Colombia and Venezuela 1992 wild potato (Solanum sect. Petota) germplasm collecting expedition: taxonomy and new germplasm resources

Summary We conducted a joint Colombia/United States/Venezuela wild potato (Solanum sect. Petota Dumort.) germplasm collecting expedition in Colombia from June 27–August 24, and in Venezuela from August 17–September 15, 1992. The goals of the expedition were to collect germplasm and study the species boundaries of all of the 23 Colombian and Venezuelan taxa accepted by current taxonomists. We made 128 collections of 16 of these taxa, 96 as true seed collections. We collected the first available germplasm collections of S. cacetanum, S. cuatrecasasii, S. estradae, S. lobbianum, S. orocense, S. paramoense, and S. sucubunense, and obtained germplasm collections of S. neovalenzuelae and S. pamplonense as a germplasm exchange from the Colombian national germplasm collection. We had problems identifying some of our collections, and currently are investigating them for species status and interrelationships. We summarize the state of germplasm collections for Colombia and Venezuela, provide our field data regarding the taxonomy of Colombian and Venezuelan wild potatoes, and provide recommendations for future collecting.     

Bolivia potato germplasm collecting expeditions 1993, 1994: Taxonomy and new germplasm resources

Summary We conducted joint Bolivia/The Netherlands/United States wild potato (Solanum sect. Petota Dumort.) germplasm collecting expeditions in Bolivia from February 1-April 15, 1993, and January 1-February 26, 1994. The goals of the expeditions were to collect germplasm and gather data for continuing taxonomic studies of the approximately 43 taxa of Bolivian wild potatoes accepted by current taxonomists. We made 223 collections, 135 as true seed collections, 54 as tubers, 19 only as herbarium collections. Two recent taxonomic treatments of Bolivian wild and cultivated potatoes have clarified the taxonomy and distribution of these plants, but there are continuing disagreements between treatments regarding species boundaries and interrelationships. These disagreements, and the variability we observed in natural populations, present problems for identifications. We summarize the state of germplasm collections for Bolivia, provide our field data regarding the taxonomy of Bolivian wild potatoes, provide recommendations for future collecting, and provide new chromosome counts for S. hoopesii, S. ugentii, and S. yungasense.     

New sources of resistance to the potato cyst nematodes Globodera pallida and G. rostochiensis in the Commonwealth Potato Collection

The Commonwealth Potato Collection contains 77 species following the incorporation of the personal collection of Professor JG Hawkes. The material originates from several expeditions to the Americas and represents a potentially valuable source of resistance to pests and pathogens, including potato cyst nematodes (PCN). The germplasm from the Hawkes collection screened in this study included taxa mainly from Mexico, Bolivia, Argentina and Peru. Seedlings of 198 accessions, from 63 different species were screened for reaction to the PCN species G. pallida and G. rostochiensis. Of the 198 accessions tested, 56% contained G. pallida-resistant clones and 53% contained clones resistant to G. rostochiensis. Twelve species in this survey are believed to contain novel, previously unreported sources of resistance. The geographical distribution of resistance indicated a contrast between the two PCN species. Although, as in previous studies, resistance to G. rostochiensis was centred on Bolivia and Argentina, G. pallida resistance was found across the geographical range of tuber-bearing Solanum. The possibility of cross-resistance arising from selective pressure from the more northern species G. mexicana is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Screening of melon (Cucumis melo L.) germplasm for multiple disease resistance

Summary Melon germplasm was screened for cucumber green mottle mosaic virus (CGMMV), powdery mildew (Sphaerotheca fuliginea), downy mildew (Pseudoperonospora cubensis) and Fusarium wilt (Fusarium oxysporum f. sp. melonis) resistance under artificial conditions except downy mildew for which screening was done under natural epiphytotic conditions. High level resistance to all the four diseases was not recorded in any of the collections tested. Nevertheless, ertheless, resistance to three diseases was located in three germplasm. Wild Cucumis species C. figarei exhibited absolute resistance to CGMMV and Fusarium wilt and high level resistance to downy mildew. Phoot or snapmelon (Cucumis melo var. momordica) — a non-dessert from of Indian origin—was highly resistant to downy mildew and resistant to CGMMV and medium resistant to Fusarium wilt. Iroquois was resistant to powdery mildew and medium resistant to downy mildew and CGMMV.     

