agronomy Review Potential of Wild Relatives of Wheat: Ideal Genetic Resources for Future Breeding Programs Alireza Pour-Aboughadareh 1,* , Farzad Kianersi 2, Peter Poczai 3,* and Hoda Moradkhani 4 1 Seed and Plant Improvement Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj P.O. Box 3183964653, Iran 2 Department of Agronomy and Plant Breeding, Faculty of Agriculture, Bu-Ali Sina University, Hamedan 65178-38695, Iran; [email protected] 3 Botany Unit, Finnish Museum of Natural History, University of Helsinki, P.O. Box 7, FI-00014 Helsinki, Finland 4 Department of Agronomy and Plant Breeding, Agricultural College, University of Tehran, Karaj 31587-77871, Iran; [email protected] * Correspondence: [email protected] (A.P.-A.); peter.poczai@helsinki.fi (P.P.) Abstract: Among cereal crops, wheat has been identified as a major source for human food consump- tion. Wheat breeders require access to new genetic diversity resources to satisfy the demands of a growing human population for more food with a high quality that can be produced in variable envi- ronmental conditions. The close relatives of domesticated wheats represent an ideal gene pool for the use of breeders. The genera Aegilops and Triticum are known as the main gene pool of domesticated wheat, including numerous species with different and interesting genomic constitutions. According to the literature, each wild relative harbors useful alleles which can induce resistance to various environmental stresses. Furthermore, progress in genetic and biotechnology sciences has provided accurate information regarding the phylogenetic relationships among species, which consequently opened avenues to reconsider the potential of each wild relative and to provide a context for how we can employ them in future breeding programs. In the present review, we have sought to represent Citation: Pour-Aboughadareh, A.; the level of genetic diversity among the wild relatives of wheat, as well as the breeding potential of Kianersi, F.; Poczai, P.; Moradkhani, each wild species that can be used in wheat-breeding programs. H. Potential of Wild Relatives of Wheat: Ideal Genetic Resources for Keywords: wheat germplasm; Aegilops-Triticum; next generation sequencing; genetic diversity; Future Breeding Programs. Agronomy breeding program; environmental stresses 2021, 11, 1656. https://doi.org/ 10.3390/agronomy11081656 Received: 22 July 2021 1. Introduction Accepted: 18 August 2021 Published: 19 August 2021 Climate change and subsequent increasing abiotic and biotic stresses threaten food security globally, as they can hinder the potential yield performance, increase the number Publisher’s Note: MDPI stays neutral of pests and diseases generations, alter synchrony between plants and pests, increase risk with regard to jurisdictional claims in of invasion by migratory pests, increase incidence of insect-transmitted plant diseases, and published maps and institutional affil- reduce the effectiveness of biological control, especially for natural enemies [1,2]. One iations. worthwhile strategy for increasing crop productivity and stability that may be applied in a wide range of environments is ‘crop genetic improvement’ through the introgression of novel genes, QTLs, and even novel alleles from wild relatives to local or modern varieties [3]. As such, breeders must simultaneously both improve the genetic background and reduce the impact of environmental stresses on the grain production. Among cereal Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. crops, wheat has a significant role in supplying the 20% of all calories consumed by people This article is an open access article worldwide. Due to climate change, mainly caused by biotic and abiotic stresses, the distributed under the terms and demand for wheat bread wheat is predicted to increase dramatically in the future as the conditions of the Creative Commons global human population increases. Hence, wheat production will have a vital bearing on Attribution (CC BY) license (https:// food security in the coming decades [4]. creativecommons.org/licenses/by/ After the green revolution, numerous bread wheat varieties were released by 4.0/). agronomists and breeders in different parts of the world. Although this task helped to Agronomy 2021, 11, 1656. https://doi.org/10.3390/agronomy11081656 https://www.mdpi.com/journal/agronomy Agronomy 2021, 11, x 2 of 31 Agronomy 2021, 11, 1656 After the green revolution, numerous bread wheat varieties were released2 of 31by agronomists and breeders in different parts of the world. Although this task helped to increase the breeding population of wheat, the genetic basis of the wheat was narrowed through the shearing of the breeding lines and various breeding cycles, which