**3. Aetiology and epidemiology of anthracnose disease of mango**

### **3.1 Aetiology of anthracnose disease of mango**

Anthracnose disease of mango is one of the serious diseases of mango worldwide as it affects the crop from nursery through growth (pre-harvest) to harvested fruits (post-harvest) [11, 13, 14]. Many reporters have confirmed that two closely related species of Colletotrichum are involve in disease initiation and development. These species are *Colletotrichum gloeosporioides* Penz and Sacc. (Teleomorph: *Glomerella cingulata*) and *Colletotrichum acutatum* (Teleomorph: *Glomerella acutata*) [15–17]. In Ghana, literature has predominantly reported that the *C. gloeosporioides* is the causal agent of the disease [18, 19].

### **3.2 Epidemiology and disease cycle**

The disease initiation, growth and development of the pathogen are influenced greatly by the nutritional and environmental factors of the host plant (Mango). Among the nutritional factors are sources of nitrogen and carbon [20] whereas the environmental factors for disease development wet, humid, hot weather [21] as well as pH and Temperature [20]. The pathogen is also considered generally inactive in dry weather [3].

It is reported that the source of primary inocula of the disease if the abundance of conidia in the tree canopy [3]. The disease attacks every part of the plant i.e. young nursery seedling leave and twigs, young flowers/flower clusters (panicles), young fruits as well as mature fruits. The cycle of the disease begins with the dissemination of the conidia (asexual spore) of the pathogen which are dispersed passively through rain splashes or irrigation water. The plant is inoculated when conidia land on the infection courts or sites (most of which are above ground parts of the plant). Infection and disease development are also achieved on young and immature fruit and tissues, conidia are germinated and penetrated in the cuticles and epidermis to ramify through the tissues. On mature fruits, infections occur immediately when spores penetrate the cuticle. However, they remain at a latent state until climacteric fruit ripening begins. During disease symptoms development, black, sunken, rapidly expanding lesions develop on affected organs. On leaves, symptoms are seen as small, brown-to-black lesions on most affected parts.

On fruits where major destruction occur both in pre and post-harvest, symptoms of black/dark is visibly as well as slightly sunken lesion with irregular shape, then gradually enlarges and subsequently causes fruit rot. The first appearance of symptoms as spots usually coalesces and penetrate deep into the fruit, resulting in extensive fruit rotting. In most green fruits, infections remain latent and largely invisible until

ripening, that fruit that appear healthy at harvest can develop significant symptoms upon ripening. The second symptom type of the fruit is one that commonly refers to as an "alligator skin" in which on the fruits consist of a "tear stain" symptoms, in which appear a linear necrotic region on the fruits that experience superficial cracking of the epidermis. Lesions on stem and fruits may produce visible, pinkish-orange spore masses under wet conditions. During reproduction of the pathogen, sticky masses of conidia and production of fruiting bodies (acevulli) on symptomatic tissues during humid conditions. Repeated cycles of the disease may occur as a result of continuous multiplication of the fungus during the season which can serious epidemics. In the absence of favourable conditions, the pathogen overwinters in plant debris such as defoliated leaves, dead branches and other volunteer tree species.
