Pre-zygotic breeding barriers between the wild diploid potato species Solanum maglia and S. kurtzianum from Argentina

Solanum maglia Schldl. is a wild tuber-bearing species from the Quebrada de Alvarado (Mendoza, Argentina) and the Valparaíso area (Chile). Only diploid cytotypes are known from Argentina, while diploids and triploids are found in Chile. Five diploid accessions from Argentina did not produce seeds upon intercrossing. Thus, the basis of this behaviour and the crossability relations of this species with S. kurtzianum, Bitt. et Wittm., another diploid species that grows in its vicinity were investigated. After checking pollen viability, intraspecific and interspecific pollinations were carried out following an incomplete diallel mating design. Five emasculated flowers were pollinated per each one of 135 different combinations of genotypes (crosses); three flowers were fixed in FAA and analyzed under fluorescent microscopy, whereas the remaining two were left on the plant for fruit and seed set. Pollen tube growth was arrested in the first third of the style and no seeds were obtained in intraspecific S. maglia crosses. In interspecific crosses and according to their direction, pollen tubes either grew normally to the base of the style or were arrested in the last third, producing no fruits or fruits with a variable number of seeds in each. It is concluded that the five S. maglia accesions are, possibly, one clone and, thus, the gametophytic auto-incompatibility system prevents seed formation upon intercrossing. On the other hand, the incompatibility reaction observed in the interspecific crosses might be controlled by one or more genes independent of the S-locus.     

LC-MS analysis of solanidane glycoalkaloid diversity among tubers of four wild potato species and three cultivars (Solanum tuberosum)

Secondary metabolites in potato tubers include both phytonutrients and plant defense compounds. The extent these small molecules vary among different potato genotypes is not well characterized. LC-MS analysis of tuber extracts from seven potato genotypes showed that one large source of small molecule variation is the glycoalkaloids. Glycoalkaloids are involved in the resistance of potatoes to pathogens and pests, but they also have implications for human health and nutrition. This study focused on glycoalkaloids with solanidane or solanidane-like aglycones, of which over 50 were tentatively identified, many of which appeared to be novel glycoalkaloids. Results suggested the variety of glycoalkaloids in potatoes is considerably greater than previously thought. Dissecting the role of these many glycoalkaloids in human health or pest and pathogen resistance will be a formidable undertaking.     

Genetic diversity of thiamin and folate in primitive cultivated and wild potato (Solanum) species

Biofortification of staple crops like potato via breeding is an attractive strategy to reduce human micronutrient deficiencies. A prerequisite is metabolic phenotyping of genetically diverse material which can potentially be used as parents in breeding programs. Thus, the natural genetic diversity of thiamin and folate contents was investigated in indigenous cultivated potatoes (Solanum tuberosum group Andigenum) and wild potato species (Solanum section Petota). Significant differences were found among clones and species. For about 50% of the clones there were variations in thiamin and folate contents between years. Genotypes which contained over 2-fold the thiamin and 4-fold the folate content compared to the modern variety Russet Burbank were identified and should be useful material to integrate in breeding programs which aim to enhance the nutritional value of potato. Primitive cultivars and wild species with widely different amounts of thiamin and folate will also be valuable tools to explore their respective metabolic regulation.     

Crossability relationships between the common potato, Solanum tuberosum spp. tuberosum, and its wild diploid relatives S. kurtzianum and S. ruiz-lealii

The common potato, Solanum tuberosum spp. tuberosum (tbr), is a tetraploid species with a narrow genetic base, but with a large number of related species that harbor great genetic diversity for numerous characters of agronomic interest. S. kurtzianum (ktz) and S. ruiz-lealii (rzl) are wild diploid relatives with potential resistance to adverse biotic and abiotic factors. To evaluate if this wild germplasm can be incorporated by conventional crosses into the tbr gene pool, pollen-pistil compatibility relations and seed set in interspecific crosses with tbr were investigated. In 4x tbr × 2x ktz crosses and the reciprocals, 89% and 52.2% of genotypic combinations (respectively) were compatible at the pollen-pistil level. Seeds were obtained from some genotypic combinations in both directions of the cross, suggesting that functional 2n gametes might be produced by particular ktz genotypes. In 2x rzl × 4x tbr crosses and their reciprocals, 35% and 11.7% (respectively) of the genotypic combinations were compatible at the pollen-pistil level, but no seeds were obtained. These results indicate that the reproductive isolation between 4x tbr and 2x ktz is incomplete, and that gene exchange between them is feasible. Moreover, further studies will have to be carried out with rzl to ascertain its crossability with 4x tbr.     

