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First Report of Tuber Rot Disease of Kala Zeera Caused by a Member of the Fusarium solani Species Complex in India

Bunium persicum (Kala zeera, also black cumin) is an economically important culinary crop that is cultivated for its seed pods and its tuberlike roots. In India, high-altitude regions of Himachal Pradesh, including the Padder valley and the Gurez area of Jammu and Kashmir, are areas of kalazeera production (3). In 2008 to 2009, tuber rot disease of kala zeera was observed during the late spring season in the Padder valley. Symptomatic plants were distributed in localized areas in the field and the symptoms included drying of foliage and rotting of tubers. White mycelia were found on the tubers at the late stages of disease development. Incidence of infection in the surveyed area was 80 to 90%. Yield losses were 50 to 60%. To isolate the causal pathogen, we cultured tissues from symptomatic tubers. Small bits of the infected tissue were surface disinfested in 0.1% mercuric chloride, followed by rinsing three times in sterile distilled water. The surface disinfested tissues were plated on potato dextrose agar (PDA) and incubated at 27°C for 4 days. Pure cultures of the mycelium from the diseased tissues were transferred to a second set of PDA for species identification. The fungus produced three types of spores: small, one-celled, oval microconidia; large, slightly curved, septate macroconidia; and rounded, thick-walled chlamydospores. Microconidia were mostly non-septate and 8.91 to 15.73 × 2.3 to 3.5 μm, whereas macroconidia were three- to five-septate and were 35.55 to 54.74 × 3.91 to 6.5 μm. On the basis of morphological characteristics (1), the fungus was identified and deposited as a member of the Fusarium solani species complex in the Indian Type Culture Collection, New Delhi (ID No. 8422.11). To confirm pathogenicity, healthy tubers were submerged for 20 min in a conidial suspension of the isolated fungus (1 × 10⁵ cfu/ml), which was prepared in potato dextrose broth, incubated for 10 days at 27°C, and centrifuged at 140 rpm. Noninoculated controls were submerged in distilled water. Inoculated and control tubers were then planted in separate pots filled with sterilized soil and kept in a shade house. Symptoms appeared on inoculated tubers 9 to 10 days after planting. Signs of the pathogen in the form of mycelia were present. The tubers rotted and died 12 to 15 days after inoculation. Control tubers did not display any symptoms. F. solani species complex was reisolated from inoculated tubers, fulfilling Koch's postulates. F. solani has been reported to cause corm rot on gladiolus and saffron (2). To our knowledge, this is the first report of the F. solani species complex as pathogenic to tubers of kalazeera in India.

References: (1) C. Booth. The Genus Fusarium. 47, 1971. (2) L. Z. Chen et al. J. Shanghai Agric. College 12:240, 1994. (3) K. S. Panwar et al. Agriculture Situation in India. 48:151, 1993.