CONTROL OF SUNFLOWER DOWNY MILDEW ( PLASMOPARA HALSTEDII) WITH ANTAGONISTIC FUNGI

摘要

Downy mildew of sunflower (Helianthus annuus L), one of the most destructive diseases for this crop, is caused by Plasmopora halstedii (Farl.) Berl. and de Toni. Biological control is a promising approach for managing this disease; however, use of biocontrol agents in the same environmental niche as that of the pathogen is very important for success with this control strategy. Isolates of AS3 (non-aflatoxigenic Aspergillus flavus Link), TRIC7 and TRIC8 (Trichoderma harzianum Rifai) from soils (Tekirdag/Turkey), which controlled black mould disease in onion, and a commercial mycorrhiza preparation (MycoZoom-inducer plant growth) were tested for their effects on plant growth and disease incidence caused by P. halstedii on sunflower in this study.Sunflower seeds surface-sterilized with sodium hypochlorite (3%) for 1 min were treated with a conidia suspension (lxlO7 conidia/ml) of potential antagonists by shaking the seeds for 1 hour. A solution of My-coZoom was applied to seeds at the recommendeddosage and duration for agitation by the manufacturer (0.075 g/100 ml water and 1 hour). In evaluation tests of disease incidence, seeds were also exposed to agitation in conidia suspension of antagonists for 6 hours. During pathogen inoculation, the seeds treated with potential antagonists and MycoZoom were germinated on sterile germination paper at 25 °C. Three-day old seedlings were immersed in a zoosporangia suspension (1x10s zoosporangia/ml) of a virulent isolate (race 771) for 7 hours at 15-16 °C in dark. The seedlings were then planted in pots filled with peat: sand: soil: vermiculite: perlite (2:2:2:1:1) and were grown under controlled greenhouse conditions at 25 °C and 12 h photoperiod regime. One week after planting, plants were put intoa growth chamber at 17 °C and relative humidity of 95% in dark until cotyledon leaves of control plants were covered by zoosporangia. Disease incidence was determined as the number of plants with infected cotyledon leaves. All treatments induced the germination of seeds. Among them TRIC8 had the highest values for plant height, leaf width, length and leaf number. TRIC7 and AS3 followed it for leaf length and number. Short-term seed treatments controlled the disease at very low rates (<50%). However, long-term seed treatments with TRIC8, TRIC7 and AS3 were found effective at rates of 72.22, 65.55 and 51.11%, respectively. This study suggests these antagonists, which have no negative effect on plant growth can be tested for downy mildew control under field conditions.