Powdery mildew resistance in Aegilops tauschii coss. and synthetic hexaploid wheats

Summary A collection of 400 Ae. tauschii (syn. Ae. squarrosa) Coss. accessions were screened for powdery mildew resistance based on the response patterns of 13 wheat cultivars/lines possessing major resistance genes to nine differential mildew isolates. 106 accessions showed complete resistance to all isolates, and 174 accessions revealed isolate-specific resistance, among which were 40 accessions exhibiting an identical response pattern as wheat cultivar Ulka/^*8Cc which is known to possess resistance gene Pm2. Expression of both complete and isolate-specific resistance from Ae. tauschii was observed in some synthetic hexaploid wheats derived from four mildew susceptible T. durum Desf. parents, each crossed with five to 38 resistant diploid Ae. tauschii accessions. Synthetic amphiploids involving different combinations of T. durum and Ae. tauschii generally showed a decrease in resistance compared with that expressed by the Ae. tauschii parental lines.     

Results of activities to maintain landraces and other material in some European countries in situ before 1945 and what we may learn from them

All three recommendations to maintain landraces in European countries, given in 1927: 1. maintenance by traditional farmers, 2. maintenance by school personnel and pupils, and 3. maintenance by small agricultural institutions, were disregarded. The present outcome: maintenance by genebanks, which often grow landraces and improved cultivars of one crop next to each other, and which often are part of a large agricultural research institute, was advised against.The above observation may be of value to those who at present advocate maintenance of landraces by traditional farmers in developing countries.It is recommended that landraces should be collected and maintained in genebanks as this will result in a partial loss of the material, whereas on farm maintenance (in situ conservation) would lead to a complete loss.     

Diversity of Nordic Landrace Potatoes (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Revealed by AFLPs and Morphological Characters

The management of genebank collections of cultivated potato is costly due to the need for in vitro maintenance and virus eradication. Therefore, it is important to set up conservation strategies, which prevent duplicates entering the collections. In this study, 32 Nordic potato landraces were studied for 57 morphological traits and analysed for amplified fragment length polymorphism (AFLP). Most landraces could be distinguished based on the morphological characters, except five accessions. Using five primer combinations to generate 114 reproducible AFLPs, of which 63 (55%) were polymorphic, the five morphologically indistinguishable accessions were placed into two groups with identical AFLP patterns, suggesting that some of the accessions were redundant for long-term preservation. The AFLP data showed that the Nordic collection of potato landraces is composed of genetically different clones, and morphological analysis revealed a wide range of variability. This variability seems to be distributed randomly over the Nordic region since the cluster analysis based on AFLPs and morphological traits revealed no grouping based on the country of origin. Principal component analysis suggests that fewer morphological traits than used in this study will be sufficient to discriminate between different genotypes of cultivated potato (Solanum tuberosum L.). Future possibilities for rationalising potato collections are discussed.     

Phenotypic diversity of durum wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> Desf.) from Jordan

Durum wheat landrace genotypes are disappearing from the main wheat areas in Jordan, because of spreading of new uniform cultivars and the serious reduction in wheat cultivation. This study was conducted to evaluate genetic diversity in durum wheat landraces from Jordan and to identify desirable agronomic traits. Landraces were collected from two target areas: Ajloun and Karak. The collected material was grown under rainfed conditions using an augmented design with five blocks and four repeated check cultivars. Data were collected for 14 morphological and agronomic traits. Phenotypic diversity index (H′) was estimated, and the relationships among accessions were measured using cluster analysis and dendrogram similarity matrix. The results revealed the presence of a wide range of variability among landraces., which possess high levels of variability for biological yield, fertile tillers, number of seeds per spike, seed weight per spike and weight of 1000 seeds. These landraces must be considered as a reservoir of genes that plant breeders need in their wheat improvement programs and should be conserved both ex situ and in situ.     

