af Anshita Jaiswal 4 år siden
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Viruses: tobacco mosaic
Bacteria : black rot of crucifers
Fungi: brown rust of wheat , late blight of poatato
when such hybrids are produced,they are better than parents and continue to be cultivated
better yeilding varieties in plants in terms of growth,size,climatic condition
reduced biological fitness in a given population because of interbreeding among related indiviuals
genetically similar plants produce reccessive traits in their progeny
Seeds are certified and packed in sealed packects as certified seeds. Each sealed packet caonatins information:
validity of certificate
special features (if any)
absence of weeds and presnce of inert matter (not more than 1%)
purity of seeds (99%)
date of test
National Seeds Corporation (NSC)streamlines raising seeds of improved varieties
high rate of germination
high order of purity
free of pathogens and pests
free of weed seeds
STEPS:
iii) Crossing the selected inbred lines to produce uniform F1 population with desired qualities and then F1 seeds can be directly grown
ii) Selfing the selected plants through several generations to produce uniform homozygous inbred lines
i) Selection of haploid plants that have the combination of desired characters
TYPES
Intergeneric: different genera
Interspecific: different species
Intervarietal: different lines or varieties of the same species
Intravarietal: same variety
STEPS
step 2: Not all hybrids show the desired characters. only, one in a few 100 to 1000 crosses show the desirable combination. such hybrid plants are sleceted
step 1: pollen grains from the desirable plant chosen as male parent are collected and placed on stigma of flowers of female parents
PROCEDURE
pollination or crossing
tagging
bagging
emasculation (stamens removed at bud stage)
Selection and Isolation ofmplants
The germplasm is evaluated and plants with desired combinations of characters are identified. selection is carried out for plants with advantageous charaters based on phenotypic characters
Clonal Selection
new genetic variability cannot be introduced
helps in conserving hybrid vigour and quality of crop
plants that multiply by vegetative propogation
Pure Line Selection
process repeated continously to obtain pure line
sown in separate rows
plants selected on basis of best agronomic characters
self pollinated crops
Mass Selection
the process is repeated many times to obtain homozygosity
plants selected for desired features and their seeds are collected
grown in same field
cross polinated plants
Types of Seeds
Cyropreserved (-196° C)
Recalcitrant Seeds (aerobic humid conditions)
Orthodox Seeds (-10° to -20° C)
Centres for plant genetic resources
International
International Board of Plant Genetic Resources (IBPGR)
indian
Central Rice Research Institute(CRRI)
International Crops Research Institute for Semi-Arid Tropics (ICRISAT
The sum total of all alleles of the genes present in the existing and past varieties of a crop and its wild relatives constitutes the germplasm
wild species related to the crop species
pur lines produced by plant breeders
old local or desi varieties
improved varities that are no mor in cultivation
all cultivated improved varieties
