Post-harvest biological control by Pantoea agglomerans (CPA-2) on Golden Delicious apples.

AIMS: To investigate the potential of Pantoea agglomerans to control the major post-harvest diseases on Golden Delicious apples. METHODS AND RESULTS: In laboratory trials, a high level of control of Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer was obtained with P. agglomerans. In semi-commercial trials at 1degrees C in air and a low oxygen atmosphere, the reduction of blue mould was 81% and 100%, respectively, and control of grey mould was achieved equally with P. agglomerans and imazalil. In trials at 1degrees C and seven atmosphere conditions, maximum reduction in decay was 80% obtained at 3% O2-6% CO2. The population of P. agglomerans on apples followed the same pattern under all three atmosphere conditions studied. CONCLUSIONS: Pantoea agglomerans could be used effectively on apples under a wide range of temperature and atmosphere conditions. SIGNIFICANCE AND IMAPCT OF THE STUDY Pantoea agglomerans can be used as a biocontrol agent on apples at 8 x 10(7) cfu ml-1, the same concentration as in pears. This will facilitate the application of this biological control agent by the growers in packing houses.

Survival of Pantoea agglomerans strain CPA-2 in a spray-drying process.

Spray drying could be a suitable method for preserving microorganisms, as it allows large quantities of cultures to be dried at low cost. The aims of this paper were to evaluate the effects of spray-drying conditions on survival of the biocontrol agent Pantoea agglomerans CPA-2, which has shown antifungal activity against Penicillium expansum and Penicillium digitatum on citrus fruits. Various compounds cited in the bibliography as carriers were tested in our spray drying, and some salts (MgSO4, K2SO4. and Na2CO3) and dairy products (lactoserum or nonfat skimmed milk [NFSM]) showed the best results in terms of recovered powder. Outlet temperature had more influence on the death of bacteria than inlet temperature. P. agglomerans was heat sensitive, and the activation energy was around 6 kcal/mol K when MgSO4 (10%) or NFSM (10%) were used as carriers and only 3 kcal/mol K when the combination of MgSO4 (10%) and NFSM (10%) was used. The highest powder recovery was obtained when NFSM was used as the rehydration medium. Although the percentage of powder recovery was not high (around 50%) and viability was low, the results suggest that with bigger spray dryers, we could expect a lower outlet temperature and probably an increased viability. Further research into spray-dryer design is needed in order to demonstrate this.

Biological control of blue mould on apple by a strain of Candida sake under several controlled atmosphere conditions.

The biocontrol potential of the yeast Candida sake (CPA-1) against Penicillium expansum decay of apples under several controlled atmosphere conditions was investigated. In a laboratory trial under different commercial cold storage conditions, increasing concentrations of C. sake improved decay control. A maximum reduction of decay was achieved at 3% O2-3% CO2 atmosphere. It amounted to a 97% lesion reduction after treatment with a suspension containing 2.4 x 10(6) CFU/ml of C. sake (CPA-1). In a semi-commercial trial at 1 degree C with wounded fruits, the reduction in decay diameter caused by C. sake exceeded 80% after 60 days at 21% O2 and 60% after 120 days of storage under controlled atmosphere conditions. For seven controlled atmosphere conditions studied, a significant influence by C. sake on the P. expansum decay was observed, and the lesion size was reduced more than 70% by C. sake at 10(7) CFU/ml. The populations of C. sake (CPA-1) on the apple surface followed the same pattern under all controlled atmosphere conditions studied. They decreased 4-10-fold during the first 2 weeks, followed by an increase to the initial level after 45 days, and thereafter the count remained constant for the period of 90 days examined. This indicated the capacity of C. sake (CPA-1) to colonize the surface of apples under various storage conditions. The ability to colonize was even higher in apple wounds.