The need for characterisation and evaluation of germplasm: kiwifruit as an example

Genetic diversity provides the raw material for breeding and plant improvement. Breeders of plant species that have little or no history of improvement tend to make the greatest use of collections of raw or unimproved germplasm. Kiwifruit (Actinidia) are one such crop in that they have been subjected to little selection pressure and are still very similar to plants in the wild. To take advantage of the diversity in the genus Actinidia, breeders need to know the extent of the diversity and also need to be able to identify the plants with which they are working. Voucher specimens should be prepared for all plants used in experimental studies. A good understanding of the reproductive biology of Actinidia should facilitate incorporation of wild germplasm into kiwifruit breeding programmes. The HortResearch Actinidia collection has already proved its worth with the development of valuable new kiwifruit cultivars.     

Identification of levels of resistance to cassava root rot disease (<Emphasis Type="Italic">Botryodiplodia theobromae</Emphasis>) in African landraces and improved germplasm using <Emphasis Type="Italic">in vitro</Emphasis> inoculation method

Cassava root rot disease is an increasing problem in Africa where yield losses of about 80% have been recorded. We evaluated 290 African landraces and 306 improved genotypes from the germplasm collections of the International Institute of Tropical Agriculture (IITA), for sources of resistance using root slice laboratory assay. Disease severity was assessed quantitatively by direct percentage estimation (PS) and by use of a rating scale (RS). Both methods of assessment were compared for identification of variability in the germplasm, and genotypes were classified into response groups using an enlarged rank-sum method that combined the PS and RS assessments. The two scoring methods revealed continuous variation (P < 0.001) for resistance in the sets of germplasm. Disease assessments based on PS and RS were highly correlated in both the improved germplasm (r = 0.75) and the landraces (r = 0.72). Based on PS assessment, 50 improved genotypes (16.3%) and 53 landraces (18.3%) showed significantly lower disease scores than the resistant control. The rank-sum method separated each set of collections into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible groups. Fifty-nine improved genotypes (16.4%) and 61 African landraces (16.9%) were identified as either highly resistant or resistant. Generally, these genotypes exhibited resistance by limiting the growth of the pathogen (reduced amount of invaded surface area). This type of rate-reducing resistance is highly heritable and a quantitative trait which can be harnessed in breeding. Genotypes subsets were identified for further studies into the genetic basis of resistance to root rot disease.     

Identification of self-incompatibility (S) alleles in Latvian and Swedish sweet cherry genetic resources collections by PCR based typing

The Latvian and the Swedish sweet cherry (Prunus avium L.) genetic resources collections comprise valuable material for breeding. The collections represent local Latvian and Scandinavian genetic resources: semi-wild samples, landraces, and cultivars developed in local breeding programmes, as well as diverse germplasm from the northern temperate zone. The objective of this investigation was to determine which S ₁ –S ₆ alleles are most important in the sweet cherry genetic resources collections and to compare the identified allelic and genotypic frequencies in material of different origin. Accessions in the two collections were screened for the presence of the self-incompatibility (S) S ₁ to S ₆ alleles, using PCR based typing. Significant differences (P < 0.05) between screened collections were found in frequencies of S ₄ and S ₅ alleles. Analysis of allele combinations identified the high occurrence of selections with the S-genotype S ₃ S ₆ in both collections. Compared to the S-allele frequencies published for over 250 sweet cherry cultivars from Western and Southern Europe, the Latvian and Swedish germplasm appeared to have a high frequency of the S ₆ allele in both collections, and a relatively high frequency of the S ₅ allele in Latvian germplasm. This study represents the first comprehensive S-allele screening for the sweet cherry genetic resources collections in Latvia and Sweden. Both sweet cherry collections contain high proportion of accessions adapted to north central European growing conditions, not typical for the majority of the documented sweet cherry genetic resources, which explains differences in certain S-allele occurrence.     

