Optimization of Growth Conditions of Citrus Anthracnose Agent Colletotrichum gloeosporioides Isolates in Tunisia

Research Article

J Pathol & Microbiol. 2021; 3(1): 1017.

Optimization of Growth Conditions of Citrus Anthracnose Agent Colletotrichum gloeosporioides Isolates in Tunisia

Ben Hadj-Daoud H, Ben Salem I and Boughalleb-M’Hamdi N*

Department of Biological Sciences and Plant Protection, High Institute of Agronomy of Chott Mariem, UR13AGR03, University of Sousse, Tunisia

*Corresponding author: Boughalleb-M’Hamdi N, Department of Biological Sciences and Plant Protection, High Institute of Agronomy of Chott Mariem, BP47 4042 Sousse, Tunisia

Received: April 06, 2021; Accepted: May 01, 2021; Published: May 08, 2021


Background: Colletotrichum gloeosporioides is important plant pathogens on a wide range of plant hosts such as citrus causing pre- or post-harvest infections as anthracnose, post-bloom fruit drop, tearstain and stem-end rot on fruit, or wither-tip of twigs.

Method: The optimization of growth conditions of this pathogen was performed (solid media, temperature, pH and water potential under laboratory experiments).

Results: Our results revealed that the maximum radial growth of C. gloeosporioides was recorded on SDA medium. All isolates were able to grow on PDA at temperatures of 15 and 30°C (over 0.7cm/day). Optimal growth radial was recorded at pH 5, 6, 7 and 8. Similar responses were obtained with both salt types, but, in general, C. gloeosporioides was more tolerant to KCl than NaCl.

Conclusion: Studies of cultural, morphological traits of the pathogen are prominent to understand the response of the pathogen in different environmental and nutritional conditions.

Keywords: Anthracnose; Citrus; Colletotrichum gloeosporioides; Osmotic potential


In Tunisia, Cap-bon area is the main location for citrus with more than 70% of the national production. The local market absorbs 80 to 90% of the production [1]. The most cultivated varieties are the oranges Thomson, Meski and Valencia late (Citrus sinensis), the clementines (Citrus reticulata) and the lemons (Citrus limon) [2]. Therefore, the study and knowledge of all the pathogens affecting this crop is imperative. The use of a polyphasic approach in the past revealed new Colletotrichum species associated with citrus [3]. Colletotrichum gloeosporioides was previously thought to be the only Colletotrichum species causing post-harvest anthracnose [4-6], but investigations that are more recent showed that several species of Colletotrichum are associated with fruit decay worldwide [7-10]. Recently, various infections caused by Colletotrichum spp. strongly compromised citrus production in different Mediterranean countries. In fact, heavy pre-harvest anthracnose symptoms appeared on orange fruits and lesions on leaves of mandarins in Italy [11,12], twig withertip symptoms were observed on cultivated orange trees in Tunisia [13], and severe anthracnose symptoms on unripe and ripe lemon fruits were recorded in Portugal [14]. The optimal development conditions of C. gloeosporioides require 25-28°C temperature, pH 5.8-6.5. This pathogen is inactive in dry season and switches to active stages when encountered favorable environmental conditions [15]. Various medium preparations were employed for the growth and sporulation of C. gloeosporioides including Potato dextrose agar, lima bean agar, malt extract agar and oatmeal agar, also, inoculums density and temperature on the spore carrying capacity and microcycle conidiation [3]. Previously, spore production of C. gloeosporioides was compared on solid media with liquid media [16]. C. gloeosporioides grow well on PDA (potato dextrose agar) and CWA (coconut watery endosperm) which contain appropriate amounts of carbohydrates, proteins, minerals and lipids [17]. The growth is completely inhibited at 10°C. Light is not necessary but enhance sporulation, pH 6 (for growth and sporulation) and germination is better on a more acidic medium. Czapek’s and yeast extract agar media give maximum growth [3].

The purpose of this present investigation was to determine in vitro the optimal growth of C. gloeosporioides using media, temperature, pH level and water potential (NaCl and KCl).


Fungal isolates

Four Colletotrichum gloeosporioides isolates were collected from leaves, peduncle and twigs from two Orange’s varieties Thomson and Malti orchards (Table 1). All isolates were purified and conserved in Plant Pathology laboratory for further uses.