Control of postharvest diseases on citrus fruit by preharvest application of the biocontrol agent Pantoea agglomerans CPA-2. 1. Study of different formulation strategies to improve survival of cells in unfavourable environmental conditions
2008
Cañamás, Teresa Paula | Viñas, Immaculada | Usall, Josep | Casals, Carla | Solsona, Cristina | Teixidó, Neus
The objective in the present study was to investigate the survival and effectiveness of different biological agent Pantoea agglomerans formulations against Penicillium spp. with different preharvest treatments. Results indicated a high sensitivity of non-adapted and osmotic-adapted P. agglomerans cells to environmental conditions in the field, resulting in preharvest treatments which were ineffective against Penicillium spp. In the second part of this study, dry conditions and solar radiation were identified as important environmental conditions that seriously affect populations of P. agglomerans cells. Different formulation strategies were tested in order to improve the resistance of cells to unfavourable environmental conditions. Osmotic-adapted P. agglomerans cells in the presence of 25gL⁻¹ of NaCl in the production medium [osmotic-adapted treatment (P25)] or at water activities (a w) of 0.98 [osmotic-adapted treatment (P98)] had higher survival rates than non-adapted cells, when these cells were sprayed on oranges and stored in hermetically sealed chambers at a low RH of 43%. Among seven additives tested, the presence of 5% Fungicover in the bacterial suspension improved adherence and persistence of P. agglomerans cells on oranges exposed to unfavourable conditions. Therefore, while P. agglomerans cells sprayed alone had log values of 0.5CFUcm⁻², in combination with Fungicover the population level of P. agglomerans cells reached log values of 5 and 4.2CFUcm⁻², at 0 and 24h after application. Lyophilised cells showed greater resistance to unfavourable environmental conditions than fresh cells. The present study has demonstrated that the formulation improvement can provide better performance of biocontrol agents under environmental conditions non-conducive for growth and survival.
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