Occurrence, characterization and management of fruit rot of immature cucumbers under greenhouse conditions in Oman

A study was undertaken to characterize and manage pathogens associated with fruit rot of immature cucumber fruits in greenhouses in Oman. A survey over five growing seasons from 2008 to 2010 in 99 different greenhouses in Oman showed that the disease was prevalent in 91 (92%) greenhouses and resulted in losses of 10 to 60% (avg. 33%) of immature fruits per plant. Incidence of the disease was not found to be affected by growing seasons, which could be attributed to the limited fluctuations in ambient temperatures in greenhouses. Isolations from diseased cucumber fruits yielded Alternaria alternata (isolation frequency = 52%), Fusarium equiseti (40%), Cladosporium tenuissimum (27%), Botrytis cinerea (6%), F. solani (6%), Corynespora cassiicola (3%), Aspergillus spp. (2%), Curvularia sp. (1%) and Bipolaris sp. (1%). With the exception of the Curvularia and Bipolaris species, all other fungi were pathogenic on cucumber fruits, with F. equiseti being the most aggressive, followed by Co. cassiicola, B. cinerea and A. alternata. Cladosporium and Aspergillus spp. were found to be weakly pathogenic. Comparing the efficacy of foliar and soil applications of carbendazim fungicide on fruit rot of cucumber showed that foliar applications significantly reduced fruit rot and increased cucumber yield when compared to soil application or to untreated experimental controls (P<0.01). This is the first report of the association of Co. cassiicola and F. equiseti with fruit rot of immature greenhouse cucumbers. This is also the first report in Oman for the association of Cl. tenuissimum with fruit rot of immature cucumbers. Factors affecting disease control in greenhouses using carbendazim are discussed in light of the experimental results from the study.