Key message Maximizing crop yield while at the same time minimizing crop failure for sustainable agriculture requires a better understanding of the impacts of plant breeding on crop genetic diversity. This review identifies knowledge gaps and shows the need for more research into genetic diversity changes under plant breeding. Abstract Modern plant breeding has made a profound impact on food production and will continue to play a vital role in world food security. For sustainable agriculture, a compromise should be sought between maximizing crop yield under changing climate and minimizing crop failure under unfavorable conditions. Such a compromise requires better understanding of the impacts of plant breeding on crop genetic diversity. Efforts have been made over the last three decades to assess crop genetic diversity using molecular marker technologies. However, these assessments have revealed some temporal diversity patterns that are largely inconsistent with our perception that modern plant breeding reduces crop genetic diversity. An attempt was made in this review to explain such discrepancies by examining empirical assessments of crop genetic diversity and theoretical investigations of genetic diversity changes over time under artificial selection. It was found that many crop genetic diversity assessments were not designed to assess diversity impacts from specific plant breeding programs, while others were experimentally inadequate and contained technical biases from the sampling of cultivars and genomes. Little attention has been paid to theoretical investigations on crop genetic diversity changes from plant breeding. A computer simulation of five simplified breeding schemes showed the substantial effects of plant breeding on the retention of heterozygosity over generations. It is clear that more efforts are needed to investigate crop genetic diversity in space and time under plant breeding to achieve sustainable crop production.

Climate change is a major environmental stress threatening biodiversity and human civilization. The best hope to secure staple food for humans and animal feed by future crop improvement depends on wild progenitors. We examined 10 wild emmer wheat ( Triticum dicoccoides Koern.) populations and 10 wild barley ( Hordeum spontaneum K. Koch) populations in Israel, sampling them in 1980 and again in 2008, and performed phenotypic and genotypic analyses on the collected samples. We witnessed the profound adaptive changes of these wild cereals in Israel over the last 28 y in flowering time and simple sequence repeat allelic turnover. The revealed evolutionary changes imply unrealized risks present in genetic resources for crop improvement and human food production.

Alfalfa (Medicago sativa L.) is an important legume forage crop. However, its genetic improvement for salt tolerance is challenging, as alfalfa’s response to salt stress is genetically and physiologically complex. A review was made to update the knowledge of morphological, physiological, biochemical, and genetic responses of alfalfa plants to salt stress, and to discuss the potential of applying modern plant technologies to enhance alfalfa salt-resistant breeding, including genomic selection, RNA-Seq analysis, and cutting-edge Synchrotron beamlines. It is clear that alfalfa salt tolerance can be better characterized, genes conditioning salt tolerance be identified, and new marker-based tools be developed to accelerate alfalfa breeding for salt tolerance.

The realized dangers of genetic erosion in plant genetic resources have prompted political and scientific movements around the world to conserve plant genetic resources over the last 50 yr. More than 7 million plant germplasm accessions are currently conserved in 1750 genebanks worldwide, and about two million accessions are estimated to be unique. The International Treaty on Plant Genetic Resources for Food and Agriculture was established to conserve and utilize these plant genetic resources. However, long‐term conservation of such a large volume of diverse germplasm remains a challenging mission. Many critical issues affecting genebank sustainability have emerged. Of note are the vulnerability of genebanks and the risk of within‐genebank genetic erosion through genetic drift and viability selection. Here, we review the overall conservation efforts over the last 50 yr, analyze the critical issues in genebanks, and identify the elements that threaten long‐term germplasm conservation. Measures are explored with the hope to mitigate variable threats for genebank sustainability and to secure a food supply for humanity for generations to come.