Phytopathological studies on Alternaria blight of Chrysanthemum (Chrysanthemum indicum L.)

Abstract

Chrysanthemum plant is considered one of the ornamental plants and cut flowers at the level of local and export production, recently. Alternaria leaf spot and blight disease are considered one of the most important diseases, which it has negatively effects on flower yield under greenhouse conditions with climate changes. This study confirmed the possibility of using plant extracts and bio-agents as a single component in an integrated control program to control Alternaria leaf spot and blight disease in chrysanthemum plants in Egypt. The disease was inventoried to the three regions of Heliopolis, (HelCa), in Darwa (MGQa) and Ezbat Al-Ahaly (MGQa) at El Qanater El Khaireya, which the symptoms were found in the form of brown spots and blight on the leaves and rotting of the flowers, also disease incidence (%) were 87.15, 61.44 and 38.72%, respectively. A total of 97 fungal isolates of Alternaria spp. were isolated. In vitro, the pathogenicity was tested by detached leaf inoculation using a single droplet technique over a period of 7-14 days, where the frequency of the high virulent isolates was (19.6%). The molecular identification was carried out using rDNA ITS for five highest pathogenic isolates, which the result was Alternaria alternata, where the process of cultural and morphological identification of MGQa–FYhd2(1-3) which the highest pathogenic isolate was completed. This isolate was tested with 10 different plant extracts that were extracted by methanolic extraction. Clude extract was the best result where EC<inf>50</inf> was 502.4 ppm and EC<inf>90</inf> was 281.6 ppm while the cinnamon extract expressed the EC<inf>50</inf> value of 1969.2 ppm and EC<inf>90</inf> was 10356.1 ppm. The bio-agents tesing showed the best treatments which inhibition of mycelial growth of the tested pathogen were Trichoderma harzianum (71.39%), and followed by Bacillus subtilis (69.41%).