Studies on Root Rot of Some Ornamental Shrubs in Egypt

Abstract

The causal pathogen of damping-off fungal diseases of Dodonaea viscosa and Thuja orienta/is as well as those of root rot of Acalypha wilkesiana and Hibiscus rosa-sinensis were identified in nurseries of three governorates tested. Pathogenic capability of the pathogens and losses in stand and plant growth as well as several measures of control were determined. Alternaria sp.; Fusarium semitectum; F. so/ani and Rhizoctonia so/ani were isolated at different frequencies from roots of Dodonaea and Thuja seedlings of the three governorates nurseries tested. However, isolation trials from Acalypha and Hibiscus root rots yielded Alternaria sp., F. so/ani, Nigrospora sphaerica and R. so/ani at different frequencies. Soaking seeds of Dodonaea and Thuja in Topsin M or Rizolex-T was effective measure in decreasing pre- and post­ emergence damping-off and increasing survival seedlings. Plant Guard, however, was better than Rhizo-N in case of F. so/ani and the opposite result was true with R. solani. On the other hand, Thymus vulgaris and Cymbopogon citratus were significantly the most effective plant extracts tested in decreasing pre- and post­ emergence damping-off as well as improving seedling survivals. Peat moss or peat moss+sand as planting media were generally effective mean in decreasing damping-off diseases. Dip treatment for Acalypha and Hibiscus cuttings in Topsin M, however, gave significant decreases in root rot disease incidence grown in infested soil than the control, followed by Rizolex-T with only Hibiscus. Plant Guard, Majorana hortensis extract and IBA (Acalypha) or NAA (Hibiscus) were the better bioproducts, plant extracts and plant hormones, respectively. Generally, different results were obtained when planting in soil infested with F. so/ani, on the disease incidence and seedling growth parameters.