Patterns of RFLP-based genetic diversity in germplasm pools of common wheat with different geographical or breeding program origins

A set of 292 accessions of common wheat (Triticum aestivum L.) representing 21 germplasm pools based on geographical or breeding program origins was assayed for RFLP diversity. Thirty cDNA and genomic DNA probes and the HindIII restriction enzyme were employed for RFLP analysis. About 61% of all 233 scored bands were present in 75% or more of the accessions. All but one of the 30 probes revealed polymorphism, and the average number of distinct patterns per probe over all accessions was 9.5.Polymorphic Information Content (PIC) values within a pool varied from 0 to 0.9 and depended on the identities of both the germplasm pool and the probe. Rare banding patterns with a relative frequency of ≤0.2 within a pool were detected. These rare patterns were more likely to occur in pools exhibiting high levels of heterogeneity. The highest level of polymorphism was observed in the Turkish landraces from Southwest Asia. The Eastern U.S. soft red winter wheat germplasm pool was more genetically diverse than the other advanced germplasm pools, and nearly as diverse as the Turkish landrace pool. RFLP-based genetic relationships between germplasm pools generally tracked expectations based on common geographical origin, breeding history and/or shared parentages. The Chinese wheat landraces from Sichuan, Tibet, and Yunnan provinces were distinct from other pools. Similarity matrices for among-pool genetic distance estimates based on either band frequencies or banding pattern frequencies showed good correlation with matrices derived from Nei and Li's mean genetic similarity estimates (r=−0.82^** and r=−0.73^**, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Onion germplasm interacts with sulfur fertility for plant sulfur utilization and bulb pungency

Summary Sixty-two onion (Allium cepa L.) entries grown under high (4.0 mequiv.liter^-1) and low (0.1 mequiv.liter^–1) S fertility were evaluated for foliar and bulb S utilization, and pungency. Significant differences were detected among entries at both S fertility levels for foliar and bulb %S, and enzymatically developed pyruvate (pungency) in bulb tissue. Correlations between foliar %S and enzymatically developed pyruvate and between bulb %S and enzymatically developed pyruvate were poor suggesting that S is differentially partitioned into flavor and non-flavor compounds in the bulbs of onion germplasm. Significant S by entry interactions were found for all variables tested indicating that selection for S utilization and bulb pungency in onions be conducted at S fertility levels indicative of targeted production areas.     

Molecular characterization of genetic diversity in European germplasm of perennial ryegrass

Summary Perennial ryegrass (Lolium perenne L.) is the most important grass species for temperate grassland agriculture. The level and distribution of genetic variation in gene bank ecotype collections is still largely unknown but of great interest for the planning of breeding programs. The objectives of this study were to (i) assess the molecular diversity of Polish ecotypes of perennial ryegrass, and (ii) compare the relationship between this group and German ecotypes and European cultivars investigated previously. A total number of 166 polymorphic marker bands were detected among the 171 individual plants of the 9 Polish ecotypes. In a joint analysis with 9 Polish and 22 German ecotypes, and 22 European cultivars 172 polymorphic RAPD markers could be found. Genetic distance among the Polish ecotypes ranged from 0.31 to 0.51, while for all 53 populations a broader range was detected (0.25–0.67). An analysis of molecular variance (AMOVA) revealed a much larger variation within populations (71%) than among them (29%). The Polish ecotypes contained the highest within population variation (74%). The largest among group difference (15%) was found between the Polish ecotypes versus all other accessions. We conclude that the Polish ecotypes represent a valuable genetic resource for enlarging the genetic variation in the West European germplasm pool of perennial ryegrass.     

