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#breeding drawbacks

2 public questions tagged with this topic.

Plant Breeding 3

A limitation of clonal selection is:

Vegetatively propagated clones maintain narrow genetic base because all individuals within variety are genetically identical, carrying same chromosomes and alleles fixed by mitosis. Uniformity, while commercially desirable, creates vulnerability to evolving pathogen races, insect biotypes, and environmental extremes, leading to boom-bust cycles such as potato late blight in Ireland. Lack of sexual recombination restricts generation of new variability for adaptation, slows response to climate change, and limited buffering through genotype mixtures reduces ecological resilience. Seed storage and exchange are challenging for perishable vegetative propagules compared to orthodox seeds, complicating germplasm conservation and international distribution. Maintenance of disease-free stock requires costly tissue culture, thermotherapy, and certification programs, increasing production cost and requiring infrastructure. Additionally, many clonal crops suffer inbreeding depression and self-incompatibility, hindering hybridization for improvement, so breeding cycle is lengthy and depends on rare flowering and complex crossing designs to create novel variation. Genetic erosion due to deployment of single clone over vast areas reduces allelic diversity available for future breeding; gene banks therefore conserve clonal germplasm through field collections, in vitro slow growth storage, and cryopreservation of shoot tips to preserve evolutionary potential and mitigate vulnerability risks.

Ref: Esnault et al. Challenges of clonal crops; FAO report on clonal genetic vulnerability

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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 controlled pollination, pollen from undesirable off-types contaminates selected individuals, diluting gains through random mating with poor types. Variability also complicates distinctness, uniformity, stability testing for variety release. In self-pollinated crops, mass selection quickly plateaus, and response to selection declines after few cycles because additive variance exhausts without deliberate recombination. Hence breeders shift to pedigree or progeny-based methods for uniformity and precise fixation. Statistical approaches like family-based selection, half-sib progeny testing, and use of augmented designs can partially overcome uniformity issues by incorporating pedigree information and spatial correction, but add complexity and cost compared to simple phenotypic mass selection in pure line crops.

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

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