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The genus Rhododendron is widely distributed and diverse, consisting of over 900 species. Although this diversity has been exploited by hybridizers for over 100 years, few single gene traits have been genetically characterized. In order to develop genetic markers useful for biological, breeding, and commercial applications, we are investigating allelic variability and mode of inheritance at enzyme loci using starch gel electrophoresis. Thus far, allozyme segregation data at 4 enzyme loci (Pgi-2, Idh-1, 6Pgd-2, Est-1) fit the Mendelian model for single gene inheritance at the diploid level. An additional 4 polymorphic loci are presently being characterized: Pgm-2, Mdh-1, Mdh-2, and 6Pgd-1. Disomic inheritance appears to be consistent across a wide array of genetic backgrounds in these crosses, most involving parents with interspecific pedigrees. Variability at these loci is fairly abundant within the Leach breeding population. This should enable us, as an initial application, to genetically `ID' many of the Leach hybrids on the basis of their electrophoretic phenotypes.
Tomato fruit firmness is a key quality component of tomatoes produced for processing applications. Fruit firmness is generally considered a quantitatively inherited trait. Pericarp firmness of modern tomato cultivars is believed to be derived from a fairly narrow genetic background and is the result of the cumulative effort of numerous breeders over many years. Despite inferior phenotypes, wild species contain loci that can substantially increase tomato fruit quality. In the current study, inheritance of fruit firmness in firm and ultra-firm processing tomato germplasm developed from transgressive segregants of interspecific Lycopersicon esculentum × L. hirsutum and intraspecific L. esculentum crosses was characterized. Large-fruited breeding lines that varied in fruit firmness from soft to firm were identified for genetic analyses. A six-parent diallel of these advanced breeding lines was developed for field trials over multiple locations. Fruit firmness in the resulting 36 lines was determined by measuring fruit elastic properties during fruit puncture and compression. Following loading for compression, stress relaxation was recorded for 15 s. A three-parameter model was used to fit the relaxation curves. There was little correlation between firmness (maximum force) and the three relaxation parameters, i.e., firmness measured the elastic component and the relaxation parameters measured the viscous portions of the texture. General and specific combining ability for firmness derived from the respective genetic backgrounds was determined. Genetic variance components for fruit firmness were estimated using a diallel analysis and narrow sense heritability was measured using parent-offspring regression.
A salt-tolerance selected F5 generation from a cross between the wild tomato species, Lycopersicon cheesmanii, ecotype LA 1401, and the cultivated species, L. esculentum Mill. (cv Heinz 1350) was compared to the wild parental line in a solution culture experiment to determine the effects of selection on salt tolerance, and ion discrimination and accumulation characteristics in the selected line. Seedlings were transplanted to nutrient solutions at the 3 to 4-leaf stage of growth and after a 1-week period of adjustment, were salinized at 25 mM NaCl day-1 (approximately -1 bar osmotic potential) to final salt concentrations of 0, 50, and 100 mM. Plasmalemma and tonoplast vesicles were isolated from fresh root samples, and ATPase and Na+/H+ antiport activity was determined using fluorescence assays. The selected line restricted Na uptake into the shoot and maintained higher shoot K+ than did the wild parent. Growth rate under salinity was greater in the selected line than in the wild species, but relative salt tolerance was higher in the wild parent. Interspecific hybridization appears to be a useful process for the transfer of salt tolerance characters from wild to cultivated tomato.
