JASSA: Journal of Applied Science in Southern Africa

Pre-harvest spoilage of avocado (Persea americana) fruits by Capnodium isolates in Zimbabwe

E Mwenje

Thirteen fungal isolates associated with pre-harvest spoilage of avocado fruits were isolated on potato dextrose agar by incubating the infected avocado fruit tissue segments at 25 oC for 7 days. Three types of fungi were isolated from the infected tissue namely Glomerella cingulata (Stonem.), Aureobasidum pullulans (De Bary) and Capnodium sp. (Mont.). Capnodium sp. had the highest frequency (90.9 %) while only a single isolate was isolated for Aureobasidium pullulans. Pathogenicity tests using avocado fruits showed that Capnodium and Glomerella cingulata isolates caused soft rot symptoms similar to those observed on infected avocado fruits on the tree. Capnodium isolates gave the highest lesion diameter (3.0-7.1 cm) while Aureobasidium pullulans did not cause any lesion or soft rot symptoms on inoculated avocados. Although avocados are known to be hosts to Capnodium sp., in Zimbabwe, this is the first report implicating Capnodium sp. in the pre-harvest spoilage of avocado fruits. Preliminary studies show that Capnodium isolates produce cell wall degrading enzymes especially pectic and cellulolytic enzymes which are known to play a major role in most soft rot diseases.

Keywords: Capnodium, sooty mould, pre-harvest spoilage, pathogenicity

Organophosphate and organochlorine exposure in selected horticultural farms in Zimbabwe

S Khoza

The epidemiology of pesticide use and pesticide exposure in the farming communities has been researched on and documented. The results from these studies, conducted in all sectors of agriculture except horticulture show high levels of occupational exposure. We present a pilot study conducted in two horticultural farms in Ruwa and Domboshawa 25 kilometres and 30 kilometres from Harare respectively in 2001.The main objective was to establish the level and prevalence of pesticide exposure in workers in the horticultural industry. Blood samples were collected from 33 workers from the two farms. Cholinesterase activity was measured using the WHO cholinesterase kit and organochlorine residues were analysed using the GC method. Organochlorine residues were detected in the following order of frequency, pp-DDT, 100%; op-DDT, 100%; aldrin, 95%; a-HCH, 100%; dieldrin, 86.4%; heptachlor, 22.7% and opDDD, 18.2% from the blood samples analysed. The ppDDT isomer was the major contributing isomer to the sumDDT. The two isomers a- and ß-HCH were also detected in the samples analysed and the former being the major contributing isomer to the sum-HCH. In Ruwa the exposed subjects had higher DDT blood levels than the control group though this was not statistically significant (p=0.1855). There was also no significant difference in the mean DDE levels of the exposed group and the control group (p=0.6851). Significant differences were however noted in the mean blood levels of a-HCH (p=0.007) and aldrin (p=0.0187). In Domboshawa there were no significant differences in the mean blood levels of organochloride residues between the exposed and the control. No significant depression of the cholinesterase activity was observed. The results demonstrated a high level of pollution of human blood with organochlorine residues. The pollution was due to both occupational and environmental exposure.

Keywords: Organochlorine, pesticide exposure, horticulture

Use of parametric and non-parametric survival analysis techniques to evaluate the effectiveness of two acaricides in controlling tsetse flies. (Diptera Glossinidae).

T Munyombwe

This paper presents parametric and non-parametric survival analysis procedures that can be used to compare acaricides. The effectiveness of Delta Tick Pour On and Delta Tick Spray in knocking down tsetse flies were determined. The two formulations were supplied by Chemplex. The comparison was based on data collected from trials carried out in Zimbabwe at Rukomichi Research Station in 2003. Rukomichi Research Station is owned by the Department of Veterinary Services and is mainly used for conducting research on tsetse flies. The Kaplan Meier estimate of survivor and hazard function was used as the non-parametric procedure for comparing survival times of tsetse exposed to Delta Tick Spray and Delta Tick Pour On. In addition the log rank statistic was also used to explore the differences between the two formulations. The parametric procedure assumed that the survival times follow a lognormal distribution after checking the suitability of the distribution and estimating the hazard, survivor function and quartiles assuming the distribution. A proportional hazard model was also fitted to compare the two formulations. The non-parametric procedure revealed that the median survival times of tsetse exposed to Delta Tick Pour On was 10 minutes compared to 12 minutes for those exposed to Delta Tick Spray. The parametric procedure showed that the median survival time of tsetse exposed to Delta Tick Pour On was 10.59 minutes compared to 13.70 for those exposed to Delta Tick Spray. The proportional hazards model indicated that the hazard of being knocked down is 1.335 more for tsetse exposed to Delta Tick Pour On than those on Delta Tick Spray (p < 0.001). Keywords: Acaricides, parametric, non-parametric survival analysis procedures, tsetse flies

Rangelands in Zimbabwe’s initial resettlement schemes: Spatial and temporal change analyses

