Cytogenetic studies and the occurrence of triploidy in the wild potato species Solanum commersonii Dun.

Summary The South American wild potato species Solanum commersonii Dun. exists as two subspecies, subsp. commersonii and subsp. malmeanum (Bitter) Hawkes and Hjerting, and as both diploid and triploid cytotypes. The two subspecies were completely cross fertile but there were reciprocal differences in the number of seeds set per berry and the mean seed weight. Crosses between diploids and colchicine-induced autotetraploids yielded only a few seeds per berry, but 16 of the 18 germinated seeds were triploid or nearly so. Such a high proportion of triploids is unusual for such crosses in potatoes. Some triploids has a high percentage of stainable pollen. The origin of naturally occurring triploids is discussed in the context of 2n gametes, a triploid block, and endosperm balance numbers.     

Vertical resistance to late blight in wild potato species from Argentina

The possible presence of vertical resistance to late blight conferred by R genes in Argentine wild Solanum species, which presumably have not evolved under the pressure of the fungus, was investigated. Solanum microdontum, S. commersonii and S. chacoense clones were tested in the greenhouse and with detached leaves in the laboratory after inoculation with a complex race and a non-virulent race of Phytophthora infestans. Two progeny tests were carried out to assess the performance of contrasting parents in regards to their resistance. A varying frequency of incompatible clones was detected among the species, with S. microdontum having the higher proportion of clones yielding incompatible reactions both in the laboratory and in the greenhouse. S. chacoense and S. commersonii showed a small but still considerable frequency of incompatible clones. The progeny tests confirmed the presence of R genes in a S. commersonii cross and their absence in a S. chacoense cross. The unexpected presence of R genes, its evolutionary significance and the consequences on the use of these species in breeding is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Overcoming interspecific barriers in Sorghum and molecular characterization of the derivatives

Crop improvement in sorghum has progressed extensively availing the variation available in the primary gene pool of S. bicolor. Crossing further, the yield plateau can be accomplished by bringing in the genes from tertiary gene pool into the cultivated gene pool. Earlier efforts for wide hybridization in sorghum with tertiary gene pool were not successful due to inhibition of wild pollen germination on the stigma of cultivated species. In the current study, elite lines of cultivated Sorghum species were pollinated with wild species using different floral treatments. The results showed that spray with the synthetic auxin, 2,4-dichlorophenoxyacetic acid, has promoted the seed set. Overall, 76% crosses showed seed set, but many seeds were underdeveloped and deformed. F₁ progeny showed traits of both cultivated and wild parents. Hybrids were confirmed through PCR analysis. Many (80%) F₁ plants were sterile, and 20% of F₁s were advanced to F₂ generation. Wide variation was observed in F₂ progeny, and the phenotype selections were made and are being evaluated in the field.     

Overcoming hybridization barriers between pea and some of its wild relatives

Pea would benefit from the plasticity and adaptability of its cross-incompatible relatives Pisum fulvum and Lathyrus sativus L., and we have tested reciprocal sexual crossings by manually cross-pollinating plants of genotypes of these three species. Studies of in situ germination of pollen grains on stigmata showed that pollen tubes were generally unable to germinate or could not reach the ovary. A few putative hybrid pods were nevertheless harvested, with one grain per pod germinated in vitro, then micropropagated for flow cytometry, isoenzyme, molecular (ribosomal ITS PCR-RFLP) and genomic in situ hybridization (GISH) studies. One such grain was recovered from an inter-generic cross of P. sativum x L. sativus and four from an inter-specific P. sativum x P. fulvumcross. A strong cross-incompatibility was shown between pea and grass pea, where the putative hybrid turned out to be pea. Conversely, with the interspecific, P. sativum x P. fulvum cross, flow cytometry and isoenzymes with leaf tissues strongly suggested hybridity, while molecular approaches and GISH confirmed the production of inter-specific hybrids, and without the need for a wild type P. sativum accession as a bridging cross.     

Tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum obtained through manipulation of ploidy and endosperm balance number (EBN)

The objectives of this study were to evaluate the tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F₁ triploid, BC₁ pentaploid‐near pentaploid and BC₂ tetraploid–near tetraploid hybrids. The F₁ triploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overcome. Indeed, the triploids produced 2n eggs, thus giving a compatible maternal to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) × 4x(3EBN) crosses. The tolerance to low temperatures of BC₁ and BC₂ hybrids was lower than that of the F₁. However, a number of genotypes were identified which were able to withstand temperatures down to ‐5°C. Some BC₂ hybrids were also tested for their tolerance to tuber soft rot, and some resistant hybrids were detected. A number of them combined the capacity for cold acclimatization with tolerance to tuber soft rot. These hybrids have an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum.     

Resistance to potato leafroll virus derived from Solanum chacoense: characterization and inheritance

Summary Resistance to potato leafroll virus (PLRV) was detected in an accession of Solanum chacoense. Inoculations with viruliferous aphids and subsequent graft challenges using Datura tatula and potato as PLRV sources determined that resistance appears to be of an extreme type. Virus was not detectable using enzyme-linked immunosorbent assay (ELISA) in S. chacoense, and in resistant F₁ and BC₁ progenies after attempts to transmit the virus through grafting. The segregation ratios of BC₁ progenies for positive and negative ELISA tests are consistent with simple dominant inheritance.     

Interspecific hybridization of a multiploid mutant of durum wheat with rye and Triticum monococcum L. results in pentaploid hybrids

The multiploid mutant of durum wheat is a genotype that produces unreduced gametes. Our objective was to test the recovery of pentaploid hybrids in crosses of the mutant with rye and Triticum monococcum L. Compared with check crosses, the mutant had a two‐third reduction in percent seed set for rye crosses, but had only a slight decrease in crossability with T. monococcum. Pentaploid hybrids were associated with plump seeds of the mutant/rye cross, and with shrivelled seeds of the mutant/T. monococcum cross. We suggest that the endosperm balance number hypothesis explains the association of pentaploid hybrids with endosperm type. This association made for easy recovery of pentaploid hybrids from crosses to both species. Mature, plump seeds from the mutant/rye cross were germinated and pentaploid hybrids were recovered. One pentaploid hybrid was recovered for every 50.5 and 15.1 florets pollinated with rye and T. monococcum, respectively. Unreduced gametes in the multiploid mutant will facilitate interspecific hybridization by reducing the time to produce pentaploid plants.     

The use of endosperm balance number for predicting gamete selection in complex polyploid interspecific Trifolium repens × T. nigrescens crosses

Endosperm balance number (EBN) was used to predict the outcome of crosses among a series of complex polyploid interspecific hybrids between Trifolium repens and T. nigrescens. Normal endosperm development, and hence seed‐set, requires a 2 : 1 maternal : paternal EBN ratio in endosperm. Based on their crossability, T. repens (2n = 4x = 32) and T. nigrescens (2n = 2x = 16) were assigned the same EBN of 4. This number was used to predict the relative success of different backcrosses and intercrosses. The method was further developed to successfully predict which gametes would effect fertilization when complex polyploid hybrids with uneven genomic constitutions (5x, 7x) produced mixtures of euploid and aneuploid gametes. This was achieved by allocating EBNs to all potential gametes of complex polyploids. Allocation of gamete EBNs enabled not only prediction of the success or failure of a cross, but also which gametes would be filtered to effect fertilization in complex crosses. This enhanced ability to understand the potential outcomes of complex crosses will increase the efficiency of plant breeding programmes that integrate secondary gene‐pools into economic species by interspecific hybridization.     

Pollen-style compatibility relations in natural populations of the wild diploid potato species Solanum spegazzinii Bitt.

Solanum spegazzinii Bitt., a wild diploid potato species endemic to Argentina, possesses resistance to adverse biotic and abiotic agents. Northwestern Argentinean populations grouped according to their morphological variability (G1 = localities East of the Calchaquí Valley, G2 = Calchaquí Valley and G3 = locality Belén) presented problems in seed set following controlled crosses. Thus, to evaluate if the morphological variability previously reported was sustained on a genetic basis, three introductions per group and five plants per introduction were used in controlled crosses (genotypic combinations). These were classified according to the number of seeds produced per fruit. Pollen-style compatibility relations were studied in those crosses that did not set seeds or that produced less than 30 seeds each. Within groups, G1 produced seeds normally, whereas hybridization barriers were found in 71.4% and 50.0% of the combinations within G2 and G3, respectively; on the other hand, from 46.7% to 73.3% of the combinations among groups exhibited similar barriers. Variability in the expression of the sites of pollen tube inhibition in the style was observed both within and among groups. Speculations are made on the possible hybrid origin of the populations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prezygotic interspecific hybridization barriers between kenaf (Hibiscus cannabinus L.) and four wild relatives

