Plant Breeding 1

Plant Breeding 1

Triticale is an example of:

Triticale exemplifies man-made intergeneric cereal synthesised by crossing wheat Triticum aestivum or Triticum durum with rye Secale cereale, two distinct genera within tribe Triticeae. Primary hybrid from this wide cross is haploid or triploid with unpaired chromosomes leading to sterility due to meiotic irregularities and univalents. To restore fertility, seedlings treated with colchicine alkaloid that inhibits microtubule polymerization preventing spindle formation, inducing chromosome doubling to create autoallohexaploid 6x or octoploid 8x with complete homologous pairing. This amphiploid

Ref: Oettler Triticale breeding Adv Agron; Linde-Laursen Genomic in situ Triticale; Singh BD Intergeneric hybrid example.

View Details

Plant Breeding 1

Removal of stamens to prevent self-pollination is called:

Emasculation removes immature androecium to render female parent incapable of self-pollination, ensuring only desired male parent contributes pollen in artificial cross. Techniques include manual method using forceps and scalpel to excise anthers before dehiscence at green bud stage, hot water emersion at 42 to 48C for 5 to 10 minutes to kill pollen in rice and sorghum exploiting differential thermo-sensitivity, and suction method aspirating anthers. After removal, flower covered immediately with butter-paper bag to exclude foreign pollen. Stigma bagged separately until receptive, indicated by

Ref: Acquaah Plant Breeding Emasculation techniques; IARI Practical Manual Hybridization steps; e-coursesonline.iasri.res.in Emasculation.

View Details

Plant Breeding 1

Hybridization involves:

Hybridization entails controlled sexual crossing between individuals differing genotypically, from intraspecific crosses within same species to interspecific and intergeneric wide crosses. Procedure starts with selection of parents complementary for yield QTL, resistance R genes and quality alleles, followed by emasculation to prevent selfing, collection of viable pollen with intact exine and pollination at stigma receptive stage when peroxidase activity high. Fertilization leads to zygote formation and segregation in F2 generation through crossing over during pachytene and independent assortm

Ref: Allard Principles Plant Breeding Hybridization; Singh BD Methods hybridization; NCBI Bookshelf Plant Breeding chapter.

View Details

Plant Breeding 1

Vegetative propagation does NOT include:

Vegetative propagation defined strictly as formation of new plant from somatic organ outside sexual process: bulb comprised of fleshy scale leaves enclosing short stem as in onion and garlic, corm solid compressed stem storing starch in gladiolus, tuber swollen underground stem with axillary buds eyes in potato, rhizome horizontal stem with nodes in ginger, runner stolon in strawberry. These structures originate from meristem and carry preformed buds capable of sprouting under favorable moisture. Seeds, in contrast, derive from double fertilization event where one sperm fertilizes egg forming

Ref: Hartmann & Kester Principles vegetative vs seed; NCERT Class XII Vegetative Propagation; ICAR Handbook.

View Details

Plant Breeding 1

Asexual reproduction in plants produces:

Asexual reproduction in higher plants bypasses syngamy, producing progeny via mitotic divisions from somatic tissues, preserving maternal genotype intact except somatic mutations. Modes include vegetative propagation through runners, rhizomes, suckers, tubers, bulbs, corms and apomictic seed formation via nucellar embryony where diploid nucellar cells develop into embryos without meiosis. Because meiosis absent, segregation does not occur and heterozygosity fixed, resulting in clones that are phenotypically uniform. Meristematic activity regulated by cytokinin-auxin balance induces adventitiou

Ref: Hartmann & Kester Plant Propagation Asexual cloning; NCERT Class XII Reproduction chapter; Acquaah Clonal crops.

View Details

Plant Breeding 1

Which mechanism promotes outcrossing?

Outcrossing promotion accomplished through dichogamy and herkogamy among others. Herkogamy specifically involves spatial separation between anthers and stigma within same flower, preventing direct contact. Examples include pin and thrum morphs in Primula heterostyly, stigma exerted beyond anthers in some Solanum, and stamen filaments recurved away. Development controlled by auxin gradients and CYCLOIDEA TCP transcription factors influencing organ growth. Herkogamy forces pollinator to brush against anthers in one flower and deposit on stigma of different flower, reducing self-pollination and g

Ref: Barrett Floral Biology herkogamy; Richards Plant Breeding Systems; Faegri Pollination Mechanisms herkogamy.

