Review of congruence between global crop wild relative hotspots and centres of crop origin/diversity

Genet Resour Crop Evol https://doi.org/10.1007/s10722-021-01114-7 (0123456789().,-volV) ( 01234567 89().,-volV) REVIEW Review of congruence between global crop wild relative hotspots and centres of crop origin/diversity Nigel Maxted . Holly Vincent Received: 22 October 2020 / Accepted: 11 January 2021 Ó The Author(s) 2021 Abstract Crop wild relatives (CWR) are important sources of adaptive diversity for plant breeding programmes. This paper aims to investigate the extent to which the centres of crop origin/diversity are congruent with areas of high CWR diversity. We established the predicted potential CWR distributions for 1,425 CWR species related to 167 crops using 334,527 known distribution locations and generated a global CWR hotspot map. This was then compared to the centres of origin/diversity proposed by Vavilov (amended by Hawkes); Zeven and Zhukovsky’s mega gene centres, Harlan’s centres and non-centres of crop domestication; and crop domestication areas identified using current archaeological evidence proposed by Purugganan and Fuller. Greatest congruence between the global CWR hotspots and other concepts was found with the concept proposed by Vavilov and amended by Hawkes, but there remained significant differences between the CWR hotspots and Vavilov’s concept. This paper concludes that all four centre concepts reviewed have some overlap with CWR diversity but that Vavilov’s original concept has the closest geographic coincidence with CWR hotspots. With the benefit of significant additional global datasets to those used by Vavilov, we were able to suggest amendments to his concept, adding further N. Maxted (&)
H. Vincent School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK e-mail: centres based on CWR hotspots in west and east USA, West Africa, South-east Brazil and Australia. As a result of this study more precise targeting of CWR and crop landrace can be implemented in future, aiding global food and nutritional security. Keywords Agrobiodiversity
Centre of origin
Conservation
Crop wild relative
Genetic diversity
N.I. vavilov Introduction The transition from hunter-gatherer communities to agriculture first occurred some 10,000 years ago in several independent localities globally (Diamond 2002). Since the mid-nineteenth century scholars have attempted to pinpoint the locations where crops were domesticated, however, the exact whereabouts have proven elusive. Alphonse de Candolle was one of the first crop geographers who wrote extensively on the geography and origins of individual cultivated plant species, using historical data, presence of related wild species, variation patterns and archaeological information to determine broad areas of plant domestication (Candolle 1855). He combined his research on individual crop species to determine three separate centres of plant crop domestication, the Fertile Crescent, Mesoamerica and South East Asia, however 123 Genet Resour Crop Evol innovative his approach, the data available to him undoubtedly restricted his conclusions. Charles Darwin also investigated the variability of domesticated species versus their wild counterparts, although he focused primarily on the processes of inheritance and selection of traits under artificial human direction (Darwin 1868), he concluded it would be extremely difficult to discover the exact centres of domestication. The person most often associated with centres of crop origin or diversity today is Nikolai Ivanovich Vavilov, the Russian geneticist and father of plant genetic resources conservation and utilisation. Inspired by the work of de Candolle and Darwin, Vavilov attempted to define global crop domestication areas more precisely and published his theory on the centres of crop origins/diversity based upon a study of crop and wild relative literature, geography and nomenclature (Vavilov 1926). Vavilov initially identified five centres of plant crop origination using a so called differential phytogeographical approach which involved the following steps: (a) delimitation of plants into Linnean species and morphological units; (b) determination of the geographical distribution of these plants in the past; (c) determination of the inherited variation of characteristics of each plant species; (d) identification of geographical areas where there is a wide range of inherited variation in crop varieties and multiple wild relative species presence (Vavilov 1992). The five centres he initially identified were geographically broad and encompassed the Mediterranean, Central and South America, the Far East and South-western Asia. The identification of these centres of crop origins/diversity formed the foundation and rationale for many of Vavilov’s collecting missions. The accumulation of information from a wide study of global plant diversity, collecting missions and an increase in archaeological findings helped Vavilov to refine his centres of crop origin and diversity theory, and increase the number of centres from five to eight, including several sub-regions, each with a wealth of crop landrace and CWR diversity (Vavilov 1935). These areas included: the Chinese centre; the Indian centre; the Indo-Malayan sub-centre; the Inner Asiatic centre; the Asia Minor centre; the Mediterranean centre; the Ethiopian centre; the Central American centre; The Peruvian-Ecuadorian-Bolivian centre with sub-centres in both Chiloe, Chile and around the Brazil-Paraguay border. Vavilov once again modified his theory in 1940 by combining the Inner Asia and 123 Asia Minor centres, whilst introducing a new subcentre around Bogota, Colombia (Vavilov 1940); the Brazil-Paraguay sub-centre was omitted from this publication for unknown reasons, although Hawkes (1983) suggests it was overlooked accidently during a period of severe personal and professional struggle for Vavilov and should be reinstated. Further, Loskutov (2020) recently pointed out a nuance that had been widely missed by those reading Vavilov in translation, that in his 1927 paper for the Fifth International Genetic Congress in Berlin, ‘‘Geographische Zentren unserer Kulturpflanzen’’ (geographical centres of our cultivated plants) Vavilov distinguishes between traditional agriculture stocks found in the centres of genetic diversity and wild or weedy relatives of crop species found in gene centres or centres of origin (Vavilov 1928). After Vavilov’s premature death, his colleagues continued to develop his centres of crop origin/diversity concept and even today, scientists are still investigating the originations of individual crops. P.M. Zhukovsky, a colleague of Vavilov’s, sought to delimit areas of crop diversity and areas of wild species diversity separately (Zhukovsky 1965). He defined 12 broad areas termed megagene centres which contained a wealth of domesticated plant diversity (Zeven and Zhukovsky 1975). The megacentres were based upon Vavilov’s centres of origin theory and showed areas of high crop an (...truncated)