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UNIVERSITY COLLEGE of AGRICULTURE

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A Presentation By

Ishtiaq Shariq

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B. Sc. (Hons.) 6th Semester Plant Breeding and Genetics

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• BIOLOGY

• ECONOMIC IMPORTANCE

• GENETICS AND CYTOGENETICS

• TECHNIQUES

• SOURCES

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TABLE OF CONTENT

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BIOLOGY

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• Major world crop

• The Saccharum species are extremely complex allopolyploids.

• S. officinarum 2n = 80

• Supplying sugar and energy.

• Grass family

• Tropical and subtropical

• Domesticated sweet cane of New Guinea and South Pacific

• Perennial grass growing 2–6 meters high

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• Not tolerant of frost.

• The genome of modern cultivated sugarcane is large and complex, highly polyploid and vary in ch. # (around 100).

• Originating from hybrids between two wild polyploid relatives, Saccharum officinarum and Saccharum spontaneum.

• The genome is of the order of 10,000 Mbp in size.

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Scientific classification

KINGDOM Plantae

ORDER Poales

FAMILY Poaceae

TRIBE Andropogoneae

GENUS Saccharum

SPECIE S. Officinarum

BINOMIAL NAME Saccharum officinarum

L.

ECONOMIC IMPORTANCE

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• Produced in the greatest quantities globally. More than 1,000 million tons of sugarcane are harvested each year.

• Source of most of the sugar produced in the world

• Efficient plant utilizing the C4 pathway of photosynthesis (in notes) *

• Brazil is largest producer of sugarcane and export of sugar

• China 3rd , Pak. 5th (2005)

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GENETICS & CYTOGENETICS

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• Chromosome numbers were determined, uncovering highly polyploid and, frequently, aneuploidy members in this genus.

• The vast majority of S. officinarum clones display 2n = 80 chromosomes

• Pairing behavior was studied in these species that showed mainly bivalents

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• Interspecific crosses can usually be made among clones of the five species within the genus Saccharum, although peculiar chromosome numbers are observed in the progenies of certain crosses.

• Due to abnormalities in fertilization and embryo formation, the somatic chromosome number is transmitted to the progeny instead of the gametic number of the pistillate parent, when S. officinarum is used as the maternal parent in crosses with S. spontaneum, S. barberi, or S. sinense.

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• In the breeding of sugarcane, it has been a general practice to cross the different species with the noble cane, S. officinarum, to combine the high sugar yield of the officinarum clones with hardiness and disease resistance of the

other species, a procedure called nobilization.

• Usually, two to three backcrosses to the noble parent are necessary to recover satisfactory sucrose content

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NOBILIZATION

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• Simple Mendelian genetic studies are virtually impossible in sugarcane owing to the high polyploid number and irregular transmission of individual chromosomes, to meiotic irregularities arising with cross fertilization, and to sterility problems that make crossing and selfing difficult.

• Greater attention is given to quantitative genetic inheritance in sugarcane than to the inheritance of qualitative characters. Inbreeding, where possible, leads to the rapid loss of vigor.

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• Inbreeding is restricted in particular clones due to presence of self sterility or self incompatibility. Quantitative inheritance studies suggest that:

• Additive genetic variance is important for many agronomic characters and disease resistance.

• Non additive variance is important for cane and sugar yield.

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TECHNIQUES

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• In the last 20 years hybridization tech. used extensively in plants.

1. Genomic in situ hybridization (GISH)

2. Fluorescence in situ hybridization (FISH)

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• Used to identify parental chromosomes in interspecific hybrids.

• To test the origin of natural amphiploids, to track down the introgression of alien chromosomes or to test the occurrence of exchange between the genomes involved

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GENOMIC IN SITU HYBRIDIZATION (GISH)

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• This technique can reveal the physical location of repeated, low-copy-number or unique DNA sequences, provide useful cytological markers and enable comparisons between physical and genetic maps. These techniques proved to be particularly relevant to refine our understanding of the genome structure of sugarcane and its taxonomy.

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FLUORESCENCE IN SITU HYBRIDIZATION (FISH)

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To answer specific questions regarding:

• Origin of S. barberi and S. sinense

• Basic chromosome number in S. spontaneum, S. officinarum and S. robustum

• Genome structure of modern sugarcane cultivars

• Introgression with other genera

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APPLICATION

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• The Basic chromosome number of X= 5, 6, 7, 8, 9, 10 and 12 suggested for Saccharum spp.

• S. officinarum 2n=80, X=10

• Basic chromosome number X= 10 most common in Andropogoneae.

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WHY STRUCTURAL DIFF. EXPECTED IN MODERN CULTIVAR?

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• Studies have shown that the two major species involved in modern cultivars have different basic chromosome number; X= 10 for S. officinarum and X= 8 for S. spontaneum.

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SOURCES

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1. Basic Information on the Sugarcane Plant 1 Robert J. Henry 2. Molecular Cytogenetics 9 Nathalie Piperidis, George Piperidis and Angélique D’Hont

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