Diversity in reproductive characteristics of potato landraces and cultivars for producing true seed

Potato production from true seed, or true potato seed (TPS) is not a new system for this vegetatively propagated crop. Andean farmers have grown potatoes in the cool highlands from true seed for many centuries. TPS appears today as a promising technology in the warm tropics, where diseases impede the production of pathogen-free potato propagules. However, the identification of suitable genetic resources for potato seed production requires the selection of clones that lack antagonism between tuber growth and seed embryo development. Furthermore, the potential TPS parents need to possess characteristics of a sexually propagated crop that is grown for the harvest of its vegetative part, i.e., the tuber. This new process of domestication requires a change in the selection methods, which starts by assessing the potential of available potato clones for both reproductive characteristics and agronomic traits, particularly those of the tuber. Tetraploid landraces and cultivars of the pathogen-tested collection of the Centro Internacional de la Papa were assessed for reproductive and agronomic characteristics during three consecutive years in San Ramón, a Peruvian location in the warm lowland tropics. The clones showed significant variation for all characteristics recorded. The Shannon–Weaver diversity index (H) was highest for flowering duration (0.617) and intensity (0.600). The lowest H was calculated for bee attraction in this location. The overall H was not significantly affected by the year-to-year variation, but some of the characteristics recorded (e.g. flowers per inflorescence, anther type, style length, plus fruit and berry set) showed distinct H according to the year of assessment. Some of the cultivars with promising TPS traits, as determined by their reproductive characteristics, also had outstanding tuber set, weight and yield. Furthermore, hybrid offspring from the selected clones from the pathogen-tested elite sample, did show high tuber yield with appropriate tuber set and reproductive traits as shown by progeny testing. Hence, the approach followed for identifying parental sources as discussed in this article appears to be appropriate.     

Evaluation of ‘di Romagna’ and ‘Frenchgrey’ shallots for quality characters connected to bulb colourand volatile oil content and composition

Local landraces of shallot from the Romagna region(Northern Italy) and North-western France, called Scalogno di Romagna and French grey,respectively, have recently been evaluated for morphological,biochemical and molecular characters. These populations appeared very different from common shallots and onions, so were re-classified as Allium oschaninii O.Fedtsch., whereas almost no variability was observed within these types. Four di Romagna and three French accessions were grown in Italy, and further evaluated for quality characters such asbulb colour and volatile oil content and composition. Colour was measured by means of a tristimulus colorimeter. Volatile oil was extracted by hydrodistillation and its components separated and identified by GC/MS. Colour parameters differentiated thedi Romagna from the French greyaccessions. Essential oil composition differed from what has been reported for most other Alliums, by a lower amount of1-propenyl- substituents. No individual oil component allowed a good differentiation of the two geographic origins.However, the French and di Romagna accessions were perfectly separated by the discriminant analysis of oil composition.Minor 1-propenyl- components seemed more critical for discrimination. The shallot types examined seemed biochemically differentiatedfrom Allium cepa. Variation in the examined quality characters was detected both between the two provenances and among the accessions of common geographic origin.     

Morphological characterization of snake melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> var. <Emphasis Type="Italic">flexuosus</Emphasis>) populations from Palestine

Genetic diversity in 50 snake melon accessions collected from Palestine (West Bank) was assessed by examining variation in 17 phenotypic characters. These accessions belonged to four important landraces of Cucumis melo var. flexuosus: Green “Baladi” (GB), white Baladi (WB), green Sahouri (GS), and white Sahouri (WS). Principal component analysis (PCA) and a dendrogram were performed to determine relationships among populations and to obtain information on the usefulness of those characters for the definition of cultivars. PCA revealed that secondary fruit skin color, flesh color, primary fruit skin color, and secondary skin color pattern were the principal characters to discriminate melon accessions examined in the present study. According to the scatter diagram and dendrogram, landraces of C. melo var. flexuosus: GB, WB, GS, and WS formed different clusters. However, based on Euclidean genetic coefficient distances, GB and WB had the least degree of relatedness with GS and WS, indicating distantly related landraces (Baladi and Sahouri). On the other hand, the highest degree of relatedness was detected between WS on one hand, and both GS and WB on the other indicating closely related cultivars. Fruit traits variability among the different snake melon landraces was evaluated and discussed in this study. This evaluation of fruit trait variability can assist geneticists and breeders to identify populations with desirable characteristics for inclusion in cultivars breeding programs.     

