Morphological characteristics and distribution of Colletotrichum isolates morphotypes infecting mango (Mangifera indica L.) in the north of Côte d’Ivoire

Abstract

Anthracnose caused by Colletotrichum species is the most important field and postharvest disease infecting mango worldwide. A survey was  conducted in the seven mango producing districts in the north of Côte d’Ivoire to identify and characterize Colletotrichum species isolates associated with mango leaves necrosis and fruit rots. A total of 70 isolates were identified based on morphological and cultural characters. Most of isolate colour were grey or grey whitish (36%), cottony (71%) with cylindrical conidia (97%) rounded on both ends (57%). Three texture types were observed in colonies of the seventy isolates. Most of the isolates were cottony (71%) followed by abundant aspect (23%) and closely appressed (6%). According to conidia shape, two species of Colletotrichum; Colletotrichum gloeosporioides (97%) and C. acutatum (3%) were identified in the seventy isolates. Conidia length and width varied respectively from 15.4 to 19.7μm and 4.8 to 5.2 μm. The Average Linear Growth Rate (ALGR) 7 days after culture varied from 0.76 to 0.91 cm day-1. Multivariate analysis grouped the 70 isolates into four morphotypes containing, respectively: 5 (7%), 7 (10%), 17 (24%) and 41 (59%) isolates. Isolates of morphotype 1 were characterized by whitish obverse and reverse colour with an abundant  mycelia aerial aspect. The second morphotypes were represented by isolates with obverse and reverse brownish grey colour and contained both conidia with two rounded ends, and one rounded and one sharped ends. The third morphotype consisted of isolates with obverse and reverse grey whitish colour. The fourth morphotype consisted of isolates with obverse and reverse respectively dark grey and grey or vice versa. Conidial length and width of morphotypes varied, respectively, from 14.5 to 17.2 μm and 4.6 to 5.2 μm. ALGR of morphotypes varied from 0.84 to 0.87 μm day-1. The present study highlighted that morphological variation of Colletotrichum species existed among the different isolates and the districts surveyed. However, to overcome the inadequacies of this traditional morphological identification, sequence analyses are needed to be carried out to confirm the identity of these Colletotrichum species isolates.

Key words: Mango, Anthracnose, Colletotrichum sp., isolate, Multivariate analysis, Morphotype, Rainy season, Dry season, Preharvest, Postharvest