GRAV infection rates of Chlorotic ringspot and line-pattern symptoms were observed, suggesting infection with Groundnut ringspot virus GRSV. Virus identity was confirmed by enzyme-linked immunosorbent assay, reverse-transcription polymerase chain reaction, and amplicon sequencing. GRSV infection rates were 0.
|Published (Last):||1 June 2008|
|PDF File Size:||13.4 Mb|
|ePub File Size:||2.89 Mb|
|Price:||Free* [*Free Regsitration Required]|
GRAV infection rates of Chlorotic ringspot and line-pattern symptoms were observed, suggesting infection with Groundnut ringspot virus GRSV. Virus identity was confirmed by enzyme-linked immunosorbent assay, reverse-transcription polymerase chain reaction, and amplicon sequencing. GRSV infection rates were 0. Most cultivars graft inoculated with GRD showed significantly reduced height, leaf area, chlorophyll content, dry haulm weight, and seed yield compared with healthy plants.
GRAV alone results in symptomless infection in peanut Naidu et al. The viral pathogens are transmitted by the cowpea or groundnut aphid Aphis craccivora Koch Okusanya and Watson GRD presents itself in two major symptom forms—a green rosette and a chlorotic rosette Gibbons , Murant and Kumar —although a mosaic rosette has also been reported Storey and Ryland GRD outbreaks are sporadic and unpredictable but can result in complete crop loss Subrahmanyam et al.
The African groundnut crop has been on the decline over the last three decades as a result of GRD Ntare and Olorunju Recurring epidemics of the disease have hampered production and expansion of the crop and greatly altered cropping patterns in several sub-Saharan African countries Naidu et al. An epidemic of the GRD in northern Nigeria in resulted in the destruction of approximately 0. This is at least partially due to viral diseases, including GRD, which is not adequately managed due to high cost and unavailability of insecticides to control the insect vectors.
Tospoviruses occur worldwide Pappu et al. GRSV is not seedborne and is naturally vectored by several species of thrips from the genus Franklinella Pappu et al. The devastating nature of GRD has necessitated the use of resistant varieties as the most economical and practical disease control solution. Sources of resistance to GRD in groundnut were first discovered in in landraces of the late-maturing Virginia groundnut Arachis hypogaea L. However, under heavy disease pressure, resistant plants succumb to infection Wynne et al.
Resistance to the aphid vector has been found in some groundnut breeding lines Herselman et al. This present study sought to test the resistance of locally grown Ghanaian groundnut cultivars to GRD in order to provide cultivars for disease management in the field and to provide groundnut breeders with robust resistant parent genotypes. It has also identified GRSV for the first time in Ghana, and this necessitates consideration of this virus in future breeding programs.
The area is characterized as coastal savannah with a bimodal rainfall pattern, having a major wet season between the months of March and June and a minor wet season around October to November each year.
The mean annual rainfall is mm distributed over less than 80 days. The cultivars were assigned to plots in a randomized complete block design with four replications. In all, 30 seeds six rows of 5 seeds of each cultivar were planted per plot, with two rows left vacant for establishing infector rows; there was a planting distance of 25 and 50 cm within and between plants, respectively.
Seed were hand sown during the second week of November for the dry-season trial and the third week of June for the wet-season trial. GRD inoculum was introduced by planting infector rows Bock and Nigam These were grown in an insect-proof house, monitored for symptom development, and then transferred to the field, establishing one row of five infector plants between two rows of test plants.
Subsequent GRD spread from the infector plants to the genotypes was through natural infection by the Aphis craccivora vector. Presence of this vector species within the trial was confirmed by taxonomic identification of sampled individuals.
No insecticide was used throughout the growth of the plants. Disease incidence data percentage of plants within each cultivar with visual presence of GRD symptoms was determined by visual assessment 10 weeks after exposure to sources of inoculum, and a cultivar resistance rating was determined based on a previously described scale Waliyar et al. Following disease assessment, a three-leaf sample from the top, middle, and bottom of each plant was taken and tested for the presence of GRAV using triple-antibody sandwich enzyme-linked immunosorbent assay ELISA Rajeshwari et al.