The effectiveness of evaluating wild species: searching for sources of resistance to bruchid beetles in the genus Vigna subgenus Ceratotropis

A species level germplasm collection representing 76% of known taxa in the genus Vigna subgenus Ceratotropis was evaluated for resistance to two species of bruchid beetles, Callosobruchus chinensis and C. maculatus. Seven taxa consisting of 29 accessions were found to be resistant to C. chinensis and 4 taxa consisting of 24 accessions were found to be resistant to C. maculatus. This compared with no resistant accessions being found in several hundred landrace accessions of mungbean, V. radiata var. radiata, in the same subgenus. Sometimes resistance was found in all accessions of a particular taxon, such as complete resistance to both C. chinensis and C. macualtus in V. umbellata. Other taxa showed intra taxon variation for resistance such as V. reflexo-pilosa andV. minima. The levels and patterns of resistance among taxa were diverse. The results suggest that various factors cause resistance to bruchid in the subgenus Ceratotropis. While the number of eggs laid on seeds generally reflected seed size, one small seeded cultivar of V. mungo var. mungo, black gram, had an unusually high number of eggs laid per seed. No correlation was found between seed size and levels of resistance. The species level germplasm collection, which reflects the core collection concept in trying to maximize genetic diversity in a limited number of accessions, has enabled a large number of potentially useful sources of resistance to bruchid beetles to be found efficiently. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stability of cassava plants at the DNA level after retrieval from 10 years of in vitro storage

Summary Cassava (Manihot esculenta Crantz) germplasm collections are conventionally maintained by continuous vegetative propagation in the field. Tissue culture techniques provide a more convenient way to conserve germplasm. The cassava in vitro gene bank held in trust at CIAT comprises nearly 6000 accessions. A study was carried out to determine whether any DNA rearrangements resulting from in vitro storage under slow growth could be detected by molecular analysis in retrieved plants. RFLPs with homologous probes, RAPDs with twenty primers and DNA fingerprinting with M13 probe were tested to detect variation at DNA level in cassava plants after ten-years in vitro storage. The molecular marker data obtained in this study supports the stability of the cassava germplasm under the in vitro storage conditions described in this work.     

Screening global <Emphasis Type="Italic">Medicago</Emphasis> germplasm for weevil (<Emphasis Type="Italic">Hypera postica</Emphasis> Gyll.) tolerance and estimation of genetic variability using molecular markers

The genus Medicago encompasses many important forage species for both temperate and tropical regions. M. sativa L., commonly known as lucerne, is one of the most important forage species grown worldwide, but its production suffers seriously from weevil (Hypera postica Gyll.) infestation. The aim of this work was to identify species/accessions with tolerance to weevil and their molecular analysis using simple sequence repeat (SSR) markers. After screening 197 global germplasm encompassing 50 Medicago species for weevil tolerance, 22 lines representing 13 species were identified where leaf damage was ≤15% (P ≤ 0.05). In total, 37 accessions of the 22 lines, five Indian lucerne cultivars with leaf damage ≥75% and 10 accessions of the 13 Medicago species with low to high infestation (>25%) were molecularly assessed using 11 SSR markers (5 newly developed) to delineate closest to lucerne lines for breeding. In total, 33 bands were scored. The SAHN clustering using UPGM algorithm resulted into two main clusters supported with high boot strap values and with genetic similarity ranging from 0.33 to 0.96. Two accessions of M. tenoreana were observed closest to Indian lucerne cultivars. The rich variability revealed can be used as potential resource for transferring genes across species. Although the inter-specific hybridization is difficult preposition in genus Medicago largely due to post fertilization barrier, the identified species/accessions can be utilized on priority in breeding programs especially employing biotechnological tools like culturing of fertilized pods, ovule-embryo culture and electroporation.     

