Efficacy of Pseudomonas syringae in the management of potato tuber diseases in storage

Silver scurf caused by Helminthosporium solani and dry rot caused by Fusarium spp. are tuber diseases of economic importance in potato-growing areas worldwide. Recently, the two pathogens have developed resistance to thiabendazole (TBZ), a post-harvest fungicide commonly used for their control. Therefore, alternative disease control strategies are needed. The present study assessed the efficacy of the biopesticides Bio-Save 10LP (Pseudomonas syringae-strain ESC-10; Ps10) and Bio-Save 11LP (P. syringae-strain ESC-11; Ps11) against silver scurf and dry rot. Approximately 30 isolates representing the genus Fusarium were obtained from symptomatic potato specimens with dry rot from New Brunswick (NB), Nova Scotia (NS), Prince Edward Island (PE) and Alberta (AB), Canada. Species isolated were Fusarium sambucinum, Fusarium tumidum, Fusarium coeruleum, Fusarium culmorum, and Fusarium avenaceum. H. solani isolated from AB, NB and PE was included in the study as the causal agent of silver scurf. The efficacy of P. syringae against F. sambucinum and H. solani was tested in vitro. Ps10 and Ps11 inhibited the growth of H. solani up to 68% (NB isolate) and 73% (PE isolate), respectively and the inhibition was more or less comparable with that of TBZ. F. sambucinum was not significantly inhibited by Ps10; however Ps11 significantly inhibited AB, PE and NB isolates by 43%, 28% and 54%, respectively. Conversely, TBZ inhibited AB, PE and NB isolates of Fusarium spp. in vitro by 86%, 88% and 100%, respectively. TBZ in combination with either Ps10 or Ps11 did not always reduce the growth of H. solani or Fusarium spp. in vitro compared to that of TBZ alone. Storage trials conducted in NB and PE assessed the efficacy of P. syringae against H. solani or Fusarium spp. in vivo and confirmed that the application of P. syringae or TBZ alone or in combination significantly reduced the incidence and/or severity of silver scurf and Fusarium dry rot. Ps11 alone or in combination with TBZ was significantly more effective than Ps10 in controlling silver scurf disease severity. The reduction in disease severity of dry rot and silver scurf in storage due to Ps10, Ps11, or TBZ or their combinations was consistently comparable. Results indicate that the use of P. syringae ( strains ESC-11 or ESC-10) as a post-harvest treatment can contribute to the management of both silver scurf and Fusarium dry rot in potato storages. (c) 2012 Elsevier Inc. All rights reserved.