Isolation and in vivo screening of yeast and Bacillus antagonists for the control of Penicillium digitatum of citrus fruit

A total of 60 yeast and 92 Bacillus isolates were isolated from the fruit surface of papaya and several varieties of citrus from various orchards in South Africa, and screened for antagonism to Penicillium digitatum. Ten yeast and 10 Bacillus isolates reduced the surface area of visible P. digitatum growth ⩾50%, when applied 3 h before inoculation with the pathogen. Two yeast isolates (B13 and Grape), when applied 48 h prior to inoculation with P. digitatum, prevented decay of navel oranges and lemons, and ⩽5% incidence on Valencia oranges, compared with an untreated control that had ⩾50% incidence of infection. The application of isolates to lemons and Valencia oranges did not produce a curative action against P. digitatum when applied 3 h postinfection. The yeast isolates B13 and Grape were superior to all the Bacillus isolates, and provided excellent control of P. digitatum, when applied to citrus fruit prior to artificial inoculation by P. digitatum.