Expression of chlorotic ringspots and line patterns suggested the presence of GRSV, which was subsequently included in tests. Leaf samples were bulked in groups of five and sap extracted by grinding 1 g of tissue in 10 ml of extraction buffer containing 20 g of polyvinylpyrrolidone, 2 g of ovalbumin, 1.
Sap extracts from known GRD-infected and healthy plants were used as positive and negative controls, respectively.
Absorbance values were measured at nm using a spectrophotometer Multiskan Ascent VI. Samples with absorbance values more than twice that of the healthy controls were considered positive for the virus. The proportion of plants infected in bulked samples was calculated using the likelihood estimator method Gibbs and Gower PCR conditions used were as described by Boari et al. Seed of the various cultivars were raised in polythene bags in an insect-proof house. Two weeks after emergence, 30 plants of each genotype were grafted with GRD-infected scions collected from the field that had tested positive for GRAV and 30 were grafted with healthy GRAV-free scions obtained from disease-free plants raised in an insect-proof house that tested negative for GRAV as controls.
The plants were maintained in the insect-proof house for 1 week, then transplanted to the field. They were assigned to plots in a randomized complete block design with three replicates. Ten plants per plot were planted at a distance of 25 and 50 cm within and between plants, respectively. The plants were sprayed at 2-week intervals with the insecticide Actellic 50 EC active ingredient: pirimiphos-methyl; Syngenta Crop Protection Ag, Basel, Switzerland to prevent external infection by incoming viruliferous aphids.
The experiment was repeated for four of the cultivars: Sinkapoporigo resistance unknown , Nkosuor moderately resistant , Otuhia resistant , and Yenyawoso susceptible.
The plants were inoculated as described above but, in this instance, plants remained within the insect-proof greenhouse. The concentration of chlorophyll in both symptomatic and healthy leaves of each cultivar was determined at four preflowering and eight during pod development weeks after inoculation using a chlorophyll content meter CCM Plus; Opti-Sciences, Hudson, NH. Leaf area of the third topmost fully expanded leaves was measured from both infected and healthy plants of each cultivar 2 weeks before harvest using a leaf area meter Area Meter AM ; ADC Bioscientific Ltd.
Plant height of both infected and healthy plants of each variety was measured from the base of the plant at soil level to the tip of the stem. At harvest, diseased and healthy plants were cut at soil level, separated into stems and leaves, and weighed. Seed yield was assessed by harvesting pods from each variety from diseased and healthy plants, which were then air dried and shelled.
Average seed yield per plant and the seed weight for diseased and healthy plants were then measured for each cultivar. Where normality was not found, data sets were arcsine transformed prior to analysis. Susceptible cultivars expressed typical GRD symptoms, including shortening of the internodes leading to severe stunting, reduced leaf size, leaf distortion, and mosaic Fig.
Most of the symptoms appeared 3 weeks after exposure to the source of inoculum. Disease spread and severity varied significantly among the cultivars between the wet- and dry-season trials, with susceptible genotypes showing more severe symptoms in the wet season.
Some plants expressed additional virus-like symptoms, including chlorotic ringspots, line patterns, and deformation of leaflets, indicative of GRSV infection Fig.
These symptoms could clearly be distinguished from those resulting from GRD. Diseased Sinkapoporigo groundnut plants within the field 8 weeks after exposure to sources of inoculum. A, Green rosette symptoms of groundnut rosette disease; B, chlorotic ringspots, leaf deformation, and line pattern symptoms of Groundnut ringspot virus infection; and C, healthy plant.
The percentage of diseased plants Table 1 varied significantly within and between seasons among the groundnut cultivars, with disease incidence higher in the wet than the dry seasons. The highest disease incidence in the dry season was found in Obolo Oboshie had the lowest proportion of diseased plants in both the dry 5.
