Diaporthe stem blight

Systematic position and type of pathogen: Diaporthe caulivora belongs to the kingdom Fungi, phylum Ascomycota, class Sordariomycetes, order Diaporthales. It is a highly specialized fungal pathogen that causes stem blight, a devastating disease of soybean crops globally, resulting in significant yield losses.

Diseases and host plants: The primary host of this pathogen is soybean (Glycine max). The disease manifests as brown, elongated lesions at the nodes of the stem. These lesions often expand, causing the stem to crack or die, eventually leading to plant wilting, premature senescence, and the death of the entire plant during the grain-filling stage.

Biology and life cycle: The pathogen survives as mycelium and fruiting bodies (pycnidia and perithecia) on infected crop debris and in seeds. Under moist conditions, ascospores and conidia are released and dispersed by splashing rain and wind onto susceptible host tissues. The fungus penetrates the host, colonizing the stem tissue and disrupting the vascular system by producing necrotic enzymes and toxins.

Conditions for development and spread: The development of Diaporthe caulivora is strongly favored by warm, humid weather. Optimal temperatures for fungal growth range from 20°C to 25°C. Extended periods of rainfall during the reproductive stages of soybean growth significantly accelerate the spread and severity of the disease throughout the field.

Harmfulness and control measures: The disease causes stunted growth and grain shriveling, leading to substantial yield losses. Management strategies include:

• Implementing long-term crop rotation schemes.
• Using disease-free, certified soybean seeds.
• Planting resistant or tolerant soybean varieties.
• Burying infected crop residues deep via tillage to promote decomposition.
• Applying foliar fungicides during the R1 to R3 growth stages if environmental conditions favor disease onset.