AbstractPuerto Rican, Columnaris, and Bourbon varieties of Coffea arabica are commonly grown in Puerto Rico. In some localities there are small plantings also of other coffees, such as Excelsa (C. excelsa) and Robusta (C. canephora). Recently some farmers have started testing several newly introduced Arabica-types coffees, such as Caturra, Villalobos, Mundo Novo, Mibirizi, and so on. The farmers generally establish mixed plantings of different coffee varieties and species rather than planting them in separate plots. The time of flowering of these coffees overlaps. These conditions are favorable to spontaneous hybridization. Spontaneous hybridization of Bourbon with Puerto Rican and Columnaris was studied, using the genetic tester "bronze." In one of the experiments 18 progenies were raised using open-pollinated seed collected from individual Bourbon trees growing mixed with Puerto Rican and Columnaris at different locations. In these progenies the proportion of spontaneous hybrids varied from 0 to 34.14 percent. Taking all the progenies into account, out of a total of 4,994 plants studied, 5.66 percent were spontaneous hybrids. In another experiment two populations were raised using openpollinated random seed samples collected from a Bourbon planting surrounded by Puerto Rican and Columnaris plantings. Out of a total of 1,126 plants of both populations, 7.54 percent were spontaneous hybrids. Taking both experiments into account, out of a grand total of 6,120 plants studied, 6.01 percent were spontaneous hybrids.
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