Dissertations
https://hdl.handle.net/20.500.12504/201
2024-03-25T19:27:15ZGenetic diversity and resistance to cassava brown streak disease in central Uganda
https://hdl.handle.net/20.500.12504/1608
Genetic diversity and resistance to cassava brown streak disease in central Uganda
Sam, Ogwal
Cassava (Manihot esculenta Crantz), a common food security crop in many sub-Saharan African countries is being threatened by cassava brown streak disease (CBSD) which causes up to 100% yield loss in susceptible varieties. Cassava brown streak disease is caused by two distinct Ipomoviruses namely Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV Cassava brown streak disease causes symptoms characterised by chlorotic patches on leaves, dark brown "streaks" on stems, cracked constricted corky, yellow-brown necrotic root tubers of cassava. However, variability of symptoms exists within cassava genotypes and CBSV strains depending on the environmental conditions. Currently in central Uganda, there is limited information on CBSV genetic and symptom diversity, as well as sources of resistance to CBSV. Yet development of CBSD control strategies requires knowledge of CBSV genetic diversity, virus-host interaction and availability of resistant cassava germplasm to CBSD. The objective of this study was therefore to 1) assess genetic diversity and distribution of cassava brown streak disease causal viruses in central Uganda. 21 unravel the symptom diversity of CBSD causal viruses on selected cassava genotypes. 3) identify potential sources of resistance to cassava brown streak disease in central Uganda.
Symptomatic leaf samples collected from the four districts in central Uganda were used for total RNA extraction using CT AB protocol. The purified samples were subjected to PCR amplification of specific DNA sequence by in vitro DNA synthesis done as prescribed by
Mullis and Faloona (1988). PCR products were separated using electrophoresis and the sequencing of PCR products was done in Netherland at Macrogen laboratory and the sequenced products were edited using Edit Seq in DNA Star, aligned using clustal logarithm
MEGA 6 software and coat protein nucleotide sequence data analysed using AMOVA. The results revealed that there was variation in nucleotide sequence and the coat protein among and within CBSV strains with isolates clustering into two groups. Additionally, CBSV was the dominant strain, followed by UCBSV and last mixed infection among 18 out of 20 symptomatic leaves sampled. Symptoms diversity and sources of resistance were identified by inoculating disease free cassava grown in screen house with CBSV strains singly and in combinations using chip bud method of grafting. Symptom diversity was identified based on the dominant symptoms from symptoms appearance at 1 MAI to 3 MAI. For resistance, incidence and severity was assessed. Later severity scores were used to compute area under disease progress curve (AUDPC). Findings showed that there was significant difference (P<0.001) in reaction of cassava genotypes to CBSV viral strains. In addition, significant variety x viral strains interactions (P<0.001) was observed. The highest CBSD incidence and severity was recorded from Kwatampola and the lowest in NASE14. Overall, NASE 14 and NAROCASS were resistant while Aladu, NASE12, Njule, Bam_unanika and Bukalasa were moderately susceptible.
Symptom diversity and severity was scored visually from symptom appearance and continued at monthly intervals for three months using a scale of 1 - 5. Findings showed Variation in symptoms of CBSD existed on leaves and stems of cassava genotypes inoculated with CBSV, UCBSV and CBSV+UCBSV strains. Infact, the symptoms varied from chlorotic spots on leaf tips to mild chlorosis, mottling of secondary to primary veins and mild stem streaks. It was concluded that CBSV and UCBSV were dominant strains of CBSV.
Additionally genotype NASE 14 was most resistant to CBSD. Accordingly CBSD symptoms varied from chlorotic spots to mild stem streaks. This study has an implication on the management of CBSD in Uganda. However another study to assess the relationship of CBSV viral load, CBSD symptom severity and resistance of cassava genotypes needs to be conducted.
xv, 90 p. : ill. (some col.) ;
2019-11-01T00:00:00ZField efficacy and economic viability of entomopathogenic fungal products for managing the tomato leafminer (tuta absoluta) in Uganda
https://hdl.handle.net/20.500.12504/1209
Field efficacy and economic viability of entomopathogenic fungal products for managing the tomato leafminer (tuta absoluta) in Uganda
Kabaale, Fred Peter
Management of the invasive tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has primarily relied on increased application of hazardous synthetic chemical pesticides with limited success. The use of entomopathogens has been advanced among safer and more sustainable management options. The field efficacy of candidate fungal isolates, Metarhizium anisopliae ICIPE 20, M. anisopliae ICIPE 69 (Campaign®) and Dudu Acelamectin (positive check) was evaluated against T. absoluta on tomato through inundative application. Experiments with treatments laid in Randomised Complete Block Design and replicated thrice, were conducted during cropping seasons April – July, 2019 (first season) and December, 2019 – March, 2020 (second season) at Mukono Zonal Agricultural Research & Development Institute, Mukono district in Uganda. Tuta absoluta incidence, injury severity on leaves and fruits, fruit yield loss, and economic viability of test treatments were assessed. Results showed generally reduced injury severity and significantly lower fruit yield loss in treated plots compared to untreated plot in both seasons. Tomato fruit yield was higher in treated plots than the untreated plot. The marketable fruit yield gain for Dudu Acelamectin, M. anisopliae ICIPE 20 and M. anisopliae ICIPE 69 treatments was respectively 130.15, 72.14 and 55.3% during first season, and 41.21, 22.01 and 15.85% during second season. The three respective treatments had Benefit cost ratio (BCR) of 8.92, 4.31 and 3.43 during first season, and 6.30, 2.84 and 2.14 during second season. The treatments showed a degree of effectiveness and economic viability in controlling T. absoluta on tomato in the field. However, the efficacy of M. anisopliae ICIPE 20 and ICIPE 69 should be assessed further at different agro-ecological zones, dosages, formulations, large scale, and their compatibility with the pesticides commonly used in tomato production systems.
