Black root rot of cucumber

The fungus Diaporthe sclerotioides (formerly known as Phomopsis sclerotioides) is a destructive soil-borne pathogen responsible for black root rot in various cucurbits. It is a highly specialized fungus that thrives in agricultural environments, primarily affecting glasshouse crops. Its ability to produce persistent survival structures ensures long-term residency in infested soils.

Cucumber is the primary host for this pathogen, suffering the most significant yield losses. While the infection can occur in field conditions, it is most prevalent in intensive protected cultivation systems. The fungus attacks the vascular and root tissues, causing systemic damage that impairs nutrient and water uptake throughout the plant's lifecycle.

Symptoms of the disease initially appear as small brown lesions on the roots, which quickly expand and turn black, characteristic of the condition. As the root system becomes necrotic and fragile, the plant begins to show signs of water stress, including wilting of foliage during the hottest parts of the day. Eventually, the entire root system may collapse, leading to stunted growth and premature plant death.

Environmental conditions favoring the development of the disease include cool to moderate temperatures and high soil moisture. Since the pathogen is easily transported via water runoff, tools, and contaminated propagation material, it can spread rapidly across a greenhouse facility. Once established, the fungus is notoriously difficult to eradicate from non-sterilized growing media.

Effective management of Diaporthe sclerotioides requires an integrated approach. Growers should prioritize the use of resistant rootstocks, which have proven highly effective in mitigating damage. Additionally, implementing rigorous sanitation practices, such as steam sterilization of soil, systematic crop rotation, and the prompt removal of infected debris, is essential to minimize the inoculum pressure and prevent future outbreaks.