Description
The pathogen and disease symptoms
The ubiquitous fungus Colletotrichum gloeosporioides is the anamorph stage (asexual stage of the pathogenic fungus). C. gloeosporioides is responsible for many diseases, also referred to as “anthracnose,” on many tropical fruits including banana, avocado, papaya, coffee, passion fruit, and others. Characterizations of worldwide populations of C. gloeosporioides indicate that strains from mango comprise a genetically and pathologically distinct population of this species. The mango population of the pathogen always predominated on mango, was not found on other tropical fruit crops, and had a restricted host range insofar as individuals from the population were highly virulent only on mango.” In other words, populations of the pathogen are essentially host-specific.
Damage
On mango, anthracnose symptoms occur on leaves, twigs, petioles, flower clusters (panicles), and fruits. On leaves, lesions start as small, angular, brown to black spots that can enlarge to form extensive dead areas. The lesions may drop out of leaves during dry weather. The first symptoms on panicles are small black or dark-brown spots, which can enlarge, coalesce, and kill the flowers before fruits are produced, greatly reducing yield. Petioles, twigs, and stems are also susceptible and develop the typical black, expanding lesions found on fruits, leaves and flowers. Ripe fruits affected by anthracnose develop sunken, prominent, dark brown to black decay spots before or after picking. Fruits may drop from trees prematurely. The fruit spots can and usually do coalesce and can eventually penetrate deep into the fruit, resulting in extensive fruit rotting. Most green fruit infections remain latent and largely invisible until ripening. Thus fruits that appear healthy at harvest can develop significant anthracnose symptoms rapidly upon ripening. A second symptom type on fruits consists of a “tear stain” symptom, in which are linear necrotic regions on the fruit that may or may not be associated with superficial cracking of the epidermis, lending an “alligator skin” effect and even causing fruits to develop wide, deep cracks in the epidermis that extend into the pulp. Lesions on stems and fruits may produce conspicuous, pinkish-orange spore masses under wet conditions. Wet, humid, warm weather conditions favor anthracnose infections in the field. Warm, humid temperatures favor postharvest anthracnose development.
Lifecycle
Dissemination: spores (conidia) of the pathogen are dispersed passively by splashing rain or irrigation water. Inoculation: spores land on infection sites (panicles, leaves, branch terminals). Infection and pathogen development: on immature fruits and young tissues, spores germinate and penetrate through the cuticle and epidermis to ramify through the tissues. On mature fruits, infections penetrate the cuticle, but remain quiescent until ripening of the climateric fruits begins. Symptom and disease development: black, sunken, rapidly expanding lesions develop on affected organs Pathogen reproduction: sticky masses of conidia are produced in fruiting bodies (acervuli) on symptomatic tissue, especially during moist (rainy, humid) conditions. Many cycles of disease can occur as the fungus continues to multiply during the season. Pathogen survival: the pathogen survives between seasons on infected and defoliated branch terminals and mature leaves.