xii,92p.:ill (some col)
2022-03-01T00:00:00ZYield loss and resistance to pineapple heart rot disease on pineapple cultivars in central Uganda
https://hdl.handle.net/20.500.12504/947
Yield loss and resistance to pineapple heart rot disease on pineapple cultivars in central Uganda
Oculi, jasper
Pineapple (Ananas comosus (L.) Merr) is of tremendous importance as a fruit crop in Uganda.
However, production in Uganda is currently threatened by outbreaks of pineapple heart rot
disease (PHRD). PHRD is the most widespread and devastating disease of pineapple in Uganda
and can cause tremendous yield loss. Although, some preliminary information exists on PHRD
in Uganda, the yield loss attributed to the disease has not quantified neither is there any
information on sources of resistance. The objective of this study was, therefore, to determine
yield loss and resistance to pineapple heart rot disease in central Uganda. In order to address
these objectives, five cultivars of pineapple were planted in the screen house and in the field in a
completely randomized design (CRD) and randomized complete block design (RCBD),
respectively. Treatments on yield loss assessment consisted of protected plot, un-protected plot
and control plot respectively. Pineapple plants in the protected plots had their suckers dipped for
three minutes in a solution of Metalaxyl (Active Ingredients: methoxyacetyl)-N-(2, 6-xylyl)-DLalaninate
8%) before planting and later sprayed with a solution of Fosetyl Al (Active Ingredients:
Aluminum trees 80%) using a backpack sprayer with Hardir flat spray nozzles three weeks after
planting. Pineapple plants in the un-protected plots were not treated with any fungicide. The
suckers were inoculated with 108m1 of zoospores using needle-mediated leaf base wound
technique. Treatments on resistance consisted of five cultivars of pineapple (Smooth Cayenne,
Victoria, Sasilimu, MD-2 hybrid and Red Spanish) Planted in a field with a history of PHRD
infestation. Results from the screen house study indicated100% yield loss in all five cultivars
after two months. Field experiments indicate that all the five cultivars used were susceptible to
PHRD although Smooth cayenne showed moderate resistance to PHRD. Additional studies,
therefore, need to be conducted using more pineapple cultivars to establish their suitability as
genetic material in breeding for resistance against PHRD and to minimize yield loss.
ix,63 p.: ill (some col)
2017-12-01T00:00:00ZMorphological identification and in vitro efficacy of fungicides in control of phytophthora causing pineapple heart rot disease in Uganda
https://hdl.handle.net/20.500.12504/945
Morphological identification and in vitro efficacy of fungicides in control of phytophthora causing pineapple heart rot disease in Uganda
Ocwa, Akasairi,
Pineapple (Ananas comosus L. Merr) production in Uganda is being constrained by a diversity of
factors including pineapple heart rot disease (PHRD). Information on PHRD causal pathogen is
limited. Also, management options are clear. The objectives of this study were, therefore, to
identify the casual pathogens causing PHRD and assess the in vitro reaction of the causal
pathogens to fungicides. Pathogen isolation was done using amended corn meal agar. Macro and
micro-morphological characteristics of the isolates were assessed. Pathogenicity of the isolates
was tested using healthy pineapple plants based on Koch's postulate. In vitro reaction was
determined using I 0% V8 media amended with 0.1 g/L Metalaxyl, 0.1 g/L Victory 72 powder,
0.01 g/Land 0.001 g/L Metalaxyl, 0.01 g/L and 0.001 g/L Fosetyl Al and unamended V8 media
as a control. There was a significant difference (P<0.05) in the growth rates, hyphae diameter
and asexual structure dimensions of the isolates. Isolates were characterized by a dense rosette
and stoloniferous mycelial growth pattern in PDA media. Sporangia were non-caduceus.
terminal, papillate and mostly ovoid, obpyriform and limoniform sporangia (32-56μm) with a
mean length/breadth ratio of 1.32: I μm . Chlamydospores were spherical and thick-walled (25-
42μm diameter). Sporangiophore branching was sympodial. All the isolates were sensitive to
Metalaxyl and Victory 72 powder treatment. Based on the morphological characteristics of
isolates, it was concluded that Phytophthora nicotianae is the species associated with PHRD in
central Uganda. Additionally, Metalaxyl was the most effective chemical against the pathogen in
vitro. Molecular characterization of the pathogen is recommended to confirm the identity of the
species. It is also recommended that the efficacy of fungicides which have shown effectiveness
be assessed further under field conditions.
xiv,65 p.: ill (some col)
2016-12-01T00:00:00Z