Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 187

The papaya, a semi-herbaceous tree, has been bred as individual seedlings planted in fields rather than as rootstocks and scions. The crop is grown from seed and has a 3- to 4-year production cycle after which the plants are too tall to harvest. With a chromosome number of 2n = 2x = 18, it is a diploid (Storey, 1941) with a hermaphrodite genome size of 2C = 0.65 pg (Araujo et al., 2010) or 372 Mb (Arumuganathan and Earle, 1991). The first harvest interval from seedlings in the field is c.9 months to 1 year. Papayas segregate for two different sex types, female and hermaphrodite or female and male. The male or staminate papaya, usually a showy, mostly staminate flowering panicle but sometimes also bearing a few hermaphrodites, is not truly male because it consists of pistillate and staminate genetic complements as does the hermaphrodite. The totally male papaya with no female elements is a lethal genetic condition. In selfed hermaphrodites, the segregation ratio is 1 female to 2 hermaphrodites because ¼ of the progeny that would have inherited only male elements aborts, resulting in ¼ female, ½ female + male (=hermaphrodite) and ¼ lethal male + male genetic complement.