Epidemic outbreaks of downy mildew caused by Plasmopara halstedii on sunflower in Thrace, part of the Marmara region of Turkey

Abstract

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 μ m wide with nipple shaped appressoria. Conidiophores were mostly erect containing a foot cell (37-64 × 7-11 μ m) followed by two or three shorter cells (8-12 × 8-10 μ m); conidia were cylindrical (26 -34 × 14 -18 μ m) 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.

Advances in sunflower downy mildew research

“…Disease risk appeared greatest if there was heavy rainfall when sunflower seedlings were at their most susceptible stage, whereas heavy rainfall before sowing or after emergence had no effect on the percentage of diseased plants. Furthermore, Göre (2009) recorded a serious outbreak of sunflower downy mildew in Turkey during the spring of 2007 and 2008. He thought that low temperature and extensive spring rains encouraged the disease, resulting in approximately 85% yield loss and lower quality of sunflower production in the Marmara region of Trace.…”

Integration of bioagents with antioxidants to control Powdery Mildew disease in sunflower

“…Antioxidants have been effectively utilized in systemic resistance induction of different plants against several plant pathogens (El- Gamal et al, 2007;Dutta, et al, 2016). Their effectiveness has been attributed to triggering several morphological and/or physiological changes in the host's defense-related compounds, which in turn increase the systemic resistance (Göre, 2009). Application of ascorbic acid significantly reduced early blight disease incidence of potato (El-Gamal et al, 2007), and had a good effect on reducing the powdery mildew disease severity in cucumber and pepper plants (Abd El-Kader et al, 2012).…”

Preliminary Investigation of Effect of Neem-Derived Pesticides on Plasmopara halstedii Pathotype 704 in Sunflower under In Vitro and In Vivo Conditions

“…Downy mildew is a major disease caused by the biotrophic oomycete Plasmopara halstedii (Farl) Berlese et de Toni. This pathogen affects sunflower yield losses, more than 85%, as well as the cost of sunflower crop protection and resistance breeding [1][2][3]. From an economic and scientific point of view, the community of oomycete molecular geneticists ranked P. halstedii as the 16th most important oomycete [4,5].…”