E. Adipala

Pest management in cowpea. Part 2. Integrating planting time, plant density and insecticide application for management of cowpea field insect pests in eastern Uganda

The focus of this study was to formulate a cost-e!ective pest management strategy for cowpea growers in Uganda. An initial experiment examined the in#uence of di!erent times of planting and plant densities on infestation levels of the major eld pests of cowpea. Results indicated that planting at the on-set of rains, at 30]20 cm2 or 60]20 cm2 gave better yields. Here, we studied the e!ect of time and frequency of insecticide application on the eld pests infestations. Results showed that a single spray at budding, #owering and podding had the highest marginal returns (3.12) in comparison to spraying throughout the season (1.77) and at seedling, #owering and podding stages (2.18). The best treatments from these two experiments were combined and compared to the single control measures, and the untreated control. Cowpea grain yields and marginal returns from plots receiving combined control measures were higher than those from plots receiving only cultural or chemical control measures. Our study provides evidence that a few well-timed sprays in combination with cultural practices are not only e!ective but also very protable. ( 2000 Elsevier Science Ltd. All rights reserved.

Metalaxyl resistance, mating type and pathogenicity of Phytophthora infestans in Uganda

Abstract A total of 81 isolates of Phytophthora infestans (Mont.) de Bary were recovered from late blight infected samples collected from different areas of Uganda in 1998/1999. They were analyzed for their resistance to metalaxyl fungicide, mating types, and cross infection between potato and tomato hosts. Sensitivity to metalaxyl was determined by growing isolates on 10% V8 medium amended with 0, 5 and 100xa0μg/ml metalaxyl. Overall 44.4% of the isolates tested were resistant to metalaxyl, 23.5% were intermediate and 31.2% were sensitive. Mating type was determined on 80 isolates using an A1 (1724) isolate and by growing the same isolates in pure culture (selfing). Fifty percent of the isolates produced oospores by matings and selfings, 22.5% by mating only and 10% by selfing only; 18% did not produce oospores in the two tests. Twenty seven of the P. infestans isolates from potato-infected tomato. The majority of these isolates were highly resistant to metalaxyl and produced oospores by either mating or selfing or both.

Influence of Season and Cropping System on Occurrence of Cowpea Diseases in Uganda

An on-farm survey was conducted for two seasons (first and second rains of 1994) to determine influence of season and cropping systems on occurrence of cowpea (Vigna unguiculata) diseases in Uganda. Viral diseases were widespread in both seasons but were more severe in the intercropped than in the nonintercropped cowpea. In contrast, scab, rust, and powdery mildew were less common and less severe when cowpea was grown in intercrops. High plant populations favored scab and anthracnose, but viral diseases were more severe under low plant populations. Higher incidence and severity of viral diseases, anthracnose, and scab were recorded during the first (wetter) season than during the second (drier) season. Disease level varied considerably among the common cultivars, but these differences may have been influenced by environmental differences.

Pest management in cowpea. Part 1. Influence of planting time and plant density on cowpea field pests infestation in eastern Uganda

Abstract Insect pests are the main constraint to cowpea ( Vigna unguiculata (L.) Walp) production in eastern Uganda, sometimes causing total crop failure. This study investigated the influence of different times of planting and plant densities on field insect pests infestations on cowpea. On-farm trials were established in eastern Uganda at 3 sites for 3 consecutive seasons. Four plant densities, i.e., 30×20xa0cm 2 , 60×20xa0cm 2 , 90×20xa0cm 2 and 120×20xa0cm 2 (subplots) were imposed on three main plots, i.e. planting at on-set of rains and, 3 and 6 weeks later. Early planting reduced infestation of aphids, thrips and pod bugs but not of Maruca. High plant density also lowered aphid population. A combination of early planting and high plant density gave the best yields. The results indicated that aphids are amenable to cultural control and that complementary management strategies are needed to control other pests of cowpeas.

Sequence analysis of the entire RNA genome of a sweet potato chlorotic fleck virus isolate reveals that it belongs to a distinct carlavirus species

SummarySince the paucity of information on sweet potato chlorotic fleck virus (SPCFV) had precluded its classification, we have determined the complete nucleotide sequence of the single-stranded RNA genome of a Ugandan isolate of SPCFV. The genome is 9104 nucleotides long (excluding the poly(A) tail) and potentially includes six open reading frames (ORFs). Based on genomic organisation and sequence similarity, SPCFV appears to be a member of the genus Carlavirus (family Flexiviridae). However, SPCFV is distantly related to typical carlaviruses, as most of its putative gene products share amino acid sequence identities of <40% with those of typical carlaviruses. Its closest relative is melon yellowing-associated virus, a proposed carlavirus from Brazil, with which it shares ORF5 and ORF6 amino acid sequence identities of 61 and 46%, respectively.

Pest management in cowpea. Part 3. Quantifying the effect of cowpea field pests on grain yields in eastern Uganda.

