Survey and estimation of pathological and edaphic causes of citrus pre-harvest fruit drop in three major citrus growing areas in Ashanti Region of Ghana.

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October 2016
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Citrus pre-harvest fruit drop is a major problem to citrus farmers in the Ashanti Region of Ghana. Farmers’ perception was assessed, pathological and soil-plant nutritional causes were researched into in three major citrus growing areas in Ashanti Region (Bekwai Municipal, Ahafo Ano South and Adansi North). Sixty farmers were interviewed with structured questionnaire to ascertain farmers’ views on the causes of citrus pre-harvest fruit drop and its management practices. Severity of the pre-harvest fruit drop was assessed by counting from all the selected areas for two varieties (late valencia and red blood). The estimation was done from mid-August to mid-September, 2015 for the red blood variety and mid-December, 2015 to mid-January, 2016 for late valencia. Using grid method, matured leaves (30 per variety from a farm) from non-bearing terminals and 12 soil cores composited for representative samples were taken from an estimated one hectare field. Twenty-four fruit samples each (dropped and un-dropped) were taken from twelve trees for analysis for each of the varieties. Plant and soil samples were analysed for N, P, K and Zn respectively at CSIR-Soil Research Institute, Kwadaso. Organic Carbon concentration was also determined. Lesioned fruits were sent to Plant Pathology laboratory of the Faculty of Agriculture, KNUST for isolation and identification of pathogen(s) associated with citrus pre-harvest fruit drop. Data obtained from questionnaire and nutritional analyses were subjected to SPSS and Genstat statistical analysis respectively. Ninety five percent of farmers were of the opinion that citrus black spot disease causes citrus pre-harvest fruit drop. Thirty-three percent of farmers indicated no control measure for fruit flies while 28.3 % of farmers combine bait application and pheromone trap in their orchards. The black spot symptoms were perceptibly seen on x matured green fruits then forces the fruits to ripe, which is called ‘kyembedie’ in the local language. However, 55% indicated that no control measure has been undertaken against the disease. Red blood variety (228) dropped more than late valencia (109) in all the major citrus growing areas. From the leaf analysis, the nutritional status for N and P at Ahafo Ano South had the highest concentrations (2.98 % and 0.17 %) whilst Bekwai Municipal had the lowest concentrations (2.29 % and 0.14 %) respectively. For K; Ahafo Ano South had the highest concentration (0.60 %) and Adansi North had the lowest (0.42 %). With zinc, Adansi North had the highest concentration (6.7 mg/kg) and Ahafo Ano South had the lowest concentration (4.9 mg/kg). It was observed that the direct relationship (r) between leaf and dropped fruit peels for zinc (0.87) and nitrogen (0.20) respectively resulted to the higher mean fruit drop (108) for late valencia. Also, the moderate the direct association for zinc (0.63) and the inverse the relationship for nitrogen (-0.37) resulted to higher fruit drop (228) at Ahafo Ano South for red blood variety. The pathogens that were found on the dropped fruits with black lesions are Phyllosticta citricarpa, Aspergillus niger, Aspergillus flavus and Collectotrichum gloeosporoides from both late valencia and red blood varieties from all the selected areas. The highest level of incidence of citrus black spot lesions for late valencia (89.64 %) was at Adansi North and red blood variety (92.18 %) at Bekwai Municipal.
A thesis submitted to the Department of Horticulture, Faculty of Agriculture, College of Agriculture and Natural Resources in partial fulfillment of the requirements for the award of the Degree of Master of Philosophy (Fruit Science),