Survey of Digitaria species (“crabgrass”) in croplands of Rio Grande do Sul state (Brazil)

Abstract

In the American continent, Brazil is the country with the largest number of crabgrass species (Digitaria spp.). However, the distribution and predominance of these species across agricultural areas of Rio Grande do Sul state (RS) are not yet well known. We aimed to identify the Digitaria species occurring in rice and soybean crops in RS and assess their representativeness in relation to the associated crop type. For that, samples of crabgrass populations were collected in soybean and irrigated rice croplands along different RS regions. We visited 19 cities and, in each one, three croplands with three geo-referenced points were sampled, thus totalizing 169 accesses. For the morphological analysis, voucher specimens were made with samples collected from all accesses. Crabgrass populations collected in RS croplands belong to six species: D. aequiglumis (Hack. & Arech.) Parodi., D. bicornis (Lam.) Roem. & Schult., D. ciliaris (Retz.) Koeler, D. eriostachya Mez., D. sanguinalis (L.) Scop., and D. ternata (A. Rich.) Stapf. Digitaria ciliaris is largely distributed, being the only species found in all visited cities and representing 73.1 and 98.4% of the accesses collected in rice and soybean croplands, respectively. Besides D. ciliaris, in downstate RS the species D. sanguinalis (19.4%), D. aequiglumis (3.7%), D. eriostachya (1.8%), and D. ternata (1.8%) were found in rice croplands, while D. bicornis (1.6%) was found in soybean ones.