Wild Species Hybrids Research Articles

Evaluation of different sources of resistance for breeding powdery mildew resistant grapevine varieties

The appearance of resistance to powdery mildew was investigated on seedling progenies of interspecific crossings. Hybrids of American and East-Asian wild species and one Vitis vinifera variety (Janjal kara) were used as source of resistance in the crossings. The resistance of foliage and of berries were tested in the field at the time of vintage. The degree of resistance was ranked into six classes.
 In American and Asian hybrid derivatives there were few highly resistant progenies, but in the hybrids of Janjal kara variety more than 90 % of the progenies proved to be highly resistant to powdery mildew. According to the distribution of classes of resistance in the populations the resistance of American and Asian sources are mostly influenced by additive gene affects. The resistance of Janjal kara seemed to be mono or digenic.
 No close correlation was found between the powdery mildew resistance of the foliage and that of the berries.

Meiotic restitution mechanisms and 2n pollen formation in a Solanum tuberosum dihaploid and in dihaploid × wild species hybrids*

AbstractA Solatium tuberosum dihaploid that proved to be a 2n pollen producer, exhibited two types of meiotic abnormality involved in 2n pollen formation: premature cytokinesis at prophase II and parallel/tripolar spindles in meiosis II. For this reason such a dihaploid was preferentially used as a seed parent in crosses with the diploid species S. tarijense, S. sanctae‐rosae, and S. phureja. Diploid interspecific hybrids were evaluated for male fertility, for 2n pollen production and stability over three years and for meiotic nuclear restitution mechanisms. Pollen stainability ranged from 6 to 85% and 2n pollen from 5 to 35% among hybrids. The meiotic mechanism generating 2n pollen was that of spindle abnormality in meiosis II and consequent dyad/triad formation. High correlation was found between fused/parallel spindles and dyads.

Progress Toward Identifying Markers Linked to Genes Controlling Chilling Requirement and Cold Hardiness in Blueberry

Progress was made in identifying molecular markers linked to genes which control chilling requirement and cold hardiness in a woody perennial, blueberry (Vaccinium, section Cyanococcus). 40Construction of RAPD (randomly amplified polymorphic DNA)-based genetic linkage maps using two testcross populations derived from interspecific hybrids of wild diploid blueberry species, V. darrowi Camp X V elliottii Chapm. and V. darrowi X V caesariense Mackenz. was continued. Mapping populations were segregating for chilling requirement and cold hardiness. Screening plants of the V. darrowi × V. caesariense-derived mapping population for cold acclimation capacity using leaf tissue collected before and after cold treatment and an electrolyte leakage assay was begun. In addition, a tetraploid breeding population (predominantly V. corymbosum L.) was screened for chilling requirement and efforts were begun to identify markers linked to genes determining chilling requirement using this population and a bulked-segregant-type analysis. [Article copies available from The Haworth Document Delivery Service: 1-800-342-9678.]

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

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.

A Modified Nodal Cutting Bioassay for Assessing Salinity Tolerance in Potato (Solanum sp.)

The potato (Solanum tuberosum L.) is considered moderately sensitive to salinity stress. Yields can be adversely affected by salinity at EC levels of 2 to 3 dS·m–1. In vitro screening and selection for salinity tolerance may be faster and more reliable than traditional field assessment. A modified nodal cutting bioassay was developed based on that of Morpurgo (1991) and used to rank the salinity tolerance of several potato cultivars, wild Solanum species, and their hybrids. Nodal cuttings were cultured in Murashige and Skoog (1962) basal medium which included NaCl at 0, 40, 80, and 120 mM. After 4 weeks at 25C and 16/8 h day/night period, vegetative growth parameters were assessed. Hybrids derived from S. chacoense outperformed hybrids of other wild species, their wild parents, and S. tuberosum cultivars. `Russet Burbank' and `Kennebec' were more salinity-tolerant than the three other cultivars tested.

Suppression of recombination in wide hybrids of Petunia hybrida as revealed by genetic mapping of marker transgenes

In the course of a heterologous transposon tagging experiment in Petunia hybrida (n=7), 135 independent T-DNA loci were tested for linkage to the target genes Hf1 and Fl, which are located on the two largest chromosomes. Approximately one-third (47) of these T-DNA loci were linked to one of these two markers. Of these 47 linkedloci, 19 mapped within 1 cM of its marker, indicating a highly non-random genetic distribution of introduced loci. However, rather than non-random integration within both of the marked chromosomes, this probably reflects a suppression of recombination around these marker loci in the particular wide hybrids used for mapping. This hypothesis was tested by measuring recombination between linked T-DNAs in an inbred background. Inbred recombination levels were found to be at least 3-fold higher around the Hf1 locus and 12-fold higher around Fl compared to the wide hybrids. These findings may reflect the origin of P. hybrida by hybridization of wild species, and while relevant to genetic mapping in petunia in particular they may also have more general significance for any mapping strategies involving the use of wide hybrids in other species.

