#crop improvement

Plant Breeding 3

Which method is best to handle segregating generations efficiently?

Efficiency in managing large segregating populations depends on ability to track ancestry, evaluate plant-to-row relationships, and apply selection with known pedigree. Pedigree breeding systematically documents parentage of each selected plant from F2 onward, maintaining detailed field diaries, numbering systems, and performance scores. This structured documentation enables breeder to handle 2500-3000 F2 plants as individually identifiable families, cull inferior families based on ancestral performance, and trace origin of superior recombinants for future crossing. Space-planted pedigree rows

Ref: Poehlman JM & Sleper DA. Breeding Field Crops, Chapter Pedigree handling. Allard RW. Principles of Plant Breeding

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Plant Breeding 3

The parent repeatedly used in backcrossing is called:

In a backcross program two parents play distinct roles. Donor parent, also called non-recurrent parent, carries elite allele missing in adapted cultivar but is otherwise agronomically inferior. Recurrent parent is the high-yielding, widely adapted cultivar targeted for improvement, used as female or male in every backcross to restore its genome. After initial F1 = donor × recurrent, selected progeny possessing donor allele is crossed again to same recurrent parent, producing BC1F1, then BC2F1, and so on. Repeated use elevates proportion of recurrent genome from 75% in BC1 to 87.5% in BC2, 93.7

Ref: Hawkes JG. The genetics of backcross. Biology LibreTexts: Recurrent and donor parent definitions

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Plant Breeding 3

Backcross breeding is mainly used to:

Backcrossing is designed to rectify a specific defect in an otherwise elite, adapted cultivar without altering its overall genetic background. A donor parent contributes one or a few desirable alleles, such as a dominant disease resistance gene Yr15, Bt, or bacterial blight gene Xa21, while recurrent parent provides superior yield, quality, and adaptation encoded by hundreds of favorable QTLs. By repeatedly crossing hybrid progeny carrying the target gene back to recurrent parent and selecting for that gene each cycle, breeder introgresses a small donor chromosomal segment. Unlinked donor geno

Ref: Allard RW. Principles of Plant Breeding, Chapter 15 Backcross. Hospital 2005, Nature Reviews Genetics

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Plant Breeding 3

In bulk breeding, selection is practiced mainly in:

Natural selection predominates during early generations of bulk method, making artificial selection ineffective because heterozygosity buffers phenotypic expression and heritability of yield is low. Plants in F2-F4 still segregate, genotype-by-environment interaction confounds single plant performance, and competitive ability may not correlate with grain yield in pure stands. Breeders therefore postpone intensive selection until F5-F7, when inbreeding coefficient approaches 0.9375 and plants become largely homozygous. At this stage environmental fitness differences have already filtered malada

Ref: Acquaah G. Chapter 11 Bulk breeding; Poehlman & Sleper Breeding Field Crops, 5th ed.

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Plant Breeding 3

Pure line selection is most suitable for:

Pure line selection most effective in self-pollinated crops because autogamy rapidly drives homozygosity and population consists of mixture of distinct homozygous lines each phenotypically uniform. Selection among lines rather than within captures additive variance of yield traits controlled by many small effect QTL. Crops such as wheat Triticum, rice Oryza, barley Hordeum, groundnut Arachis and chickpea Cicer predominantly selfing with outcrossing below five percent, already purged severe deleterious load, so inbreeding depression minimal and homozygous lines vigorous. Johannsen experiments w

Ref: Johannsen 1903 Pure line theory; Allard Principles Plant Breeding pure line selection self pollinated; Singh BD methods.

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Plant Breeding 1

Plant breeding is best defined as:

Plant breeding is defined as art and science that genetically improves crops to meet human requirements for food, feed, fiber, fuel, and aesthetic purposes. As science it draws upon Mendelian genetics describing segregation and independent assortment, population and quantitative genetics estimating heritability and gain from selection, cytogenetics understanding chromosome behavior and polyploidy, molecular genetics including marker assisted selection using SSRs and SNPs, and biotechnology employing transgenesis and genome editing tools CRISPR-Cas9. As art it involves breeder intuition, experi

Ref: Acquaah G Principles of Plant Genetics and Breeding 3rd Ed Definition art and science; Sleper & Poehlman Breeding Field Crops 6th Ed objectives.

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