Alstroemeria, the Inca lily or lily-of-the-Incas, is becoming a popular garden plant in the United States. In past years, the primary interest in Alstroemeria has been for its cut flowers. However, recent cold-hardy introductions (USDA hardiness zone 5) have expanded the interest of this colorful plant as a garden perennial throughout the U.S. Previously, garden interests were restricted to warmer zones in the southern United States where Alstroemeria could over-winter. This research describes a breeding procedure which has been used with the objective to develop a cold-hardy, white flowered Alstroemeria. The interspecific hybrids were bred with the use of in ovulo embryo rescue. Reciprocal crosses were made between several white-flowered cultivars and the cold hardy Chilean species, Alstroemeria aurea during the summers of 2004 and 2005. Ovaries were collected 10–23 days after hand pollination and their ovules were aseptically excised. Ovules were placed in vitro on 25% Murashige and Skoog (MS) medium under dark conditions until germination. Three weeks after germination they were then placed on 100% MS medium, and subcultured every three to four weeks thereafter until they were large enough for rooting. After rooting and acclimation, plants were transferred to the greenhouse. Successful hybrids that were produced in 2004 were evaluated under greenhouse and field trials during 2005. Data on the flower color for each of the hybrids were recorded, as well as certain morphological characteristics that can indicate cold-hardiness. Hybrid plants are being overwintered outside in Ithaca, N.Y. (USDA zone 5), and Riverhead, N.Y. (USDA zone 7), during the next several years for a more accurate assessment of cold-hardiness. Self pollinations and reciprocal crosses with the white-flowered parent were performed on the F1 generation in the summer and fall of 2005 in order to determine segregating characteristics. Few ovules were obtained from F1 generation crosses. Successful F2generation plants are being grown in vitro and will be transferred to the greenhouse where flower color will be noted. Root squashes and pollen staining were completed to determine ploidy levels and assess male sterility of the F1 generation.
Abstract
A nondestructive measurement technique for predicting the developmental stage of young embryos was devised and used to study developmental patterns of 2 Phaseolus crosses. While selfed P. coccineus Lam. produces normal seeds, P. coccineus × P. vulgaris L. aborts embryos when the seeds reach 10 mm in length. Seed growth of the interspecific cross was reduced with respect to days after pollination. Other characteristics of the interspecific cross included reduced pod length, an increased (pod length)/(number seeds per pod) ratio, reduced embryo fresh weight, and an increased volume of liquid endosperm. Between the self and the cross, pod thickness did not differ, and thus can be used to predict developmental stage of young embryos.
Abstract
Freshly harvested seeds of 10 Rubus crosses were germinated in vitro on modified Lepoivre medium without growth regulators. Among several seed preparation treatments, the best germination and subsequent survival in soil was achieved with halved seeds. In vitro germination bypassed the need for cool moist stratification and resulted in 57% to 81% germination within 8 to 12 days. This system provides an alternative method to secure high germination when a breeder is working with limited seed number, as in some interspecific Rubus crosses.
We planted grafted and seedling chestnuts of six cultivars in Lansing, N.Y., in April 1995 to evaluate performance of the different cultivars in our region and to compare grafted and seedling trees. We used the following cultivars: the Chinese chestnut cultivar Mossbarger (Castanea mollissima) and five interspecific hybrid cultivars [Douglas 1A (C. mollissima × C. dentata), Eaton [C. mollissima × (C. crenata × C. dentata)[, Skioka (C. mollissima × C. sativa), Layeroka (open-pollinated daughter of `Skioka'), and Grimo 142Q (an open pollinated daughter of `Layeroka')]. Growth was not significantly different between cultivars. There were no notable correlations between trunk cross-sectional area at planting and any measurement after the first year. Significant differences between cultivars were found for mortality, yield, and yield efficiency. `Eaton' had the lowest mortality rate (2%) of all cultivars. `Grimo 142Q' and `Layeroka' had the highest dry weight yields and the greatest yield efficiencies, although `Grimo 142Q' had significantly larger nuts than `Layeroka'. In 1998, the largest nuts (5.2 g) were harvested from `Mossbarger' and `Eaton trees'. `Skioka' had the highest mortality (48%), lowest yield, lowest yield efficiency, and smallest nut size. In the first 2 years, most grafted trees showed significantly higher yields and greater yield efficiency than seedling trees. By the third year, differences in yield between grafted and seedling trees were no longer significant for most cultivars. Over the 3 years most grafted trees revealed higher mortality and slower growth than seedlings of the same cultivar. Seedlings did not show more variability in measurements than grafted trees of the same cultivar.
