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- Author or Editor: H. Y. Nakasone x
Sexual changes in papaya (Carica papaya L.) from the normal hermaphroditic elongata flower toward femaleness by means of stamen carpellody are discussed in relation to the transition from the bisexual elongata flower toward maleness. A series of changes occurs that involves reduction in ovary size and shape, and in numbers of stigmatic rays, dorsal vascular bundles, carpels, and placenta. Placentation is normally parietal in papaya but there is evidence of ancestral axil placentation.
Intercrossing within dioecious Carica species (C. pennata (Heilborn) Svensk, C. parviflora (A. DC.) Solms, C. cauliflora Jacq., C. goudotiana (Tr. & PL) Solms) produce staminate and pistillate plants in equal proportions. Carica monoica Desf., a monoecious species, produces only monoecious offspring upon selfing or intercrossing. Crosses between C. monoica as the pollen parent and pistillate plants of dioecious Carica produce a monoecious F1 and an F2 ratio of 3 monoecious: 1 pistillate. When C. cauliflora is used as the pollen parent with C. monoica, the F1 ratio is 1 staminate: 1 monoecious. Backcrossing monoecious F1 plants of this cross with staminate plants of C. cauliflora produces 1 monoecious: 1 pistillate:2 staminate. The cross between C. goudotiana (seed parent) and Carica monoica (pollen parent) was obtained but the reciprocal cross never succeeded. The backcross, using staminate C. goudotiana, produces only staminate and pistillate plants in a 1:1 ratio. Varying degrees of androecium suppression causing seasonal production of staminate flowers were observed in the F1 and F2 generations of the cross, C. goudotiana x C. monoica, while occasional production of hermaphroditic flowers was observed in monoecious F1 and F2 individuals of the cross, C. cauliflora x C. monica.
These results are discussed in relation to two hypotheses used to explain sex determination in Carica species.
The inheritance of 8 monogenically controlled plant, fruit, and seed characters in Carica species is reported. The gene for red stem is dominant to that for green stem and the gene for red petiole is dominant to that for green stem and the gene for red petiole is dominant to that for green petiole. Genes for white and purple-blush flower colors are dominant to those for pale yellow; while the gene for red skin color of ripe fruit is dominant to that for yellow. However, the gene for red skin color is not dominant to that for orange skin color; the heterozygote has pink-skinned fruits. The gene for ridging on the fruit (carpel fusion lines) is dominant to that for wide groove, which in turn is dominant to that for narrow groove. Spiny vs. non-spiny seed coat produces an intermediate F1, indicating no dominance. The gene for succulent fruit pulp is dominant to that for dry pulp. The gene for bushy branching is dominant to that for sparse branching.
The period between flower bud emergence and anthesis for Carica goudotiana (Tr. & Pl.) Solms, C. cauliflora Jacq., C. parviflora (A. DC.) Colms., C. monoica Desf. and C. papaya L. ranged from 27-47 days. Flowers of C. parviflora showed peak anthesis between 8 and 10 AM, while in the other 4 species, peak anthesis occurred between 4 and 8 PM. Pollen of the 5 species and C. pennata Heilborn, Svensk showed satisfactory viability in vitro. Pollen germination was best in media at pH 5.5-7.5. Sibmating C. cauliflora, C. pennata, and C. parviflora produced fruit sets above 80%, although seed viability of the latter 2 species was low. Under the conditions of this study, relatively strong intraspecific incompatibility was shown between green and red segregants of C. goudotiana and between El Salvador and Venezuela collections of C. cauliflora as indicated by low fruit set percentages. Only C. cauliflora from El Salvador produced good fruit set and high seed viability from sib-pollinations.
Interspecific hybridizations among 6 Carica species, including the edible papaya, produced 2 hybrids previously unreported: C. monoica Desf. × C. goudotiana (Tr. & PI.) Solms (A)R and C. parviflora (A. DC.) Solms. × C. goudotiana (A)R. Other crosses producing viable seeds were: C. monoica × C. cauliflora Jacq., its reciprocal; C. goudotiana (A, B) × C. monoica and C. cauliflora (A, B) × C. pennata Heilbron, Svensk.
