Inheritance of heterodichogamy in pecan

The pecan (Carya illinoensis (Wang.) K. Koch) is a monoecious wind-pollinated diploid species with a system of heterodichogamy to insure cross-pollination. Inheritance patterns for type of dichogamy (protogynous or protandrous) were determined from breeding records of the USDA's pecan breeding program at Brownwood, Texas. One clone (the Mahan cultivar) produced only protogynous progeny, while crosses among protandrous clones produced only protandrous progeny. Progeny phenotypes of other crosses involving heterozygotes generally support the hypothesis that a single Mendelian factor determines dichogamy type, with protogyny being dominant (PP or Pp) and protandry being recessive (pp). That this qualitative inheritance pattern, the first determined in Carya, is common throughout the Juglandaceae family (pecan, other hickories, and walnuts) is strengthened by data from other sources. Theoretical frequencies in native pecan populations, and their evolutionary significance also are discussed.