Cucumis hystrix Chakr. is a rare cucurbit species native to Asia. The species is valued by breeders because of its multiple branching habit and has been used in interspecific crosses with Cucumis sativus. However, individual C. hystrix plants have not been identified in the wild since 1990. Therefore, it was our objective to develop a micropropagation protocol that would allow us to clonally propagate plants in cultivation. Shoots tips (2 cm) were excised from a single C. hystrix plant grown in the greenhouse. All tendrils and leaves were removed before surface-sterilization in 1.25% NaOCl for 5 or 10 min and rinsed six times with sterile distilled water. Shoot tips were trimmed to 1 cm (meristem with two to three young leaf primordia) and placed into 25 × 125-mm test tubes containing 25 ml of initiation medium [MS plus (per liter) 100 mg inositol, 30 g sucrose and 5 g Agargel; pH 5.7-5.8]. PGR combinations tested were initiation medium with 1 μM BA, and initiation medium with 1.7 μM IBA, 0.5 μM kinetin and 0.3 μM GA3 (IKG). Explant survival was greater when shoot tips were surface-sterilized for 5 min (75%) compared to 10 min (33%). More axillary shoots formed when shoot tips were cultured in IKG medium (10.8) than in medium with BA (5.5). Shoots were considerably longer (10 mm) when cultured in medium with IKG compared to BA (1.5 mm). About 64% of shoots place in medium containing 8 μM NAA formed roots and were acclimatized to greenhouse conditions.
The current Cucumis taxonomic classification places C. hystrix Chakr. in subgen. Cucumis based on its morphological similarities to cucumber (C. sativus L., 2n = 14). However, the chromosome number of C. hystrix was identified as 2n = 24, the same number as in subgen. Melo. Cucumis hystrix is therefore considered the first wild Cucumis species of Asiatic origin possessing 12 basic chromosomes. Thus, any research regarding its biosystematics would challenge the basic chromosome number and geographic location theories that govern the current taxonomic system. The production of the amphidiploid species (Cucumis ×hytivus Chen and Kirkbride, 2n = 38) obtained from the cross between C. hystrix and C. sativus and subsequent chromosome doubling would provide an effective means of investigating the relationship between Cucumis species with two different basic chromosome numbers. Thus, RAPD markers were used to study the taxonomic placement of C. hystrix and its interspecific hybrid with cucumber. Of the 220 arbitrary primers screened, 31 were used for analysis where 402 (96.3%) fragments were polymorphic among the germplasm examined. A UPGMA-based cluster analysis partitioned 31 accessions into two main groups [C. sativus (CS) and C. melo (CM)]. Under the similarity coefficient threshold of 0.23, these two groups can be further divided into five clusters with C. hystrix, C. ×hytivus, and C. sativus as separate clusters in the CS group. A modified taxonomic system is proposed based on these results and findings of a previous chloroplast DNA analysis with the genus Cucumis containing subgen. Cucumis with three species and subgen. Melo with six series.
Recently, a technology known as DArT (diversity array technology) has been developed to increase throughput in marker assisted selection (MAS). DArT utilizes microarray technology as a method to potentially compare thousands of molecular markers in one test to a single DNA sample. We used DArT on two sets of interspecific tomato [Solanum lycopersicum (Fla 7613) × S. pennellii (LA 716 or LA 2963)] segregating populations (BC, F2, and F1). We compared over 300 segregating plants to 3840 random tomato genomic fragments. After the 3840 markers were prepared, it took about 2 weeks of laboratory time to perform the experiments. With experience, this time can be reduced. We identified a total of 654 polymorphic markers usable for developing a DArT tomato genetic map. Depending on the particular cross, 13 to 17 linkage groups were identified (LOD 3) per population. Most recently, the amplified polymorphic DNA (AFLP) technique has been used for rapid genetic mapping of large numbers of anonymous genomic fragments. Besides the additional effort and reagents using AFLPs compared to DArT, a desired AFLP polymorphic band is often difficult to clone and process into a PCR based marker, whereas in DArT all markers are already cloned and immediately available for such experiments. A drawback to DArT is that it requires specialized software and equipment and is technically demanding. However, once the equipment and software are secured, techniques are optimized, and segregating populations developed, marker throughput is increased by orders of magnitude. Although challenging, the application of DArT can dramatically increase MAS throughput, thus facilitating quantitative trait and saturated mapping research.