Abstract
Seed-borne infection by Bipolaris sorokiniana decreased the percentage germination of barley seeds and the emergence of seedlings. Infection levels were higher in non-germinated than in germinated seeds. Seed treatment with organomercurial fungicide or imazalil improved the percentage emergence but a low number of diseased seedlings still remained in the crops. The fungus caused a reduction in grain yields in most experiments and also decreased their value as sowing seed, if the weather conditions were favourable for compute disease expression. Yield losses in greenhouse experiments varied from 7.2 to 38.5 % and in the field from 5 to 11 %, and showed a strong correlation with the infection levels in the seed stocks. Higher losses were associated with the six-row cultivars. Organomercury seed treatment resulted in a slight but in significant increase in yields but it was able to prevent an occurrence of secondary infection in the crop resulting in a lower seed infection levels of the grain. In field experiments in Inari (69° N.L.) seed-borne inoculum could be demonstrated clearly to be the only source of a severe disease outbreak. The inoculum remaining in the soil was capable of initiating soil-borne infection of barley seedlings during the following two growing seasons.
Highlights
IntroductionBipolaris sorokiniana (Sacc. ex Sorok.) Shoem. (syn. Helminthosporium sativum Pamm., King & Bakke), perfect state Cochliobolus sativus (Ito & Kurib.) Dastur has been recently reported to be increasingly common in commercial barley seed stocks in Present address: Agricultural Research Centre Department of Plant Pathology SF-31600 JOKIOINEN, FinlandNorth Western Europe (de Tempe 1964, Jorgensen 1974, Hewett 1975, Olofsson 1976, Kurppa 1984)
Seed stocks used for sowing in the experiments originated from a field experiment at Viikki (Kurppa 1985 b.), or were selected from commercial stocks examined at State Seed Testing Institute
The seed-borne inoculum of Bipolaris sorokiniana is unquestionably of great importance in initiating root rot and foliar diseases on barley grown in cool and temperate regions with relatively high rain fall during growing seasons. This significance is supported by the lifecycle of the fungus as well as by the high incidences of seed infection on barley reported by de Tempe (1964), Jorgensen (1974), Whittle (1977) and Kurppa (1984)
Summary
Bipolaris sorokiniana (Sacc. ex Sorok.) Shoem. (syn. Helminthosporium sativum Pamm., King & Bakke), perfect state Cochliobolus sativus (Ito & Kurib.) Dastur has been recently reported to be increasingly common in commercial barley seed stocks in Present address: Agricultural Research Centre Department of Plant Pathology SF-31600 JOKIOINEN, FinlandNorth Western Europe (de Tempe 1964, Jorgensen 1974, Hewett 1975, Olofsson 1976, Kurppa 1984). Helminthosporium sativum Pamm., King & Bakke), perfect state Cochliobolus sativus (Ito & Kurib.) Dastur has been recently reported to be increasingly common in commercial barley seed stocks in. Estimates concerning its economic importance have been variable but the latest information assumes losses in yield of up to 15 % due to a high level of seed infection (Whittle & Richardson 1978). Diseased plants from infected seeds have been found serving as important sources for spore liberation during later developmental stages of the crop, and their residues remain. Index words: Bipolaris sorokiniana, Helminthosporium sativum, Cochliobolus salivus, common root rot, kernel blight objects for further sporulation (Chinn 1977, Reis & Wunsche 1984). Seed treatment with organomercurial or systemic fungicides (Hewett 1975, Chinn 1978, Whittle & Richardson 1978) has resulted in satisfactory control of the disease
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