Meiosis and pollen grain viability in Helianthus mollis,Helianthus salicifolius,Helianthus maximiliani and their F1 hybrids with cultivated sunflower

Three diploid perennial sunflower species are useful for variety improvement: Helianthus mollis, because of sessile leaves, H. salicifolius, because of a high oil concentration, and H. maximiliani, a potential source of resistance to Sclerotinia sclerotiorum. The crossability of these species to cultivated sunflower was examined.Hybrids were obtained from eight combinations, with 3–15 F₁ plants per combination. The F₁'s exhibited the dominant phenotype of the wild species. Pollen viability varied between 32.1 and 69.9%. Meiosis was irregular in the F₁ hybrids. At diakinesis, bivalents (62.7–97.9% of meiocytes), univalents (0–31.23%), and multivalents (3.84–7.68%) were detected. At anaphase I, chromosome bridges were detected in 6.77 to 11.44% of meiocytes. Fast chromosomes in metaphase I, and lagging chromosomes in anaphase I and telophase II were evidenced in a high percentage of meiocytes.     

Cytogenetic study of Helianthus laevigatus and its F1 and BC1F1 hybrids with cultivated sunflower, Helianthus annuus

Although the wild sunflower species Helianthus laevigatus has not been extensively studied it may be considered for sunflower breeding as a potential source of desirable genes for Sclerotinia stalk rot resistance and high contents of proteins and linoleic acid in the seed. A set of six H. laevigatus populations was crossed to cultivated sun~ower lines and produced nine F₁ (2-14 plants) and 66 BC₁F₁ hybrid combinations (1-13 plants). Male sterility occurred in F₁ and BC₁F₁ hybrid combinations and pollen viability was lower in the progenies than in the parents (51.6-77.2%in F₁ and in F₁ and 4.8-34.0% in BC₁F₁). Meiosis was normal in the H. laevigatus populations It was found that this tetraploid species also occurred in a hexaploid form Numerous irregularities were observed in the meiosis of the F₁ interspecific hybrids During diakinesis, quadrivalents and hexavalents were recorded in addition to bivalents Dislocated chromosomes and chromosome bridges were present in the other phases The chromosome number in F₁ was 68 (tetraploid). Irregularities in chromosome pairing were observed in the interspecific hybrids at BC₁F₁. There were many univalents, and trivalents quadrivalents and hexavalents were also present The chromosome number in the BC₁F₁ generation ranged from 34 to 60. The occurrence of meiotic irregularities in the F₁ and BC₁F₁ interspecific hybrids indicates that H. laevigatus and the cultivated sunflower differ in genome constitution.     

Inheritance of resistance to broomrape (Orobanche cumana Wallr.) race F in a sunflower line derived from wild sunflower species

Genetic resistance to broomrape (Orobanche cumana Wallr.) race F in sunflower line J1, derived from the wild perennial species Helianthusgrosseserratus Martens and Helianthus divaricatus L., has been reported to be controlled by dominant alleles at a single locus, Or6. However, deviations from this monogenic inheritance have been observed. The objective of the present study was to gain insight into the inheritance of resistance to broomrape race F in the sunflower line J1. F₁, F₂, F₃ and BC generations from crosses between J1 and three susceptible lines, P21, NR5 and HA821 were evaluated. F₁ hybrids showed both resistant (R) and moderately resistant (MR) plants, the latter having a maximum of five broomrape stalks per plant compared with >10 in the susceptible parents. This indicated incomplete dominance of the Or6 alleles. F₂ plants were classified as R, MR or susceptible (more than five broomrape stalks per plant). Three different segregation ratios were observed: 3 : 1, 13 : 3 and 15 : 1 (R + MR : S), suggesting the presence of a second gene, Or7, whose expression was influenced by the environment. A digenic model was confirmed, based on the evaluation of F_2:3 families.     