Genetic diversity and relationships in accessions from different cultivar groups and origins in the tree tomato (<Emphasis Type="Italic">Solanum betaceum</Emphasis> Cav.)

Tree tomato (Solanum betaceum) is an Andean small tree cultivated for its juicy fruits. Little information is available on the characterization of genetic resources and breeding of this neglected crop. We have studied the molecular diversity with AFLP markers using 11 combinations of primers of a collection of 25 S. betaceum accessions belonging to four cultivar groups, most of which had been previously morphologically characterized, as well as one accession of the wild relative S. cajanumense. A total of 197 AFLP fragments were scored, of which 84 (43 %) were polymorphic. When excluding S. cajanumense from the analysis, the number of polymorphic AFLP fragments was 78 (40 %). Unique AFLP fingerprints were obtained for every accession, but no AFLP fragments specific and universal to any of the four cultivar groups were found. The total genetic diversity (H _T ) of cultivated accessions was H _T  = 0.2904, while for cultivar groups it ranged from H _T  = 0.1846 in the orange group to H _T  = 0.2498 in the orange pointed group. Genetic differentiation among cultivar groups (G _ST ) was low (G _ST  = 0.2248), which was matched by low values of genetic distance among cultivar groups. The diversity of collections from Ecuador, which we hypothesize is a center of diversity for tree tomato, was similar to that from other origins (H _T  = 0.2884 and H _T  = 0.2645, respectively). Cluster and PCoA analyses clearly separated wild S. cajanumense from the cultivated species. However, materials of different cultivar groups and origins were intermingled in both analyses. The Mantel test correlation coefficient of the matrices of morphological and AFLP distances was low (−0.024) and non-significant. Overall, the results show that a wide diversity is present in each of the cultivar groups, indicate that Ecuador may be regarded as a center of accumulation of diversity for this crop, and confirm that AFLP and morphological characterization data are complementary. The results obtained are of value for the conservation of genetic resources and breeding of tree tomato, as an assessment of the genetic diversity and relationships among different cultivar groups and geographic origins is obtained.     

Analysis of bulked and redundant accessions of Brassica germplasm using assignment tests of microsatellite markers

This study was conducted to determine if Brassica germplasm bulks created and maintained by the USDA-ARS North Central Plant Introduction Station (NCRPIS) were made with genetically indistinguishable component accessions and to examine newly identified putative duplicate accessions to determine if they can be bulked. Using ten microsatellite primer pairs, we genotyped two bulks of B. rapa L. ssp. dichotoma (Roxb.) Hanelt comprising four accessions and three bulks of B. rapa L. ssp. trilocularis (Roxb.) Hanelt comprising fourteen accessions, as well as four pairs of putatively duplicate accessions of B.␣napus L. Assignment tests on ten individual plants per accession were conducted using a model-based clustering method to arrive at probabilities of likelihood of accession assignment. The assignment tests indicated that one of the two bulks of B. rapa ssp. dichotoma involves genetically heterogeneous accessions. It was observed in the B. rapa ssp. trilocularis bulks that the component accessions could be differentiated into groups, with misassignments observed most frequent within groups. In B. napus, only one of the four pairs of putative duplicates showed significant genetic differentiation. The other three pairs of putative duplicates lack differences and support the creation of bulks. The results of the assignment tests were in agreement with cluster analyses and tests of population differentiation. Implications of these results in terms of germplasm management include the maintenance and/or re-creation of some Brassica germplasm bulks by excluding those accessions identified as being unique in this study.     

