Phomopsis stem blight of lupin

Diaporthe leptostromiformis is an ascomycete fungus that serves as the primary causal agent of Phomopsis stem blight, a significant disease affecting various lupin species. This pathogen is highly specialized and known for its ability to produce toxic metabolites within the plant tissues, which makes the disease particularly damaging not only to crop yields but also to the safety of the harvested biomass for animal feed.

The disease primarily targets the genus Lupinus, affecting both commercial and wild varieties. The pathogen can colonize stems, petioles, and pods, leading to systemic infections that impair the plant's physiological functions. Field observation shows that the disease can manifest at any growth stage, though it is most devastating when environmental conditions favor the rapid colonization of host tissues.

Symptoms typically appear as dark, necrotic brown lesions on the stems. As the infection progresses, these lesions may expand, leading to stem breakage and premature plant death. Under high humidity, the fungus produces pycnidia — small, black fruiting bodies that erupt through the epidermis. These structures serve as the primary source of inoculum, releasing spores that are easily spread by wind and rain splash.

The development of the disease is strictly governed by climate factors, with high humidity and moderate temperatures acting as key catalysts for fungal sporulation and infection cycles. The pathogen survives between growing seasons in infected crop debris, the soil, and contaminated seeds. Effective disease management requires an integrated approach that addresses these inoculum sources to break the infection cycle in subsequent years.

Control strategies for Phomopsis stem blight involve a combination of cultural and chemical measures. These include:

• Utilizing resistant or tolerant lupin cultivars.
• Treating seeds with appropriate systemic fungicides.
• Practicing strict crop rotation, ensuring a gap of several years between lupin crops.
• Managing crop residues through deep burial or removal to minimize inoculum buildup.
• Implementing regular field scouting to monitor for early signs of infection.