Attempts to hybridize gloxinia and Streptocarpus

Summary Hybridization work was done between gloxinia and streptocarpus cultivars and species. No hybrid seeds were obtained. It is concluded that Sinningia speciosa cultivars and Streptocarpus sp. do not hybridize using conventional methods, in spite of positive reports in literature. The origin of these hybrids may probably be explained by the irregular occurrence of peloric flowers in streptocarpus, and zygomorphic flowers in gloxinia.     

Intersubgeneric crosses within the genus Pelargonium

Summary The two cultigens, Pelargonium X domesticum (n=11), subgenus Pelargium, and P. X hortorum (n=9), subgenus Ciconium, were crossed reciprocally and with P. peltatum (n=9), subgenus Dibrachya. Diploid and tetraploid cultivars of P. X hortorum and P. peltatum and tetraploid cultivars of P. X domesticum were used. Viable seeds were obtained from crossing P. X hortorum and P. peltatum and four hybrid plants were produced. Only fruit set occurred in the cross P. X domesticum x P. X hortorum. In all other combinations no fruit set and no seeds were produced.In P. X domesticum x P. X hortorum and P. X domesticum x P. peltatum pollen tubes penetrated the stigma but not the style or ovary. Although the styles elongated in P. X domesticum x P. X hortorum, the ovules did not grow. Fruit set also occurred when the emasculated florets of P. X domesticum were bagged and not pollinated. Fruit set in this cross was apparently a physiological response of the plant, perhaps to the cold temperature, 5°C, used to induce flowering and not a response to either pollination or fetilization.     

Accelerating and synchronizing germination of strawberry seeds by osmotic pre-treatments

Summary Pre-soaking strawberry seed (Fragaria ananassa Duch.) in osmotic solutions accelerated and partially synchronized their germination. Pre-soaking advanced 50% germination from about 4 weeks to 4 or 5 days. Two to three weeks pre-soaking in a mineral solution of -10⁶Pa nominal osmotic potential at about 20 C was satisfactory. The resulting synchronization of germination could allow seedlings to be selected for rate of growth by directly comparing seedling in bulk sowings.     

Inheritance of resistance to Phytophthora fragariae Hickman in strawberry

Summary It has been found that complete resistance of the strawberry cultivars and selections Earliglow, Guardian, MdUS 2700, MdUS 2929, MdUS 3816 and Redchief to Phytophthora fragariae is inherited in a one-to-one ratio, suggesting that these genotypes have one major resistance gene effective to the races present in the test field.The high level of partial resistance of Cambridge Favourite has clearly been recovered in its progenies. However, from results presented here, no conclusions could be drawn with regard to the number of genes involved in the partial resistance of Cambridge Favourite. It is, however, suggestive that about half the susceptible selections derived from crosses with Cambridge Favourite have shown a relatively high level of partial resistance. The selections concerned were obtained by selection on horticultural characters in seedling populations planted on an uninfested field.     

Triple fusion of the primary endosperm nucleus as a cause of interspecific cross-incompatibility in Avena

Summary Using five diploid, two tetraploid and three hexaploid Avena species (x=7) 78 reciprocal crosses were made. Of these 74 were successfull, though the frequency of seed set varied greatly. The development of hybrid seeds differed widely between cross combinations, especially in reciprocal crosses. Hybrid seeds were grouped into four types, (1) normal kernels, well developed and germinative (designated as D+); (2) shrivelled-empty kernels, which do not germinate (E–); (3) small viable kernels (Rd+) and (4) small inviable kernels (Rd–). Some rare intermediate types were found in certain crosses.The results are well interpreted in terms of a hypothesis of polar-nuclei activation in which the strength of the activating action of the male nucleus, and the reaction of the female nucleus at double fertilization are expressed as activating value(AV) and response value(RV), respectively. The degree of seed failure is closely related to the activation index(AI) of the polar nuclei, AV/2RV (or × 100). In a selfed plant the activation index is always 1/2=0.5 (or50%), and this usually results in the formation of normal seeds. If AI deviates from 50% the endosperm often stops developing or degenerates.Based on the degree of abnormality of hybrid seeds, activating values of the ten species were arbitrarily assigned from 0.4 in A. ventricosa (2x) to 3.0 in A.sterilis (6x). For comparison A.strigosa (2x) was used as a standard and set at 1.0. Among the 74 succesful interspecific crosses the AI of the polar nuclei varied widely, from 7 to 375% Generally speaking, AI values of less than 20, 20–30, 30–80, and more than 80% show the R-, Rd+, D+ and E-kernel types, respectively. In other words, if the AV of the pollen parent is < 40 or >160% that of the maternal parent hybrid seeds fail to develop. Thus in double fertilization of Avena or probably angiosperms, the triple fusion of two polar nuclei with a secondary male nucleus is apparently a sexual isolation mechanism, being a barrier to interspecific hybridization.Professor Emeritus of Kyoto University, Faculty of Agriculture, Kyoto.     

