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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Date
October 2016
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Abstract
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.
Description
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),