Abstract We used regression analysis to quantify yield variations in cowpea due to major insect pests, i.e., aphids (Aphis craccivora Koch), thrips (Megarulothrips sjostedti Trybom), Maruca pod borer (Maruca vitrata Fabricius) and a complex of pod-sucking bugs. Variability in pest infestation was created by growing Ebelat (an erect cowpea cultivar) in two locations over three seasons and under different insecticide spray schedules. Stepwise regression for individual locations and seasons’ data indicated that most of the variation in cowpea grain yields was caused by thrips. We estimated that to the total variation in cowpea grain yields, on average, the major pests contribute 51–69% in Pallisa and 24–48% in Kumi. Thrips alone contribute 35–41% and 13–19% at these two sites, respectively.

Effect of crop protection management practice on yield of seven cowpea varieties in Uganda

Abstract Field experiments were conducted during the first and second rainy seasons of 1994 to evaluate the seed yield potential of two commonly grown cowpea varieties and five introduced lines under different pest and disease situations. The highest yields (4654.7 kg/ha, 2083.5 kg/ha and 974.6 kg/ha, respectively) were obtained from the lines IT82D‐522–1, IT85F‐1987 and Katumani‐80, and the least yield was from Icirikukwai, a local line. Between 32.5% to 70.7% yield depression was obtained in plots where pests were not controlled, whereas 9.2% to 16.0% yield depression was attributed to fungal diseases. These results indicate that insect pests are the most important biotic constraint to cowpea production in Uganda.

Characterization and Distribution of a Potyvirus Associated with Passion Fruit Woodiness Disease in Uganda

This article describes the incidence and etiology of a viral disease of passion fruit in Uganda. Symptoms, including those characteristic of passion fruit woodiness disease (PWD), were observed on 32% of plants in producing areas. Electron microscopic observations of infected tissues revealed flexuous filaments of ca. 780 nm. Enzymelinked immunosorbent assays indicated a serological relationship with Cowpea aphid-borne mosaic virus (CABMV) and Passion fruit ringspot virus (PFRSV). In host range studies, only species in the families Solanaceae and Chenopodiaceae were susceptible, and neither Vigna unguiculata nor Phaseolus vulgaris became infected. Coat protein (CP) gene sequences of eight isolates exhibited features typical of potyviruses and were highly similar (88 to 100% identity). However, the sequences had limited sequence identity with CP genes of two of the three potyviruses reported to cause PWD: East Asian Passiflora virus and Passion fruit woodiness virus (PWV). Deduced amino acid sequences for the CP of isolates from Uganda had highest identity with Bean common mosaic necrosis virus (BCMNV) (72 to 79%, with evolutionary divergence values between 0.17 and 0.19) and CABMV (73 to 76%, with divergence values between 0.21 and 0.25). Based on these results and in accordance with International Committee for Taxonomy of Viruses criteria for species demarcation in the family Potyviridae, we conclude that a previously unreported virus causes viral diseases on passion fruit in Uganda. The name Ugandan Passiflora virus is proposed for this virus.

Host Range, Purification, and Genetic Variability in Sweet potato chlorotic fleck virus

Sweet potato chlorotic fleck virus (SPCFV) has recently been classified as a putative new member of the genus Carlavirus (family Flexiviridae) on the basis of its molecular properties. In this study, SPCFV was characterized in terms of host range, physical and biological characteristics, and genetic variability. In addition to sweet potato, SPCFV infected some plant species in the families Convolvulaceae, Chenopodiaceae, and Solanaceae. Limited numbers of virus particles were observed in the assimilation parenchyma cells of infected plant tissues; some cells had a distorted and enlarged endoplasmic reticulum though without any cytoplasmic and amorphous inclusions. The normal length of SPCFV particles was determined to be approximately 800 nm. In enzyme-linked immunosorbent assays, polyclonal antibodies raised against purified SPCFV virions were able to detect the virus in infected sweet potato and indicator plant tissues. In immunoelectron microscopy, SPCFV particles were all strongly decorated when reacted with homologous antiserum. Comparison of the 3 terminal part of the genome of a range of geographically diverse isolates revealed a high level of genetic diversity. The amino acid sequence identity in the coat protein and the nucleic acid binding protein ranged from 89 to 99.7% and from 75.9 to 99.2%, respectively. Phylogenetic analysis of both proteins showed a geographically associated clustering into two genogroups.

Relationship between headblast severity and yield of finger millet.

Abstract Relationships between headblast (Pyricularia grisea) and yields of 16 finger millet lines were studied in Uganda for two seasons. Each finger millet line was subjected to application of carbofuran at planting; mancozeb spray from establishment to physiological maturity; carbofuran + mancozeb; and an untreated control. Yield significantly (P= 0.0001) varied with the finger millet genotype during the first rainy season and chemical treatment during the second rains (P= 0.0049). Application of carbofuran increased the numberof spikelets/plant probably because of the control of shootflies while on susceptible genotypes, blast severity was significantly reduced by application of mancozeb and mancozeb + carbcfuran. Significant yield losses attributed to blast were recorded on the susceptible lines during both the first and second rainy seasons and averaged 55%.