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Ecology and Epidemiology

The Effect of Fallow Periods on Common Root Rot of Wheat in Rio Grande do Sul, Brazil. J. A. Diehl, Centro Nacional de Pesquisa de Trigo, EMBRAPA, C.P. 569, 99100, Passo Fundo, RS, Brazil; R. D. Tinline(2), R. A. Kochhann(3), P. J. Shipton(4), and A. D. Rovira(5). (2)Agriculture Canada Research Station, Saskatoon, Saskatchewan, Canada S7N 0X2; (3)Centro Nacional de Pesquisa de Trigo, EMBRAPA, C. P. 569, 99100, Passo Fundo, RS, Brazil; (4)North of Scotland College of Agriculture, Aberdeen, AB9 1UD, Scotland; (5)C.S.I.R.O., Division of Soils, Glen Osmond, S.A. 5064, Australia. Phytopathology 72:1297-1301. Accepted for publication 2 January 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982.. DOI: 10.1094/Phyto-72-1297.

In 1979, the incidence and intensity of common root rot of wheat in 17 fields in Rio Grande do Sul, Brazil, increased during the season from 31 and 9%, respectively, at growth stage 8–9, to 82 and 47% at growth stage 11.1–11.3. Much less disease developed in fields that were fallow for 3 or 4 yr or not previously cropped to wheat than in those cropped annually or after 1 or 2 yr fallow. Near plant maturity, the incidence and intensity averaged 68 and 25% in the former and 98 and 72% in the latter fields. The estimated yield loss in these groups of fields averaged 9.1 and 23.1%, respectively. The dominant pathogen isolated from underground parts of infected plants was Cochliobolus sativus. The relative abundance of its conidia in the upper 3 cm of soil sampled when wheat was maturing averaged 264 spores per gram in fields cropped annually or after 1 or 2 yr fallow, compared to 114 spores per gram in fields cropped less frequently.