Three reciprocal pollinations of the above crosses and 9 other pollinations produced fruits with under-developed seeds which were non-viable. Carica papaya L. (Line 26) pollinated with pollen of C. cauliflora (A), C. parviflora, C. monoica and C. goudotiana (A)R produced fruits with non-viable seeds. Three crosses, C. pennata × C. goutotiana (B), C, papaya (Line 5B) × C. pennata and C. goudotiana (A)R × C. cauliflora (A) produced parthenocarpic fruits (ovules completely undeveloped). Most cross pollinations which failed to set fruit were reciprocals of those which produced non-viable seed and parthenocarpic fruits. Differences in compatibility and seed viability were shown by lines of C. cauliflora from El Salvador and Venezuela and by C. goudotiana from Colombia and Venezuela.
Four interspecific hybrids are described. Heterosis was shown in 2 hybrids for tree height, trunk circumference, and number and wt of fruits.
Only C. cauliflora and its hybrids did not show the usual visible reaction to a virus with symptoms resembling papaya mosaic and distortion ringspot. As the trees progressed in age, many died of root rot (associated with Phytophthora palmivora Butl. and Pythium aphanidermatum (Edson) Fitz.). Symptoms of this disease were not apparent in plants of C. cauliflora or its hybrids with C. monoica, although the latter species has been observed to be highly susceptible.
Five inbred lines of papaya (Carica papaya L.) ranging from susceptible to resistant to phytophthora root rot (Phytophthora palmivora Butl.) were crossed in a diallel, and inbred parents and F, progenies were inoculated with P. palmivora isolate P170. The diallel analysis of mortality from phytophthora infection indicated significant general combining ability and specific combining ability; the GCA: SC A mean square ratio of 15.7 indicated GCA to be more important than SCA. Parental means correlated well with hybrid array means (r=0.89).
Virtually 100% flowering of the pineapple, Ananus comosus (L.) Merr., cv. Smooth Cayenne, was induced by night application of a small piece of dry calcium carbide into an adequate amount of water in the center of the plant. During daylight neither dry carbide nor acetylene solution resulted in high floral induction, except for applications just before or just after sunrise. A repeat application of dry carbide or acetylene solution 3–5 days following the first, increased the amount of flowering. Low floral induction with day applications was probably due to; a) larger amounts of acetylene required for floral induction during the day than at night; b) greatly reduced penetration of acetylene into the plant tissues; or c) combination of the 2 conditions. Although a second application might have provided only a limited additional amount of acetylene, this could have been sufficient to raise the level to that which would stimulate the biochemical processes of floral induction.
Pollen of Psidium guajava L. germinated at pH levels of 4.5-7.0 up to 33 hr after anthesis. Germination of fresh pollen was depressed at pH 7.0 but germination of older pollen was enhanced. Pollen 1-2 days old which failed to germinate in vitro still induced fruit set when used in pollination, indicating that it was still functional.
Pollen germination in vitro of the species studied varied considerably. Generally, pollen of species with high chromosome numbers germinated poorly.
Pollination studies indicated partial self incompatibility in all species studied. Reciprocal interspecific crosses showed pronounced differences in compatibility.
The occurrence of intra-ovarian ovaries in certain strains of Carica papaya L. is not uncommon. Approximately 150 hermaphroditic and 25 female ovaries from a hybrid progeny contained internal ovaries in stages of development ranging from thread-like appendages to round or elongated pistils of various sizes and shapes. A few were large enough to fill the entire seed cavity of the primary fruit and possessed their own cavities with non-viable seeds.
Internal ovaries originate either from stimulated growth of rudimentary pistillate structures extending from the central axis of the receptacle or from placentae in positions normally occupied by ovules. The placenta may be in its normal parietal position or a single strand may become free, extended from the base of the primary ovary and support a mal-shaped secondary ovary as well as ovules. The occurrence of internal ovaries supports theories proposed by other investigators on the evolution of floral morphology in the papaya.
Polyploidy within Psidium guajava appears to be uncommon but the genus Psidium is represented by di-, tetra-, hexa- and octoploid species. The species and their respective chromosome numbers are: P. guajava and P. polycarpum, 2n = 22; P. guineense and P. cujavillus, 2n = 44; P. friedrichsthalianum (El Salvador), 2n = 44; P. friedrichsthalianum (Costa Rica), 2n = 66; P. cattleianum f. lucidum, 2n = 66. Two plants of P. cattleianum were found to be 2n = 77, a heptaploid number, but whether these plants represent horticultural variants has not been established.
Close resemblance in vegetative characters of the species and gross appearance of the chromosomes of P. guajava and P. polycarpum on the one hand and those of P. guineense and P. cujavillus on the other casts some doubt as to their identities.