SAO PAULO, Oct 31 (Reuters) - Roadblocks in at least 12 Brazilian states by truckers who support outgoing President Jair Bolsonaro could affect agricultural exports in one of the world's top food producers, according to the head of a key state farm lobby.His complete radio silence has raised concerns about the orderly handover of power, while also adding to doubts about how long the blockades could last.Brazil's Federal Highway Police (PRF) said on Monday that truckers have partially or fully blocked roads in 12 states, up from the six states an independent truckers group had estimated earlier on Monday.However, Normando Corral, president of farm group Famato, said the roadblocks in the top grains-growing state of Mato Grosso could disrupt agricultural shipments if they persist.Rota do Oeste, a toll road operator that administers an 850-km (530-mile) stretch of the BR 163 highway that cuts through Mato Grosso, said at 10.50am local time there were blockages in the regions of Nova Mutum, Sorriso, Sinop and Lucas do Rio Verde."