Formulation development of the biocontrol agent Bacillus subtilis strain CPA-8 by spray-drying

Abstract

Aims: To prepare commercially acceptable formulations of Bacillus subtilis CPA-8 by spray-drying with long storage life and retained efficacy to control peach and nectarine brown rot caused by Monilinia spp.

Methods and results: CPA-8 24-h- and 72-h-old cultures were spray dried using 10% skimmed milk, 10% skimmed milk plus 10% MgSO(4) , 10% MgSO(4) and 20% MgSO(4) as carriers/protectants. All carriers/protectants gave good percentages of powder recovery (28-38%) and moisture content (7-13%). CPA-8 survival varied considerably among spray-dried 24-h- and 72-h-old cultures. Seventy-two hours culture spray dried formulations showed the highest survival (28-32%) with final concentration products of 1·6-3·3 × 10(9) CFU g(-1) , while viability of 24-h-old formulations was lower than 1%. Spray-dried 72-h-old formulations were selected to subsequent evaluation. Rehydration of cells with water provided a good recovery of CPA-8 dried cells, similar to other complex rehydration media tested. Spray-dried formulations stored at 4 ± 1 and 20 ± 1°C showed good shelf life during 6 months, and viability was maintained or slightly decreased by 0·2-0·3-log. CPA-8 formulations after 4- and 6 months storage were effective in controlling brown rot caused by Monilinia spp. on nectarines and peaches resulting in a 90-100% reduction in disease incidence.

Conclusions: Stable and effective formulations of biocontrol agent B. subtilis CPA-8 could be obtained by spray-drying.

Significance and impact of the study: New shelf-stable and effective formulations of a biocontrol agent have been obtained by spray-drying to control brown rot on peach.