RESUMO
In Uganda, the severe Maize lethal necrosis (MLN) disease, which threatens subsistence maize production is caused by co-infection of maize plants with Maize chlorotic mottle virus (MCMV) and Sugarcane mosaic virus (SCMV). However, there is no information about natural hosts of MLN causing viruses and their role in epidemiology of MLN in Uganda. The aim of this study was to determine existence of natural alternative weed and cultivated crop hosts of MLN causing viruses. Three seasonal surveys between 2014 and 2015 were carried out in five major maize growing agroecological zones of Uganda. Weeds and cultivated crops growing in proximity to maize were observed for virus symptoms and tested for MLN causing viruses using Double Antibody Sandwich Enzyme-Linked Immunosorbent Assay and Reverse Transcriptase Polymerase Chain Reaction. Data was collected on frequency of occurrence of weeds and cultivated crop species and MLN virus disease incidence. Digitaria abyssinica, Bidens pilosa and Commelina benghalensis were the most common weed species while Phaseolus vulgaris, Manihot esculenta, Arachis hypogaea), Musa sp, Glycine max and Ipomoea batatas were most common cultivated crops. Pennisetum purpureum, Digitaria abyssinica, Cyperus rotundus, Amaranthus spinosus, Commelina benghalensis and Eleusine indica weeds species are natural hosts of Maize chlorotic mottle virus. Among the cultivated crops, Phaseolus vulgaris, Manihot esculenta and Sesamum indicum are natural hosts of MCMV. Only Sorghum (Sorghum bicolor) and sweet potato (Ipomoea batatas) tested positive for SCMV. MCMV incidence in weeds ranged from 2% to 63%% and 2% to 29% in cultivated crops. MLN causing viruses were prevalent in weeds and cultivated crops located in known hotspots for MLN in Uganda. The study has revealed that alternative hosts of MLN-causing viruses are present in major maize growing agroecological zones of Uganda and act as sources of inoculum to sustain MLN epidemics.
RESUMO
The exotic cotton mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) invaded India during 2006, and caused widespread infestation across all nine cotton growing states. P. solenopsis also infested weeds that aided its faster spread and increased severity across cotton fields. Two year survey carried out to document host plants of P. solenopsis between 2008 and 2010 revealed 27, 83, 59 and 108 weeds belonging to 8, 18, 10 and 32 families serving as alternate hosts at North, Central, South and All India cotton growing zones, respectively. Plant species of four families viz., Asteraceae, Amaranthaceae, Malvaceae and Lamiaceae constituted almost 50% of the weed hosts. While 39 weed species supported P. solenopsis multiplication during the cotton season, 37 were hosts during off season. Higher number of weeds as off season hosts (17) outnumbering cotton season (13) at Central over other zones indicated the strong carryover of the pest aided by weeds between two cotton seasons. Six, two and seven weed hosts had the extreme severity of Grade 4 during cotton, off and cotton + off seasons, respectively. Higher number of weed hosts of P. solenopsis were located at roadside: South (12) > Central (8) > North (3) zones. Commonality of weed hosts was higher between C+S zones, while no weed host was common between N+S zones. Paper furnishes the wide range of weed hosts of P. solenopsis, discusses their significance, and formulated general and specific cultural management strategies for nationwide implementation to prevent its outbreaks.