cross between a pummelo ( C. grandis Osbeck) and a sweet orange [ Citrus sinensis (L.) Osbeck] ( Barrett and Rhodes, 1976 ; Gmitter, 1995 ; Scora, 1975 ; Scora et al., 1982 ). The increasing competition and popularity of grapefruit in international
Abstract
‘Matou’ wentan (pummelo) is usually seedless in Taiwan. However, about 8% of the fruits on the market are seedy. In controlled pollination tests, ‘Matou’ was self-incompatible and highly parthenocarpic. Seedy fruits in commercial orchards are apparently from pollination by trees of other cultivars such as ‘Liucheng’ (C. sinensis Osb.), ‘Ponkan’ (C. ponkan Tan.), and especially ‘Paiyu’ and ‘Hwungyu’ (C grandis). Seedy fruits of ‘Matou’ wentan could be prevented by excluding other citrus cultivars from the orchard.
The morphological characteristics and reproductive potential of a haploid plant obtained from the cross between `Banpeiyu' pummelo (Citrus grandis) and `Ruby Red' grapefruit (C. paradisi Macf.) were investigated. The haploid was confirmed to be derived from female gamete of `Banpeiyu' pummelo by isozyme and random amplified polymorphic DNA (RAPD) analysis. Flow cytometry analysis revealed that the haploidy was maintained in several tissues and organs of this plant. It also had the typical morphology of a haploid, such as small leaves and flowers, and had slightly fertile pollen grains. Furthermore, diploid progenies were obtained from the cross between `Kiyomi' tangor and the haploid. The hybridity of these seedlings was confirmed by assessment of the leaf characteristics and RAPD analysis. These results suggest that this haploid produced fertile unreduced pollen grains (n = 9).
This research was supported in part by BARD (Binational Agricultural Research and Development Fund) grants US-1887-90 and US-2410-94CR and by a grant from the Florida Citrus Production Research Advisory Council.
A greater saturation of the previously constructed genetic linkage map of Citrus is important in the long term goal of mapping quantitative trait loci (QTL) such as those controlling cold and salt tolerance. Segregation for cold tolerance appears to be greatly enhanced in the intergeneric F1 population of Citrus grandis × Poncirus trifoliata as compared to the BC1 population previously used for mapping due to the higher percentage of P. trifoliata genes present. This is not unexpected since P. trifoliata is the source of cold tolerance in this cross and is a highly heterozygous species. An integration of the maps of the two populations using about 50 random amplified polymorphic DNA (RAPD) markers common to the two populations is possible using the JoinMap computer program. This will allow the placing of approximately 100 new polymorphic RAPD markers from the F1 population identified by screening from 42 random oligonucleotide primers onto the Citrus map. This saturated map will be used to locate QTL following bulk segregation analysis of cold tolerance in the F1 population.
citrus cultivation in China. Li et al. (2015) reported that soil acidification was a major problem in ‘Guanximiyou’ pummelo ( Citrus grandis ) orchards in Pinghe county, which is in the southern region of Fujian province in China, with an average pH of
Abstract
In 5 separate field-planted groups at 2 climatic locations, F1 populations and 3-way crosses involving pummelo as an immediate parent have all shown significantly larger mean trunk size, and generally larger canopy size, than crosses which lack pummelo. The other parents included oranges, mandarins, tangors (tangerine × orange), grapefruit, and the related genus Poncirus. F2 progenies and backcrosses to non-pummelo cultivars showed less vigor than the compared F1’s. Fruiting has occurred earlier and in higher proportions of trees among the pummelo crosses with Poncirus, and often with the other pummelo hybrids. These characteristics seem to represent hybrid vigor based on favorable combining ability of the pummelo, although only a limited number of pummelo cultivars were tested. The species appears to be relatively homogenous, and is one of the few Citrus species which reproduce entirely by sexual embryony. The behavior of its hybrids supports the concept that pummelos carry fewer unfavorable genes, and may be more homozygous, than Citrus species and cultivars which reproduce largely by asexual embryony.
principally as a rootstock for sweet orange and other Citrus biotypes. Scora (1975) and Barrett and Rhodes (1976) proposed that sour orange originated from C. reticulata and C. grandis . The suggestion was supported by isozyme study ( Fang, 1993
Specific primers were designed for 61 cloned RAPD fragments and from 10 Citrus EST sequences for the production of SCAR, CAPS, and STS markers for a Citrus grandis `DPI 6-4' × Poncirus trifoliata `Rubideaux' F1 pseudo-testcross population. Fifteen SCAR, three CAPS, and one EST/STS markers were developed. An additional 17 SCAR and CAPS primer pairs developed at the Citrus Research and Education Center for a Citrus grandis `Thong Dee' × (Citrus grandis `Thong Dee' × Poncirus trifoliata `Pomeroy') BC1 population were screened in the pseudo-testcross population. A total of 27 markers were identified and scored in the pseudo-testcross population in which 24 were mapped; 13 in the Citrus parental linkage map on seven linkage groups and 11 in the Poncirus parental map on five linkage groups. In the BC1 population, 20 of 27 markers tested were found to be polymorphic and 13 mapped to seven of nine linkage groups. Of these, 11 were mapped in both populations and could be used for aligning presumed homologous regions on the three linkage maps.
Ten-month-old seedlings, grown from seed extracted from 22 individual pummelo [Citrus grandis (L.) Osbeck] × trifoliate orange [Poncirus trifoliata (L.) Raf.] citrus hybrid trees that survived -15C freezes near Monticello, Fla., were cold-acclimated in controlled-environment rooms and freeze-tested at -6.7C for 4 h. Freeze damage to open-pollinated progeny was ranked by the number of uninjured seedlings and percentage of leaves killed and wood dieback. Morphological segregation was not associated with differences in freeze survival, and the dominant trifoliate gene was readily evident. Progeny from one tree, identified as 98-71, are considered the most likely candidates for further study in developing cold-hardy citrus trees.