Breeding potential of Solanum tuberosum–S. commersonii pentaploid hybrids: fertility studies and tuber evaluation

Twenty-one (near) pentaploid hybrids between sexually incompatible Solanum commersonii [2x(1EBN)] and cultivated S. tuberosum [4x(4EBN)] were characterized for tuber traits and fertility. A number of genotypes resembled the S. tuberosum type in terms of stolon length and eye depth and produced tubers under long day conditions. Tuber yields were not as high as expected, probably due to lack of adaptation of the S. commersonii genome to the environmental conditions in southern Italy (on average 325 g·pt⁻¹ and 285 g·pt⁻¹ in 2003 and in 2004, respectively). Compared to 2004, in the summer of 2003, characterized by extremely high temperatures, hybrids gave a higher tuber yield than the S. tuberosum control, suggesting that in our environmental conditions the wild S. commersonii genome, rather than resulting in heterosis for tuber yield, provides better adaptation to harsh environments. Although aneuploidy has often been associated with reduced fertility, several hybrids were fertile in crosses with S. tuberosum when used as female parents. In particular, the average berry set and number of seeds per berry were 38.2% and 31.8%, respectively. Based on significant relationships between ploidy levels and all yield and fertility data measured, the presence of extra chromosome affected the parameters considered: tuber yield in 2003 and 2004, percentage of fruit set, number of seeds per berry and number of seeds per pollinated flower. Regression analysis also indicated that “Residuals” were significant for all parameters measured. Therefore, additional factors (e.g. the genetic makeup of hybrids) may be key to fertility and yield.     

Variation for agronomic and processing traits in Solanum tuberosum haploids × wild species hybrids

Summary The broad range of wild and cultivated species relatives of the commerical potato (Solanum tuberosum L.), guarantees the existence of a gene reservoir to be screened for traits that are absent or present only in low frequencies in the cultivated germplasm. Haploids (2n=2x=24) extracted from the cultivated tetraploid (2n=4x=48) germplasm cross easily with diploid (2n=2x=24) potato species and produce fertile progeny. As most haploid × species hybrids tuberize under long day conditions they can be maintained clonally and evaluated for the traits of interest. Three populations involving Tuberosum haploids × Solanum bukasovii (tub x buk), Tuberosum haploids × Solanum sparsipilum, (tub × spl) and Tuberosum haploids × Solanum berthaultii (tub x ber) clones, were planted at two locations in Wisconsin. The haploids were derived from W231, a selected clone from the University of Wisconsin Potato Breeding Program. The objectives were: to evaluate the H-S populations for agronomic and processing traits, and to determine the phenotypic associations between them. Data were recorded on haulm maturity (HM), tuber weight (TW) and tuber number (NT) per plant, specific gravity (SG), chip color after harvest (CH), and chip color after storage at 4° C and one week of reconditioning at room temperature (CH1). Results for SG and CH indicated good potential of the germplasm evaluated to introgress these traits into the commercial potatoes. For instance, the SG mean for tub x buk, tub x spl and tub x ber were 1.079, 1.086 and 1.082, respectively, and their means for CH were 4.8, 3.9 and 3.5. Chip color after storage and reconditioning was found in low frequency in the populations. Four clones in the tub x spl population, and three clones in the tub x ber population had CH1 4.0, the commercially acceptable score for this trait. Significant (p 0.01) phenotypic correlations (r) were found between HM and SG (r=–0.46 in tub x buk, r=–0.61 in tub x spl, and r=–0.34 in tub x ber), NT and TW (r=0.79 in tub x buk, r=0.88 in tub x spl, and r=0.71 in tub x ber), and TW and SG (r=0.40 in tub x buk, and r=0.36 in tub x spl). The correlation coefficients between processing traits were not significant, which may indicate the presence of separate genetic mechanisms governing the inheritance of these traits.     