Inheritance of potato chip color at the 24-chromosome level

Potato chip color is an important trait in determining quality and acceptability of cultivars for processing. Therefore, the genetics of potato chip color is important in varietal breeding. The use of 2xS. tuberosum Group Tuberosum haploid × 2x wild species hybrids provides disomic inheritance for genetic analysis of chip color. Two hundred forty haploid-species hybrids representing crosses between 15 haploids and 10 species were evaluated for potato chip color after 21 days reconditioning (18 to 20C) following 6 months at 4C. Phenotypic variation for chip color was found among the haploid-species hybrids. Crosses between good, medium, and poor performing clones were made in all combinations and 136 families were obtained. Progeny were evaluated for reversion resistance (chipping direct from 10C storage) and reconditioning (chipping from 4C after tuber warming) chip color. Variation for chip color was found among the progeny for each trait. Significant correlations between reversion resistance and reconditioning were found. Yet, the use of at least two chip tests (one for reversion resistance and one for reconditioning) is more informative than the use of one test and subsequent predictions made, regarding the other trait. A three locus hypothesis for both reversion resistance and reconditioning is proposed for the inheritance of each trait. One dominant allele at each of the three loci is necessary for good chipping. One or two loci may be common to both characteristics. Good chipping 2x hybrids that produce 2n pollen can be used to transfer this trait to the 4x level through use of 4x × 2x crosses.

Genetic manipulation of rice: from protoplasts to transgenic plants.

Protoplasts are versatile tools for genetic manipulation of plant cells. The ability of genetically modified protoplasts to differentiate into complete plants offers novel experimental systems in various fields of plant biology. Among major graminaceous species (cereals), rice is the only one in which wellestablished protoplast system is available. By using protoplasts as an experimental system, we have obtained and characterized various mutations some of which are being used for breeding new varieties. Somatic hybrids of rice and wild Oryza species were generated and cytoplasmic male sterility of an indica rice was transferred to japonica rice by cell fusion. Most importantly, an efficient method of genetic transformation was developed which opened up a new area of research in rice. Variously modified genes can be now introduced and expressed in transgenic rice and various mutations were generated by introduced transposable elements, Ac/Ds. Initial attempts on genetic engineering of rice has also begun. These suggest that rice can be a model cereal in which genetic as well as reverse-genetic approaches can be taken for various basic and applied studies.

Breeding for 2n egg production in haploid × species 2x potato hybrids

The identification of diploid(2x), Tuberosum haploid × wild species hybrids (HS) which produce high frequencies of 2n eggs and have good tuber appearance is important for obtaining 4x progeny from 2x × 2x crosses in potato. More than 1700 HS clones were screened for the occurrence and frequency of 2n eggs through 2x × 4x crosses during two pollination periods. The resulting seed/fruit provides an estimate of 2n egg frequency. About 650 HS clones produced 2n eggs; 63 had 10–114 seeds/fruit; and 27 were selected for good tuber type. There was a large variation in seed set after 2x × 4x crosses, both within and between clones. Comparison of fruit and seed set between the two pollination periods using the same 595 clones indicated that environmental factor significandy affected 2n egg frequency. The mode of 2n egg formation was mainly due to omission of the second meiotic division controlled by a recessive gene (os). The gene frequency foros varied from 0.28 to 0.76 among six, 2x taxa. Both additive and dominance variance were significant for seed set after 2x × 4x crosses. Narrow sense heritability was estimated as 0.24. The average degree of dominance was equal to 1.66 which could indicate overdominance. Alternatively, this could be due to linkage disequilibrium,i.e. pseudooverdominance. However, dominance variance was greater than the additive variance indicating recurrent selection can be useful for improving the frequency of 2n egg production in the 2x population. The selected individuals, based on their phenotypic performance, should be progeny tested to identify the best parents for use in the next cycle of recombination.