Predicting interspecific compatibilities in beans (Phaseolus) by seed protein electrophoresis

Summary Seed proteins of 17 wild species of Phaseolus were separated by electrophoresis on SDS polyacrylamide gels. There was very little variation of the protein pattern within most species, while considerable variation among species was evident. Relative interspecific similarities of protein patterns were estimated using Jaccard's similarity index, and a cluster analysis was performed on these values. The resultant dendrogram generally agreed with previous research on interspecific relationships in Phaseolus based on morphological characteristics, and also generally agrees with current information on interspecific similarities based on hybridization studies. Suggestions are made regarding interspecific hybridization among Phaseolus species which have not been attempted, but which may be possible based on cluster analysis. These hybrids include P. vulgaris × P. polystachyus, P. vulgaris × (P. polystachyus × P. metcalfei) and P. anisotrichos × P. angustissimus.Supported by the USDA Specific Cooperative Agreement to the University of Puerto Rico 458-7B30-0-203 Bean Improvement by Interspecific Crosses.     

Synthesis and preliminary characterization of a new species (amphidiploid) in Cucumis

A successful interspecific hybridization between cucumber (Cucumis sativus L., 2n = 14) and a wild it Cucumis species, C. hystrix Chakr. (2n = 24) was made via embryo rescue. Hybrid plants (2n = 19; 7 from cucumber and 12 from C. hystrix) were sterile, but morphologically uniform. Self-pollination and backcrossing of F₁ hybrid plants to either parent confirmed presence of both male- and female-sterility that were likely caused by lack of homology and improper pairing during meiosis. While the multiple-branching habit, densely brown hairs (on corolla and pistil), orange-yellow corolla, and ovate fruit of F₁ hybrid plants were similar to that of the C. hystrix parent, the appearance of the first pistillate flower was more similar to that of C. sativus parent. The diameter and internode length of the stem, and the shape and size of leaves and flowers were intermediate when compared to the parents. The chromosome number in the hybrid was doubled through somaclonal variation during embryo culture and regeneration process to restore the fertility. Pollen grains were released and fruits with viable seeds matured on fertile, synthetic amphidiploid plants. The results from flow cytometry indicated that, on average, 7.3% of the morphologically unique regenerants had the 4C DNA content of 2.35 pg relative to the 2C DNA content of the original F₁ hybrid at 1.17 pg and, therefore, were likely chromosome-doubled F₁ hybrids (2n = 38). Nutrition alanalysis indicated that the synthetic species had higher protein (0.78%)and mineral (0.35%) content compared to the normal pickling cucumber(0.62% and 0.27%, respectively), and could be considered a new Cucumis crop having a special place in the future agriculture. Preliminarily evaluation indicates that C. hystrix possesses a high level of root-knot nematode resistance, and that this resistance is partially expressed in the interspecific F₁ and chromosome-doubled F₁. This and the fact that the fruit morphology of the fertile amphidiploid differs during the growing season (e.g., short and long fruit) suggest that it could be useful in broadening the germplasm base of cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Introgression of unique characteristics of floral initiation under 24 hour day-length of Fragaria chiloensis ‘CHI-24-1’ into F. × ananassa

A unique flower initiation of the wild Junebearing strawberry strain ‘CHI-24-1’ in Fragaria chiloensis occurs under 24 h DL and high temperature conditions. To introduce the floral initiation characteristics of ‘CHI-24-1’ into cultivated strawberries of F. × ananassa, a cross pollination was conducted between ‘CHI-24-1’ and the Japanese short-day type strawberry cultivar ‘Nyoho’. The floral initiation of ‘CHI-24-1’ was induced in both parent and daughter plants linked with runners under a 24 h DL and 23/20 ^∘C, but not 8 and 16 h DLs at the same temperatures. Of the 21 F1 hybrids grown under the 24 h DL, 12 showed flower truss production in the parent and/or daughter plants linked with runners. Among 64 F1 hybrids, 26 exposed to 8, 16 and 24 h DLs for 30 days produced no flower trusses. However, 32, one and five F1 hybrids produced flower trusses under the 24 h DL alone, 8 h DL alone and both the 8 and 24 h DLs, respectively. The results of the experiments indicated that none of the F1 hybrids were day-neutral plants, but approximately 60% had the characteristics of floral initiation under 24 h DL, which was inherited from the pollen parent of ‘CHI-24-1’. The importance of the unique floral initiation characteristics under 24 h DL with high temperature for strawberry breeding was discussed.     

