Control of penicillium digitatum growth on citrus fruit using two plant extracts and their mode of action

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Fresh produce and marketing

More than 98% of the fruit produced in Ethiopia are supplied to the nearest local markets. Most of the produce on the local market is supplied by UAAIE and HDE farms, which is marketed to Addis Ababa, Nazareth, Methahara, Diredawa and Harar.
The fruit produce from Toni, Hursso and Errer Gota is supplied to the eastern capital cities (Dire Dawa, Harar) and to a lesser extent to Addis Ababa. Fruits from the North Central Ethiopia citrus farms (Merssa, Tisabalima and Jarri) are marketed to Dessie, Woldya and Mekele towns. A very small proportion of fruit produce (2%) from the central east parts of Ethiopia (UAAIE, Tonni, Hursso and Error Gota) is exported to the neighbouring countries i.e. Djibouti and Somalia. Movement of produce across the border is mainly by private dealers using railway transport and trucks where there are no cooling facilities except spraying water manually over the surface of the fruit during the long hours (10-12 hr) of travel, which could also be at night.

CONCLUSION and RECOMMENDATION

The wide range of altitudes, climates and soil types in Ethiopia allowed for effective production of a variety of crops. Citrus is one of the high value crops cultivated in the country next to coffee in terms of local production. However, the production and export of citrus fruit to international markets is minimal and/or non-existent. Pre- and postharvest practices attribute to quality deterioration of citrus fruit. Improvements in the following practices are therefore crucial:
1. Selection of known disease resistance root stock varieties,
2. Improvement in field sanitation and controlling of weeds, infected trees and/or other crops growing around or in citrus farms. Cultivation of legumes (Lablab purpureus L.) (Fabaceae) under the orchard after land clearing during the onset of the second harvesting season (e.g. at Tisabalima, South Wollo), control weed growth and ameliorate soil nitrogen,
3. Development of appropriate alternative irrigation practices to replace the currently used double ring basin system,
4. Maintaining the water balance between onset of flowering, fruiting and ripening of fruit to avoid saltiness and fruit burst,
5. Improvement in harvesting practices and in fruit handling, and the subsequent training of these workers in best practices,
6. Although fruit volumes on the Ethiopian local fruit market is fast moving, the use of cold storage and clean packinghouse facility is important to retain quality,
7. Establishment or upgrading of centres for disease and pest identification and control studies, and 8. Careful integration of production and marketing for local and export products to improve the Ethiopian citrus industry.

In vitro antagonist screening assay for broad spectrum activity

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In vitro screening of antagonists for broad-spectrum activity was done according to the method described by Spadaro et al. (2002) with slight modifications. Three postharvest fungal pathogens: P. digitatum (UPPed-1), G. candidum (UPGec-1) and Colletotrichum gloeosporioides Penz (UPCog-1) obtained from the culture collection of Plant Pathology Laboratories, (University of Pretoria) were used as a test pathogens. Fungal cultures grown on Malt Extract Agar (MEA) (Merck, Johannesburg) for seven days at 25 ºC were placed under UV light for 7-14 days until sporulation. A standard concentration (105 spores ml-1) of each pathogen suspension were prepared in Ringer’s solution and used immediately in the subsequent trials. Eighteen potential antagonists selected from the in vivo experiments on citrus in section 4.2.4 were used. The growth rates of antagonists were tested on four different solid media (PDA, MEA, STD-1NA and citrus peel-agar). For the citrus peel agar medium preparation, 5% v/v of citrus peel were homogenised and filtered through Whatman no. 1 and added to 20g l-1 of Agar-Agar (pH 5.5). A standard concentration of antagonist suspension (108 cells ml-1) determined using Petroff Hauser counting chamber was used in the challenge test against the three pathogens. Ten micro litres of antagonist cell suspension was streaked on one side of MEA medium in 90 mm Petri dishes, 2mm from the border and three streaks per plate was made at each opposite side at equal distance from the centre. The same volume of pathogen suspension was put at the centre and plates were air dried and incubated at 25 ºC for seven days. Percentage growth inhibition of the pathogen was calculated according to Skidmore (1976) using the formula: (C-r) x 100/C, where, C = growth diameter of pathogen alone, r = growth diameter of pathogen grown with an antagonist.

CHAPTER ONE GENERAL INTRODUCTION 
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CHAPTER TWO LITERATURE REVIEW 
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CHAPTER THREE CITRUS (CITRUS SINENSIS ) DISEASE SURVEY: KNOWLEDGE, ATTITUDE AND MANAGEMENT PRACTICES IN ETHIOPIA 
Abstract
Introduction
Material and Methods
Results and Discussion
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CHAPTER FOUR DEVELOPING ETHIOPIAN MICROBIAL BIOCONTROL AGENT(S) FOR CITRUS POSTHARVEST DISEASE CONTROL 
Abstract
Introduction
Material and Methods
Results
Discussion
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CHAPTER FIVE IN VITRO ANTIMICROBIAL ASSAY OF SOME MEDICINAL PLANTS FROM ETHIOPIA AGAINST PLANT AND FOOD BORNE PATHOGENS 
Abstracts
Introduction
Material and Methods
Results
Discussion
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CHAPTER SIX CONTROL OF PENICILLIUM DIGITATUM GROWTH ON CITRUS FRUIT USING TWO PLANT EXTRACTS AND THEIR MODE OF ACTION 
Abstracts
Introduction
Material and Methods
Results
Discussion
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CHAPTER SEVEN SEMI COMMERCIAL EVALUATION OF PLANT EXTRACTS ON QUALITY RETENTION IN CITRUS SINENSIS 
Abstract
Introduction
Material and Methods
Results
Discussion
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CHAPTER EIGHT GENERAL DISCUSSION AND CONCLUSION 
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RESUME 

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