Biodiversity is continually declining, according to global biodiversity indicators (Butchart et al. in Science 328:1164–1168, 2010 ). Population trends, habitat extent, habitat condition, and composition of species communities—indicators of the state of diversity—are declining, while at the same time pressures on biodiversity posed by resource consumption, invasive alien species, pollution, overexploitation, and climate change are increasing. The rate of current loss of species is reported to be 100–1000 times the natural background rate (Chivian and Berstein in Sustaining life on earth. How human health depends on biodiversity. Oxford University Press, New York, 2008 , Chivian and Berstein in How our health depends on biodiversity. Center for Health and the global environment. Harvard medical school, Boston, 2010 ; Pimm et al. in Science 344, 2014 ). Dramatic though that figure is, it underestimates the full loss of diversity because it ignores loss at both genetic and population level (Myers in Seeds and sovereignty. The use and control of plant genetic resources. Duke University Press, Durham, 1988 ; Mendenhall et al. in Biol Conserv 151:32–34, 2012). One of the first publications alerting the world about the losses of genetic diversity within species, later termed “genetic erosion,” was published in 1914 (Baur in Die Bedeutung der primitiven Kulturrassen und der wilden Verwandten unserer Kulturpflanzen fuer die Pflanzenzuechtung; Jahrbuch Deutsche Landwirt, 1914). The first concern about loss of diversity regarded agriculturally important species, as these are of direct and daily use to people. One hundred years later, genetic erosion is addressed at the global level in international agendas that set targets and propose actions to reduce the loss of genetic diversity, such as the Global Plan of Action (GPA) for Plant Genetic Resources for Food and Agriculture (PGRFA) of the FAO Commission on Genetic Resources for Food and Agriculture (CGRFA) and the Aichi biodiversity targets of the Convention on Biodiversity (CBD). The fact that genetic erosion today is addressed at global level implies that the crucial importance of genetic diversity for sustaining life on earth has been recognized. Strategies and actions to reduce the ongoing loss of genetic diversity are now in place. However, these measures have been found only partially successful as only few significant reductions in rates of decline were observed (Butchart et al. in Science 328:1164–1168, 2010 ), and global estimates of the extent of genetic erosion are still lacking. This chapter focuses on the importance of genetic diversity in PGRFA, how diversity of PGRFA is affected by genetic erosion, development of activities undertaken by international bodies to address genetic erosion, options to improve knowledge about the underlying processes that lead to genetic erosion, and the need for systematic monitoring of genetic diversity to better safeguard, conserve, and use PGRFA.
Ahuja, M. R., & Mohan Jain, S. (2015). Genetic Diversity and Erosion in Plants: Case Histories (Vol. 2, pp. 1–33).