Integration of biocontrol, hot water dip and potassium silicate for the control of Penicillium digitatum (Green mould) on citrus fruit
Abraha Abraham, Mark Laing, J. Bower and Celeste Clark
Abstracts Book, 6th International Postharvest symposium, 8-12 April 2009, Antalya, Turkey. 256 pages.
2009
บทคัดย่อ
Synthetic fungicides have been widely used to control Penicillium digitatum Sacc., the causal agent of green mould of citrus. However, in many countries, postharvest fungicides are no longer effective, due to resistance. We have found some South African isolates of P. digitatum to be resistant to Imazalil®. Alternative measures to control the disease are necessary, such as biological control. Sixty yeast and 92 Bacillus isolates were screened for their antagonistic activity against P. digitatum. None of the yeasts or Bacillus isolates produced a curative action against P. digitatum on oranges. However, the yeast Isolate B13(Candida fermentati (Saito) Bai comb. nov.) provided excellent preventative control of P. digitatum, superior to all the Bacillus isolates, if it was applied to citrus fruit prior to artificial inoculation by P. digitatum. Yeast Isolate B13 reduced P. digitatum incidence to 2%, compared with 12% after treatment with Imazalil® in commercial packhouse trials. Electron microscopy showed that yeast Isolate B13 inhibited conidial germination of P. digitatum. For control of P. digitatum pre-harvest, trees were treated with potassium silicate for a full season (monthly or two monthly, per tree, 5 l x 1000 mg (l-1). Regular potassium silicate treatments resulted in a significant reduction in the level of P. digitatum infection on both navel and Valencia oranges. For the control of latent infections of inoculated Valencia oranges, hot water treatment at 56°C for 1 min provided the best control of the pathogen. The integrated treatment of citrus fruit with (1) the application of potassium silicate fertilization pre-harvest; (2) a hot water dip (56°C x 1 min); (3) and application of the yeast Isolate B13, combined to provide excellent control of P. digitatum in applied packhouse trials.