Gibberella fujikuroi
Introduction
Gibberella fujikuroi is a species of fungus that belongs to the Fusarium genus. It is known for causing a disease in rice plants known as "bakanae", which translates to "foolish seedling" in Japanese. The disease is characterized by the elongation of the internodes, leading to the abnormal growth of the plant. This fungus is also significant for its ability to produce a variety of mycotoxins, including fumonisins, which are harmful to both humans and animals.
Taxonomy and Nomenclature
The species was first described in 1902 by Japanese mycologist Shotaro Hori, who named it Fusarium fujikuroi. The name was later changed to Gibberella fujikuroi to reflect its sexual stage. The genus name "Gibberella" is derived from the Latin word "gibber", which means hump, referring to the hump-like shape of the fungus's ascospores. The species name "fujikuroi" is a tribute to the Japanese scientist who first identified the disease in rice plants.
Morphology and Growth
Gibberella fujikuroi is a filamentous fungus that grows in a mycelial form. The mycelium is white to pink in color and can produce a variety of pigments. The fungus produces macroconidia, which are sickle-shaped and have a pointed apex and a foot-shaped base. The macroconidia are typically four to five celled and measure 30-60 µm in length. The fungus also produces microconidia, which are oval to kidney-shaped and typically one to two celled.
The fungus grows optimally at a temperature of 25°C and a pH of 6.0. It is capable of growing on a variety of substrates, including rice, corn, and other cereals. The fungus can also grow on artificial media, such as potato dextrose agar.
Pathogenicity and Disease Cycle
Gibberella fujikuroi is a pathogen of rice plants, causing a disease known as bakanae. The disease is characterized by the elongation of the internodes, leading to the abnormal growth of the plant. The fungus infects the plant through the roots and travels up the plant through the xylem, causing the plant to grow taller than normal. The infected plants are often sterile and produce no grain.
The disease cycle begins when the fungus produces spores that are dispersed by wind or water. The spores land on the rice plant and germinate, penetrating the plant tissue. The fungus then grows inside the plant, producing toxins that cause the plant to grow abnormally. The infected plant eventually dies, and the fungus produces more spores that are released into the environment to infect new plants.
Mycotoxin Production
Gibberella fujikuroi is known for its ability to produce a variety of mycotoxins, including fumonisins, moniliformin, and gibberellins. Fumonisins are a group of mycotoxins that are harmful to both humans and animals. They are associated with a variety of health problems, including esophageal cancer in humans and pulmonary edema in pigs. Moniliformin is another mycotoxin produced by the fungus that is toxic to poultry. Gibberellins are a group of plant hormones that are produced by the fungus and cause the abnormal growth seen in bakanae disease.
Control and Management
Control of Gibberella fujikuroi and the bakanae disease it causes is challenging due to the fungus's ability to survive in the soil for long periods. However, several strategies can be employed to manage the disease. These include the use of resistant rice varieties, crop rotation, and the application of fungicides.
Resistant rice varieties are the most effective way to control the disease. These varieties are bred to be resistant to the fungus and the toxins it produces. Crop rotation can also help to reduce the amount of fungus in the soil. By rotating crops, the fungus is deprived of its host, reducing its ability to survive in the soil. Fungicides can also be used to control the fungus. However, their use should be limited due to the potential for the development of fungicide resistance.