Yes, we have some undesirable consequences

While plant breeding has brought about numerous benefits, it is important to acknowledge that there can be some undesirable consequences associated with this practice. Here are a few examples:

Loss of Genetic Diversity: Intensive plant breeding efforts often focus on a limited number of high-yielding or desirable traits, leading to the selection and propagation of a small number of elite varieties. This can result in a loss of genetic diversity within crop populations. Reduced genetic diversity can make crops more vulnerable to diseases, pests, and environmental changes, potentially leading to crop failures and reduced resilience in the long run.

Genetic Erosion: The widespread adoption of a few high-yielding varieties can result in the displacement and abandonment of traditional or locally adapted varieties. This process, known as genetic erosion, can lead to the loss of unique traits and genetic resources that may be valuable for future breeding programs. It can also disrupt traditional farming systems and cultural practices tied to specific crop varieties.

Narrow Genetic Base: Many of the improved varieties of a given crop have one or more parents (immediate or somewhat removed in the ancestry) in common with each other. For example, many semidwarf varieties of rice during seventies and eighties had IR8 or TN1 as one of their parents, while IR8 and TN1 are themselves related to each other by their common parent Dee-geo-woo-gen, the source of their semi dwarfing gene. Similarly, almost all the semidwarf wheat varieties have Rht1, Rht2 or both these genes for reduced height; these genes have been derived from a single wheat variety, Norin 10. Thus, the improved varieties of a crop species are becoming increasingly similar to each other due to the commonness of one or more parents in their ancestry. This has led to the narrowing down of the genetic base of these varieties. Genetic base refers to the genetic variability present among the cultivated varieties of a crop species. The narrow genetic base has created genetic vulnerability, which refers to the susceptibility of most of the cultivated varieties of a crop species to a disease, insect pest or some other stress due to a similarity in their genotypes.

Increased Reliance on Chemical Inputs: Some modern plant breeding efforts focus on developing crop varieties that are highly responsive to specific inputs, such as fertilizers or pesticides. While this can increase yields in the short term, it may lead to a greater dependence on chemical inputs. Excessive reliance on these inputs can have adverse environmental impacts, such as soil degradation, water pollution, and negative effects on non-target organisms.

Neglected Nutritional Quality: Plant breeding programs often prioritize traits such as yield, disease resistance, and uniformity, while nutritional quality may receive less attention. As a result, some modern crop varieties may have reduced nutritional content compared to traditional varieties. This can have implications for the nutritional value of diets that heavily rely on these crops.

Increased Susceptibility to Minor Diseases: Another problem has been generated by the almost exclusive emphasis on breeding for resistance to major diseases and insect pests. This has often resulted in an increased susceptibility to thus far minor diseases. As a result, these diseases have gained in importance and, in some cases, produced severe epidemics. A case in point is the epidemic caused by Botrytis cinerea (grey mold) in chickpea during 1980-81 and 1981-82 crop seasons in Punjab, Haryana and parts of U.P. and Bihar. Another example is the severe infection by Karnal bunt (Tilletia indica) on some wheat varieties, e.g., WL711. This problem is difficult to overcome since resource constraints may never permit a breeder to screen his material against all the diseases and pests of a crop species. We may probably have to, so to say, learn to live with this problem and tackle it as and when it arises.

Yield Plateau: A crop species' yield variability eventually reaches its limit, and breeding is unable to produce any more yield increases, causing the yield to plateau. Before the use of semi dwarfing genes, such plateaus in wheat and rice yields were noticeable, and they are now occurring once more. In these situations, the breeding populations must be exposed to new variability in order to break the plateau. More and more evidence points to the possibility that wild relatives of domesticated species may contain the "yield genes" needed to break yield plateaus. When crop yields reach a plateau, a novel breeding strategy may be helpful, such as the creation of hybrid rice varieties.

Unintended Environmental Consequences: Plant breeding can inadvertently lead to unintended environmental consequences. For example, the cultivation of certain high-yielding varieties may require increased irrigation or more intensive use of water resources, which can contribute to water scarcity or depletion. Additionally, the introduction of genetically modified crops may have potential ecological impacts, such as the unintended spread of transgenes to wild relatives or the development of resistant pest populations.

Socioeconomic Impacts: The adoption of new plant varieties can have socio-economic implications, particularly for small-scale farmers. While some farmers may benefit from increased yields and improved livelihoods, others may face challenges in accessing and affording new seeds or keeping up with changing market demands. This can contribute to inequalities and disparities within agricultural systems.

Reference: Principles of Plant Breeding (2022) - B D Singh