HR ETEBARIAN¹, ES SCOTT² and T WICKS ³

¹Abourayhan Institute of Tehran University, Tehran, Iran; ²Department of Crop Protection, University of Adelaide, Australia; ³South Australian Research and Development Institute, South Australia

Background and objectives
The antagonistic activities of members of the genus Trichoderma have been extensively studied against plant pathogens. The objective of this investigation was to determine the potential of using Trichoderma virens and Trichoderma harzianum 739 isolate (Trichodex 25% powder) for biocontrol of Phytophthora erythroseptica. Protection from wilting of potato and pink rot of potato tuber were tested in glasshouse and laboratory.

Materials and methods
One isolate of T. virens which was isolated from Pen Field Garden South Australia and T. harzianum T39 isolate (Trichodex 25% powder) were evaluated for their potential for control of pink rot. Four isolates of P. erythroseptica, namely C2209, C2211, C2249 and C2252, were used in this study. The dual culture [1] and cellophan overlay techniques were used for antagonistic activities of Trichoderma species in culture media [2].

Glasshouse studies were performed to test the ability of T. virens and Trichodex to control the incidence and severity of pink rot. Potato tuber cultivars of Pontiac and Russeti burbank were surface sterilized and planted in 20 cm plastic pots, one tuber in each pot. The pots contained pasteurized soil infested with P. erythroseptica. Colonized rolled oat with T. virens or Trichodex were incorporated to soil 1 day after pathogen inoculation. Treatments were aranged in a split plot design with 4 replications. Potato cultivars were main plots and Trichoderma treatments were sub-plots. Percentages of inhibition of radial growth which were determined in laboratory and percentage of survival plants 45 days after planting were subjected to an arc sine square root transformation; data on severity and weight of tuber at terminal of experiment were analysed directly. Analysis of variance was performed and means were separated using Duncan's multiple range test.

Results and conclusions
T. virens proved more antagonist than T. harzianum in culture. Treatments with pathogen and antagonist, or combinations of Trichodex and T. virens with pathogen, reduced disease severity in shoots and roots of potatoes. The potato yield of pots treated with P. erythroseptica+T. virens (12.88 g) was significantly greater than pathogen control (2.14 g) and healthy control (6.57 g). Treatments of pots with antagonist increased the yield of potato.