Cultivars were rated for resistance based on wet-season results, which provided the greatest disease pressure. Oboshie 7. With the exception of Oboshie, Nkosuor, and Otuhia, all the improved cultivars with putative resistance to GRD succumbed to the disease.
Table 1. Groundnut rosette disease incidence and resistance rating of 12 groundnut cultivars based on visual symptoms. The proportions of infected plants for both viruses were generally lower in the dry than the wet season. In the wet season, all plants of Oboshie and Jenkaar succumbed to infection with GRAV while the least infection occurred in Bremaowuo Of particular interest was Oboshie, which had very low levels of disease in both seasons but very high levels of GRAV infection in the wet season.
Table 2. Where required GRSV data sets , data were arcsine transformed prior to statistical analysis. In the wet season, there were no significant differences in GRSV infections among the cultivars. In the dry season, Sinkapoporigo and Jenkaar had the highest proportion of plants with mixed infection Plants were tested 10 weeks after exposure to sources of inoculum. Vertical bars indicate standard errors. Plant height, leaf area, chlorophyll content, dry haulm weight, and seed yield were all reduced by GRD Table 3.
Similarly, plant height was reduced in all cultivars tested in the greenhouse, with Sinkapoporigo showing the greatest reduction. The greatest reductions were found in Obolo In the greenhouse, the greatest reduction in leaf area was found in Otuhia Table 3. Effect of groundnut rosette disease on plant height, leaf area, chlorophyll content, haulm dry weight, and yield of groundnut cultivars.
Before flowering, the greatest reduction occurred in Otuhia After flowering, diseased plants of Yenyawoso, Oboshie, Otuhia, and Azivivi had their chlorophyll content significantly reduced by Chlorophyll was not significantly reduced in diseased Sinkapoporigo, Obolo, and Nkosuor plants during pod development. In the greenhouse, Sinkapoporigo, Otuhia, Nkosuor, and Yenyawoso had their chlorophyll content reduced by The highest reductions in haulm weight were observed in Obolo In the greenhouse, haulm weight was reduced in virus-infected plants of all cultivars but the reduction was significant in Otuhia only.
Infected plants had numerous pegs, unfulfilled pods, and a few single-seeded pods when compared with healthy plants Fig. In the greenhouse, the reduction was significant for all cultivars and ranged from Oboshie and Nkosuor showed the greatest reduction in average yield per plant and in seed weight in the field and greenhouse, respectively.
Example of the effect of groundnut rosette disease on yield of Sinkapoporigo groundnut pods. The trials resulted in effective screening of groundnut cultivars for GRD.
Susceptible cultivars expressed typical symptoms of the disease, including shortening of the internodes leading to severe stunting, reduced leaf size, leaf distortion, and mosaic Waliyar et al.
Resistance to GRD was found in four of the local cultivars while resistance was confirmed in three of the improved cultivars. The relatively harsh environmental conditions associated with the dry season, with lack of rainfall and high temperatures, would have reduced volunteer plants and vector populations and led to the reduced disease incidence observed compared with the wet-season trial.
Groundnut rosette disease
Rosette is the most destructive disease of groundnut in Africa. The disease is endemic to sub-Saharan Africa and its off-shore islands, including Madagascar. Two main forms of the disease, chlorotic rosette and green rosette have been described based on symptoms. The groundnut aphid, Aphis craccivora , is the principal vector of the disease. Rosette disease has been and continues to be responsible for devastating losses to groundnut production in Africa.
Plantwise Factsheets for Farmers
It is transmitted between plants by insect vectors such as the groundnut aphid Aphis craccivora. The groundnut Arachis hypogaea originated in South America where it has long been domesticated. More recently it has been cultivated in other parts of the world and is an important subsistence crop in Sub-Saharan Africa. Groundnut rosette virus was first described in Africa in and causes serious damage to groundnut crops on that continent. The virus can spread rapidly through a crop. In a study in Tanzania, the first affected plants were seen six days after the first aphids were observed.