Production and cyto-morphological analysis of intergeneric hybrids of Sorghum × Saccharum

Four intergeneric hybrids were produced by crossing sorghum [ Sorghum bicolor (L.) Moench, 2n =20] as a female parent with sugarcane ( Saccharum officinarum L., 2n = 112). The hybrids were morphologically similar to the sugarcane parent, but lacked vegetative vigour. Sorghum characters present in the hybrids included soft texture of the leaves, tight clasping of the leaf sheaths, presence of aerial roots and triangular ligule. All the hybrids were highly susceptible to natural incidence of mites. Somatic chromosome number of the hybrids ranged from 2n = 62–66, indicating n+n transmission. This is the first report of Sorghum × Saccharum hybrids with sorghum cytoplasm. This revised version was published online in July 2006 with corrections to the Cover Date.     

Parental effects on the performance of cultivated × wild species hybrids in potato

Valuable genetic diversity in diploid wild Solanum species can be accessed through crosses to haploids (2n = 2×) of the tetraploid cultivated potato, Solanum tuberosum. Haploid-wild species hybrids segregate for the ability to tuberize in the field. In addition, they vary in male fertility, vine size, stolon length, and tuber size. In this study, three haploids were crossed with nine diploid wild Solanum species and 27 hybrid families were evaluated in the field for two years. The proportion of male fertile hybrid clones varied depending on the wild species parent. A large effect of the female parent was detected for vine size, stolon length, tuber size, percent tuberization, and percent plants selected for agronomic quality. An exceptional haploid (US-W4) was identified for the production of agronomically desirable haploid-wild species hybrids. In hybrids derived from US-W4, differences among wild species parents were observed for agronomic quality. Superior hybrids were produced by S. berthaultii and S. microdontum. Reciprocal crosses were evaluated for a subset of families. When the wild species was used as the female parent, male fertility was restored, but tuberization and tuber size were reduced. Careful selection of both haploid and wild species parents can result in a large proportion of fertile, agronomically desirable hybrid offspring.     

Occurrence of metaxenia and false hybrids in Brassica juncea L. cv. Kikarashina × B. napus

Imported genetically modified (GM) canola (Brassica napus) is approved by Japanese law. Some GM canola varieties have been found around importation sites, and there is public concern that these may have any harmful effects on related species such as reduction of wild relatives. Because B. juncea is distributed throughout Japan and is known to be high crossability with B. napus, it is assumed to be a recipient of B. napus. However, there are few reports for introgression of cross-combination in B. juncea × B. napus. To assess crossability, we artificially pollinated B. juncea with B. napus. After harvesting a large number of progeny seeds, we observed false hybrids and metaxenia of seed coats. Seed coat color was classified into four categories and false hybrids were confirmed by morphological characteristics and random amplified polymorphic DNA (RAPD) markers. Furthermore, the occurrence of false hybrids was affected by varietal differences in B. napus, whereas that of metaxenia was related to hybridity. Therefore, we suggest that metaxenia can be used as a marker for hybrid identification in B. juncea L. cv. Kikarashina × B. napus. Our results suggest that hybrid productivity in B. juncea × B. napus should not be evaluated by only seed productivity, crossability ought to be assessed the detection of true hybrids.     

Embryo lethality in wheat × rye hybrids—mode of inheritance and the identification of a complementary gene in wheat

Crosses between hexaploid wheat and rye can only succeed when pre- and post-zygotic barriers have been overcome. A rye gene determining embryo lethality (Eml-R1), which is involved in post-zygotic isolation, has been mapped to chromosome 6R. In the present paper the mode of inheritance of Eml-R1 was studied by employing a wheat/rye chromosome 6R addition line. We show that Eml-R1 exists in at least two alternative forms, with the mutant allele Eml-R1b being dominant with respect to wild-type Eml-R1a. Furthermore, we have exploited nulli-tetrasomic lines of wheat to detect a complementary wheat gene present on chromosome 6A. This gene has been designated Eml-A1.     

