Detection, transmission and control of Drechslera teres in barley seed

The objectives of the present work were to compare methods to detect Drechs lera 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 ev aluate fungicide seed treatments. Results from the two types of assays used to detect D. teres, deep freezing (Jorgensen, 1983) and selective medium f or Cochliobolus sativus (Ito et Kurib.) (Reis 1983), differed significantly . In all cases, the selective medium was more sensitive and revealed a high er incidence of seed infection. Symptom and symptomless transmission of D. teres from seeds to plumules and coleoptiles of barley were quantified in e xperiments carried out under greenhouse conditions. The pathogen was detect ed 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 secon d weeks after sowing but it increased later to 1094 conidia/100 coleoptiles at the fifth week. Transmission efficiency of D. teres from seed to coleop tile tips in symptomless seedlings was 21.7%. Passsage of the pathogen, bas ed on symptoms to plumule was 9%. The seed treatment studies indicated that the fungicides used in Argentina such as thiram, tebuconazole and flutriaf ol, were less effective against D. teres than iminoctadine, guazatine + tri ticonazole, iprodione + triticonazole, and iprodione + thiram.