Resistance to a single UK isolate ofColletotrichum acutatum in strawberry germplasm from Northern Europe

Summary Colletotrichum acutatum on strawberry was first introduced to the UK on runners of cultivar Brighton, which were imported from California in 1983. Recently further outbreaks have been reported following the importation of infected runner plants from mainland Europe. Phytosanitary precautions have so far been successful in controlling the disease but the current trend in the UK is for increasing late season production. This increases the likelihood of there being fruiting plants when the environmental conditions are favourable toC. acutatum. Fifteen cultivars and 19 HRI breeding lines were tested for susceptibility toC. acutatum using the most pathogenic isolate found on plants imported into the UK. It is likely this isolate was originally of Californian origin. Potted plants were spray inoculated and subsequently rated in the glasshouse using a disease severity rating (DSR) with the range from 0–4, where a rating of 4 indicated severe disease symptoms. In contrast to results from California and Italy standard deviations were variable and often large and consequently it was considered unsafe to classify the susceptibility of the genotypes on the basis of mean DSR alone. Classification was thus based on a combination of the mean value and the distribution of the scores but in some cases the results were inconclusive. It was possible to classify five lines as having a high level of resistance (Elvira, Honeoye, EM99, EM224, EM255); six lines had a useful level of resistance but did show symptoms on some plants (Cambridge Favourite, Gorella, Pandora, Pantagruella, EM17 and EM290); five lines were highly susceptible (Elsanta, Redgauntlet, Tamella, EM237 and EM319). The remaining 18 lines could not be classified with the same degree of certainty but 10 were probably resistant.     

A quantitative classification method for assessing resistance to Phytophthora fragariae var. fragariae in strawberry

Summary Race specific resistance to red core (red stele) root rot, caused by Phytophthora fragariae var. fragariae, is known to occur in the cultivated strawberry (Fragaria × ananassa Duch.), but frequently this resistance does not completely prevent infection. We therefore developed a classification method which distinguishes partial and complete resistance. It accounts for differences in the aggressiveness of isolates and in the appropriateness of experimental conditions for infection. This method is based on the microscopically assessed disease severity of a tested strawberry genotype relative to that of an universally susceptible reference cultivar. If the tested genotype is significantly (P0.01) less diseased, it is considered to possess resistance. Data from 18 genotype-isolate combinations, including five genotypes (Blakemore, Md683, Redgauntlet, Del Norte, Yaquina A) and four North American isolates (A2, A4, A6 and A10) demonstrated the validity of our classification scheme.Abbreviations PIRT Percentage of Invaded Root Tissue     

A test of the mentor pollen technique in the genus Ipomoea

Summary A major barrier to hybridization of some Ipomoea species is located at the stigma-style interface. In 5 interspecific combinations examined with the aid of fluorescence microscopy, pollen was found to germinate and penetrate the stigma surface without, however, passing into the style. In the cross I. hederacea x 1. purpurea, pollen tubes were observed in the style and capsules were set, but no full seeds were produced. Attempts to facilitate hybridization among Ipomoea species using mentor pollen-foreign pollen mixes were unsuccessful.     

An allotriploid derived from a amphidiploid × diploid

A fully fertile interspecific hybrid (Cucumis hytivus Chen and Kirkbride, 2n =4x =38) between Cucumis hystrix Chakr. (2n= 2x =24) and C. sativus L. (2n = 2x = 14) was previously produced by means of F₁ (2n = 19) embryo rescue and subsequent chromosome doubling. This amphidiploid, a new synthetic species, may serveas a genetic bridge in Cucumis, and thus is a source for broadening the genetic base of C. sativus. The identification and characterization of fertile progeny possessing lower ploidy levels would facilitate bridging among Cucumis species. Putative allotriploids (2n = 26) were recovered from C. hytivus × C. sativus matings by means of embryo culture, and experiments were designed to confirm their genetic constitution, describe their morphology, and establish an efficient protocol for their micropropagation. Apical and axillary buds of these putative allotriploid plants were used as explants to establish a micropropagation system for subsequent verification and characterization of ploidy. Of the array of micropropagation media tested, then ability to be most effective for the induction of adventitious buds (desginated Stage II) was a Murashige and Skoog (MS)growth media containing 13.3μM BA + 1.1μM NAA or containing10 μm BA only. The mean number of adventitious buds per explant in the two media was 6.8 and 6.5, respectively. Shoots resulting from adventitious buds produced roots (Stage III) in relative abundance (39 of 42, 92.8%) on half-strength MS medium containing 1.0 μm IBA. The survivorship of rooted plantlets after acclimatization as assessed by relative production of leaves in plantlets (designated Stage IV) was 91.4% (148 of 162). The chromosome number in putative allotriploid plants as determined in mitotic root tip figures in all plants was 2n = 26, the number expected for allotriploids derived from such a mating. An examination of pollen viability in five samples of each plant by cytochemical staining revealed stainability to be < %.Compared to their parents, the allotriploid genotypes possess a high degree of parthenocarpy (84.8%) as measured by setting fruit in pollen-free conditions. While allotriploid fruit are black-spined and similar to the maternal parent C. hytivus, the dark green leaves typical of allotriploid plants mirrors that of the paternal C. sativus parent. This revised version was published online in July 2006 with corrections to the Cover Date.