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- Author or Editor: H. U. Mekako x
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.