Use of interspecific hybridization in genetic improvement of kenaf (Hibiscus cannabinus), a multipurpose crop, is limited by low cross‐compatibility. Previous hybridization studies suggest that part of incompatibility barrier is prezygotic. Pollen germination, stigma receptivity and growth of alien pollen on kenaf pistil were studied using wild relatives of kenaf. Four wild and semi‐domesticated species, H. surattensis, H. acetosella, H. radiatus and H. vitifolius, were used as pollen donors in the present experiment. H. radiatus exhibited highest pollen germination (65.89%) on H. cannabinus stigma. For closely related species (H. surattensis, H. acetosella, H. radiatus), stylar incompatibility was noticed, while for distantly related species H. vitifolius, the incompatibility was stigmatic. Number of pollen tubes entering ovule of H. cannabinus pistil was higher for H. radiatus (1.30). Alien pollen growth and penetration of pollen tube through ovule were higher in species sharing same genome of H. cannabinus. High callose deposition was observed in incompatible crosses, suggesting a general mechanism for prezygotic incompatibility in Hibiscus section Furcaria. Callose deposition in incompatible crosses increased with time.     

Diversity in the wild potato species Solanum chacoense Bitt.

Summary The morphological and isozyme variation was studied in 22 accessions of Solanum chacoense from Paraguay and Argentina. Clear geographic groups were identified through the use of multivariate analyses. S. chacoense from mountain sites in Argentina could be readily distinguished from plains forms from Paraguay, on the basis of several correlated morphological characters. Three isozyme systems, namely phosphoglucose isomerase (PGI), glutamate-oxaloacetate transaminase (GOT) and peroxidase (PRX) were studied using starch gel electrophoresis. The banding patterns indicated that for each isozyme there were several loci, which were polymorphic. A genetic interpretation of one of the PGI loci was made, and indices of genetic diversity and genetic identity calculated. Principal components analysis, cluster analysis and genetic diversity indicated a close relationship between the geographical groups. These results are discussed in the context of in situ genetic conservation.     

Crossability between cultivated and wild tuber-and non-tuber-bearing Solanums

The cultivated potato has over 200 extant wild relatives many of which contain genes valuable for disease resistance, hardiness, processing and agronomic traits. Crossability of these wild species directly with the cultivated potato is complicated by several reproductive phenomena such as stylar and ploidy barriers and Endosperm Balance Numbers (EBN). However, a systematic analysis of crossability with many of these wild relatives has never fully been examined. Reciprocal crosses were made between cultivated potato and over 400 wild potato accessions; stylar barriers and 2n gamete production were examined as was the fertility of many of the putative hybrids. Generally, the seed/fruit ratio increased the more closely related the species were to the cultivated potato. However, a few crosses were successful in spite of predicted failure due to ploidy or EBN differences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Prefertilization barriers to interspecific hybridization involving Gossypium hirsutum and four diploid wild species

Interspecific hybridization among species of cotton has lead to improvement in productivity, earliness, fibre quality and resistance to pests and diseases. However, wide crosses is often limited by the operation of either pre‐ or/and post‐fertilization barriers. An investigation on pollen tube behaviour of four wild species in the pistils of Gossypium hirsutum was taken up. Pollen germination was normal in crosses involving Gossypium triphyllum and Gossypium armourianum and markedly inhibited in the crosses involving Gossypium davidsonii and Gossypium thurberi. Pollen tubes reached the pistils and fertilization was accomplished within 8 h after pollination (HAP) in control cross. Even though delay in pollen tube was a common phenomenon in all the four crosses successful fertilization was observed in crosses involving G. triphyllum and G. armourianum, as they reached the ovary at 24 HAP. In crosses with G. davidsonii and G. thurberi, pollen tubes failed to reach the ovary even at 24 HAP indicating the presence of strong stylar and ovarian incompatibility. Measures to overcome such barriers to interspecific hybridization in the incompatible crosses are discussed.     