Occurrence of 2,3-dihydrofarnesoic acid, a spidermite repellent, in trichome secretions of Lycopersicon esculentum × L. hirsutum hybrids

The sesquiterpenoid spidermite repellent, 2,3-dihydrofarnesoic acid, occurs in trichome secretions of LA1363, an accession of the wild tomato Lycopersicon hirsutum. To better understand the inheritance of this sesquiterpene acid and its relationship with the quantity trichome secretions, interspecific crosses were made with five inbred lines of L. esculentum. Limited seed set and frequent seedling mortality led to small populations for each generation. Concentrations of residues in leaflet washes, comprised of trichome secretions and concentrations of 2,3-dihydrofarnsoic acids were determined in F1, F2 and backcross generations. Low concentrations of this acid occurred in F1 hybrids, suggesting there was dominance for low levels of the acid. However, concentrations of 2,3-dihydrofarnesoic acid were below minimum levels of detection in two backcross generations and in one of two F2 generations. Concentrations of leaflet wash residues were high on the L. hirsutum parent and low on the L. esculentum parents. Concentrations on hybrids were generally intermediate. However, high residue concentrations were present on a few F1 and F2 hybrids, Residue and 2,3-dihydrofarnesoic acid concentrations were not correlated in F1 or in backcross generations and were uncorrelated in one of two F2 generations. In the F2 obtained by sib-mating, residue concentrations were correlated with 2,3-dihydrofarnesoic acid concentrations. Although small population sizes and perhaps other factors did not allow delineation of genetic control of the presence or abundance of 2,3-dihydrofarnesoic acid, interspecific hybrids that produce 2,3-dihydrofarnesoic acid provide the experimental plants essential for research designed to provide a better understanding of the role of 2,3-dihydrofarnesoic acid in host-plant resistance of tomato to mites and insects.     

Effect of Zinnia angustifolia HBK genotype on morphology and flowering of Z. angustifolia × Z. elegans Jacq. hybrids

Summary Interspecific hybrids were generated from crosses between 4 Zinnia angustifolia clones (maternal parents) and an inbred line of Z. elegans Orange King (paternal parent) to investigate the influence of Z. angustifolia genotype on morphology and flowering of hybrids. Leaf length, leaf width, flower diameter, number of ray petals, and days to flowering of interspecific hybrids were significantly influenced by Z. angustifolia clonal genotype. Genetic analysis of hybrid morphology and development was performed using 2 parental Z. angustifolia clones and 18 F₁ (9 seedlings from each of 2 populations generated from reciprocal crosses between parental clones) as maternal parents in crosses with Z. elegans Orange King. Genotype of Z. angustifolia significantly affected plant height, fresh weight, number of nodes, and days to flowering of interspecific hybrids. Control of these traits was through the Z. angustifolia nuclear genome. Improvement in interspecific hybrid morphology or development, i.e., shorter stature, earlier flowering, or larger flowers, may be possible by selection of superior-performing Z. angustifolia clones as parents.     

Genotypic diversity enhances recovery of hybrids and fertile backcrosses of Phaseolus vulgaris L. × P. acutifolius A. Gray

Summary Homozygous and heterozygous Phaseolus vulgaris and P. acutifolius parental genotypes were hybridized to determine if genotypic diversity would aid gene transfer between these species. Certain P. vulgaris female parents resulting from diverse intraspecific crosses increased the frequency of species hybrids obtained. From a total of 19 self-sterile hybrids, 20 backcross-1 (BC₁) lines (P. vulgaris recurrent parent) were produced from 4 partially female-fertile hybrids, each of which had a heterozygous P. vulgaris female parent. Heterozygous P. acutifolius male parents did not influence the frequency at which interspecific hybrids could be produced but apparently improved female-fertility. Fertility of the F₁BC₁ generation was highly variable. The frequency of fertile individuals increased in each subsequent backcross generation (F₁BC₂ and F₁BC₃).Purdue University Agricultural Experiment Station Publication 9946.     

Interspecific hybrids of Cucumis metuliferus × C. anguria obtained through embryo culture and somatic embryogenesis

Summary Interspecific crosses between Cucumis metuliferus Naud. and C. anguria L. were obtained through embryo culture. Embryos in the rabbit-ear to advanced fluke-shaped stages were rescued 34–99 days after pollination. Plants were obtained through direct embryo culture, and through somatic embryogenesis from immature embryos. For direct embryo culture, fluke-shaped embryos were stored in sterile water in darkness for three days at 25C prior to transfer on Murashige and Skoog (MS) culture medium plus 1.0 M 6-benzylamino-purine. Multiple plants were obtained from single embryos through somatic embryogenesis of rabbit-ear stages on MS plus 10 M indole-3-acetic acid and 5 M 6-benzylamino-purine. Evidence of hybridization included leaf shape intermediate between the two parents, penduncle shape prior to fertilization which resembled the male parent, low pollen viability and isoelectric focussing of protein bands for acid phosphatase of leaf extracts.     

