Allelism of Endosperm Balance Number (EBN) in Mexican tuber-bearing Solanum species

Summary Endosperm Balance Number (EBN) is a genetic, dose-dependent crossability system functioning in tuber-bearing Solanum species. Each species has been assigned 1EBN, 2EBN, or 4EBN. Species thus designated cross only within their EBN group. Doubling of chromosome number also doubles the EBN. The ploidy: EBN ratio is not consistent among Solanum species. Some diploids are 2EBN while others are 1EBN. Some tetraploids are 4EBN while others are 2EBN. Species from Mexico typically have EBNs that are one-half of their ploidy [e.g. 2x(1EBN), 4x(2EBN)]. Hybrids of Mexican species and a South American species, 2x(1EBN) S. Commersonii, and its 4x(2EBN) colchicine derivative were made and crossed to 1, 2, and 4EBN standard testers to determine the relationship of the genetic organization of EBN among and within these species. Diploid hybrids crossed only to 1EBN standard testers. Hybrids of 4x(2EBN) S. commersonii and 4x(2EBN) Mexican species crossed almost exclusively to 2EBN standard testers. Complex tetraploid hybrids involving S. commersonii, S. stenophyllidium (a Mexican diploid), and Mexican tetraploids of series Longipedicellata also crossed only to 2EBN testers. The apparent lack of recombination and segregation for EBN in these hybrids indicates that the genomes of the Mexican diploid and tetraploid species carry EBN in a way genetically similar to that of the South American species S. Commersonii.Cooperative investigation of the U.S. Department of Agriculture, Agricultural Research Service and the Wisconsin Experiment Station. Supported in part by the USDA/Cooperative States Research Service Competitive Grant No. 83-CRCR-1-1253     

Endosperm dosage relationships among Lycopersicon species

Summary Accessions of eight Lycopersicon species and five yellow-flowered Solanum species were used as males in crosses with 2x and 4x L. esculentum to observe seed set and progeny ploidy. Species which failed in crosses to L. esculentum were crossed as males to 2x and 4x L. peruvianum. In cases of low seed set, chromosome counts were undertaken to establish the nature of the progeny. Endosperm Balance Number (EBN) relationships were determined for the crossability groups. Results support the basic concept of an L. esculentum crossability complex and an L. peruvianum crossability complex. Within the L. esculentum complex, all EBNs appear identical with a value of 2. Within the L. peruvianum complex, more variability appears to exist. The EBN values of this group are higher, and may be approximately double those of the L. esculentum complex. The EBN of L. peruvianum var humifusum appears to be somewhat lower than other L. peruvianum types. The EBN values of S. lycopersicoides, S. rickii, S. ochranthum and S. juglandtfolium could not be determined experimentally. Differential aspects of Lycopersicon and tuber-bearing Solanum evolution may be interpreted on the basis of endosperm compatibility.Co-operative investigation of the Vegetable Crops Research Unit, U.S. Department of Agriculture, Agricultural Research Service, and the Wisconsin Agricultural Experiment Station     

Genetic control of Endosperm Balance Number (EBN): three additive loci in a threshold-like system

Summary The genetic control of Endosperm Balance Number (EBN) was investigated by a complete diallel of four exceptional diploid Solanum commersonii-S. chacoense hybrids (1 1/2 EBN) and backcrosses to their species parents, S. commersonii (1 EBN) and S. chacoense (2 EBN). Crosses in which the female parent had a higher EBN value than the male, S. chacoense (2 EBN)XF₁ (11/2 EBN) and F₁ (11/2 EBN)X S. commersonii (1 EBN), produced viable seed to aborted seed ratios of 11.1 and 11.3, respectively, and had average to small sized viable seed. Crosses in which the female parent had a lower EBN value than the male, S. commersonii (1 EBN)XF₁ (11/2 EBN) and F₁ (11/2 EBN)XS. chacoense (2 EBN), produced viable seed to aborted seed ratios of 1 7.9 and 1 6.7, respectively, and had average to large sized viable seeds. The results of these crosses appear to be consistent with the relative EBN values of the male and female parent. A model is proposed for the system regulating endosperm development. The assumptions of this model are: (1) three unlinked loci control the system; (2) the loci are homozygous within a species; (3) the genes have additive effects and are of equal strength within a species; (4) the genes within S. chacoense have twice the effect with respect to endosperm regulation as those within S. commersonii; and (5) a slight excess maternal dosage will produce the qualitative effect of small but viable seed. This model, in which quantitative genes operate in a dosage dependent system bears many similarities to classical, threshold-type genetic models.     

