Corynespora cassiicola

Corynespora cassiicola is a species of fungus well known as a plant pathogen. It is a sac fungus in the family Corynesporascaceae. It is the type species of the genus Corynespora. This fungus infects over 530 species of plants in 53 families. It is most common in the tropics and subtropics. It has also been isolated from nematodes and from human skin. The fungus is known as a pathogen of many agricultural crop plants, especially cowpea, cucumber, papaya, rubber, soybean, and tomato. It has caused crop failures resulting in high economic losses in over 70 countries, including losses of over US$3000 per acre in tomato crops in Florida in the United States. On several plants, such as tomatoes, the fungus causes a disease called target spot or target leaf spot. The disease is identified by leaf damage taking the form of target-shaped spots with light centres and dark margins, as well as pits on the fruit. The fungus also causes a disease on the cultivated rubber tree Hevea brasiliensis called corynespora leaf fall (CLF). It is one of the most economically significant fungal pathogens of rubber trees in Asia and Africa, causing 'fishbone'- or 'railway track'-shaped lesions on the leaves. In regards to detection of Corynespora cassiicola, it is useful to inspect the plant's bottom leaves while looking for ring-patterned spots that can be up to 10 mm in diameter. This pathogen is able to show symptoms on a vast host range and on several different structures. That being said, it is beneficial to additionally check the plant's roots, stems, and fruit exterior for symptoms. There are several cultural control practices that may be useful for managing this pathogen. Before planting begins, measures should be taken for prevention. These measures include avoiding planting crops next to ones known to already have the disease. In order to do so, seedlings should be checked for these leaf spots previously mentioned. If the Corynespora cassiicola is discovered on the plant during its development, management of the disease includes removing and burning the plant's lower leaves. Additionally, it's important to ensure that there are no weeds present on the plant plots because these weeds may act as hosts and harbor the fungus. Additionally, weeds can be considered disadvantageous in a field because they work to compete against the host for nutrients. Some tactics for managing weeds include applying mulch to the soil or introducing a natural pathogen of the weed as a method of biocontrol. If the pathogen is discovered after harvesting the host, management includes burning the infected crop in the attempt to rid the disease from the environment. Furthermore, practicing plant rotation and waiting three years before replanting the host on the same land can be beneficial for pathogen prevention. Chemical control may also be employed to promote disease prevention. Several researchers at the University of Florida conducted a study in which they tested a variety of fungicides on the pathogen. They tested 11 Corynespora cassiicola isolates and concluded that all tested isolates were highly resistant to the fungicides azoxystrobin and pyraclostrobin. This information suggests that because QoIs are not advantageous fungicides to use for Corynespora cassiicola management, fungicides with different FRAC codes may be more useful. So, farmers should consider fungicides with modes of action that are different from QoI when determining which chemical to apply. Although Corynespora cassiicola has been reportedly located in a wide distribution throughout the world, the conditions in which this pathogen best spreads and develops are found in the tropics and subtropics. The locations of these reports include plant species in American Samoa, Brazil, Malaysia, and Micronesia. Furthermore, the pathogen was reported in Mexico in 2013 and China in 2014. Corynespora cassiicola requires high humidity for infection and is additionally favored in locations with substantial periods of high moisture (16–44 hours). In other words, the leaf wetness is likely a major environmental factor driving the disease for this fungal pathogen. The humidity may be used as a surrogate for leaf wetness, as it is an essential component of an environment and has data that can be easily measured. This pathogen is an especially prominent foliar disease of tomato in Florida, which provides the optimal high humidity environment for the disease growth and development. Images of the symptoms in this opportune environment have been provided by professors of plant pathology from Florida, Dr. Ken Pernezny and Dr. Gary Vallad. In regards to the symptoms on the leaves of tomato plants, there is evidence of chlorosis as well as small, brown circular spots covering the leaves. The symptoms of the tomato fruit exterior include larger, brown circular deformations on the plant's exterior skin. These illustrations are important to note because they depict the symptoms of Corynespora cassiicola on a tomato plant that is developing in its favorable environment.