Detection, transmission and control of Drechslera teres in barley seed.

Abstract

The objectives of the present work were to compare methods to detect Drechslera teres (Sacc.) Shoem. in barley seed, to analyze the potential role of seed borne D. teres as primary inoculum for net blotch epidemics, and to evaluate fungicide seed treatments. Results from the two types of assays used to detect D. teres, deep-freezing (Jorgensen, 1983) and selective medium for Cochliobolus sativus (Ito et Kurib.) (Reis 1983), differed significantly. In all cases, the selective medium was more sensitive and revealed a higher incidence of seed infection. Symptom and symptomless transmission of D. teres from seeds to plumules and coleoptiles of barley were quantified in experiments carried out under greenhouse conditions. The pathogen was detected in symptomless seedling coleoptile tips beginning at 7 days after sowing and reaching the maximum infection incidence on the fourth week. Number of conidia of D. teres on coleoptile tips was zero during the first and second weeks after sowing but it increased later to 1094 conidia/100 coleoptiles at the fifth week. Transmission efficiency of D. teres from seed to coleoptile tips in symptomless seedlings was 21.7%. Passsage of the pathogen, based on symptoms to plumule was 9%. The seed treatment studies indicated that the fungicides used in Argentina such as thiram, tebuconazole and flutriafol, were less effective against D. teres than iminoctadine, guazatine + triticonazole, iprodione + triticonazole, and iprodione + thiram.