Inheritance of resistance to race F of broomrape in sunflower lines of different origins

A new race F of broomrape overcomes all known resistance genes in cultivated sunflower, but recently, sources of resistance against race F have been developed. The objective of the present research was to study the inheritance of resistance to race F in crosses between 12 resistant sunflower breeding lines, derived from three different sources of resistance, and the susceptible male‐sterile line P‐21. Parental lines and F₁, F₂, F₃ and BC₁ generations were evaluated for broomrape resistance. Segregations in the F₂ and BC₁ to resistant parent approached resistant to susceptible ratios of 1: 15 and 1: 3, respectively, in most of the crosses, suggesting a double dominant epistasis. However, segregations of 3: 13 and 1: 1 for F₂ and BC₁, respectively, indicating a dominant‐recessive epistasis, were also found. The F₃ data confirmed these results. Owing to the recessive nature of this resistance, it must be incorporated into both parental lines for developing resistant hybrid cultivars.     

Introgression of Cajanus platycarpus genome into cultivated pigeonpea, C. cajan

Summary Cajanus platycarpus, an incompatible wild species from the tertiary gene pool of pigeonpea (C. cajan (L.) Millspaugh), has many desirable characteristics for the improvement of cultivated varieties. To necessitate such transfers, embryo rescue techniques were used to obtain F₁ hybrids. The F₁ hybrids were treated with colchicine to obtain tetraploid hybrids, that were selfed to obtain F₂, F₃ and F₄ progenies. All of the hybrids and subsequent progenies had an intermediate morphology between the two parents. Backcrossing of the tetraploid hybrids with cultivated pigeonpea was not possible given embryo abortion, with smaller aborted embryos than those obtained in the F₀ parental cross.As a route of introgression, diploid F₁ hybrids were backcrossed with cultivated pigeonpea and BC₁ progeny obtained by in vitro culture of aborting embryos. BC₂ plants were obtained by normal, mature seed germination. Although embryo rescue techniques had to be used to obtain F₁ and BC₁ plants, it was possible to produce BC₂ and subsequent generations through direct mature seed. Every backcross to cultivated pigeonpea increased pollen fertility and the formation of mature seeds.Special project assistant till December, 2003.     

Ploidy Manipulation and Introgression of Resistance to Alternaria Helianthi from Wild Hexaploid Helianthus Species to Cultivated Sunflower (H. annuus L.) Aided by Anther Culture

The present investigation discusses the scope for transferring of resistance to leaf spot disease incited by Alternaria helianthi from two hexaploid wild species (H. tuberosus and H. resinosus) to diploid cultivated sunflower. Interspecific hybrids produced between sunflower and these two hexaploid species were partially fertile with tetraploid chromosome status. Backcrosses of these interspecific hybrids with cultivated sunflower resulted in the formation of sterile triploid plants. To overcome the problem of sterility and facilitate backcrosses with cultivated sunflower, anther culture of the tetraploid interspecific hybrids was carried out to bring down their chromosome number to diploid status. Anthers from both interspecific hybrids were cultured on basal Murashige and Skoog media supplemented with varying concentrations of organics and the growth regulators benzyladenine and naphthaleneacetic acid. Anthers of interspecific hybrids involving H. resinosus responded well and regenerated through an embryogenic route at a frequency of 98.7%. But in interspecific hybrids with H. tuberosus, anthers formed callus and subsequently regenerated shoots through an organogenic pathway. DNA ploidy analysis of anther culture plants of interspecific hybrids derived from H. tuberosus crosses was carried out to identify plants with desired diploid status. In vitro screening of parents, interspecific hybrids and anther culture plantlets against A. helianthi showed resistance in 68.5% of the anther culture plants of interspecific hybrids from H. tuberosus and in 24.3% of the plants derived from interspecific hybrids involving H. resinosus.     