A restorer gene for genetic-cytoplasmic male sterility in cultivated potatoes

Fifty-nine clones (cultivars and advanced selections) ofSolanum tuberosum Group Tuberosum were pollinated with two Group Phureja-haploid Tuberosum hybrids, which produce FDR 2n pollen (ps/ps) and are heterozygous for a dominant gene (Ms/ms) which interacts with Tuberosum cytoplasm to result in male sterility. Twenty-eight and thirty-four plants from each family were transplanted to the field in two different locations, respectively. Pollen samples were collected from each plant and stained with acetocarmine glycerol jelly. Plants with over 95% unstainable pollen were considered male sterile. The families could be put into distinct classes according to the ratio of male sterile to male fertile plants; 3 sterile: 1 fertile (23 clones), 2 sterile: 3 fertile (24 clones), 1 sterile: 5 fertile (3 clones), and 0 sterile: 1 fertile (3 clones). Four families deviated significantly from any expected ratio. The variation for male fertility among families resides in the tetraploid parent, since the male parents have the same genotype (Ms/ms) for theMs locus. The locus of this gene is very distal to the centromere such the 2n gametic output is 1 Ms/Ms : 2 Ms/ms : 1 ms/ms. The variation in male sterility is explained by the presence or absence of a dominant allele of a restorer gene (Rt) in tetraploid Tuberosum. This locus is also very distal to the centromere. The frequency of theRt gene was estimated to be 0.20 in Tuberosum. The finding ofRt gene explains some of the conflicting results in male fertility of haploid Tuberosum x 2x cultivated and wild species hybrids. It also provides an opportunity to partially circumvent this male sterility. Haploids (2n = 2x = 24) extracted from 4x clones withRt genes would have male fertile progeny in crosses with species carrying theMs gene.

Performance of haploid x wild species, 2x hybrids (involving five newly evaluated species) in 4x × 2x families

The 4x × 2x breeding scheme in potato allows introgression of germ-plasm from the 2x wild species into the cultivated tetraploid. Eighteen 4x × 2x, forty-five 4x × 4x, seven 4x-selfs, and five open pollinated (OP) families were transplanted in a randomized complete block design with two replications and 18 plants per family per replication. The 2x parents of the 4x × 2x families were seven haploid x wild species hybrids. These hybrids involve five 2x, wild species,Solanum bukasovii, S. gourlayi, S. muhidissectum, S. vermi, andS. verrucosum, which had not previously been evaluated in the 4x × 2x breeding scheme. Data were recorded for family yield, maturity, tuber uniformity, tuber number, and general tuber appearance. The 4x × 2x families as a group performed as well as or better than the 4x × 4x, 4x-self, and 4x-OP groups for all traits except maturity. Within family maturity distributions for 4x × 2x families indicate the possibility to select early maturing clones from high yielding families. Eleven of the fifteen families in the top 25% of the 4x × 2x and 4x × 4x families for yield were 4x × 2x families. Three of the four 2x parents evaluated for parental performance gave highly significant responses for increased yield. 4x × 2x families with Chiquita as a parent were the poorest yielding while several of the 4x x 4x families of which it was a parent were among the highest yielding: This indicates that the benefits of maximum heterozygosity may be overridden if the percentage of unadapted germplasm is too high.

Selection of Potato Haploid Parents for Use in Crosses with 2x (2 Endosperm Balance Number) Wild Species

Haploids (2n = 2x = 24) of Solanum tuberosum L. may be used to tap the genetic diversity present in the related wild species by producing haploid ✕ species hybrids (2n = 2x = 24). The purpose of this study was to identify elite haploids for use in crosses to wild species based on percentage tuberization of their progeny, number of fruit per pollination and seeds per fruit, and their genotype for parallel spindles (ps), a meiotic mutant causing 2n pollen formation. A group of 73 haploids were selected for good flowering and cultivartype haulms. To determine their respective ps‐locus genotypes, the haploids were testcrossed as females to four plants of S. chacoense BITT. (psps). All 21 of the haploids that were successfully crossed to S. chacoense BITT. produced families with a high percent tuberization. Only one of the 39 families tested had percentage tuberization that was significantly lower than the average family performance. Eighteen of the 21 haploids were Psps, one was psps, and two gave families that deviated significantly (P < 0.05) from a 1:1 ratio. Six haploids had average seed set of greater than 40 seeds per fruit in all combinations for which twenty or more pollinations were made. Selection of elite haploids should increase the potential of the 4x ✕ 2x breeding scheme by: (i) increasing the amount species germplasm that may be selected among, (ii) making production of haploid ✕ wild species hybrids morefficient, and (iii) increasing the amount of the germplasm pool that can be transferred to the tetraploid level using 2n pollen.

Triple hybridization with cultivated barley (Hordeum vulgare L.)