Host-plant resistance to Pseudomonas solanacearum in tomato germplasm

Seedlings of two hundred and thirty-three accessions of the tomato collection maintained at the Centro Agronómico Tropical de Investigación y Enseñanza, Turrialba, Costa Rica (CATIE) and 7 cultivars used as controls were evaluated for host-plant resistance to 4 virulent strains of Pseudomonas solanacearum representing race 1 biovars 1 and 3. In general, biovar 3 strains wilted seedlings faster than biovar 1 strains but, after 20 days post-inoculation, no significant differences were noted in susceptible control ratings. Significant differences for disease index were noted, but no line with complete resistance was found. For the USA biovar 1 strain UW-25, only 5 accessions, CATIE 17331, 17334, 17349, 17739, 17740, and 2 of the control cultivars, Hawaii 7998 and UC-82B showed some degree of resistance. Conversely, both the frequency and the degree of resistance were high for Costa Rican biovar 1 strain UW-256. For biovar 3, the Costa Rican strain UW-255 was more virulent than the Peruvian strain UW-130. Eight CATIE accessions, 5539, 17331, 17333, 17334, 17345, 17349, 17742, and MIP-CH1, were as resistant as the resistant control Hawaii 7998 to 3 strains and accession 17740 was as resistant as Hawaii 7998 to all 4 strains.Journal Paper No. J-16011 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 3123.     

Agro-morphological diversity of Spanish traditional melons (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) of the Madrid provenance

The variability of 14 landraces belonging to a Madrilean village historically specialized on melon cultivation, Villaconejos, was evaluated based on 58 quantitative and qualitative morphological traits. These landraces were compared to a reference array composed of 14 accessions which represented the main varieties cultivated in Spanish fields. Individual data related to plant, fruit, seed and phenology have been analysed using a multivariate analysis. This analysis showed intra- and inter-varietal diversity, as emphasized the most discriminant morphological traits in order to define similarities. Villaconejos accessions were morphologically distinct from the reference accessions (RA). Only the landraces belonging to Piel de Sapo market class showed common morphological affinities with the RA, grouping with them. The majority of Villaconejos traditional varieties clustered in five different groups, with no RA within, showing distinctive morphological singularities not described previously. Two of these groups showed some particularities in fruit traits, which are appreciated as quality marks for Spanish consumers. These results indicate that these accessions must be conserved as valuable genetic resources to enrich the Inodorus genetic bases for future breeding proposes worldwide. Furthermore, it should be considered the opportunity of promoting their cultivation under the shelter of a Protected Geographical Indication as a high quality melon. Finally, the discovering of such a high variability presented in a very small area, gives a clue for focusing, with an elevated probability of success, future surveys in similar ancestral European villages which in the past times, also supplied more populated cities with their farming products.     

Reduction of duplication in a Brassica oleracea germplasm collection

Summary To reduce the number of accessions in the Brassica oleracea collection of the Centre for Genetic Resources The Netherlands (CGN) groups of accessions were bulked. Accessions in a group were selections from the same landrace or old variety, and were chosen, with the help of crop experts, on the basis of their history and morphology. Since this approach was received rather sceptically in the genebank community, a genetical analysis of some of the groups and their components (named varieties) was made to justify the procedures. A selection of white cabbage and Brussels sprouts, representing two crop types of B. oleracea, was made: eleven white cabbage groups comprising 43 components, and nine Brussels sprouts groups comprising 24 components. Each group and all of its components were described on the basis of electrophoresis of nine isoenzymes on 30 plants. Most components were rightly classified; 16 percent were misclassified. All these misclassifications were within similar groups. It could be concluded that pooling of the components included in this study was justified. In two cases the isozymic patterns suggested that the groups could even have been larger. Only in the case of the two groups of Brussels sprouts Bedfordshire this was a real option. In the other case involving the white cabbage groups Langedijker Bewaar Gewoon, Langedijker Bewaar Graag and Late Herfstdeen this was not an option since these landraces, although having a common genetic background, clearly have a distinct identity as defined by morphology and history. Editorial footnote: We will encourage the publication of further results of research programs in our journal referring to such often controversially discussed concepts, and would appreciate if collections of crops with different breeding systems could be analysed in this respect.     

Genetic diversity of Musa diploid and triploid accessions from the Brazilian banana breeding program estimated by microsatellite markers

Banana (Musa spp.) is one of the most consumed fruits worldwide. Production is based mainly on triploid cultivars, and most genetic improvement programs aim to generate tetraploid hybrids obtained from the crossing of established triploid cultivars with a diploid parent genotype, improved or wild, exhibiting the trait of interest, normally resistance to biotic factors. Microsatellites were used to investigate the genetic variability and relationships between 58 Musa genotypes, including 49 diploids and nine triploid cultivars maintained at the Musa germplasm collection of the Brazilian dessert banana breeding program. Thirty-three primer pairs developed for banana were tested, and nine amplified reproducible and discrete fragments, producing a total of 115 alleles. The average number of alleles amplified per primer was 12.8, ranging from 10 to 15. The diploid genotypes presented the largest genetic variability, demonstrated by the large number of alleles detected, and the low similarity between the clones. The phenetic analysis clustered the triploid cultivars in a separated group, with the exception of the Nanica and Gros Michel cultivars, which showed high similarity with the diploid cultivar Mambee Thu. It was not possible to separate the wild diploid genotypes from the cultivated ones, indicating a common origin of these genotypes. A high proportion of duplicated alleles and/or loci was observed for diploid and triploid genotypes. The information gathered about the similarity between diploid and triploid accessions will help to define potential crosses to maximize the recovery of the typical fruit qualities required in Brazil (AAB, Pome and Silk dessert banana).     