The production of alien monosomic additions in Beta vulgaris as a source for the introgression of resistance to beet root nematode (Heterodera schachtii) from Beta species of the section Patellares

Summary Experiments were carried out for adding the chromosome carrying resistance to beet root nematode (Heterodera schachtii) from the wild Beta species of the section Patellares (B. procumbens, B. webbiana and B. patellaris) to the genome of B. vulgaris. Preliminary experiments indicated that crosses between the wild species and B. vulgaris cultivars of the mangold type yielded on average more viable F₁ hybrids than crosses with sugar and fodderbeet. However, crossability varied strongly between individual parental combinations. It was concluded that most types of B. vulgaris can be hybridized with the wild species of the section Patellares if a sufficient number of pair-crosses is made. Crosses between diploid cultivars or species of the section Vulgares and diploid wild species of the section Patellares yielded many hybrids which, however, were highly sterile. From crosses between tetraploid B. vulgaris and the wild species a great number of viable allotriploid and allotetraploid hybrids was obtained. In the backcross progenies of allotriploid hybrids 26% alien monosomic additions occurred, of which 4.1% carried the resistance bearing chromosome of B. procumbens or B. patellaris. The programme will be continued by sereening progenies of the resistant monosomic addition plants for the occurrence of resistant disomic introgression products.     

Cytogenetic studies in hexaploid Helianthus species and their F1 hybrids with cultivated sunflower, H. annum

Hexaploid sunflower species provide potential sources of desirable genes in breeding for resistance to pathogens as well as high protein and oleic acid content. The possibility of using them in sunflower breeding was studied by testing the crossability of hexaploid species to cultivated sunflower, by the analysis of meiosis and pollen viability in the F₁ interspecific hybrids. The hybrids were obtained from 16 combinations, with 1–18 F₁ plants per combination. The F₁ hybrids in general exhibited the dominant phenotype of the wild species. Sterility ranged from 0 to 87.5% per F₁ combination, while pollen viability ranged from 43.0 to 70.2%. Meiosis was almost normal in the species analysed but irregular in the F₁ hybrids. Most of the meiocytes showed predominantly bivalents (86.79–90.22%), but univalents (0.00–4.99%) and the multivalents (8.23–10.09%) occurred as well. At anaphase I, chromosome bridges were detected in 6.88–8.48% of meiocytes. Fast chromosomes in meta-phase I and lagging chromosomes in anaphase I and telophase II were observed in many meiocytes.     

Introgression from wild Cicer reticulatum to cultivated chickpea for productivity and disease resistance

Interspecific hybridization is known to improve productivity and resistance to diseases in many crops. Therefore, an attempt was made to introgress productivity and disease resistance into chickpea from wild Cicer species. The true F₁ hybrids of cultivated chickpea genotypes ‘L550’ and ‘FGK45’ with C. reticulatum were backcrossed twice to their cultivated female parents to minimize the linkage drag of undesirable wild traits. The pedigree method was followed to advance the segregating populations from straight crosses (without backcross) and BC₁/BC₂ generations to F₅–F₇. The interspecific derivatives recorded up to a 16.9% increase over the check cultivars and a 25.2% increase over the female parent in a preliminary yield evaluation trial. Of the 22 interspecific derivatives thus derived, four desi and two kabuli lines were further evaluated for seed yield in replicated trials at three diverse locations. These lines possess a high degree of resistance to wilt, foot rot and root rot diseases, and recorded a 6.1–17.0% seed yield increase over the best check cultivars.     

Interspecific hybrid of Helianthus annuus × H. simulans: Characterization and utilization in improvement of cultivated sunflower (H. annuus L.)

