Damping-Off and Root Rot of Pepper Caused by Fusarium oxysporum in Almería Province, Spain

Abstract

Bell pepper (Capsicum annuum L.) is intensively cropped in ~9,920 ha of plastic houses in southern Spain. In summer 2013, pepper seedlings cv. Melchor, Acorde, Galena, Prometeo, and Souleria, with 4 to 8 leaves, grown in a nursery greenhouse near El Ejido, Almería Province, exhibited root rot and stunting. Incidence of symptomatic plants was ~35% among over 10 million. Fusarium sp. was consistently isolated on potato dextrose agar (PDA) from primary and secondary roots of symptomatic plants. Eight single spore isolates (FC1, FC2, FC3, FC4, FC5, FC6, FC11, and FC12) were identified on PDA, carnation leaf-piece agar medium, and Spezieller Nährstoffarmer agar medium as Fusarium oxysporum because of their production of macroconidia (20.5 to 38.2 × 3.9 to 5.8 μm) containing mostly three or rarely four septa, with foot-shaped basal cells. Microconidia (5.9 to 16.5 × 2.6 to 4.7 μm) with 0 to 1 septa formed on false heads on short monophialides and chlamydospores. DNA was extracted from various isolates used in the pathogenicity test, and a portion of the elongation translation factor 1-alpha using primers EF-1 and EF-2 was amplified and sequenced. All the pathogenic isolates were identical, and they differed from the non-pathogenic in 6 to 8 base pairs. The isolates had 99% homology with several isolates of F. oxysporum corresponding to different specialized forms (vasinfectum, lilii, lycopersici, and radicis-lycopersici) at the Fusarium-ID database (1) and GenBank. The sequences of two isolates, FC-6 and FC-12, were deposited in GenBank with accession nos. KF928930 and KF928931, respectively. The pathogenicity of these eight isolates was tested on pepper cv. Melchor in 1-liter containers filled with vermiculite in August and October. Seedlings were inoculated at sowing. PDA plates fully covered with the colony of each isolate were separately blended and homogenized with 300 ml of sterile distilled water. Inocula (5.0 × 105 to 9.4 × 106 conidia/ml) were poured at 50 ml per container. Each experiment had four replicates and 5 to 6 plants per replicate. Treatments with different isolates were arranged in a randomized complete block design. In both experiments, the same number of uninoculated seedlings served as controls. The plants were maintained for 40 days following inoculation in a greenhouse with mean temperatures of 24.0 to 32.4°C and 23.6 to 31.20°C for August and October experiments, respectively. In both experiments, all control plants and those inoculated with FC2, FC3, and FC4 remained asymptomatic. The first wilting occurred 11 days after inoculation. At the end of the August experiment, plants inoculated respectively with FC1, FC5, FC6, FC11, and FC12 showed symptoms in 60, 70, 65, 80, and 90% and 25, 0, 15, 40, and 25% died. At the October experiment, plants showed symptoms in 91.7, 95.8, 100.0, 91.7, and 87.5% and 83.3, 75, 62.5, 83.3, and 79.2% died. Symptomatic plants exhibited damping-off, necrosis of the primary and secondary roots, and sometimes necrotic streaks on the stem. F. oxysporum was consistently recovered from the primary root of symptomatic plants in both experiments and 10 of these isolates were inoculated in a third pathogenicity test, being all pathogens, thus fulfilling Koch's postulates. Although F. oxysporum was reported in peppers (2), to our knowledge, this is the first report of F. oxysporum as the causal agent of damping-off and root rot in pepper seedlings in Almería Province. References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) K. Pernezny et al. Compendium of Pepper Diseases. APS Press, St. Paul, MN, 2009.