in turn increase the breeding population of wheat, the genetic basis of the wheat was narrowed throughdecreased the species shearing variability. of the breeding Wild relatives lines andof wheat various offer breeding great possibilities cycles, which for breeders in turn decreasedto develop species new variability.varieties with Wild relativesa more ofappropriate wheat offer genetic great possibilities background for breedersfor various to developagricultural new varietiessystems with[5]. Hence, a more appropriatethe use of an genetic ancestors’ background gene forpool various is an agriculturalappropriate systemsstrategy [5for]. developing Hence, the usenew ofsuperior an ancestors’ bread wheat gene pool cultivars. is an appropriateWheat wild strategyrelatives forare developingclosely related new species superior that bread have wheata long cultivars.history in Wheatwheat breeding, wild relatives mostly are for closely abiotic related stress speciestolerance. that These have aspecies long history are identified in wheat as breeding, the critical mostly resources for abiotic required stress tolerance.to sustain Theseglobal speciesfood supply are identified [4]. The as tribe the critical Triticeae resources, which requiredis part of to the sustain Pooideae global subfamily food supply of the [4]. grass The tribefamilyTriticeae Poaceae, which, includes is part the of thegeneraPooideae Triticumsubfamily and ofAegilops the grass L. familyThese Poaceaerelatives, includes provide theimportant genera Triticum gene poolsand forAegilops wheat-breedingL. These relatives programs, provide since important they are connected gene pools to for the wheat- most breedingimportant programs, agricultural since crop, they Triticum are connected aestivum L. to [6]. the In most this importantreview, we agriculturalhave summarized crop, Triticumthe phylogenetic aestivum L. relationships [6]. In this review, among we wild have wh summarizedeats and their the phylogenetic potential applications relationships in amongwheat wildbreeding. wheats and their potential applications in wheat breeding. 2.2. TheThe TrendTrend of of Bread-Wheat Bread-Wheat Evolution Evolution WheatWheat waswas domesticateddomesticated fromfrom itsits wildwild relativesrelatives duringduringthe the pre-pottery pre-potteryNeolithic Neolithic (PPN)(PPN) period period nearly nearly 12,000 12,000 years years ago, inago, the in Middle the Middle East’s Fertile East’s Crescent, Fertile Crescent, which included which severalincluded wide several ranges wide of geographicalranges of geographical zones from zones Lebanon, from Israel,Lebanon, Jordan, Israel, and Jordan, Syria viaand southeastSyria via Turkey, southeast as well Turkey, as into as Iraq well and as western into Iraq Iran and via thewestern Tigris andIran Euphratesvia the Tigris rivers and [7] (FigureEuphrates1 ). Researchrivers [7] conducted(Figure 1). Research by Weide cond et al.ucted [8] reported by Weide that et theal. [8] first reported hybridization that the betweenfirst hybridization wild wheats between occurred wild in thewheats west occurred of Iran. in the west of Iran. Figure 1. The position of the Fertile Crescent (FC) in the Middle East and world. This region Figure 1. The position of the Fertile Crescent (FC) in the Middle East and world. This region embraces embraces a wide geographical range between the Persian Gulf and the eastern coast of the a wide geographical range between the Persian Gulf and the eastern coast of the Mediterranean Sea Mediterranean Sea (highlighted in green). (highlighted in green). Triticum and Aegilops are two key genera which include various wild wheat with Triticum and Aegilops are two key genera which include various wild wheat with differentdifferent genomicgenomic constitutionsconstitutions andand whichwhich havehaveplayed played directdirector or indirect indirect roles roles in in wheat wheat domestication. Table1 shows some of the key articles that have denoted how wheat evolution occurred. Agronomy 2021, 11, 1656 3 of 31 Table 1. Some key articles regarding the trend of wheat evolution. Article Reference Evolution in the genus Triticum and the origin of cultivated wheat [9] Genome symbols and plasma types in the wheat group [10] Cytogenetics of wheat and its close wild relatives-Triticum and Aegilops [11] Genome symbols in the Triticeae (Poaceae) [12] Phylogenetic relationships of Triticum and Aegilops and evidence for the [13] origin of the A, B, and D genomes of common wheat (Triticum aestivum) Evolution of domesticated bread wheat [14] Wheat domestication: Lessons for the future [15] Distinguishing wild and domestic wheat and barley spikelets from early [16] Holocene sites in the Near East Emergence of agriculture in the