The first success at interspecific hybridization between cultivated sunflower(H. annuus) and a diploid perennial species, H. simulans is reported. The F₁s from both direct and reciprocal directions exhibited dominance of the wild species phenotype and were pollen sterile. Meiosis was irregular in the F₁ hybrids and both univalents and multivalents were observed. Multiplication of the interspecific hybrids was achieved through in vitro culture of nodal sections on Murashige & Skoog medium supplemented with 0.5 mg l^-1 benzyladenine. Fertility of the interspecific hybrids was improved by subjecting the in vitro proliferating shoots to 0.001% colchicine incorporated in the shoot multiplication medium. The amphiploids serve as fertile bridges and facilitate interspecific gene transfer through conventional breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Introgression of resistance to Columbia and Northern root-knot nematodes fromSolanum bulbocastanum into cultivated potato

Summary Resistance toMeliodogyne chitwoodi races 1 (MC1) and 2 (MC2) andM. hapla (MH) derived fromSolanum bulbocastanum was introduced into the cultivated potato gene pool through somatic fusion. The initial F₁ hybrids showed resistance to the three nematodes. Resistance to reproduction on roots by MC1 was accompanied by resistance to tuber damage in F₁ clones. Tuber damage sometimes occurred, however, in hybrids of BC₁ progeny resistant to reproduction on roots when MC2 and MH were the challenging nematodes. Resistance to reproduction was transferred into BC₁ individuals, but a greater proportion of BC₁ progeny was resistant to MC1 than to MC2 or MH. Resistance to MC1 appears to be dominant and discretely inherited. F₁ and BC₁ progeny were pollen sterile, but seed were produced from crosses using cultivated tetraploid pollen sources. Approximately 11 and 33 per cent of pollinations produced berries on F₁ and BC₁ pistillate parents, respectively. Seed yield increased fourfold overall in crosses with F₁ compared to BC₁ individuals.Abbreviations MC1 Meloidogyne chitwoodi race 1 - MC2 Meloidogyne chitwoodi race 2 - MH Meloidogyne hapla - Rf Reproductive factor     

Widening the gene pool of cultivated lentils through introgression of alien chromatin from wild Lens subspecies

Wild Lens species/subspecies are a potential source for increasing genetic diversity in cultivated lentil. Four intraspecific crosses were attempted between cultivated and wild lentils. Viable hybrids were produced between L. culinaris ssp. culinaris × L. culinaris ssp. orientalis and L. culinaris ssp. culinaris × L. culinaris ssp. odomensis. Normal meiosis and pollen fertility were observed in the first set of crosses, whereas chromosomal abnormalities and reduced pollen fertility were observed in the second set of crosses. These crosses were also studied for some quantitative traits. The range, mean and coefficient of variation were calculated in parents, F₁, F₂ and BC₁ generations to determine the extent of variability generated in the cultivated lentil through introgression of genes from wild lentil. The cultivated lentil × L. culinaris ssp. orientalis crosses showed substantially higher variability for all the traits than crosses involving cultivated lentil ×L. culinaris ssp. odomensis. The results of the present study indicated that these wild subspecies can be exploited for breeding purposes and their variation can easily be utilized to widen the genetic base of the cultivated lentil.     

Interspecific hybridization between sunflower and wild perennial Helianthus species via embryo rescue

Interspecific crosses were made between the cultivated sunflower inbred line HA89 and accessions of five wild perennial Helianthus species (H. giganteus L., H. laevigatus T. & G., H. resinosus Small, H. pauciflorus Nutt. and H. decapetalus L.) resistant to broomrape ( Orobanche cernua Loefl.). Using the genetic male-sterile isogenic version of that line as female, successful reciprocal crosses were also obtained with all these wild species except with H. decapetalus. Five-day-old hybrid embryos were excised and cultured in vitro. In all cases, few mature plants were obtained from embryos in early developmental stages (early heart and globular) but up to 28% mature plants were obtained from embryos in later stages of development. Very immature embryos were difficult to excise without damage. Hybrid embryos and mature plants were obtained from all five wild species. Interspecific hybrid embryos from different wild species showed distinct developmental potentials, the proportion of hybrid embryos in different developmental stages varying among species. Differences in the proportion of hybrid embryos at the several developmental stages were also obtained for the reciprocal crosses (cultivated × wild), which showed higher proportion of fully developed embryos. Hybrids involving H. giganteus and cultivated sunflower were difficult to obtain without the use of embryo culture. Embryo culture proved to be an useful tool to overcome post-zygotic hybrid incompatibility in different Helianthus spp., and facilitated interspecific transfer of resistance to O. cernua. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of Resistance in Vicia sativa L. to Orobanche crenata Forsk.

