He brought the poison
When Bloom makes a lewd joke about cigars and Zoe says, "Go on. Make a stump speech out of it," he launches into an indictment of tobacco that begins with the historical tradition that "Sir Walter Raleigh brought from the new world that potato and that weed." These two plants were imported from the Americas in the early modern era, but the tradition crediting Raleigh is suspect on several counts.
Walter Ralegh, as his name was spelled in his own time, was a gentleman adventurer favored by Queen Elizabeth with various royal patents and charters to explore, plunder, and settle the New World. The 1580s founding of the Roanoke colony in Virginia was his venture, but he never personally traveled to North America. It is now thought that Hernández de Boncalo brought tobacco seeds to Spain in 1559, three and half decades before Ralegh's expeditions to South America to find the City of Gold, El Dorado. (The seeds were planted in an area outside Toledo known as Los Cigarrales for its many cigarras, or cicadas.) Although Ralegh did not bring tobacco to Europe, either personally or by proxy, he probably popularized its use. A widespread legend tells of the time his manservant first saw him smoking a pipe and, alarmed that his master was on fire, fetched water to pour on him.
The history of how potatoes were introduced to European fields appears to be even less certain than that of tobacco. One tradition credits another Elizabethan adventurer, Sir Francis Drake: a large bronze statue of him in Offenburg, Germany praises him for having done so "in the Year of Our Lord 1586." However, in The History and Social Influence of the Potato (Cambridge UP, 1949, rpt. 1985), Redcliffe Salaman notes that no work of European literature mentions the potato until John Gerard's Catalogue (two editions in 1596 and 1599) and his famous Herball (1597), which devotes a chapter to the plant (77-78). Many Europeans planted potatoes in the 1600s, though they were often thought to be poisonous and fed only to animals. After saying that Ralegh brought both tobacco and potatoes to Europe, Bloom immediately corrects himself: "That is to say he brought the poison a hundred years before another person whose name I forget brought the food."