First Report of Fusarium oxysporum f. sp. lycopersici Race 3 and F. oxysporum f. sp. radicis-lycopersici in Tomatoes in the Azapa Valley of Chile

Abstract

Tomato (Solanum lycopersicum L.) is an important crop in the Azapa Valley (18°35′ S, 69°30′ W) in northern Chile, with approximately 600 ha of fresh tomatoes under greenhouses. Cultivars resistant to Fusarium oxysporum f. sp. lycopersici (FOL) races 1 and 2 are mainly used. However, in 2012 and 2013, Fusarium wilt incidence was 2 to 3%. Symptoms appeared unilaterally and consisted of yellowing, leaf wilting of lower leaves, dark brown vascular discoloration, and plant death. The aim of this study was to determine the causal agent of tomato wilt in seven tomato greenhouses in the Azapa Valley. Stem samples (5 × 5 mm) were obtained 10 cm of the stem base from wilted tomatoes ‘Naomi’ (BIOAMERICA S.A., Chile) or from Maxifort tomato rootstock (De Ruiter Seed, USA), both FOL resistant to races 1 and 2. Samples were washed with tap water, surface sterilized with 1% NaClO for 3 min, and incubated on sterile moist paper towels in petri plates for 5 days at 22°C. Mycelial fragments from white colonies, emerging from diseased tissues, were transferred to PDA. Six Fusarium isolates were characterized by the presence of hyaline macroconidia, mostly 3 to 5 septate, slightly curved (19.2 to 32.1 × 2.9 to 4.5 μm) and single-celled, oval to elongated microconidia (3.1 to 8.9 × 2.0 to 4.0 μm). Chlamydospores were single or in pairs. These isolates were identified as F. oxysporum (3). The identity of F. oxysporum was confirmed by PCR assays using genomic DNA of each isolated and the universal primers Uni F and Uni R that generate a 672-bp PCR product. The pathogenic form and races were determined by PCR assays using the specific primers uni, sp13, sp23, and sprl that were able to discriminate all the three FOL races as well as F. oxysporum f. sp. radicis-lycopersici (FORL) isolates (2). The sp13 and sp23 primers amplified DNA bands of 445 and 518 bp, confirming the identity of FOL race 3. However, sprl amplified a fragment of 947 bp corresponding to FORL (2). Pathogenicity tests were conducted on 25-day-old seedlings (10 seedlings per isolate) of tomato ‘Poncho Negro,’ which is susceptible to FOL and FORL. Seedling roots were cut, submerged for 5 min in conidial suspension of 2 × 106 conidia/ml, and transplanted to 250-ml plastic containers with sterile substrate (sand/peat, 1:1). Equally treated non-inoculated seedlings were left as controls. The first symptoms induced by each of the five FOL isolates appeared 8 days after incubation under greenhouse and were characterized by yellowing of older leaves, sometimes affecting one side of the plant, vascular discoloration of the stem, and eventually plant death. In contrast, all seedlings inoculated with a FORL isolate developed a necrotic lesion and vascular discoloration at the base of the stems near the soil line, followed by wilting and plant death. Control plants remained asymptomatic. F. oxysporum was re-isolated only from inoculated plants, completing Koch's postulates. FOL and FORL were reported earlier in other tomato growing areas of Chile (1), located over 1,000 km south of the Azapa Valley. However, this is the first report of FOL race 3 and FORL in the Azapa Valley and FOL race 3 is reported for the first time in Chile. References: (1) S. Acuña. Compendio de Fitopatógenos de Cultivos Agrícolas. Servicio Agrícola y Ganadero. Gobierno de Chile, 2008. (2) Y. Hirano and T. Arie. J. Gen. Plant Pathol. 72:273, 2006. (3) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006.

A study on the pathogen species and physiological races of tomato Fusarium wilt in Shanxi, China

“…Furthermore, these primer pairs were also used in the identification of physiological races of F. oxysporum f. sp. lycopersici in Northeast Brazil and Chile (Barboza et al 2013;Sepúlvedachavera et al 2014). This experiment, through the molecular identification method, showed that in addition to race 1 and race 2, there is also race 3 in Shanxi, which is the first report of physiological race 3 causing tomato Fusarium wilt in China.…”

Overexpression of Lectin Receptor-Like Kinase 1 in Tomato Confers Resistance to Fusarium oxysporum f. sp. Radicis-Lycopersici

“…Decades of research have revealed that crop succession can lead to soil-borne diseases such as Fusarium crown and root rot (FCRR), an emerging disease that seriously threatens tomato (Solanum lycopersicum L.) production in most countries (Polizzi et al, 2011;Cordero-Ramirez et al, 2013;Sepulveda-Chavera et al, 2014). FCRR can occur from the seedling stage to the fruiting stage in tomato plants.…”

Antifungal Nanoformulation for Biocontrol of Tomato Root and Crown Rot Caused by Fusarium oxysporum f. sp. radicis-lycopersici

“…radicis-lycopersici (Forl), with race 3 and Forl causing the greatest damage [ 16 ]. The majority of commercial hybrid tomato varieties have resistance to Fol 1 and 2, but not Fol 3 nor Forl , leaving plants without resistance to these two particular forms [ 17 ].…”