Cultivation of lotus (<Emphasis Type="Italic">Nelumbo nucifera</Emphasis> Gaertn. ssp. <Emphasis Type="Italic">nucifera</Emphasis>) and its utilization in China

Lotus (Nelumbo nucifera Gaertn. ssp. nucifera), one of 12 aquatic species used as vegetable, has been cultivated for more than 2,000 years, and now has been widely cultivated in almost all provinces in China. The largest area under cultivation of lotus is located in the regions surrounding mid-down Yangtse River, including Hubei, Jiangsu, Zhejiang, Anhui, Jiangxi and Hunan provinces. According to different purposes or morphological differences, the Chinese lotus (N. nucifera ssp. nucifera) is usually classified into three types: rhizome lotus, seed lotus and flower lotus. Rhizome lotus is mainly cultivated in Hubei, Jiangsu, Anhui and Zhejiang provinces; Seed lotus in Jiangxi, Fujian and Hunan, and flower lotus in Wuhan, Hubei province, and Beijing. Up to the year 2002, a total of 572 lotus accessions (including landraces, cultivars and breeding lines) were conserved in National Garden of Aquatic Vegetable, Wuhan, Hubei province, including those collections from 153 counties in 18 provinces, and lines bred by breeders. Out of these accessions, 310 were rhizome lotus which contains 201 landraces and 109 breeding lines; 229 were flower lotus including 172 cultivars and 57 breeding lines; and the rest 33 were seed lotus with 18 cultivars.     

Genetic variability evaluation in a Moroccan collection of barley, Hordeum vulgare L., by means of storage proteins and RAPDs

The genetic variation existing in a set of barley (Hordeum vulgare L.) landrace samples recently collected in Morocco was estimated. Two kinds of genetic markers, seed storage proteins (hordeins) and random amplified polymorphic DNA (RAPD), were used. Only six out of 31 landraces were subjected to RAPD analysis. Both kinds of markers, RAPD and storage proteins, yielded similar results, showing that the level of variation observed in Moroccan barley was high: all landraces showed variability; 808 different storage protein patterns (multilocus associations) were observed among 1897 individuals (2.32 seeds per association, on average) with an average of 43 multilocus associations per accession. In general, genetic variation within accessions was higher than between accessions. The 100 polymorphic RAPD bands generated by 21 effective primers were able to generate enough patterns to differentiate between uniform cultivars and even between individuals in variable accessions. One of the aims of this work was to compare the effectiveness of RAPD versus storage protein techniques in assessing the variability of genetic resource collections. On average hordeins were more polymorphic than RAPDs: they showed more alternatives per band on gels and a higher percentage of polymorphic bands, although RAPDs supply a higher number of bands. Although RAPD is an easy and standard technique, storage protein analysis is technically easier, cheaper and needs less sophisticated equipment. Thus, when resources are a limiting factor and considering the cost of consumables and work time, seed storage proteins must be the technique of choice for a first estimation of genetic variation in plant genetic resource collections.     

Effect of farmers' seed selection on genetic variation of a landrace population of pepper (Capsicum annuum L.), grown in North-West Italy

Recognition by the European Community of élite landraces encourages farmers to grow these and earn more than is possible by growing modern varieties. However, farmers often exercise strong selection by collecting seed from a limited number of plants which best embody a few characters of prime interest. This, in the long run, may be responsible for considerable genetic erosion. In Southern Piedmont, North-West Italy, a local landrace of pepper (Capsicum annuum L.) known as Cuneo is grown; it deserves particular attention because of its hardiness, late production and fruit quality. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers to assess the effect, on genetic composition of a population, of seed sampling carried out using the selection criteria adopted by the farmer. After two reproductive cycles using selection, it was already possible to detect loss in genetic variation and a change in allele frequencies, while no significant effect was found after two cycles of random sampling. Over this period, farmer selection pressure led to disappearance of eight low-frequency alleles, while only three alleles were lost in randomly sampled populations. Our results stress the need to adopt appropriate techniques for seed sampling in order to avoid genetic erosion of local landrace gene pools.     

