#animal breeding

Plant Breeding 3

Recurrent selection is mainly practiced in:

Recurrent selection was conceptualized by Hayes and Garber for improving cross-pollinated populations where individuals are heterozygous and open-pollinated progeny expose combining ability and additive effects. In maize, brassicas, and alfalfa, gamete pool is shared through random mating, allowing allele frequencies to be altered gradually without immediate fixation. Recurrent cycles involve selection of superior individuals based on phenotype or testcross performance, intercrossing selected individuals in isolation to form new population for next cycle, increasing frequency of favorable addi

Ref: Hallauer AR & Darrah LL. Recurrent selection in maize; Sprague GF. Iowa St. J. Sci.

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Plant Breeding 3

A disadvantage of mass selection is:

Retaining many parental plants without progeny testing yields genetically heterogeneous population where individual plants differ in maturity, height, and quality, reducing market acceptability and certification standards. Seed lot lacks uniformity required for mechanized harvesting, DUS testing, and uniform product quality demanded by modern industry. Phenotypic selection confounds environment with genotype, so inferior heterozygous plants with favorable micro-environment may be selected, limiting genetic advance, especially for low heritability traits like yield where h² below 0.2. Without c

Ref: Allard RW. Chapter 8 – Limitations of mass selection. Poehlman 1995: uniformity issues

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Plant Breeding 3

A major advantage of mass selection is:

Because mass selection avoids intensive inbreeding and retains many selected parents bulked together, resulting population preserves substantial genetic diversity and heterozygosity buffer. Broad base of alleles confers buffering against diverse environmental stresses, disease races, and climatic fluctuations, granting stable performance across years and locations. Unlike pure lines that may fail in off-type environments, mass-selected varieties contain mixture of genotypes complementary in stress tolerance, maintaining yield stability due to population buffering mechanism described by Allard.

Ref: Harlan JR. Crops and Man – landrace adaptation; Ceccarelli S. Participatory breeding for wide adaptation

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Plant Breeding 3

Mass selection is more effective in:

Effectiveness hinges on population structure and genetic variance. Cross-pollinated species such as maize, pearl millet, and sunflower maintain high heterozygosity, large additive genetic variance, and expose extensive segregation each generation due to allogamy and random mating mediated by wind or insects. Mass selection in such highly variable base populations can shift allele frequencies rapidly because selected individuals outcross, recombining favorable alleles through pollen mixing. In self-pollinated wheat or rice, landraces already consist of homozygous pure lines; selecting best phen

Ref: Frey KJ. Iowa State – Mass selection in open-pollinated crops. Hallauer & Miranda Quantitative Genetics in Maize

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Plant Breeding 3

Mass selection is based primarily on:

Mass selection operates directly on visible phenotypic values of individual plants in a population. Breeder walks field, visually scores traits such as plant height, earliness, seed color, or disease-free appearance, and harvests seeds from best looking individuals to constitute next generation bulk. Underlying genotype is not tested through progeny rows, molecular markers, or combining ability assays. Success depends on high heritability where phenotype mirrors additive genetic value, correlation between observable character and breeding value, and low environmental noise. It is simplest bree

Ref: Gardner CO. Mass selection genetics; Acquaah Chapter 10 – Phenotypic selection basis

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Plant Breeding 3

Backcross breeding is commonly used for transfer of:

Backcrossing excels at transferring discrete, simply inherited traits governed by one or few genes where phenotype reliably identifies presence of donor allele. Disease resistance genes such as Sr2 for stem rust, Pi54 for blast, and Lr genes in wheat are typically dominant monogenic traits with major effect and high heritability, easily screened by inoculation in each backcross generation using pathogen isolates. Introgression of quantitative, polygenic traits like yield is inefficient because many loci would need simultaneous transfer, epistasis complicates selection, and linkage drag would i

Ref: Brar DS & Khush GS. Alien introgression in rice, Plant Molecular Biology 1997. Collard & Mackill 2008 MAS review

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