Resistance to Phytophthora infestans in Potato Genotypes Originating from Wild Species

The reaction to P. infestans in the foliage and tubers of potato was evaluated in resistant genotypes and in their progeny. The genotypes originated from wild species known to carry genes for specific resistance. Evidence was obtained that three types of resistance to P. infestans were presented in the genotypes: (1) Resistance due to major, dominant genes was predominant. The presence of these genes was expressed in both foliage and tubers and did not influence maturity. Some of the genes were R genes, providing specific resistance, but for others this could not be determined as they were effective against the fungus inoculum with the highest virulence available: 1.2.3.4.5.7.10.11. (2) Resistance was present, associated with late maturity. (3) Tuber resistance was present, expressed after inoculation of whole tubers but not after inoculation of tuber slices. Testing of the progeny was essential for the determination of the type of resistance present in the genotypes evaluated.     

Diversity of potato genetic resources

A considerable number of highly diverse species exist in genus Solanum. Because they can adapt to a broad range of habitats, potato wild relatives are promising sources of desirable agricultural traits. Potato taxonomy is quite complex because of introgression, interspecific hybridization, auto- and allopolyploidy, sexual compatibility among many species, a mixture of sexual and asexual reproduction, possible recent species divergence, phenotypic plasticity, and the consequent high morphological similarity among species. Recent researchers using molecular tools have contributed to the identification of genes controlling several types of resistance as well as to the revision of taxonomical relationships among potato species. Historically, primitive forms of cultivated potato and its wild relatives have been used in breeding programs and there is still an enormous and unimaginable potential for discovering desirable characteristics, particularly in wild species Different methods have been developed to incorporate useful alleles from these wild species into the improved cultivars. Potato germplasm comprising of useful alleles for different breeding objectives is preserved in various gene banks worldwide. These materials, with their invaluable information, are accessible for research and breeding purposes. Precise identification of species base on the new taxonomy is essential for effective use of the germplasm collection.     

Heritility of field resistance to potato leafroU virus in cultivated potato

Potato progenies in a line x tester mating design and the clonal parents were screened for field resistance to potato leafroll virus (PLRV) to determine the heritability of this trait. Twelve advanced potato clones or varieties were crossed as pistillate parents to two pollen testers. The seedling progenies and clonal parents were exposed to aphid-transmitted potato leafroll virus for two growing seasons. Cumulative infection by potato leafroll virus was determined by post-season sero-logical indexing of foliage grown from sprouted tubers after 2 years of exposure. Narrow-sense heritability was estimated from regression of mid-parent on progeny as h = 0.72. This estimate indicates a high level of useabie genetic variance for PLRV resistance in advanced breeding materials. Although variation in resistance to PLRV appears to be a quantitative trait in susceptible and moderately resistant clones, per-formance of the most resistant parents suggests that genes with major effects may be present. These results are similar to the conclusions of other researchers who found one or two genes controlling the pheno-types of extreme resistance, resistance to infection, or suppression of virus titre.     

A biosystematic study of the origin of the cultivated diploid potato,Solanum x Ajanhuiri Juz. et Buk.

Summary The origin and nature of the diploid cultivated potato species S. ajanhuiri Juz. et Buk. was studied. Several lines of evidence indicate that S. ajanhuiri might be derived from natural crosses between primitive cultivars of the diploid species S. stenotomum and the wild species S. megistacrolobum. Morphological comparisons were made between S. stenotomum x S. megistacrolobum F₁ hybrids and naturally occurring S. ajanhuiri to investigate this hypothesis. Comparisons were also made between S. ajanhuiri x S. stenotomum crosses and the F₂ generation of the first-mentioned cross.Crosses between the two major groups of S. ajanhuiri cultivars, Ajawiri and Yari, showed not only genetic breakdown but also a wide range of phenotypic variation similar to those of artificial F₂ families of S. stenotomum x S. megistacrolobum. Furthermore, there was strong evidence showing that the Yari group of S. ajanhuiri could almost certainly be an F₁ S. stenotomum x S. megistacrolobum hybrid, whereas the Ajawiri group could be a backcross of an F₁ hybrid to S. stenotomum. These results added further support to the hypothesis of a hybrid origin of S. ajanhuiri, as well as indicating its putative parents. It is suggested that this hybridogenic taxon be retained at the species level under the name Solanum x ajanhuiri.     

