Root Rot of Geranium transplants and Its Biological Control

Abstract

Geranium is one of the most popular greenhouses potted and bedding plants in Egypt. Root rot disease is responsible for important losses in geranium plant production. A total of 11 fungal isolates were isolated from rotted roots of geranium plants, collected from nurseries in Shoubra El-Khima and El-Qanater El-Khaireya, during winter 2012-2013. Disease plants were stunted with yellowed leaves and decayed root system with browning of the surface of the basal portion of the stem. The isolated fungi include: Fusarium anthophilum, F. equiseti, F.proliferatum, F. semitectum, F. solani and Pythium ultimum, where the highest frequency was Fusarium semitectum (36.36%). A total of 10 bacterial and 5 fungal isolates, were isolated from rhizospheric soil of 3 different ornamental plants, and tested, in vitro, in addition to a known bio-agent, Pseudomonas fluorescens (strain3339), for their antagonistic effect against the pathogens of root rot. In vitro assays indicated that Trichoderma harizinum (TCNu1) was highly antagonistic against F. anthophilum, F. proliferatum and F. semitectum, while it gave slight antagonistic effect against P. ultimum. As for Pseudomonas fluorescens, it showed moderate antagonistic effect against 3 tested Fusarium spp., however, it slightly reduced growth of P. ultimum. Under greenhouse conditions, soil treatment with Pseudomonas fluorescens (strain3339) significantly reduced foliar disease severity, while Trichoderma harzianum gave the highest reduction of root rot incidence and severity. Treatment with Trichoderma harzianum and Pseudomonas fluorescens improved growth of geranium plants grown in pathogen infested soil, where main shoot length, main root length, fresh and dry weights of plants were increased. However, both bio-agents had no significant effect on number of flowers/plant. Therefore, this study confirms the potential of Trichoderma harzianum (TCNu1) and Pseudomonos fluorescens (strain3339) to be used as one component in integrated program to control root rot disease in geranium transplants in Egypt.