The genetics of resistance of common vetch (Vicia sativa L.) to broomrape (Orobanche crenata Forsk.) was studied for two years by using the P₁, P₂, F₁, BC¹, BC₂, F₂ F₃, and F₄ generations obtained from crosses between resistant and susceptible lines. Resistant lines were selected by screening a world collection m a naturally infested plot. Resistance was tested both under field and greenhouse conditions. The best index to measure resistance was the number of emerged broomrapes per host plant. The results fit the additive-dominance model. The main component of the variation was additivity; dominance and interaction effects seemed to depend on the environment. When dominance is expressed, a low number is dominant over a high number of broomrapes per host plant.     

A cytogenetic study of the progenies of hybrids between Brassica napus and Brassica oleracea, Brassica bourgeaui, Brassica cretica and Brassica montana

In this cytogenetic study the progeny of all crosses were investigated in F₁, F₂ and backcross (BC₁) hybrids. Brassica napus and F₁ hybrids between B. napus and B. oleracea, and between B. napus and three wild relatives of B. oleracea (B. bourgeaui, B. cretica and B. montana). Each of the wild relatives has 18 somatic chromosomes. Interspecific F₁ hybrids were obtained through ovary culture mean. These had 28 and 37 chromosomes and their mean pollen fertility was 10.7% and 93.0%, respectively. Many F₂ and BC₁ seeds were harvested from the F₁ hybrids with 37 chromosomes after self‐pollination and open pollination of the F₁ hybrids, and backcrossing with B. napus. Many aneuploids were obtained in the F₂ and BC₁ plants. It is evident from these investigations that the F₁ hybrids may serve as bridge plants to improve B. napus and other Brassica crops.     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. II. The crossability of resistant species

Summary Over 2400 pollinations were made to investigate the crossability relationships between cultivated potatoes, and wild diploid species from Series Tuberosa and Circaeifolia, as well as wild polyploid species in Series Tuberosa and Longipedicellata resistant to potato cyst nematode, Globodera pallida pathotypes P₄A and P₅A. Wild diploids in Series Tuberosa crossed easily with cultivated diploid species, except with Solanum lignicaule where most pollinations failed, and seed set was extremely low (0.2 seeds per pollination or less). It is suggested that this species is 1EBN. S. capsicibaccatum is clearly isolated from Series Tuberosa, but can form hybrids with S. lignicaule, which can act as a bridging species to S. tuberosum haploids. S. gourlayi and S. oplocense can be crossed with both subspecies of S. tuberosum, but S. papita, Series Longipedicellata is reproductively isolated from the tetraploid cultigens. The crossability data are discussed in the light of germplasm utilisation for breeding potato varieties resistant to potato cyst nematode.     

Interspecific hybrids of sunflower as a source of Sclerotinia resistance

Sclerotinia sclerotiorum is considered the most devastating pathogen of sunflower grown in humid environments. In this study, progenies of partial hybrids between Helianthus maximiliani, a wild species that has been shown to be resistant to S. sclerotiorum, and H. annuus were characterized by amplified fragment length polymorphism (AFLP) analysis to identify whether there are introgressions from H. maximiliani into the cultivated sunflower at the molecular level. Wild species‐specific fragments as well as fragments not found in either parent were detected. Progenies tended to cluster together according to the original partial hybrids in the dendrogram by the use of bootstrap procedures. The progenies were studied for their reaction to S. sclerotiorum using artificial inoculation of sunflower heads. Some of the progenies showed a higher level of resistance compared with resistant inbred lines. It was possible to identify two AFLP‐fragments which seem to be linked to Sclerotinia resistance.     

