In biological taxonomy, race is an informalrank in the taxonomic hierarchy, below the level of subspecies. It has been used as a higher rank than strain, with several strains making up one race. Various definitions exist. Races may be genetically distinct populations of individuals within the same species, or they may be defined in other ways, e.g. geographically, or physiologically. Genetic isolation between races is not complete, but genetic differences may have accumulated that are not sufficient to separate species. The term is recognized by some, but not governed by any of the formal codes of biological nomenclature.
Other terms
In botany, the Latin wordsstirps and proles were traditionally used, and proles was recommended in the first botanical Code of Nomenclature, published in 1868.
Definitional approaches
Races are defined according to any identifiable characteristic, including gene frequencies. "Race differences are relative, not absolute". Adaptive differences that distinguish races can accumulate even with substantial gene flow and clinal habitat variation. Hybrid zones between races are semi-permeable barriers to gene flow, see for example the chromosome races of the Auckland tree wētā. The term race has also historically been used in relation to domesticated animals, as another term for breed; this usage survives in combining form, in the term landrace, also applied to domesticated plants. The cognatewords for race in many languages may convey meanings the English word does not, and are frequently used in the sense of 'domestic breed'.
If the races are sufficiently different or if they have been tested to show little genetic connection regardless of phenotype, two or more groups/races can be identified as subspecies or, and given a name. Ernst Mayr wrote that a subspecies can be "a that is sufficiently different taxonomically to be worthy of a separate name." Study of populations preliminarily labelled races may sometimes lead to classification of a new species. For example, in 2008, two populations of the brown planthopper in the Philippines, one adapted to feeding on rice, and another on Leersia hexandra grass, were reclassified from races into "two distinct, but very closely allied, sympatric species", based on poor survival rate when given the opposite food source, barriers to hybridization between the populations, uniform preference for mating between members of the same population, differences in mating sounds, oviposition variances, and other distinguishable characteristics. For pathogenic bacteria adapted to particular hosts, races can be formally named as pathovars. For parasitic organisms governed by the International Code of Nomenclature for algae, fungi, and plants, the term forma specialis is used.
Classification of fungal microbes into races is done frequently in mycology, the study of fungi, and especially in phytopathology, the study of plant diseases, which are often fungal. The term "physiologic race" was recommended for use over "biologic form" at the International Botanical Congress of 1935. Although historically the term has been used inconsistently by plant pathologists, the modern trend is to use race to refer to "groups of host genotypes permitting characterization of virulence". Commercial Cucumis melo production, for example, has been engaged in a biological "arms race", since 1925, against cucurbit powdery mildew, caused by successively arising races of Podosphaera xanthii fungus, with new cultivars of melons being developed for resistance to these pathogens. A 2004 literature review of this issue concluded that "race identification is important for basic research and is especially important for the commercial seed industry", but was seen as having little utility in horticulture for choosing specific cultivars, because of the rapidity with which the localpathogen population can change geographically, seasonally, and by host plant. Classification of fungal races can be difficult because host plants' responses to particular populations of fungi can be affected by humidity, light, temperature, and other environmental factors; different host plants may not all respond to particular fungal populations or vice versa; and identification of genetic differences between populations thought to form distinct fungal races can be elusive.
