Sphacelia sorghi

The fungus is characterized by its ability to infect the ovaries of sorghum florets. It is classified as an ascomycete, functioning as an obligate parasite of the Sorghum genus.

In the field, it is identified by the presence of sticky honeydew-like exudates on the panicles during the flowering stage, which serves as a key diagnostic indicator.

Microscopic analysis reveals a dense fungal mycelium filling the ovary cavity, producing masses of conidia that are responsible for the secondary spread of the disease.

Conidial dispersal is facilitated by environmental factors such as wind, splashing rain droplets, and insect activity, which aid in moving spores between inflorescences.

The host range of Sphacelia sorghi includes grain sorghum, sweet sorghum, broomcorn, and Sudan grass, causing significant losses in yield.

The pathogen specifically attacks the reproductive organs of the plant, replacing the healthy grain with fungal structures, thereby preventing the development of viable seeds.

In addition to direct yield reduction, the presence of the pathogen lowers the quality of the harvested grain and potential forage, potentially introducing toxic compounds.

Economic impact is significant in regions with humid climates during the flowering period, where the disease can reach epidemic levels if not managed properly.

Financial losses occur not only from reduced grain weight but also from the increased cost of sorting infested grain and implementing phytosanitary controls.

The infection cycle begins during the flowering stage of the sorghum plant, when the susceptible ovaries are exposed and vulnerable to spore colonization.

High relative humidity and moderate temperatures are the primary drivers of disease development, favoring the rapid germination of conidia.

Frequent rainfall or heavy morning dew provides the necessary moisture for the rapid spread of secondary infections throughout the field.

The incubation period, from the time of infection to the visible appearance of honeydew, typically lasts between one to two weeks, depending on the environment.

By the end of the growing season, hardened sclerotia develop in place of the seeds, allowing the pathogen to persist in crop residues and soil until the next season.

The most obvious symptom is the secretion of sticky, sugary honeydew from the florets, which attracts insects and can lead to secondary mold growth.

A white or pinkish conidial layer forms on the surface of the infected panicle parts, which gradually darkens as the infection progresses.

Infected kernels are replaced by fungal tissue (sclerotia), which often appear as elongated or deformed structures compared to healthy grains.

In advanced stages, dark, hard sclerotia become visible within the panicle, serving as resting structures for the fungus during unfavorable conditions.

General panicle health declines, often resulting in distorted grain development and an overall decrease in the structural integrity of the sorghum head.

The primary control strategy involves planting resistant or tolerant sorghum hybrids, which effectively restrict the fungus from colonizing the florets.

Crop rotation and field sanitation help reduce the amount of primary inoculum surviving in the soil, which is crucial for long-term disease management.

Managing planting dates to ensure that flowering does not coincide with periods of high rainfall can significantly reduce the risk of infection.

Cleaning seeds to remove sclerotia and using high-quality seed treatments are essential preventative steps to minimize early-season disease outbreaks.

While fungicide application during flowering is a theoretical option, its effectiveness is often limited by the timing of application and the nature of the infection cycle.