Generation and characterisation of colchicine-induced polyploid Lavandula × intermedia

Double podding in cultivated chickpeas (Cicer arietinum L.) can increase yield and yield stability. In the present study, we performed reciprocal crosses of ‘kabuli’ (double podded) and ‘desi’ (single podded) chickpeas to determine (i) the expressivity and penetrance of double podding, (ii) the correlations of yield and yield components, and (iii) the heritability of double podding, flower color, and stem pigmentation in F₂ plants. Reciprocal crosses were performed with two genotypes, AC 2969 (kabuli) and ICC 4969 (desi), to generate F₁ and F₂ plants. The results indicated hybrid vigor (heterosis) for yield in F₁ plants and better performance of F₂ plants. Yield and yield components of some lines in F₂ were superior to the best parent, indicative of transgressive segregation. In particular, the presence of double podding (‘s’ allele) significantly increased yield in some of the transgressive segregants. Expressivity and penetrance of the ‘s’ allele depends on the background of the female parent. Some of the double podding progeny had greater seed yields than those of the single podding progeny and greater seed yields than the best parents. Double podding, stem pigmentation, and pink flowers each appears to be governed by a single recessive gene. Stem pigmentation and pink flowers appear to be linked traits that depend on the genetic background of the crossed chickpeas. Taken together, our studies of reciprocal crosses of kabuli and desi chickpeas clearly showed that yield could be improved by selection for transgressive phenotypes that have double podding.     

Genotype × environment interaction for resistance to the white potato cyst nematode (Globodera pallida,pathotype E) in Solanum vernei x S. Tuberosum hybrids

Summary The standard root-ball test for assessing quantitative resistance of Globodera pallida in host material derived from Solanum vernei has produced variable results. This study of two sets of clones shows that genotype x environment interactions are responsible and that linear regressions (b) of phenotypic means on environments may enable good predictions to be made of the effects of the interactions. A relationship between the regression value (b) and phenotypic mean is shown for this material. The implication of this for a screening procedure in a potato breeding programme aimed at increasing potato cyst nematode resistance in adapted cultivars of S. tuberosum is discussed.     

Anther culture of recalcitrant indica × Basmati rice hybrids

Fertile, green, di-haploid plants were obtained at high frequencies from several indica × Basmati rice F₁ hybrids and/or F₂ plant populations using an improved anther culture procedure. Anthers from cold-pretreated (10 ^°C for 10 d) panicles of six indica (HKR120, HKR86-3, HKR86-217, PR106, Gobind andCH2 double dwarf) and two Basmati rice (Basmati 370,Taraori Basmati) varieties and 14 heterotic indica ×Basmati F₁/F₂ hybrids were cultured in modified agarose-solidified N6M, Heh5M and RZM media. Best callus induction frequencies (2.6–78%) were obtained in RZM medium containing 4% (w/v) maltose,2,4-D, NAA and kinetin. F₂ plants compared to F₁ hybrids and parental rice varieties, were more responsive to anther culture. Androgenesis frequencies of 31–78% were obtained for indica × Basmati F₂ plants in RZM medium in just 30 d which are comparable to or higher than that reported for japonica rice varieties and hybrids involving japonica rice parent(s). Agarose (1.0% w/v)-solidified MS medium containing 3.0% maltose, kinetin, BAP, and NAA, induced green shoot regeneration in 0–51% of the anther-derived callide pending upon the genotype. High plant regeneration frequencies (67–337 green plants per 1000 anthers)were obtained from anther calli of several F₁hybrids (Gobind × Basmati 370 and HKR120 ×Taraori Basmati) and F₂ plants (Gobind × Basmati370, Gobind × Taraori Basmati, HKR86-3 × TaraoriBasmati). A sample of 498 plants obtained from the above hybrids, were transferred to pots with>90% survival; 8–78% of these plants had >5%spikelet fertility and were diploid. In addition,18% of the haploid plants could be diploidized by submerging in 0.1% colchicine solution for 16–18 h. The improved anther culture procedure reported here, resulted in several fold increase in the recovery of green plants from recalcitrant indica × Basmati rice hybrids compared to previous published procedures. The study may accelerate the introgression of desirable genes from indica into Basmati rice using anther culture as a breeding tool. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytogenetic studies of the F1 hybridSolanum indicum L. ×S. melongena L. and its amphidiploid