A preliminary study on the effects of E-Z Mixin® and EquiPlus® extenders supplemented with Edible Bird’s Nest on the quality of chilled Arabian stallion semen

The aim of this study was to evaluate the effects of adding different concentrations of edible bird’s nest (EBN) which is secreted by swiftlet birds (Aerodramus fuciphagus), into EquiPlus® and E-Z Mixin® extenders on the quality of chilled Arabian stallion semen at various storage times (0, 24 and 48 h). Ten ejaculates were collected from five stallions, and diluted using the two extenders containing 0% (control), 0.12%, 0.24% and 0.24% of EBN + seminal plasma (SP). All the diluted semen samples were then cooled and stored at 5 °C, and examined at 0, 24 and 48 h. Sperm kinetic parameters were assessed using computer assisted sperm analysis (CASA) and viability were assessed using Hoechst33342/PI stain. In both extenders, total motility (TM) and progressive motility (PM) were significantly higher at 0.12% and 0.24% compared to 0.24% + SP at 24 and 48 h. At 0.12%, E-Z mixin® treated semen had significantly higher TM and PM than EquiPlus^® at 24 and 48 h. At 0.12% and 0.24%, average path velocity (VAP), straight-line velocity (VSL) and curvilinear velocity (VCL) were significantly higher in E-Z mixin® treated semen compared to EquiPlus^® at 24 and 48 h. Comparisons between the two extender types at different concentrations of EBN showed no significant difference in lateral head amplitude (ALH), linearity (LIN), straightness (STR), beat cross frequency (BCF) and viability, irrespective of the storage time. The percentage of viable was significantly higher in E-Z mixin® than EquiPlus® at 0 and 48 h in control and 0.12%. Supplementation of the E-Z mixin^® extender with 0.12% and 0.24% EBN concentrations in the absence of SP provided better CASA parameters such as TM, PM, VAP, VSL, and VCL at 24 and 48 h storage time. In conclusion, the results of this study indicated that chilled semen from Arabian stallion that was extended using E-Z mixin® and supplemented with 0.12% and 0.24% EBN concentrations performed better and yielded superior results in sperm kinetic parameters and % viable compared to EquiPlus® at 24 and 48 h storage time.     

Fertile Solanum tuberosum+S. commersonii somatic hybrids as sources of resistance to bacterial wilt caused by Ralstonia solanacearum

 The wild potato relative Solanum commersonii is reported to carry resistance to bacterial wilt disease caused by Ralstonia solanacearum. To overcome sexual incompatibilites due to differences in ploidy and endosperm balance numbers, somatic hybrids were made that combine the S. tuberosum and S. commersonii genomes. The resulting somatic hybrid plants are vigorous, but their disease resistance level and their fertility was unknown. We therefore tested the S. commersonii and S. tuberosum source material cv Superior, potato cv Atlantic and six somatic hybrid lines for resistance to a virulent strain of R. solanacearum (race 3, biovar 2) at 28°C. As expected, S. commersonii was significantly more wilt-resistant than the cultivated potatoes. In five of the six somatic hybrid lines, disease resistance levels were similar to that of the resistant S. commersonii parent. The resistance level of the sixth somatic hybrid was intermediate, significantly different from both S. commersonii and S. tuberosum. In controlled crosses, the somatic hybrids in this study proved both to be male- and female-fertile and were self-compatible. More importantly, the somatic hybrids can be crossed with S. tuberosum to produce viable seeds. Received: 23 June 1998 / Accepted: 13 October 1998     

Introgression of resistance to root-knot nematodes from wild Central American Solanum species into S. tuberosum ssp. tuberosum

 Crossing experiments were conducted to introduce resistance to the root-knot nematodes, Meloidogyne chitwoodi and M. fallax, from various polyploid Central American Solanum spp. into the cultivated potato, S. tuberosum ssp. tuberosum. The most effort was put into producing tetraploid hybrids through inter-EBN (Endosperm Balance Number) crosses. From the crosses of tetraploid S. tuberosum (4 EBN) with tetraploid S. stoloniferum and S. fendleri (both 2 EBN), few seeds were derived that led to viable plants. In vitro culture of immature seeds also yielded several hybrid plants. From crosses of diploid S. tuberosum (2 EBN) with hexaploid S. hougasii (4 EBN) four hybrids were obtained through in vitro culture. Backcrosses were made with selected hybrids and a variable number of seeds was produced depending on the hybrid genotype. The successful introgression of resistance into backcross populations is shown. A scheme is presented for the introgression of traits at a tetraploid level from allotetraploid Solanum species into autotetraploid S. tuberosum through sexual crosses. The relevance of EBN for potato breeding is discussed. Received: 25 November 1996 / Accepted: 14 February 1997     

Taxonomic and evolutionary implications of the Endosperm Balance Number hypothesis in potatoes

Summary The Endosperm Balance Number (EBN) hypothesis can explain to a considerable degree the crossability between tuber-bearing Solanum species. It has been shown to be genetically controlled and is dosage dependent. There is a good correlation between EBN and the postulated evolution and present taxonomy of potatoes. The primitive white stellate-flowered species from Mexico are 1EBN, and this condition is also found in species from South America with flowers of the same colour and shape. The evolution of a rotate corolla seems to be correlated with 2EBN. It is postulated that the 2EBN state arose as a reproductive isolating mechanism in South America. The taxonomic and evolutionary implications of the EBN hypothesis are discussed.