A crossing programme for trispecific hybridization including cultivated barley (Hordeum vulgare L.) as the third parent was carried out. The primary hybrids comprised 11 interspecific combinations, each of which had either H. jubatum or H. lechleri as one of the parents. The second parent represented species closely or distantly related to H. jubatum and H. lechleri. In trispecific crosses with diploid barley, the seed set was 5.7%. Crosses with tetraploid barley were highly unsuccessful (0.2% seed set). Three lines of diploid barley were used in the crosses, i.e. 'Gull', 'Golden Promise' and 'Vada'. Generally, cv 'Gull' had high crossability in crosses with related species in the primary hybrid. It is suggested that 'Gull' has a genetic factor for crossability not present in cv 'Vada' and cv 'Golden Promise'. One accession of H. brachyantherum used in the primary hybrid had a very high crossability (seed set 54.7%) in combination with cv 'Vada' but no viable offspring was produced. In all, two trispecific hybrids were raised, viz. (H. lechleri x H. brevisubulatum) x 'Gull' (2n=7-30) and (H. jubatum x H. lechleri) x 'Gull' (2n=20-22). The first combination invariably had a full complement of seven barley chromosomes plus an additional chromosome no. 7, but a varying number of chromosomes (19-22) of the wild-species hybrid. The second combination had a full set of barley chromosomes. The meiotic pairing was low in both combinations.

Evaluation of tuber traits of 10,2x(2EBN) wild species through haploid × wild species hybrids

The wild species of potato do not tuberize under long day conditions making evaluation of their tuber characteristics difficult. HaploidTuberosum × wild species hybrids provide a means of evaluating the tuber characteristics of the 2x, wild species. Seventy-eight haploid × wild species hybrid families were evaluated for yield, specific gravity, percent tuberization per family, general tuber appearance, number of tubers per hill, and dormancy. The wild species parents wereS. bukasovii, S. canasense, S. gourlayi, S. infundibuliforme, S. kurtzianum, S. multidissectum, S. sparsipilum, S. spegazzinii, S. vernei, andS. verrucosum. Variation existed for all traits examined. Percent tuberization per family was greater than 50% in 72 of the families supporting the use of haploids to capture species germplasm for maintenance and evaluation. The mean specific gravity for all hybrids with each of seven species as a parent was greater than 1.085 (acceptable processing level). The analysis of variance for yield indicated that the effect of species parent was significant while the effect of haploids was not. Thirty-eight percent (608 of 1623) of the hybrids which tuberized had eight or more tubers per hill which would allow for further replicated evaluation at multiple locations. Dormancy ranged from 83 to 270 days post-harvest facilitating selection of clones suited to a variety of culture and storage conditions.

Comparison of 2n and Non-2n Pollen-Producing Haploid × Wild Species Hybrids in Potato

Haploid × wild species hybrids (2n=2x=24) provide a means of capturing the germ plasm of the 2x, 2EBN wild Solanum spp. in a form in which it can be maintained and evaluated. 2n pollen-producing and non-2n pollen-producing hybrids were compared from the same population in regard to seven agronomic and breeding characteristics to determine appropriate selection strategies

Potato breeding with haploids and 2n gametes

Potato breeding methods that utilize haploids of Solanum tuberosum group Tuberosum or group Andigena and 2n gametes exploit the genetic diversity, including both valuable traits and allelic diversity, available in exotic germ plasm. Three essential components are involved: (i) the wild and cultivated 2x relatives of the cultivated 4x potato are a valuable source of genetic diversity; (ii) haploids (2n = 2x = 24) of cultivars (2n = 4x = 48) are effective in capturing diversity (germ plasm enhancement); (iii) 2n gametes, resulting from first division restitution, are an efficient method of transmitting this genetic diversity to cultivated 4x potatoes. Heterosis for total and marketable tuber yield and specific gravity occurs in 4x families from crosses between 4x cultivars and 2x haploid Tuberosum × 'Phureja' hybrids. Selected 4x clones from relatively small 4x × 2x families have been released as cultivars based on their earliness and heat tolerance in the tropics. Other 4x clones from 4x × 2x crosses, where the 2x parents were haploid – wild species hybrids, have good yield, excellent tuber type, high specific gravity, low reducing sugars, storage quality, and stress tolerance. The seedling vigor, uniformity, and large tuber yields of progeny from 4x × 2x crosses also makes this an effective breeding method for producing potatoes from true potato seed. This breeding method is also being successfully exploited in alfalfa, red clover, sweet potatoes, yams and several species of grasses, fruits, and ornamentals.Key words: potato, haploids, 2n gametes, germ plasm, allelic diversity.

