GREY STEM SPOT IS A NEW DISEASE OF SUNFLOWER IN RUSSIA
All-Russian Plant Protection Institute (VIZR), 189620 St Petersburg, Pushkin-6, Podbelsky 3, Russia
Background and objectives
Materials and methods
Results and conclusions
Phomopsis) helianthi, previously identified on sunflower in Yugoslavia. The fungus forms only beta conidia in its pycnidia. The perithecia with ascospores appear on infected residues after overwintering. In different climatic zones intensive emission of ascospores, as a rule, takes place in May-July. We have estimated that the temperature optimum for the pathogen in pure culture is about 25°C. It was proved in laboratory and field experiments that in Russia the primary source of sunflower grey stem spot infection is infected seeds. Sowing infected material spreads disease to damaging levels, reaching 15% and sometimes up to 40%. Ascospores, a second source of infection, promote the wider spread of the disease. Phomopsis affects sunflower more strongly in zones of Russia where growing period can have short rains and the average daily air temperature exceeds 20°C for 3 months. The biological damage threshold of the disease is 5% of totally affected plants. In Russia, with a wide variety of climatic conditions and crop agroecosystems, the Northern Caucasus, Central Chernozem Region, Middle Povol'zhe and South Ural are zones of the greatest risk for grey stem spot of sunflower.