Poster Presentation Science Protecting Plant Health 2017

Etiology of Parsley Summer Root Rot in Australia (#233)

Len Tesoriero 1 , J Archer 1 , F Lidbetter 1 , S Mulholland 1 , D Cameron 1 , L Spohr 1 , A Harris 1
  1. NSW Department of Primary Industries, Ourimbah, NSW 2258, Australia

Parsley production in Australia is valued at $10M per annum. A root and collar rot over the summer months can decimate crops causing plants to wilt and collapse. Curly leaf cultivars are particularly susceptible. Crop surveys in NSW, Queensland, Victoria and Western Australia determined that disease occurrence is widespread in both soil and soilless production systems. Previous studies of parsley root rot postulated that this summer disease was distinct from those occurring in cooler months that were attributed to species of Pythium. Those studies identified Fusarium oxysporum as a potential causal pathogen and/or an uncharacterised Pseudomonas sp. Diagnostic pathology on samples collected during this project produced an array of F. oxysporum, F. solani, Pythium spp, and bacterial isolates. These were partially characterised and used in pathogenicity experiments. Several experiments were conducted in potted parsley plants as well as soilless systems using the nutrient film technique or rockwool blocks. Inocula were applied to plants as single isolates or as combinations of different isolates or species. Only treatments that included isolates of either of two Pythium species were capable of inducing disease symptoms. The more commonly occurring of these was P. sulcatum which is an aggressive pathogen of apiaceous plants. It is known to cause the diseases cavity rot and forking of carrots as well as root rots of parsley and coriander. It has a wide temperature range for growth so could be solely responsible for parsley root rots throughout the year. However, there are some unexplained issues from our results and observations. Often early disease symptoms appear at the plant collar. Why do coriander and flat leaf parsley crops appear to be less affected? Could there be other contributing factors such as residual herbicides or fertiliser interactions? Is there a cryptic pathogen that we have not identified?