, high yielding maize

ALBIO9700/2006JK

Inbreeding depressionInbreeding depression

ALBIO9700/2006JK

• Double cross hybridisationDouble cross hybridisation was used as a was used as a selective breeding tool to increase maize yields selective breeding tool to increase maize yields between 1920 and 1960 from 1.5 to 4 tonnes per between 1920 and 1960 from 1.5 to 4 tonnes per hectarehectare

• In order to carry out the inbreeding or to carry out In order to carry out the inbreeding or to carry out a cross to form a hybrid, pollen from a specific a cross to form a hybrid, pollen from a specific male parent must be used to fertilise a specific male parent must be used to fertilise a specific female parent – anthers are removed from some female parent – anthers are removed from some flowers which will form the female parent – pollen flowers which will form the female parent – pollen transferred from anthers of male parents flowers to transferred from anthers of male parents flowers to stigmas of flowers without anthers – muslin bags stigmas of flowers without anthers – muslin bags are placed around fertilised flowersare placed around fertilised flowers

• Selection for measurable characteristics i.e. yieldSelection for measurable characteristics i.e. yield• Selection for disease or pest resistanceSelection for disease or pest resistance• Seeds are grown and plants showing desirable Seeds are grown and plants showing desirable

characteristics are bred again – can be repeated characteristics are bred again – can be repeated for many generationsfor many generations

ALBIO9700/2006JK

ALBIO9700/2006JK