Variation in the ribosomal RNA units of the generaLens andCicer

Summary Investigation of the organization of the tandemly repeated 5S and 18–25S ribosomal RNA (rRNA) genes was carried out on members of the generaLens andCicer using restriction endonuclease digestion and Southern hybridization. The 5S rRNA unit (gene+spacer) inLens (0.38 to 0.50 kb) andCicer 0.50 to 0.44 kb) is the largest among the legumes. InL. nigricans andL. culinaris ssp.odemensis a second repeat size was detected. Restriction maps for the 18–25S units ofLens andCicer species were developed. The 18–25S rRNA unit varied from 8.3 to 9.8 kb inLens and 10.5 to 11.4 kb inCicer. The only detectable variability in theLens andCicer 18–25S rRNA unit was in the length of the intergenic spacer (IGS) region, except for a HindIII site in the IGS region ofL. nigricans ssp.nigricans and in allCicer species.Similarities in the size of both 5S and 18–25S rRNA units were noted betweenL. culinaris ssp.culinaris andL. culinaris ssp.orientalis, which supports previous evidence thatL. culinaris ssp.orientalis is the progenitor of the cultivated lentil. Differences in the arrangement of both 5S and 18–25S rRNA units were noted betweenL. nigricans ssp.nigricans andL. nigricans ssp.ervoides, indicating either divergent evolution of these subspecies or alternatively incorrect taxonomy.On the basis of the size of the 5S rRNA unit,C. bijugum, C. chorassanicum andC. echinospermum formed a group with a slightly smaller unit than the otherCicer species. Similarities in the length of both 5S and 18–25S rRNA units ofC. arietinum andC. reticulatum possibly confirmC. reticulatum as the progenitor ofC. arietinum. Cicer cuneatum has a smaller 18–25S rRNA unit than the otherCicer species as a result of a smaller intergenic spacer.     

Evaluation of Triticum aestivum germplasm from Croatia and Yugoslavia for aluminium tolerance

Summary Aluminium tolerance of 90 genotypes of Triticum aestivum L. germplasm from the breeding programmes of eight Croatian and Yugoslav institutions was evaluated in nutrient solutions having Al³⁺ activities of 0, 12.5 and 25M. Overall distribution of Al tolerance of wheat genotypes was skewed toward lower tolerance rankings. Average Al tolerance differed among gene pools created at different breeding institutions. Genotypes tolerant enough to be useful in the breeding programmes aimed at selecting cultivars with improved Al tolerance are identified in germplasm from four institutions. No correlation was found between chemical characteristics of soils used over the years by breeding institutions for their field trials and the Al-tolerance ranking of the corresponding germplasm material.Abbreviations HSD Tukey's Honestly Significant Difference - RRL-4 relative root length, in % (25M Al³⁺/0 Al)     

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.     

Evaluation of Paspalum germplasm for variation in leaf wax and heat tolerance

Summary The genus Paspalum contains a number of important forage grasses, including P. dilatatum Poir. (dallisgrass) and P. notatum Flugge (bahiagrass). Even though many Paspalum species are adapted to moist, humid areas, they frequently are subjected to extended periods of drought stress which reduces forage productivity. This study was initiated to determine the range of variation for different indicators of drought tolerance in several Paspalum species. Fifteen species representing a broad cross section of germplasm were grown in a replicated field nursery and sampled for leaf epicuticular wax content on four dates over three years. Wax was extracted with chloroform and quantified by the dichromate oxidation technique. Heat tolerance (solute leakage technique) was also determined by calculating the ratio of the conductivity of the external bathing solution of leaves following a heat treatment to the conductivity of the bathing solution after leaves were boiled. Wax values of the entries ranged from 5.7 to 0.88 mg/dm². Both relative rankings and absolute wax values were very consistent across all sampling dates. The accessions of Paspalum nicorae Parodi and P. quandrifarum Lam. were consistently high in wax content, while the accessions of P. commune Lillo and P. unispicatum (Scribn. et Merr.) Nash were consistently low. The heat tolerance testing demonstrated that the accession of P. notatum var. saurae Parodi was the most heat tolerant of the entries. Results from this investigation demonstrate the wide range of diversity that exists for both epicuticular wax and heat tolerance within the genus Paspalum.