Interspecific hybrids between helianthus PetiolarisNutt. and H. Annuus L.: Effect of backcrossing on meiosis

Summary Interspecific substitutions of the nucleus of Helianthus annuus (2n=34) into the cytoplasm of H. petiolaris (2n=34) were obtained by successive backcrossing using cultivated sunflower, H. annuus, as the recurrent pollen parent.Meiosis in the F₁ was characterized by multivalents, suggesting that 10 of the 34 chromosomes were heterozygous for chromosomal interchanges. An additional pair of chromosomes also contained a paracentric inversion. Continued backcrossing resulted in rapid elimination of the meiotic aberrations evident in the F₁. In the BC₁, 1 of 11 plants had normal meiosis and by the BC₂, only 13 of 54 plants had meiotic aberrations similar to those of the F₁. However, trisomic progeny (2n=35) were found in 3 of the 11 BC₁ plants and 20 of the 54 BC₂ plants. No meiotic aberrations were observed in BC₃ or BC₄ plants. Plants with indehiscent anthers, and considered to be male sterile (M.S.), first occurred in the BC₁ and, by the BC₂, 51 of 54 plants were M.S. All 19 BC₃ and 16 BC₄ plants were M.S. Preliminary investigations suggest that the pollen from such plants is sterile and that the sterility is cytoplasmic rather than genetic.Disc-flower measurements were a useful technique for selecting samples at the correct stage of microsporogenesis, but could not be used to distinguish between successive backcrosses.     

Isozyme variation in Helianthus petiolaris and sunflower,H. annuus

Summary Helianthus petiolaris is a wild species used in genetic improvement of sunflower, as a donor of cytoplasmic male sterility and of genetic resistance to diseases. Isozyme variation for ADH, ACP, EST, GDH, LAP, PGI, PGD and SKDH in this species was studied using starch gel electrophoresis. The patterns thus obtained were compared with zymograms of inbred lines, hybrids and open pollinated varieties of H. annuus. The same alleles for EST and SKDH isozymes were found in both species, while ACP showed an allele that has not been found in sunflower. The rest of the isozyme systems showed both common alleles and characteristic ones for each species. ACP, GDH and PGD were monomorphic in H. petiolaris, while ADH and LAP were monomorphic in H. annuus. The isozyme markers obtained here could be useful in breeding programs involving interspecific crosses, and studies on introgression and on genetic variation in other populations of this wild species.     

Hybrids of <Emphasis Type="Italic">Avena sativa</Emphasis> with two diploid wild oats (CIav6956) and (CIav7233) resistant to crown rust

Two diploid accessions of wild oat, CIav6956 and CIav7233, were identified as carrying seedling resistance to oat crown rust (caused by Puccinia coronata f. sp. avenae; Pca). Two vigorous interploidy F₁ hybrids were generated from crosses involving the hexaploid oat cultivar Wintaroo and the diploid oat Avena strigosa Schreb. accession CIav6956. An additional interploidy F₁ hybrid, designated “F1-Aa1”, was produced from a cross of Wintaroo and the diploid oat accession CIav7233. All three hybrids were more vigorous and taller than the cultivated parent Wintaroo. The three F₁ hybrids contained full chromosome complements from both parents (2n = 4x = 28), but no seeds were obtained when the three F₁ hybrids were selfed. Meiotic analyses of the hybrids indicated that they exhibited a high degree of inter-genome and intra-genome pairing. Trivalent configurations were detected in 95–96% of meiotic cells and a minimum of three bivalents was present in all cells. An average chiasma frequency of 7.2–7.9 per cell was observed for the three F₁ hybrids. A fourth F₁ hybrid was subsequently generated from a cross between the diploid oat accession CIav7233 and Wintaroo. One octaploid (2n = 8x = 56) was generated from this hybrid and progeny were resistant to two Pca races. The chromosome number of the octaploid progeny varied between 51 and 54 chromosomes. Development of a chromosome addition line(s) with the crown rust resistance should be possible from these partial-octaploids.