Identificação, padrão espacial de viroses em alho e efeito da piraclostrobina em plantas infectadas.

Abstract

Due to the vegetative propagation mode of garlic (Allium sativum L.), Brazilian producers have to overcome several limitations in its crop management, such as the occurrence of pests and diseases that can be perpetuated from one generation to another through the bulbils used as seeds. Thus, despite Brazil being the fifth largest per capita consumer of garlic in the world, a large part of this commodity is imported to meet its domestic demand. Among the pathogens that affect garlic production, virus species belonging to the Potyvirus, Carlavirus and Allexivirus genera are the most frequent in crops, known to cause losses that can reach 100% of yields. Therefore, there is a demand for alternatives that make it possible to control or minimize the losses caused by the planting of infected seeds, since the availability of completely virus-free seeds is practically non-existent. In this work, a survey of the main viral species present in São Gotardo, Alto Paranaíba region in Minas Gerais, as well as their incidence and spatial analysis in ten commercial production fields was carried out. Considering that pyraclostrobin is known to promote increase in the yield and induction of virus resistance in host plants, in this work was also investigated the effect of two commercial products containing this molecule in the yield of virus-infected garlic plants. The incidence of virus in 4 of out of ten evaluated areas ranged from 2.9% to 16.7%, while in two others it was higher: 42.9% and 86.4%, respectively. The remaining four areas showed an incidence of 100%. The pattern of spatial distribution of infected plants was aggregated in 90% of the blocks according to the run test and 63.3% of random distribution according to the doublet test. There was also a dispersion index of 63.3% of the blocks with a regular spatial pattern. Samples of plants with and without symptoms that were collected were positive for the presence of one or more species of viruses belonging to the genera Potyvirus, Carlavirus and Allexivirus, indicating a possible transmission by seeds with subsequent dissemination by vectors in the field. Although no statistical difference was observed in the weight and diameter of the bulbs and in the number of bulbs of the plants treated with different doses of pyraclostrobin, two of the treatments indicated an increase in production above 4%. These treatments should be repeated in combination with increasing doses of nitrogen fertilization, to test the possibility of gains already observed in other pathosystems.