Fluxo Gênico em Milho Sob Diferentes Tamanhos de Amostras e Distâncias de Amostragem

RESUMO - A preocupacao a respeito do fluxo genico entre lavouras de milho transgenicas e convencionais tem recebi-do cada vez mais atencao no âmbito tecnico e politico no Brasil. Diante disso, objetivou-se, com este trabalho, estimar o fluxo genico em lavouras comerciais de milho, bem como estabelecer um tamanho de amostra adequado para estimar a taxa de contaminacao por transgenicos nos campos convencionais de milho com o uso de amostragem sistematica. As coletas das amostras foram realizadas em campos de producao de graos comerciais nos municipios de Itumirim e Madre de Deus, MG, na safra 2010/2011 e na cidade de Ingai, MG, na safra 2011/2012. Foram coletadas amostras em cinco distâncias do campo convencional em relacao ao campo de transgenicos: 5 m, 10 m, 20 m, 50 m e 100 m. Foram tambem coletados quatro diferentes tamanhos de amostra: 1 espiga, 5 espigas, 10 espigas e 15 espigas em quatro re-peticoes. Apos as coletas, retirou-se de cada amostra uma aliquota de 300 sementes para realizacao do PCR em tempo real para a estimacao do fluxo genico. Nao houve diferenca significativa entre os diferentes tamanhos analisados nos tres locais. Em Itumirim e em Madre de Deus, tambem nao houve diferenca entre as distâncias analisadas; ja no campo do municipio de Ingai, as amostras coletadas na distância de 10 m apresentaram maior taxa de contaminacao. Em todos os campos, a contaminacao media ficou abaixo de 1%. Palavras-chave: Zea may L, transgenico, contaminacao. ANALYSIS OF GENE FLOW IN MAIZE UNDER DIFFERENT SAMPLE SIZES AND SAMPLING DISTANCES ABSTRACT – The concern about gene flow between transgenic and conventional maize farming has been received increasing attention in technical and political scope in Brazil. Thus, the objective of this work was to estimate the gene flow in commercial maize farms, as well as the establishment of an adequate sample size to estimate the contamination rate by transgenic in conventional maize fields, using systematic sampling. The samples collections were carried out in fields of grain commercial production in the Itumirim and Madre de Deus municipalities, both in Minas Gerais state, in 2010/2011 crop season and in Ingai, also Minas Gerais state, in 2011/2012 crop season. Samples were collected at five distances between conventional and transgenic field: 5, 10, 20, 50 and 100 m. Four different sample sizes were also collected: 1, 5, 10 and 15 spikes, with four replications. After collection, a portion of 300 seeds of each sample was used in a real-time PCR for the gene flow estimation. There was no statistical difference among the different sample sizes analyzed at the three sites. In Itumirim and Madre de Deus also no statistical difference was observed among the distances analyzed; the samples collected in Ingai field in a distance of 10 m had a higher rate of contamination by transgenics when compared to the other samples. The average contamination was below of 1% in all fields. Palavras-chave: Zea mays, transgenic, contamination.