2n pollen in eleven 2x, 2EBN wild species and their haploid x wild species hybrids

Sixty-three plants producing 2n pollen were identified among 65 introductions of 11 2x, 2EBN wild species. They were found in 27 of the 65 introductions representing ten of 11 species. The gene frequencies for the allele controlling 2n pollen formation ranged from 0.19 to 0.65. Seventyeight haploid x wild species hybrid families were produced using the previously identified 2n pollen plants as male parents. One hundred and thirty-two plants that produced 2n pollen were identified among the haploid x wild species hybrids at one location and 44 at another. The high number of haploid x wild species hybrids that produced 2n pollen and the large number of hybrids with acceptable pollen stainability demonstrate the potential of the hybrids in 4x × 2x germplasm transfer. Potato breeders can unleash the genetic diversity present in the 2x, 2EBN wild species by screening them for 2n pollen and crossing the 2n pollen producing plants to haploids.

Hybrids of rice (Oryza sativa L.) and wild Oryza species obtained by cell fusion

Cell fusion was used to obtain hybrid plants of rice (Oryza sativa L.) and four wild Oryza species, O. officinalis, O. eichingeri, O. brachyantha, and O. perrieri, to incorporate useful traits of the latter species into rice. A total of 250 mature hybrid plants were obtained by electrofusion and nurse culture methods. The hybrid nature of these plants was confirmed by karyotypic, morphological, and isozyme analysis. The hybrids of O. sativa+O. eichingeri, O. sativa+O. officinalis and O. sativa+O. perrieri produced viable pollen and the O. sativa+O. eichingeri hybrid has produced a progeny plant. Our study demonstrates the use of cell fusion for future rice improvement.

Resistance of Wild Species of Peanut to an Insect Complex1

Abstract A complex of insects which can cause moderate to severe crop damage attacks peanuts in the North Carolina-Virginia production area. Wild species representing the seven sections of the genus Arachis L. were evaluated for resistance to tobacco thrips (Frankliniella fusca Hinds), corn earworm (Heliothis zea Bodie), and potato leafhopper (Empoasca fabae Harris) during a 3-year field study. Very high levels of resistance for these insects were identified in several species collections. Because collections in section Arachis were among the species with the highest resistance levels, utilization of the germplasm resources to improve cultivated peanuts should be possible. In addition to evaluating species collections, 40-chromosome (A. hypogaea x wild species) hybrid derivatives were evaluated for resistance to the three insect pests plus southern corn rootworm (Diabrotica undecimpunctata howardi Barber). Selections with resistance levels equal to or greater than the cultivar NC 6 were made for corn earworm and southern corn rootworm. Laboratory tests of several Arachis species indicated that a mechanism of resistance to H. zea is antibiosis. Because the levels of resistance to several insects have been greatly increased in lines of A. hypogaea, evidence exists for germplasm introgression from wild to the cultivated species of peanuts.

Cytology and leafspot resistance in Arachis hypogaea x wild species hybrids

Introgression of germplasm from diploid wild Arachis species to A. hypogaea has great potential for improving pest resistance in cultivated peanuts. This investigation evaluated methods for incorporating exotic germplasm into cultivated peanuts, especially for Cercospora arachidicola Hori resistance. Interspecific hybrids between A. hypogaea (cvs. NC 2 and NC 5) and the wild species A. cardenasii Krap. et Greg. nom. nud. and A. chacoense Krap. et Greg. nom. nud. were analyzed cytologically and for leafspot resistance. All F1 hybrids were sterile, had irregular meiosis, and very few multivalents. They were highly resistant to C. arachidicola in field tests and had a 10-fold reduction of conidia per lesion in the greenhouse as compared to A. hypogaea cultivars. After colchicine treatments of F1 hybrids, hexaploids (2n=60) and aneuploids (2n=54, 56, 63) were observed. The hexaploids had up to 18 univalents per pollen mother cell and very few multivalents, indicating a low frequency of intergenomic chromosome pairing. For C. arachidicola resistance, significant differences were not found among wild species parents, F1 hybrids and two generations of hexaploids. Most hexaploids were stable at 2n=60 and embryos aborted when backcrosses with the respective wild species were attempted. However, when hexaploids were backcrossed to A. hypogaea, several fertile pentaploid (2n=50) offspring were obtained. Use of self-pollinating pentaploids is believed to be the quickest method to recover 40-chromosome hybrid derivatives in these hybrids.