Plant disease - 2007

Saffron (Crocus sativus L.) is highly desirable as a condiment and is also used for medicinal purposes. In India, saffron is cultivated in 2,825 ha with a production of 6,048 t and an average yield of 2.28 kg/ha. Approximately 70 to 80% of the saffron crop in 25 commercial fields in the Kishtwar District of Jammu and Kashmir, India was affected with a corm rot from October 2005 to 2006. In newly infested fields, the disease occurred in small patches that gradually enlarged each year. Symptoms appeared as brown-to-dark brown sunken, irregular patches below corm scales. Lesions were usually 1 mm deep with raised margins. Severely infected corms had foliage that dried from the tip downward. White fungal mycelia appeared on the bulbs that rotted at later stages of disease development. Sclerotia formation was observed. For isolation of the pathogen, small bits of the infected tissue were surface sterilized in 0.1% mercuric chloride and washed three times in sterile distilled water. The surface-sterilized pieces were placed aseptically on potato dextrose agar and incubated at 28 ± 1°C for 3 days. The fungus was characterized by hard, brown-to-black sclerotia that was 1 to 2.1 mm in diameter with a pseudoparenchymatous rind. These were produced on sterile, cottony white mycelium with clamp connections. On the basis of morphological characteristics (3), the fungus was identified and deposited as Sclerotium rolfsii Sacc. at the Indian Type Culture Collection Center, IARI-New Delhi as ID No. 6491.07. Pathogenicity tests were carried out in a growth chamber maintained at 28 ± 1°C. S. rolfsii was grown in potato dextrose broth for 7 days and then blended to make a mycelial suspension. Fifty milliliters (1 × 104 hyphal fragments per ml) of the suspension was mixed in each kilogram of sterilized soil and placed in pots. Healthy saffron corms were planted in 10 pots containing soil infested with S. rolfsii, and five pots with noninfested soil served as controls. Symptoms appeared on eight corms 9 to 10 days after planting. Signs of the pathogen in the form of mycelia and sclerotia were also present. The corms rotted and died 12 to 14 days after inoculation. Control plants did not display any symptoms. S. rolfsii was reisolated from infected bulbs, thus proving Koch's postulates. Corm rot caused by Fusarium spp., Penicillium spp., and Rhizoctonia spp. is also reported on saffron (2). Fusarium oxysporum f. sp. gladioli has been reported in Italy (1). To our knowledge, this is the first report of S. rolfsii as being pathogenic on saffron from India.