Association of Neonectria macrodidyma with Dry Root Rot of Citrus in California

Abstract

During yearly surveys that started in 2010 to identify pathogens associated with dry root rot disease of citrus in California, samples with root rot symptoms were collected in Tulare County. Small pieces of tissue from root samples were plated onto potato dextrose agar amended with 0.01% tetracycline and incubated at 25°C. Pure cultures of fungal isolates were identified by morphology and sequence analysis of the Internal Transcribed Spacer and Beta Tubulin regions. Neonectria macrodidyma (Cylindrocarpon macrodidymum) was first recovered in 2011 and has subsequently been recovered multiple times from citrus samples. The pathogen appeared to be widely distributed in association with citrus dry root rot and possibly interacts with Fusarium solani, Phytophthora nicotianae and P. citrophthora, the major soil borne pathogens that were frequently identified from plant samples with root and/or crown rot of citrus in California. The fungal genus Cylindrocarpon (Teleomorph: Neonectria wolenw=Dactylonect ria=Ilyonectria) contains ubiquitous soil borne pathogens that cause black foot disease on a wide range of hosts, including grapevine, strawberry, apple, and conifers. Hosts typically become infected through natural wounds on roots and other below ground parts. In this report, we present strain UCR3312, which is the most recently isolated pathogenic strain in 2015. Considering the potential damage that this organism may cause to the citrus industry, detailed studies are recommended to better understand its distribution, epidemiology, and the general pathogen biology to improve the disease management practices.

Morphological and Molecular Identification of Dactylonectria macrodidyma as Causal Agent of a Severe Prunus lusitanica Dieback in Italy

“…Generally, these fungi are considered opportunistic necrotic pathogens that usually infect their hosts through wounds producing toxins and cell wall degrading enzymes to invade host tissues. Under favorable conditions such as stress and/or reduction of plant vitality, they have the potential to be damaging pathogens and can be of great economic importance [15,16].…”

“…These fungi are considered opportunistic necrotic pathogens, and they can survive in the soil for a long time in the absence of the host crops [12,13], producing different types of propagules (mycelium within crop debris, conidia which spread in soil water, and chlamydospores) [11,14]. In the presence of favorable conditions such as stress and/or reduction of plant vitality, the epidemic potential of Cylindrocarpon-like fungi is very high [15,16].…”