Distribuição espacial da leprose dos citros e seu vetor em dois sistemas de cultivo na Amazônia Oriental

Abstract

Brazil is the world's largest orange producer (Citrus sinensis L. Osbeck), whose production in 2014/2015 amounted to approximately 16.7 million metric tons and with an expected decrease in production of 14.3 million metric tons for the 2015/2016 crop. The orange production would be even greater, if it were not for damages caused by citrus leprosis viruses (Citrus Leprosis Virus - CiLV), transmitted by citrus leprosis mites of the genus Brevipalpus spp. found in all citrus producing regions of the world. Citrus leprosis is considered one of the most important viruses in citrus orchards in Brazil with significant results on the reduction of production and life span of plants, due to lesions and premature fall of fruits and leaves. It may also cause death of branches and shoots. Thus, researches aimed at the proper management of the virus vector are becoming increasingly necessary to reduce production costs and increase fruit quality and plant longevity. Therefore, studies were carried out in an area of monoculture of citrus, and in other areas with system of cultivation in consortium of citrus with teak, in the citrus growing areas of the state of Pará aiming to study the spatial distribution of citrus leprosis associated with its vector and abiotic factors in the Brazilian Amazon through geostatistics, and to test the spatial distribution by means of dispersion indices Morisita index (Iδ), Green coefficient (Cx), exponent k of the negative binomial distribution, Taylor's power law, and estimation of the common k exponent) to elaborate a sequential sampling plan for the citrus leprosis mite under local conditions, in order to optimize the sampling method. It was verified that for the methods studied, the citrus leprosis and its vector presented an aggregated spatial distribution in the two evaluated citrus cultivation systems. Using geostatistics, it was verified that the spatial dependence of the citrus leprosis mite varied from 15 to 80 meters in a monoculture system, and from 28 to 44 meters in a consortium system with teak, whereas for citrus leprosis the spatial dependence was from 25 to 75 meters in monoculture, and 20 to 40 meters in a consortium system. For the sequential sampling plan, it is concluded that the spatial distribution model that best represented the data was the Negative Binomial Distribution and, for the number of mites per plant, the expected maximum number of sample units for decision making is 21 mites per plant in both cropping systems, while for the number of mites in six branches this value is 28 sample units.