View Details

Plant Breeding 1

Cross-pollination between different plants is called:

Xenogamy constitutes true outcrossing between genetically distinct individuals of same species, mediated by vectors carrying pollen across plants. Mechanism ensures fusion of gametes bearing dissimilar alleles, increasing heterozygosity and generating novel multilocus genotypes through recombination in meiosis. Many plants enforce xenogamy via self-incompatibility systems: gametophytic S-RNase in Solanaceae degrades self-pollen RNA, sporophytic SRK-SCR interaction in Brassicaceae triggers callose deposition blocking self-tube. Such biochemical barriers regulated by S-locus multiallelic haploty

Ref: de Nettancourt Incompatibility in Angiosperms; NCERT Biology Chapter Pollination Xenogamy; Lodish S-locus molecular biology.

View Details

Plant Breeding 1

Reduced vigor due to repeated selfing is known as:

Inbreeding depression emerges as phenotypic deterioration in vigor, height, fecundity and stress tolerance following repeated selfing of naturally outcrossing species. Underlying genetic architecture includes dominance hypothesis: many loci carry partially recessive deleterious mutations in genes governing chlorophyll biosynthesis, auxin transport, root elongation and defense signaling. Increased homozygosity makes these recessives expressed, reducing enzyme activity and hormone levels. Pseudo-overdominance where two linked loci in repulsion mimic overdominance also contributes. Quantitative s

Ref: Charlesworth & Willis Annu Rev Ecol Inbreeding depression; Falconer Quantitative Genetics; Singh BD Inbreeding depression cause.

View Details

Plant Breeding 1

Repeated selfing leads to:

Repeated self-fertilization progressively eliminates heterozygosity because each heterozygous locus segregates 1 AA:2 Aa:1 aa, only half progeny retain heterozygosity. Mathematically heterozygosity after t generations Ht equals H0 multiplied by one-half raised to power t, so after seven generations approximately 0.8 percent remains. Continuous inbreeding drives allele fixation toward homozygous states, exposing recessive homozygotes for selection. In breeding this rapid homozygosization underlies development of pure lines, recombinant inbred lines for QTL mapping and near-isogenic lines via re

Ref: Allard Principles Plant Breeding homozygosity; Hartl & Clark Population Genetics selfing equation; Falconer Quantitative Genetics.

View Details

Plant Breeding 1

Transfer of pollen between different flowers of the same plant is:

Geitonogamy describes pollination accomplished between different flowers situated on same individual plant, facilitated when pollinators such as bumblebees, honeybees or wind carry pollen from one blossom to another on same genet. Although physically involving two flowers resembling cross-pollination, genetically equivalent to selfing because male and female gametes originate from same sporophyte sharing identical genome, thus no new allelic diversity introduced and inbreeding coefficient equivalent to autogamy. Distinguished from xenogamy where pollen arrives from distinct plant genotype. Mon

Ref: Faegri & van der Pijl Pollination Ecology geitonogamy; Barrett Mating systems; NCERT Class XII.

View Details

Plant Breeding 1

Cleistogamy promotes:

Cleistogamy represents floral syndrome where flowers remain closed throughout anthesis, perianth never unfolding, thus anther dehiscence occurs inside bud envelope and pollen deposited directly onto adjacent stigma. Controlled by genes regulating lodicule expansion, corolla opening and jasmonic acid signaling affecting anther elongation. In cleistogamous rice mutant cl7 and barley cly1, suppression of petal opening enforced by mutation in AP2 transcription factor. Consequence obligate self-pollination ensuring seed set under rain or low pollinator activity, protecting pollen from desiccation a

Ref: Lord EM Cleistogamy Encyclopedia; PubMed Rice cleistogamous cl7 gene; Campbell Biology pollination control.

View Details

Plant Breeding 1

Self-fertilization within the same flower is termed:

Autogamy denotes self-pollination within same flower involving anthers and stigma of same bisexual blossom. Mechanism relies on synchronous maturation called homogamy, contact via filament curvature and gravitational pollen fall. At genetic level self-compatibility occurs when S-locus haplotypes identical still allow pollen germination, pollen tube growth through transmitting tissue mediated by pectinase and callase dissolving callose plug. Selfing preserves coadapted gene complexes, increases homozygosity and fixes recessive traits, valuable for pure line extraction. Ecologically provides rep

Ref: Richards AJ Plant Breeding Systems autogamy; NCERT Class XII Chapter 2 Pollination; Acquaah Breeding Selfing crops.

View Details