T Chinuwo

Change in size and extent of cultivation and vegetation cover was analysed in three villages of an initial resettlement scheme in Zimbabwe using change detection depicted on serial aerial photographs taken at eight-year intervals from inception in 1981 to 1997. A geographic information system was used as an analytical tool. Interpretations were done using aerial photographs and 1995 Spot Images. The spot images were geo-referenced to Universal Transverse Mercator (UTM) coordinate system to ensure continuity of features. All images were enhanced using TNTmips to come up with clearer images. Aerial photographs for the three selected villages were scanned and geo-referenced and then exported to ARC VIEW 3.2 for on-screen digitising of land parcels as cultivated and vegetation theme layers. Overlay and spatial analysis were also done in ARC VIEW 3.2 for change detection. Results showed an average increase in size of cultivated areas by 281% between 1981 and 1997 and a increase of 52% between 1989 and 1997 in the three villages. Rangelands declined by a mean 42% during 1981 and 1997. There was a shift in land-use in 1987/8, which exaggerated cultivated areas due to fuzzy classification of land reverting to grazing areas by 1989. This shift in cultivation sites was adequately captured on overlaid aerial photographs for each of the three villages. It was concluded that spatial and temporal changes occurred in resettlement schemes rangelands and were due to the actions of resettled farmers.

Keywords: Resettlement schemes, change detection, spatial analysis.

Influence of cowpea and melon populations on weed infestation and farmers’ attitude to weed control practice

AJ Udoh

Small farmers in the humid regions of tropical Africa spend 30–42% of their total farm labour input in controlling weeds. Chemical weed control is normally recommended but high cost of herbicides and environmental pollution are specific problems with chemical weed control. A three year bio-weed control system with three populations of cowpea (20, 33, and 50 x 103 plants ha-1) and melon (5, 10 and 15 x 103 plants ha-1) in a cassava/maize intercrop was conducted to check weeds at 3, 5 and 8 weeks after planting (WAP) in the southeastern humid derived savanna and humid rainforest zones of Nigeria. Cowpea and melon populations at 50 x 103 and 15 x 103 plants ha-1 significantly reduced weed infestation in the cropping system. Since rural women constitute 50–60% of the farming population and are a significant source of labour in weeding operations then a weed control strategy with melon crop which provides oil and protein to farm families may be highly innovating to them. One hundred women farmers were invited to visit the research extension plot at 3, 5 and 8 WAP, before weeding. At 5 WAP, 80% of the farmers and at 8 WAP, 100% of them preferred to adopt 50 x 103 cowpea with 15 x 103 melon plants ha-1 since this combination gave the most effective weed control. Cassava grown as sole crop produced higher root yield ha-1 than when grown with maize, cowpea and melon in the three years and at both locations. Grain yield of maize was significantly depressed in the intercrop system. Cowpea grain yield increased with increase in population, but the increase per unit change in population was much higher in sole cowpea. Similarly, seed yield of melon increased significantly with increase in its population in intercropped and sole cropped melon. The highest net incomes of N83,540, N138,350 and N158,530 for 1989, 1990 and 1991 at Ogoja location and N134,000, N255,590 and N289,240 at Uyo for the respective years were obtained from a four-crop combination of 50 x 103 cowpea and 15 x 103 melon populations and with cassava and maize at 10 x 103 and 20 x 103 plants ha-1. Though sole crop of melon at 50 x 103 ha-1 gave a higher and significant seed yield, it was not profitable and sustainable to small-holder resource poor farmers.

Keywords: Cowpea, melon, weed control, economic analysis, farmers’ attitude

Assessment of the Prevalence of Glucose-6-Phosphate Dehydrogenase (G-6-PD) Deficiency among Patients in Harare

AR Mandisodza

Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is widely
associated with oxidant induced haemolytic episodes, especially in
people on malaria treatment. A cross sectional study on the prevalence
of G6PD deficiency in was carried out on 200 blood samples from
various private surgeries and three major Hospitals in Harare during
October and November, 2001. The blood samples were screened for the
prevalence of G6PD deficiency using the NAPD oxidoreductase method.
One hundred and eight (54%) were males and 92 (46%) were females. A
p-value of 0.1096 indicated no statistically significant difference between
the two sexes. Twenty-three out of the 200 (12 %) were G-6-PD deficient
while the remainder 177 (88%) were found to be normal. Stratifying the
23 optical density values of the deficient samples in this study showed
that four (17%) had values equal to and more than (>) 0.400 indicating
severe deficiency and 19 (83%) had values between 0.330 and less than
0.400 indicating mild deficiency. Optical density stratification may give
a possible grading system in the deficiency rates. A well planned, large
and more controlled research study is required to assess G6PD deficiency
in Zimbabwe more effectively.

Key words: Glucose-6-phosphate, oxidant, haemolysis, malaria, optical density

"Shell and space structures in modern engineering: Challenges and opportunities" - An Inaugural Lecture

A Zingoni

An Inaugural Lecture Given in the University of Zimbabwe On 4 July 2001

"Tissue oxygen tension, a determinant of resistance to infection and healing" - An Inaugural Lecture

K Jönsson

An Inaugural Lecture Given in the University of Zimbabwe on 21 June 2001