Widespread introgression of Solatium phureja DNA in potato (S. tuberosum) dihaploids

Dihaploids were assumed to be of parthenogenic origin but cv. ‘Pentland Crown’ dihaploids produced at the Scottish Crop Research Institute (SCRI), Dundee, Scotland, are known to contain DNA from the S. phureja dihaploid inducer. This study investigates whether inducer DNA occurs in dihaploids of cultivars ‘Aminca’, ‘Brio’, ‘Lizen’ and ‘Sirtema’, produced at INRA, Ploudaniel, France. Two microsatellite markers and five simple sequence repeat 5′-anchored polymerase chain reaction (PCR) primers were used to generate markers. Markers originating from the dihaploid inducer were detected in 13 of the 19 INRA dihaploids and in some dihaploids from each cultivar. Greater introgression occurred in ‘Lizen’ dihaploids than in ‘Brio’ dihaploids, suggesting that the female (S. tuberosum) parent influences introgression. The percentage of INRA dihaploids containing inducer DNA was similar to that for ‘Pentland Crown’ dihaploids (c. 65%). The micro-satellite markers provided the first evidence of the transfer of specific, potentially useful, genes from the inducer to the dihaploid offspring. Interspecific introgression during dihaploid induction is more widespread than previously thought and researchers should be aware that it may influence the results of research using dihaploids.     

Natural hybridization between Solanum acaule Bitt. and S. megistacrolobum Bitt. in the province of jujuy,Argentina

Summary Evidence is provided that hybridization of the tetraploid (2n=4x=48), self-fertile tuber-bearing species Solanum acaule Bitt. with the diploid (2n=2x=24), self-incompatible, tuber-bearing S. megistacrolobum Bitt. takes place in several localities of the province of Jujuy in the high, cold plateaux of the Argentine Puna. The triploid hybrids (2n=3x=36) closely resemble S. acaule in growth habit, leaf morphology and floral structures and for this reason they can be easily overlooked for that species in the field. Experimental data show that S. acaule can be crossed with S. megistacrolobum though the crossability is rather low and variable according to the particular cross considered. The artificial hybrid obtained compares well with the natural hybrid in morphology and chromosome number. The hybrids, though almost completely male sterile, are successful colonizers of disturbed areas around farmers' dwellings, cattle enclosures and other areas where the soil is rich in organic matter.There is some evidence that the Tilcara material of S. acaule subsp. aemulans and the hybrids of S. acaule x S. megistacrolobum have some characters in common, which can be interpreted as having a similar origin.It is postulated that S. acaule subsp. aemulans, in Jujuy at any rate, is not a primitive form of S. acaule as thought by Hawkes and Hjerting, but rather a fertile hybrid derivative of S. acaule x S. megistacrolobum through the functioning of 2n gametes.We also provide evidence that S. bruecheri Correll should not be considered a hybrid of S. acaulle x S. megistacrolobum but a synonym for S. gourlayi Hawkes. The new name, S. x indunii Okada et Clausen, is proposed to designate this hybrid.     

Overcoming barriers: Myanmar's recent elections and women's political participation

Myanmar's 2015 elections have been credited with bringing about a myriad of changes within the country. Much has been written about the changing political climate within Myanmar. One topic which has not yet been discussed adequately, however, is the role of Burmese women in these recent elections. This paper seeks to examine women's political participation in Myanmar's recent move towards democratisation. Using rates of female candidacies in Burmese elections, comparing these figures with rates of female participation in other Southeast Asian countries, and ethnographic research with the Burmese voting public, this paper will contribute to the sparse scholarship regarding the role of women in new democracies and regime transitions. This paper finds that beliefs about traditional gender roles, rooted in traditional Buddhism, still shape the way both men and women in Myanmar view women's political participation. While women are better represented in Myanmar's government than they were in the past, this paper suggests that measures such as quotas or reserved seats based on gender may be the best way to increase Burmese women's political representation in the future.