Embryo rescue was successfully applied to develop hybrids between Ornithogalum dubium Houtt. (short inflorescence with orange flowers) and O. thyrsoides Jacq. (tall inflorescences with white flowers]. Meiosis in these hybrids showed abnormalities such as univalents, laggards, and bridges. The F, hybrids were partially fertile, and F2 and BC1 progeny were produced. The backcross hybrids segregated for flower color and, inflorescence traits and introgressed seedlings with orange pigmented flowers on tall inflorescences were obtained in the population.
R.J. Griesbach, F. Meyer, and H. Koopowitz
Doru Pamfil, R.H. Zimmerman, S.K. Naess, and H.J. Swartz
RAPD analysis was performed on 44 species of Rubus. These species included representatives from seven of the 12 subgenera within the genus and several series within the Idaeobatus (raspberries) and Eubatus (blackberries) subgenera. For all species, up to five plants were initially analyzed by two 10-mer primers. The most heterozygous of these individuals was then analyzed using 13 additional primers. Wide band diversity exists among Rubus species; these differences were analyzed using the PHYLIP software program. These differences are repeatable, for example color sports of `Heritage' red raspberry produced identical banding patterns. The genetic similarity between eastern United States blackberries (Eubatus) and numerous species was compared to the ability of these same species to act as a suitable pollen parent for eastern blackberries. These data were used to construct a dendrogram of the subgenera studied here.
Jinq-Tian Ling, N. Nito, and M. Iwamasa
Protoplasts were isolated from embryogenic calli of Citrus reticulata cv. Ponkan and Citropsis gabunensis, and fused in electric fields. The maximal fusion efficiency was obtained by application of AC at 75 V/cm (1.0 MHz) and DC square-wave pulse at 1.125 KV/cm for 40 usec. Fusion-treated protoplasts were cultured on MT medium without phytohormone, solidified with 0.6% agar. Colonies from the protoplasts were proliferated on MT medium with zeatin 1 mg/l and 0.9% agar. Selection of somatic hybrid callus was based on chromosome count and isoenzyme analysis. The somatic hybrids were tetraploid (2n=36). C. reticulata and C. gabunensis were both homozygous at Got-1 locus, but distinguishable easily because band of the latter migrated faster than that of the former. In zymogram of somatic hybrid, both parent bands were retained and a new hybrid band was also evident between them. Embryos from somatic-hybrid callus regenerated intact plant. The hybrid plants showed intermediate morphological characteristics of the parents.
Jude W. Grosser, Frederick G. Gmitter Jr., J.L. Chandler, and Eliezer S. Louzada
Protoplasm culture following polyethylene glycol-induced fusion resulted in the regeneration of tetraploid somatic hybrid plants from the following attempted parental combinations: Cleopatra mandarin (Citrus reticulata Blanco) + Argentine trifoliate orange [Poncirus trifoliata (L.) Raf.]; `Succari' sweet orange [C. sinensis (L.) Osb.] + Argentine trifoliate orange; sour orange (C. aurantium L.) + Flying Dragon trifoliate orange (P. trifolita); sour orange + Rangpur (C. limonia Osb.); and Milam lemon (purported sexual hybrid of C. jambhiri Lush × C. sinensis) + Sun Chu Sha mandarin (C. reticulate Blanco). Protoplasm isolation, fusion, and culture were conducted according to previously published methods. Regenerated plants were classified according to leaf morphology, chromosome number, and peroxidase, phosphoglucomutase, and phosphoglucose isomerase leaf isozyme profiles. All of the somatic hybrid plants were tetraploid, as expected (2n = 4x = 36), and all five selections have been propagated and entered into commercial citrus rootstock trials.
Sandra M. Reed
The objectives of this study were to evaluate self-fertility and to determine the effectiveness of pollinations made over a 4-day period in Japanese snowbell, S. japonicum Sieb. & Zucc. Pollen germination and pollen tube growth were observed in stained styles following cross- and self-pollinations made from 1 day before to 2 days after anthesis. One month after pollination, fruit set averaged 40% in cross-pollinations and 14% in self-pollinations. Two months later, about one-third of the fruit resulting from cross-pollinations had aborted and only one fruit remained from the self-pollinations. This study demonstrated that stigmas of S. japonicum are receptive for at least 4 days and that flowers should be emasculated prior to making controlled cross-pollinations.
Jude W. Grosser and Frederick G. Gmitter Jr.
Christopher S. Cramer and Todd C. Wehner
Recurrent selection has been used as a breeding method to improve traits having low heritability such as fruit yield, earliness, and fruit shape. The objective of this study was to measure the progress of recurrent selection in four slicing cucumber populations in terms of hybrid performance when crossed with a common tester. The four populations, North Carolina wide-base slicer (NCWBS), medium-base slicer (NCMBS), elite slicer 1 (NCES1), and Beit Alpha 1 (NCBA1) populations, which differed in their genetic diversity and mean performance, were developed using modified intrapopulation half-sib recurrent selection to improve fruit yield and quality. Eleven S0 families were taken randomly from each of three selection cycles (early, intermediate, and advanced) from each population. Those families were self-pollinated to form S1 families, and the S1 families were crossed to `Poinsett 76', a popular slicing cucumber cultivar. The experiment was a splitplot treatment arrangement in a randomized complete-block design with 22 replications per population, with the four populations as whole plots and the three cycles as subplots. When 10% of fruit were oversized (>60 mm in diameter), plants were sprayed with paraquat to defoliate them for once-over harvest. Plots were evaluated for total, early, and marketable yield and fruit shape. Recurrent selection for improved fruit yield and shape per se resulted in improved hybrid performance of the NCWBS and NCBA1 populations for fruit yield and shape rating when tested in the selected or nonselected environment. The NCWBS population had the largest gain (21%) in hybrid performance averaged over all traits. In addition, early yield was improved an average of 18% from early to late cycles for each population. Even though the fruit yield and shape rating of `Dasher II' was greater than the hybrid performance of each population mean for the same traits, several F1 families within each population exceeded the fruit yield of `Dasher II'.
Richard C. Pratt, Joseph C. Scheerens, and Soon J. Park
Jude W. Grosser, Victor Medina-Urrutia, Govindarajulu Ananthakrishnan, and Patricia Serrano
Sour orange has been a premier citrus rootstock worldwide due to its ability to perform on challenging soils and to produce and hold high-quality fruit. However, increasingly widespread quick-decline isolates of citrus tristeza virus (CTV) have destroyed entire industries on sour orange in some countries, and are in the process of destroying millions of trees on sour orange in Florida. CTV also threatens other citrus locations planted heavy to sour orange, including Texas and Mexico. An acceptable alternative rootstock to replace sour orange is in high demand but has yet to be developed. Molecular analyses have recently determined that sour orange is probably a hybrid of pummelo and mandarin. We report the production of 12 new mandarin + pummelo somatic hybrids produced by protoplast fusion from selected superior mandarin and pummelo parents, in efforts to develop a suitable replacement sour-orange-like rootstock that is resistant to CTV-induced quick decline. Somatic hybrids from all 12 parental combinations were confirmed by a combination of leaf morphology, flow cytometry, and RAPD analyses (for nuclear hybridity). These new mandarin + pummelo somatic hybrids are being propagated by rooted cuttings as necessary to conduct quick-decline resistance assays and to assess horticultural performance in replicated field trials.