Verdure: The origins of Poa annua
Poa annua found its way into the scientific literature in the 1930s, but another 20 years would pass before its parental species were pinpointed.
Beth Guertal, Ph.D.
Since 1937, turfgrass scientists have been writing about Poa annua (aka annual meadowgrass or wintergrass). In that year, Bulletin No. 630 from the New Jersey Agricultural Experiment Station featured an article titled “Annual bluegrass (Poa annua L.), and its requirements for growth,” by the great turfgrass pioneers Howard Sprague, Ph.D., and Glenn Burton, Ph.D. This publication detailed the effects of fertilization, competing grass type and light on annual bluegrass performance. The authors simply discussed the grass as an existing species — one to be managed on a golf course — and no information was provided regarding the origin of the species.
That chore was left to T.G. Tutin, a professor at the University of Leicester, who, in 1957, published a key article on the species, “A contribution to the experimental taxonomy of Poa annua L.” Most subsequent work that examines Poa annua breeding or genetics references the Tutin paper, which discussed the wide variety of habitats in which Poa annua could be found, and how this habitat diversity led to variability in the species itself. Tutin’s research objective was to identify the parents of Poa annua by making viable hybrid crosses from the parental species.
Four different populations of annual bluegrass were obtained from areas in the United Kingdom near Leicester and Norfolk. These grasses had been observed for more than six years, and were selected because they looked quite different, and each also retained its distinct appearance. Plants were taken indoors and allowed to produce seed, which was then collected and planted. The plants showed great variability in the length of their life span (from less than one year to more than three years) and their time to achieve seedhead production.
Tutin knew that the chromosome number of Poa annua had been determined by scientists back in the late 1930s, and that Poa annua was closely related to six other Poa species. Of the other species, the two that were likely candidates for Poa parents were Poa infirma and Poa supina, because they had correct chromosome numbers for crossing, and because they were distributed worldwide. From the appearance of the plants, Tutin hypothesized that Poa annua was a hybrid of Poa infirma and Poa supina. The proof would be to show that such a hybrid cross could be made.
To do this, Tutin collected seed of Poa infirma from Jersey, U.K., and he obtained Poa supina from the Swiss Alps. Plants were grown and allowed to flower, and then he crossed them. Seven seeds were obtained from the Poa infirma × Poa supina crosses, and three germinated. These plants were sent to a botanical expert, who was not told of their origin, and they were keyed as Poa annua.
But how (and when) did Poa infirma meet up with Poa supina to become Poa annua? Because Poa supina is found in the mountains of central and northern Europe, and Poa infirma is found in arid Mediterranean regions, it was proposed that the two species got together as glaciers moved during the (relatively) warmer Quaternary ice age (about 2.5 million years ago), making Poa annua a species of relatively recent origin. Tutin also mentioned that the grass spread rapidly around the world, and that the cause of that rapid spread was Poa annua’s association with humankind.
Source: Tutin, T.G. 1957. A contribution to the experimental taxonomy of Poa annua L. Watsonia 4:1-10.
An excellent article that confirms some of Tutin’s work, and adds more information:
Mao, Q., and D.R. Huff. 2012. The evolutionary origin of Poa annua L. Crop Science 52:1910-1922.
Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the president-elect of the Crop Science Society of America. She is a 20-year member of GCSAA.