Evolution and improvement of cultivated amaranths with reference to genome relationship among A. cruentus, A. powellii and A. retroflexus

Meiotic studies were carried out in four accessions of three grain species, viz. Amaranthus cruentus, A. powellii and A. retroflexus and their F1 hybrids to elucidate the genome relationships between the cultivated and wild types and the cytogenetical mechanisms involved in speciation. All the three species were morphologically distinct and cytologically uniform with 17 bivalents at metaphase I. Morphologically the interspecific hybrids were either intermediate or had an overall dominance of wild parents. Chromosome analysis at meiotic metaphase I in the F1 interspecific hybrids of A. powellii with the Indian and Mexican accessions of A. cruentus showed an average of chromosome association of 1.0 IV + 0.10 III + 14.78 II + 0.14 I and 1.0 IV + 0.45 III + 14.20 II + 0.25 I and 5.81% in the former and 8.44% in the later pollen grain fertility, respectively and that of A. retroflexus with A. cruentus (Indian and Mexican) showed almost similar chromosomal associations. These studies show close genomic homology amongst all these three species involving certain chromosomal aberrations resulting in their evolution.     

Phylogenetic relationships among Triticum L. and Aegilops L. species as genome progenitors of bread wheat based on sequence diversity in trnT-F region of chloroplast DNA

Cultivated wheat, (Triticum aestivum L.), is one of the most important food crops in the world. The Aegilops L. genus is frequently utilized by plant breeders for improving the current wheat cultivars due to their close relationships. Therefore, understanding the phylogenetic relationships among the species of these genera is not only valuable for plant taxonomy, but also for plant breeding efforts. The presented phylogenetic analysis was based on the sequences of trnT-F chloroplast DNA containing three non-coding sub-regions. Twelve genotypes belonging to four species of Triticum L. genus and twenty-four genotypes belonging to eight species of Aegilops genus were used in the current study. The results postulated a close genetic relationship between diploid Aegilops species containing the BB genome and polyploid Triticum species. With the exception of Aegilops cylindrica Host (CCDD), all other Aegilops species having the CC genome were alienated from Aegilops speltoides Tausch (BB) and clustered together. These two clusters joined by a third cluster including the AA genome containing diploid Triticum species.     

Allium vavilovii M. Popov et Vved. and a new Iranian species are the closest among the known relatives of the common onion A. cepa L. (Alliaceae)

A wild onion species from Karaj valley east of Tehran istaxonomically described as Allium asarense R. M.Fritsch et Matin. Sharing the bubble-like inflated lower scapewith A. vavilovii, the newspecies differs by semi-cylindrical leaves and small flowerswith translucent greenish-yellow tepals from all other knownspecies of Allium sect.Cepa. Molecular data suggest a closerelationship to A. cepa(but to a lesser degree than A.vavilovii) and indicate a still weakerphylogenetic connection of A.oschaninii to the common onion. The questionabout the possible wild ancestor of A.cepa is discussed against this background, and akey for determination of the Oschaninii-alliance of sect.Cepa is presented.     

Assessment of genetic diversity in cultivars and wild accessions of Luohanguo (<Emphasis Type="Italic">Siraitia grosvenorii</Emphasis> [Swingle] A. M. Lu et Z. Y. Zhang), a species with edible and medicinal sweet fruits endemic to southern China,using RAPD and AFLP markers

Genetic variation of wild populations and cultivars of Luohanguo (Siraitia grosvenorii), a plant species endemic to southern China, was assessed using random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers. Based on the results for 130 individuals from seven populations, a high level of genetic diversity of Luohanguo was observed at the species level. The percentage of polymorphic loci (P) was 89.4%, Nei’s gene diversity (H _e) was 0.239, and Shannon’s information index (H _o) was 0.373 based on the combined AFLP and RAPD data. There was a high degree of genetic differentiation, with 45.1% of the genetic variation attributed to differences between the populations. The genetic diversity of the Luohanguo cultivars is much lower than that of wild populations (P = 41.8%, H _e = 0.141, H _o = 0.211), and a distinct genetic differentiation is observed between the cultivars and wild accessions. The pool of genetic variation in the wild populations provides an excellent gene resource for Luohanguo breeding.     

Cytological and RAPD data revealed genetic relationships among nine selected populations of the wild bramble species, <Emphasis Type="Italic">Rubus</Emphasis><Emphasis Type="Italic">parvifolius</Emphasis> and <Emphasis Type="Italic">R. coreanus</Emphasis> (Rosaceae)

Rubus parvifolius L. and R. coreanus Miq. are the two morphologically distinct, endemic wild brambles in East Asia that may be useful in raspberry breeding and cultivar development. In this study, genetic relationships among a total of nine populations of these two species, collected from Sichuan Province in southwestern China, were investigated by cytological and RAPD analyzing. With the exception of ploidy levels, R. parvifolius and R. coreanus had similar cytological features. Six R. parvifolius populations included diploids, triploid, tetraploid, and mixed diploid-tetraploid cytotype plants; among them, the population that produced the fewest seeds was the triploid, while the three R. coreanus populations were all diploid. But obvious genetic differentiation between R. parvifolius and R. coreanus was revealed by RAPD markers, the Euclidean’s GS coefficient generated by UPGMA cluster analysis between R. parvifolius and R. coreanus was only 0.442, about half of that observed within species. Both genetic relationships among these populations and the origin of polyploidy in R. parvifolius populations are also discussed.