Changes in seed Morphology, Dormancy and Germination from wild to Cultivated Hyacinth bean Germplasm (Lablab purpureus: Papilionoideae)

Morphological and physiological seed characteristics of the hyacinth bean (Lablab purpureus) were investigated in a set of 18 different germplasm accessions, from wild over semi-domesticated forms to landraces and current cultivars. The objective of this study was to improve the understanding of the domestication of this tropical legume crop. Wild accessions were easily distinguished by morphological characters, such as small, greyish-brown, mottled seeds. Cultivated or semi-domesticated forms showed a much wider variation in size, colour and shape. Seed mass of cultivated accessions reached up to almost 10 times that of wild accessions. Most wild accessions showed a greater spread of germination and larger proportions of hard seeds, up to about 70%, than most cultivated and so-called semi-domesticated accessions. Cluster analysis applied separately to morphological and germination data and a subsequent discriminant analysis did not help integrating the morphological variability observed. The presumed occurrence of semi-domesticated accessions within the germplasm tested as well as the crop's origin from Africa alone or both Africa and Asia are debated on the basis of seed germination and hard seed coat dormancy.     

Evaluation of Gossypium arboreum L. Germplasm for resistance to thrips

Summary As part of a project to assess the U.S. Asiatic Cotton Germplasm Collection as a source of genes for pest resistance, forty-three accessions of Gossypium arboreum L. were evaluated for resistance to thrips. Thrips, Thysanoptera spp., are a minor, but widespread pest on cotton, G. hirsutum L. and G. barbadense L. Accessions were planted in free-choice field tests in 1988, 1989, and 1990 at the Cotton Branch Experiment Station, Marianna, Arkansas. Damage ratings, based on a scale of 0 (no damage) to 7 (severe damage), were made approximately one month after planting. Relative score was computed by dividing the rating of each accession by the rating of the reference, G. hirsutum Stoneville 506. The relative score averaged over all G. arboreum accessions by year varied with the year, but was less than 100 (relative score for Stoneville 506) in each case. When data were combined for all three years, twenty-five accessions were significantly better than Stoneville 506. Introgression of the better accessions into G. hirsutum is now in progress.Abbreviations NPGS National Plant Germplasm System - STV 506 G. hirsutum Stoneville 506     

Genetic Diversity Among Brazilian Cultivars and Landraces of Tomato Lycopersicon Esculentum Mill. Revealed by RAPD Markers

Random amplified polymorphic DNA markers (RAPD) were used to estimate the variability of 35 tomato accessions (Lycopersicon esculentum Mill.). A total of 257 reproducibly scorable bands were obtained from 20 primers, 78.6% of which were polymorphic. The percentage distribution of RAPD markers shows a bimodal distribution, and the frequency of rare alleles is similar in commercial and landrace accessions. Genetic distances among accessions were calculated and a dendrogram showing the genetic relationships among them was constructed allowing for the separation of four groups. Twenty out of 23 Brazilian landraces fell within one group, whereas commercial cultivars were distributed in the four groups. AMOVA analysis of RAPD data showed that, despite the high within Brazilian landraces and commercial cultivars variation, these two groups are significantly different, indicating that landraces can be a source of variation for breeding programs.     

Imbibition behavior and flooding tolerance of rapeseed seed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) with different testa color

In this study, the correlations among these characters were investigated in 18 rapeseed (Brassica napus L.) accessions with different seed coat color. The results indicated that seed water uptake and flooding tolerance were significantly correlated with seed color and melanin pigment content of testa. The red or black-seeded accessions had higher melanin content in testa, showed slower water uptake and lower leakage and higher flooding tolerance. The majority of yellow-seeded rapeseed accessions which had low melanin pigments content in testa showed a rapid water uptake and higher leakage than the red or black-seeded, which led to imbibition damage and lower flooding tolerance. The results suggest that the yellow-seeded cultivars experienced poor field emergence and more serious pre-harvest sprouting in raining weather than the dark-seeded cultivars. Some yellow-seeded accessions showed a slow imbibition behavior and relative high flooding tolerance, indicated these accessions can be used as a genetic resource to improve the flooding tolerance and reduce imbibition damage for the yellow-seeded B. napus L.