Broomrape (Orobanche aegyptiaca Pers.), an important obligate root parasitic weed in India, has a wide host range including several members of the Solanaceae, Leguminaceae, and Brassicaceae families, among others. Orobanche plants produce thousands of tiny seeds (250 × 300 μm), which can remain viable in the soil for as long as 13 years (3). Rapeseed-mustard (Brassica spp.) is one of the major oilseed crops in India, cultivated on 5.77 million ha with 6.59 million t produced during 2009–2010. Broomrape has been observed in India as a major angiospermic parasitic plant on rapeseed-mustard, tobacco, tomato, and potato. During a field visit to an experimental farm at the Directorate of Rapeseed-Mustard Research, Bharatpur (27°12′N, 77°27′E) in the winter of 2009-2010, symptoms of wilt disease were observed on Orobanche plants, 32.6% of which had wilted completely following root infection. Initial symptoms appeared as a browning of the flowering stalk with wilting. Direct observation of below ground plant parasite tissues revealed a necrosis starting at the radical and advancing to the collar region that shredded later on. Tissue fragments, excised from the internal portions of the diseased tissue, were surface sterilized with 0.1% HgCl2, plated on 2% potato dextrose agar (PDA) adjusted to pH 7.0, and incubated at 22 ± 2°C for 7 days. The colonies that grew on PDA plates produced a bright purple color. Single-spore culturing of the fungus yielded Fusarium solani on the basis of morphological characteristics (2). The Fungal Identification Service, Mycology and Plant Pathology Group, Agharkar Research Institute, Pune, India (Accession No. 2156) confirmed the identity. The pathogenicity of the fungus was tested by inoculating five healthy Orobanche plants that were parasitizing Brassica spp. at the radicle region with 10-ml spore suspensions (2 × 105 conidia/ml of sterile distilled water) derived from 7-day-old cultures of the fungus. Control plants were treated with sterile distilled water. F. solani-inoculated radicles developed typical wilting symptoms within 2 weeks of treatment, while the control as well as the Brassica spp. plants remained healthy. F. solani was reisolated from inoculated wilted plants, thus fulfilling Koch's postulates. To our knowledge, on the basis of the literature, this is the first report from India showing that F. solani infects O. aegyptica on Brassica spp. There are reports of fungi (50 different species) infecting different hosts in Southern Italy, including F. oxysporum and F. solani, which have been found to be pathogenic to O. ramose. The most pathogenic Fusarium isolates significantly increased the number of dead spikes of broomrape (1). Control of Orobanche spp. poses a challenge because of the lack of effective and economic control measures. F. solani thus offers a potentially promising management strategy that should be explored in the future for the control of O. aegyptiaca.
References: (1) A. Boari et al. Biol. Control 30:212, 2004. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. 1st ed. Pennsylvania State University Press, University Park, 1983. (3) M.C. Press et al. Parasitic Plants. Chapman and Hall, London, UK, 1995.