Bitter rot of apple

The term “bitter rot” has consistently been associated with this disease in literature from the United States going back through the 1800s. During the 1950s to 1980s there was literature out of Great Britain and Ireland that used the common name of “bitter rot” for apple rots caused by Neofabraea (or the older synonym of Gloeosporium) species, which are now referred to as lenticel rot or bulls eye rot. Literature from South Korea often uses the name of "apple anthracnose". Some scientists distinguish between rots caused by the C. gloeosporioides and C. acutatum species complexes, calling them "Glomerella rot" and "bitter rot", respectively. However "bitter rot" or the more specific "bitter rot of apple" or "apple bitter rot" are the most common terms used in English language literature. == Causal species ==

Historical names The fungi that cause bitter rot of apple were first formally described in 1856 by Miles Berkeley of Great Britain as Gloeosporium fructigenum. Bertha Stoneman later observed that G. fructigenum was similar to certain fungi from citrus that Pier Andrea Saccardo had placed in the Genus Colletotrichum. In the early 1900s Perley Spaulding and Hermann Von Schrenk lumped several indistinguishable fungi together under the name Glomerella cingulata. While technically only the name for the teleomorph, in practice the name G. cingulata was used for both the sexual and asexual fungi that were causing bitter rot. In the United States it was noted that the fungi that cause bitter rot could broadly be divided into an asexual northern form and a faster-growing perithecia-producing (sexually reproducing) southern form. Though rarely used to describe the fungus that caused bitter rot, the anamorph (asexual form) went by multiple different names that usually differed based on what host plant they were isolated from. In 1957 the great lumper of fungal species Josef Adolf von Arx created some order out of the chaos and synonymized over 600 fungal names into the single name of Colletotrichum gloeosporioides. However, von Arx went just a touch too far, and less than a decade later the isolates that had acute (pointed) conidia (asexual spores) were named Colletotrichum acutatum. G. cingulata and C. gloeosporioides were the teleomorph and anamorph (sexual and asexual) stages of the same fungus, while C. acutatum was an anamorph for which a teleomorph was almost never observed. While the name of G. cingulata was most common, the fungi that cause bitter rot were categorized under the names of G. cingulata, C. gloeosporioides, and C. acutatum up through the early 2000s. Within the C. acutatum species complex, the species of C. fioriniae, C. godetiae, C. nymphaeae, C. salicis, C. orientalis, C. cuscutae, C. acerbum, C. acutatum sensu stricto, C. melonis, C. rhombiforme, C. limetticola, C. paranaense, and C. simmondsii have so far been identified as causing bitter rot. Of these C. fructicola, C. chrysophilum, C. siamense, and C. noveboracense are by far the most common species associated with bitter rot. == Disease Cycle ==

The Colletotrichum species that cause bitter rot overwinter in infected fruit mummies, buds, twigs, and branch cankers. Spores are dispersed throughout the year during periods of leaf wetness when the temperature is between 10°C and 32°C. Apple fruit can become infected during the growing season anytime spores are available and temperature and wetness hours are optimal for infection. In a pattern typical of hemibiotrophs, the bitter rot infection will establish itself without causing rot, then will often wait until the fruit ripens and is less resistant to rot to switch to necrotrophy and form the dark sunken bitter rot lesions. Fruit that is infected during the summer will often not show any symptoms of rot until close to or after harvest. == Management ==

Cultural control Bitter rot of apple management begins with good horticultural practices that includes the planting of trees that are less susceptible to bitter rot, the removal of infected fruit, dead twigs, and cankers during the dormant season, good horticultural practices to maintain the health and vigor of the tree, and training and pruning the tree to allow airflow into the tree canopy to dry it out and reduce the amount of time the fruit is wet. Fungicides Even with good horticultural practices, successful control of bitter rot on susceptible cultivars under warm and wet conditions requires regular applications of fungicides. == References ==