First report of powdery mildew on Mexican sunflower in India

Tithonia diversifolia is a perennial garden plant commonly known as Mexican sunflower, belonging to the Asteraceae. Crude extracts of T. diversifolia leaves have intrinsic antimalarial properties (Ajaiyeoba et al., 2005). Diseased plants of T. diversifolia were collected from Barapani, Meghalaya (1010 m above m.s.l.), were found to be heavily infected by powdery mildew during June and July 2007. Almost 70% of the plants surveyed in Barapani were infected. Disease symptoms included greyish white irregular patches consisting of epiphytic mycelia and conidia on both surfaces of the leaves. Symptoms were also present on stem, ray and disc florets. Infected leaves later became necrotic. A specimen has been deposited in Herbarium Cryptogamiae India Orientalis (HCIO), New Delhi, India (HCIO No. 47968). Hyphae were between 5–7 µm wide with nipple shaped appressoria. Conidiophores were mostly erect containing a foot cell (37–64 × 7–11 µm) followed by two or three shorter cells (8–12 × 8–10 µm); conidia were cylindrical (26–34 × 14–18 µm) and produced in chains. The basal septum of the conidiophore was just adjacent to mycelium. Fibrosin bodies were absent. Shoulder germination of conidia was also observed. These morphological characters suggest this is the anamorph of Golovinomyces cichoracearum (Braun, 1987). No perfect stage (chasmothecium) was found. Pathogenicity was confirmed by dusting conidia on healthy potted plants of T. diversifolia, non-inoculated plants serving as control. Inoculated plants developed symptoms after a week whereas control plants remained healthy. Necrosis developed 18 days post-inoculation. The only occurrence of powdery mildew on T. diversifolia was reported in Zambia (Hirata, 1986), but this is the first record of powdery mildew of T. diversifolia in India. This disease is also of regulatory significance since it has not been reported from adjoining countries like Sri Lanka where this crop is grown for the purpose of green manuring. Authors would like to thank Dr. Prof. Uwe Braun for helping in identification of the pathogen.