Summary The F₁ hybrid (S. indicum ×S. melongena) resembled the wild parent and exhibited hybrid vigour. In spite of normal meiosis, it was partly sterile with 48.9% stainable pollen. Its sterility is attributed to cryptic structural hybridity.The amphidiploid (S. indicum — melongena) obtained through colchicine treatment was fully fertile. It showed a low multivalent formation during meiosis and it is classified as a segmental allopolyploid. p ]The practical value of the hybrid in eggplant breeding has been indicated.Part of Ph. D. thesis accepted by Annamalai University.     

Growth and reproductive characteristics in backcross hybrids derived from Trifolium repens L. × T. nigrescens Viv. interspecific crosses

Interspecific hybridisation with the close relative, Trifolium nigrescens (Ball clover) is a possible strategy to achieve increased reproductive potential of white clover (Trifolium repens). Fertile F₁ plants have been used as the basis for two generations of backcrossing to T. repens as the recurrent parent. F₁ and backcrossed plants were assessed in both glasshouse and field for a range of morphological traits, including inflorescence production, and the level of water soluble carbohydrates in the stolons. Plants resulting from two generations of backcrossing had an increased allocation of dry matter to inflorescence production in comparison with T. repens. Variation within these plants for agronomic traits (e.g. stolon length, dry weights etc.) suggests that selection for these traits is feasible and in combination with increased inflorescence production offers a potentially valuable approach to germplasm improvement in white clover. This revised version was published online in August 2006 with corrections to the Cover Date.     

Postharvest ultraviolet-C irradiation suppressed Psy 1 and Lcy-β expression and altered color phenotype in tomato (Solanum lycopersicum) fruit

Mature green cherry tomato fruit were harvested and treated with ultraviolet-C (UV-C) irradiation at a predetermined dose of 4.2 kJ m⁻², and stored at 18 °C for 35 days. The effects of UV-C treatment on color change, pigment contents, and the expression of major genes involved in carotenoid metabolism, including Psy 1, Pds, Lcy-β, and Lcy-ɛ, encoding phytoene synthase, phytoene desaturase, lycopene β-cyclase and lycopene ɛ-cyclase, respectively, were examined. The UV-C treated fruit developed a pink red color in contrast to the normal orange red color of control fruit. Lycopene accumulation during ripening in UV-C treated fruit was significantly inhibited but its final content was not affected. However, both accumulation and final content of β-carotene were significantly suppressed in UV-C treated fruit. The lower content of β-carotene, leading to a higher lycopene to β-carotene ratio, is probably responsible for the altered color phenotype in UV-C treated fruit. Psy 1, a major gene involved in lycopene synthesis was inhibited by UV-C irradiation. Significantly suppressed expression of Lcy-β gene was also observed in UV-C treated fruit. Thus it is possible that the lower transformation from lycopene to carotenes contributed to the relatively stable content of lycopene.     

Phenotypic segregation and relationships of agronomic traits in Monastrell × Syrah wine grape progeny

The aim of this work was to study the phenotypic segregation of different agronomic and fruit quality traits, and their relationships, in Monastrell × Syrah wine grape progeny. Twenty-two agronomic traits were evaluated and compared for three consecutive years in this progeny. The results show the phenotypic diversity existing in a cross between two different wine grape cultivars. Most of the phenological, productive, morphological, and enological parameters evaluated displayed continuous variation within the progeny, suggesting a polygenic inheritance. Some correlations between traits were detected by the Spearman correlation test, although high coefficients were not found for most of them. Cluster analysis of the progeny grouped the hybrids based on criteria with significance for wine grape breeding. Also, we investigated the relationship between the skin color and total content of anthocyanins with the VvmybA genotype, using the CAPS (Cleaved Amplified Polymorphic Sequence) marker 20D18CB9. The results show that hybrids with two copies of the functional color allele tend to have increased anthocyanins content. Based on this study, 14 genotypes were pre-selected from the breeding population for additional quality studies.