USE OF IPOMOEA-TRIFIDA (HBK) G DON GERM PLASM FOR SWEET-POTATO IMPROVEMENT .2. FERTILITY OF SYNTHETIC HEXAPLOIDS AND TRIPLOIDS WITH 2N GAMETES OF IPOMOEA-TRIFIDA, AND THEIR INTERSPECIFIC CROSSABILITY WITH SWEET-POTATO

Twenty-two synthetic hexaploids and 33 triploids with 2n pollen production of Ipomoea trifida were used in crosses to estimate their male and female fertility and their crossability with sweet potato, Ipomoea batatas (L.) Lam. Several important conclusions were drawn. (i) The fertility of pollen of the triploid plants was confirmed, which suggested they are truly functional 2n pollen. (ii) The average male fertility of hexaploid plants was higher than that of triploid with 2n pollen production plants. (iii) 2n egg production was observed in several triploid genotypes. (iv) From a polycross, 3079 seeds with normal shapes were produced. These represent a population of hexaploid I. trifida with a wide genetic base, and they may be important material for sweet-potato improvement. (v) A total of 3275 seeds were obtained from crosses with six sweet-potato female parents, of which only 60 germinated, indicating the existence of an interspecific barrier. The implications of 2n gametes for breeding and evolution of sweet potato are also discussed.