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First Report of Fusarium acuminatum Wilt in the Broomrape Parasite of Processing Tomato in China

Chai, A.-L., Li, P.-L., Guo, W.-T., Li, B.-J., Aisimutuola, P.
Plant disease 2018 v.102 no.3 pp. 676
Dianthus caryophyllus, Fusarium acuminatum, Orobanche aegyptiaca, Solanum lycopersicum var. lycopersicum, agar, alcohols, chlamydospores, conidia, crop production, culture media, databases, flowering, gene banks, genes, internal transcribed spacers, leaves, mitochondria, mycelium, oligodeoxyribonucleotides, parasites, parasitism, pathogenicity, peptide elongation factors, pigmentation, ribosomal DNA, sodium hypochlorite, sporodochia, stems, tissues, tomatoes, translation (genetics), tubulin, wilting, China
Broomrape (Orobanche aegyptiaca Pers.) is a holoparasitic plant that has become a serious threat to processing tomato (Lycopersicon esculentum Mill.) production in the Xinjiang Uygur Autonomous Region, China, causing about 20 to 70% yield losses. Xinjiang is the largest center for processing tomato production in China, accounting for 90% of China’s production and approximately 25% of the world’s production. During July to August 2015, diseased broomrapes on processing tomatoes were collected from fields in Changji Hui and Korla Bayingolin Mongol Autonomous Prefecture, Xinjiang. Diseased broomrapes exhibited symptoms that started as browning of the flowering stalk and small necrotic spindle-shaped lesions on stems. Later, necrotic lesions that expanded longitudinally were evident and caused the whole plant to wilt. To isolate the causal organism, fragments (4 × 4 mm) of symptomatic broomrape stem tissues from 10 plants were surface disinfested with 75% alcohol and 0.1% NaOCl, followed by three washes with sterile distilled water. The fragments were placed on potato dextrose agar (PDA) and incubated at 26°C in the dark. Five isolates with similar morphology were single spored for further characterizations. Colonies on PDA produced whitish-pink aerial mycelium and carmine to rose pigmentation. On carnation leaf agar, abundant macroconidia were formed in sporodochia. Macroconidia were falcate, slender, equilaterally curved with elongated apical cell, mostly 3 to 5 septa, measuring 28.3 to 47.6 × 3.9 to 6.1 μm. Chlamydospores formed in chains. Microconidia were not observed. Morphologically, the isolates were identified as Fusarium acuminatum (Ell. & Kellerm) (Gerlach and Nirenberg 1982). Pathogenicity of the three isolates was tested on 10 broomrape plants that were parasitizing greenhouse-grown processing tomato. The plants were inoculated by applying a 10-ml of conidial suspension (1 × 10⁶ conidial/ml) at the artificially wounded stem region of each plant. Control plants were treated with sterile distilled water. Seven days later, inoculated plants developed typical wilting symptoms identical to those observed in the field, whereas the control as well as the processing tomato plants remained healthy. F. acuminatum was reisolated from symptomatic stems but not from the controls. Total genomic DNA of the five isolates was extracted, and the internal transcribed spacer regions (ITS), the translation elongation factor 1-alpha (TEF-1α), the mitochondrial small subunit ribosomal (mtSSU rDNA), and the beta-tubulin gene (TUB2) were amplified and sequenced with primer pairs ITS1/ITS4, EF1/EF2 (Geiser et al. 2004), T1/T22 (O’Donnell and Cigelnik 1997), and NSM1a/NSM2b (Li et al. 1994). The resulting 544-bp ITS, 682-bp TEF-1α, 688-bp mtSSU rDNA, and 1,299-bp TUB2 sequences of isolate LD1508081502 were deposited in GeneBank (MF523230, MF523228, MF523225, and MF523231, respectively), and BLAST searches showed 100% identity with those of F. acuminatum sequences (KY365571.1, KY365613.1, KJ396329.1, and KF181223.1, respectively). The ITS and TEF-1α sequences revealed 99.81 and 99.55% identity to F. acuminatum FD_01726 in the FUSARIUM-ID database. To our knowledge, this is the first report from China showing that F. acuminatum infects broomrape on processing tomato (Farr and Rossman 2017). Therefore, this study offers a potentially promising strategy for the control of broomrape in China.