Morphological and Molecular Identification of the Causal Agent of Anthracnose Disease of Avocado in Kenya.

S K Kimaru,E Monda,J Mbaka,R C Cheruiyot,A Alakonya

doi:10.1155/2018/4568520

Abstract

Anthracnose disease of avocado contributes to a huge loss of avocado fruits due to postharvest rot in Kenya. The causal agent of this disease has not been clear but presumed to be Colletotrichum gloeosporioides as reported in other regions where avocado is grown. The fungus mainly infects fruits causing symptoms such as small blackish spots, “pepper spots,” and black spots with raised margin which coalesce as infection progresses. Due to economic losses associated with the disease and emerging information of other species of fungi as causal agents of the disease, this study was aimed at identifying causal agent(s) of the disease. A total of 80 fungal isolates were collected from diseased avocado fruits in Murang'a County, the main avocado growing region in Kenya. Forty-six isolates were morphologically identified as Colletotrichum spp. based on their cultural characteristics, mainly whitish, greyish, and creamish colour and cottony/velvety mycelia on the top side of the culture and greyish cream with concentric zonation on the reverse side. Their spores were straight with rounded end and nonseptate. Thirty-four isolates were identified as Pestalotiopsis spp. based on their cultural characteristics: whitish grey mycelium with black fruiting structure on the upper side and greyish black one on the lower side and septate spores with 3-4 septa and 2 or 3 appendages at one end. Further molecular studies using ITS indicated Colletotrichum gloeosporioides, Colletotrichum boninense, and Pestalotiopsis microspora as the causal agents of anthracnose disease in avocado. However, with this being the first report, there is a need to conduct further studies to establish whether there is coinfection or any interaction thereof.

Highlights

The anthracnose disease is a common disease with wide host range causing severe economic loss
This paper aimed to identify the causal agent(s) of anthracnose of avocado in Kenya
A total of 46 isolates had whitish, greyish, or creamish colour and cottony, velvety mycelium on the top side and greyish cream with circular orange-pinkish colour on the reverse side, Figure 2(a). Their spores were straight with rounded end (Figure 2(b)), typical of C. gloeosporioides [29]

Summary

Introduction

The anthracnose disease is a common disease with wide host range causing severe economic loss. Species of the genus Colletotrichum and Pestalotiopsis have been reported as causal agents of anthracnose in avocado [5, 6]. Symptoms of anthracnose appear as pepper spot or speckle spot on immature fruit while still on tree and after fruit harvest during ripening as darkly, black coloured, sunken rounded spots with raised margins on fruit skins [12]. These lesions enlarge rapidly on the fruit skin and into the pulp leading to the death and rotting of the infected plant tissues [13]. The lesions may develop salmon-coloured, sticky spore masses typical of anthracnose diseases of this and many other plant species

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