Cocoyam (Xanthosoma spp.) is the most important export crop of all the root and tuber crops grown in Nicaragua. Despite its importance, the total planted area and yield have significantly decreased during the past few years, a decrease that is mainly due to diseases that are disseminated through the planting material. In this study virus-free (NI) and virus-infected (I) in vitro plants from three genotypes were established in a non-traditional production area. The aim was to evaluate their agronomic performance, and to study the re-infection of dasheen mosaic virus (DsMV) and its effect on yield. Repeated measurements of morphological traits were made during the experimental period. The height of the plants, the diameter of the pseudo-stem and the leaf area increased continuously up to 217 days after planting after which the growth curves declined. The genotypes differed in all yield components, except in yield per plant. Regardless of genotype, the NI plants produced a larger number of cormels that were heavier and longer than the cormels produced by I plants. This resulted in a higher yield from NI plants (18.2 t ha−1) compared with I plants (13.6 t ha−1). Seven months after planting between 60 and 90 % of the NI plants, depending on genotype, were infected with DsMV. Aphis gossypii was the only aphid observed in the field trial and is therefore most probably the vector responsible for the transmission of the virus.
Dasheen mosaic virus (DsMV) is an important constraint to production of cocoyam (Xanthosoma spp.) in Nicaragua. Reverse transcription polymerase chain reaction was used to amplify the coat protein (CP) region from ten Nicaraguan DsMV isolates. These isolates showed high nucleotide identity to DsMV isolates from the USA, eastern Asia and Australasia. All Nicaraguan isolates except one shared a tandem repeat in the N-terminus of the CP. Phylogenetic analyses showed that the Nicaraguan isolates formed two distinct subgroups correlated with geographic origin. This can be explained by different origins of the cocoyam genotypes grown in these regions.
To evaluate the water percolation in the soil, the water balance method is common. This method requires different daily data, which are often incomplete or not verified in field, in addition to some uncertainty regarding crop evapotranspiration. In this research, the parameters that control deep percolation were identified, based on estimation of daily local water balances with different crop coefficients, using data from weather stations and edaphic parameters. At the study site, constant monitoring of the phenological stages of a wheat crop (temporal) was carried out, and monthly soil sampling was performed for one year at different points within the site. At the same time, data were collected from weather stations, evaporation was measured with the evaporimeter tank, evapotranspiration of the crop was estimated for a single coefficient, dual and adjusted for stress based on the FAO manual, and deep percolation was determined from these data. When the soil surface was saturated or supersaturated, evapotranspiration of the crop was negligible. In addition, maximum vertical plant growth was 1.02 m, and root depth was 0.35 m. Daily rainfall greater than 10 mm or cumulative of three consecutive days greater than 18 mm of rainfall led to deep percolation, but this decreased to almost drip as thickness of the root zone increased from 0.30 m to 0.52 m. Crop growth, root zone thickness and incidence of precipitation on the soil surface controlled deep percolation. The values obtained allow us to more closely approximate the actual value groundwater recharge.
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