Growth and spore production of Plectosporium tabacinum

Abstract

Plectosporium tabacinum (van Beyma) M.E. Palm, W. Gams, et Nirenberg has been evaluated as a bioherbicide for the control of Galium spurium L. (false cleavers). Little is known, however, about the specific culture and sporulation requirements of this fungus on standard agar media. In addition, information on submerged liquid culture spore production is not available. This information is important for the successful culture and further development of this fungus as a biocontrol agent. This study characterized mycelial growth and sporulation of Plectosporium tabacinum on 14 different standard agar media over a range of light regimes, pH, and temperatures. Conditions required for submerged liquid culture spore production and resulting weed control efficacy were also assessed. This included the effect of liquid culture medium and pH and the effect of carbon source, nitrogen source, carbon concentration, and carbon–nitrogen (C:N) ratio. Potato dextrose agar is the best agar medium for growth and spore production. On standard agar media, growth and spore production was not influenced by light regime. Medium pH did not affect mycelial growth and spore germination but the optimal pH for spore production was 7.0. The optimal temperature for the mycelial growth was between 22 and 25°C, but the optimal temperature for spore production was at either 20 or 30°C, depending upon the nutrient medium. Temperatures above 20°C were required to achieve greater than 90% spore germination. For submerged liquid culture spore production, Richard's solution (RS) is the best liquid medium for spore production. The optimal pH was 7.0 for RS but varied with culture media. Potassium nitrate and corn starch were the best nitrogen source and carbon source, respectively. A medium with a carbon concentration of 12.6 g/L and a C:N ratio of 7.5:1 is optimum for spore production and weed control efficacy.Key words: Plectosporium tabacinum, bioherbicide, mass production, fermentation, false cleavers, Galium spurium.