1,721,069 research outputs found
Problematiche e approcci metodologici per l’identificazione di varietà essenzialmente derivate.
No full textEssentially derived are those varieties (EDV) obtained from an initial protected one (IV) that, although distingui- shable from the IV, conform strictly to it in the expression of essential characteristics. Many breeding methods are available for the derivation process and particularly modern biotechnological approaches which allow a fast and accurate development of these genotypes. Such procedures impair the rights acquired by the breeder of the protected IV who, if demonstrates the genetic conformity between original and new variety, can claim the dependence of the latter. Therefore, a crucial requirement to solve disputes on illegal derivation is the definition of a genetic similarity threshold, between IV and the new variety, above which essential derivation is suspected. Molecular markers are ef- ficient tools for measuring genetic similarity and their adoption in disputes regarding the derivation process has been recommended. Similarity thresholds can be identified according to three approaches: “calibration principle”, “tail principle” and “pedigree principle”. The first one is based on previous knowledge of the similarity between unrelated and closely related (hence essentially derived) genotypes. The second, which does not require pedigree information, sets the threshold at a given percentile of the similarity distribution of a reference population of unrelated genotypes. The threshold limit defined by the third approach is founded on the a priori definition of breeding techniques that lead to essentially derived varieties. Critical aspects of the different procedures are discussed. A similarity exceeding the threshold value is not, however, a conclusive demonstration of the dependence from the IV.
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Aspetti sementieri nella produzione di ibridi di frumento
No full textAspects of hybrid seed production in wheat Hybrid wheat breeding began during the sixties after the discovery of a male sterility system induced by nuclear substitution in alien cytoplasm. Triticum timopheevii was a promising cytoplasm source of male sterility due to its negligible negative effects on agronomic traits; nuclear genes for fertility restoration were found as well in this species, but the need of several of them to achieve a satisfactory fertility in a wide range of environments limited the practical utilisation of this source. Other donors of sterile cytoplasm or restorers have been investigated, although with little success so far. Alternative biotechnological approaches, implemented in other crops, were proposed in the last two decades also for wheat. Among them the “barnase–barstar” system, and more recently the “split gene”, a derivation of the previous one but easier to implement in the breeding work, and the “Seed Production Technology” system, particularly interesting because it produces non-transgenic hybrids. Since these tools are not yet available for wheat, current production of hybrid varieties is based on the use of chemical hybridizing agents whose efficiency has improved in recent years. Morphological traits favourable for cross pollination are also discussed
Ibridi di orzo: problematiche e realizzazioni
No full textBarley hybrids: issues and achievements The success of hybrid varieties depends on the economic advantages achievable with them compared to traditional varieties, and on the availability of a cost-effective mechanism to promote cross-pollination, a crucial aspect in a strictly autogamous spe- cies such as barley. A genetic male-sterility system, based on the use of a balanced tertiary trisomic (BTT), was initially adopted, even though on a limited scale, but it was abandoned after a few years due to the high cost for parent reproduction. A more suitable system, relying on a genetic-cytoplasmic male-sterility derived from a wild barley accession, was later implemented, making seed production reliable and competitive and therefore allowing the spread of hybrids in several European countries. These achievements were also possible by applying the strategy of “mix planting” parental lines in hybrid seed production fields in order to attain a high level of hybridization. On the legislative side, however, the adoption of this solution required the lowe- ring of genetic purity standards for certified seed. Hybrid varieties can be superior to pure lines in terms of yield, yield stability and resistance to biotic and abiotic stresses, provided that suitable agronomic techniques are applied
The relationship between three cold test temperatures, accelerated ageing test and field emergence of maize seed
No full textThe standard cold test temperature for maize of 10°C may not be suitable for all genotypes because of variation in cold hardiness. The aim of the present work was to study the effect of three cold test temperatures on seed vigour of a large number of maize seed lots in comparison with the standard germination test and accelerated ageing (AA) test and to determine the relationship between all tests and field emergence. Thirty maize (Zea mays L.) seed lots with high germination but differing vigour were germinated in trays in sterile sand at 25°C after 0 (standard germination test) or a 7-day cold treatment at 10, 7.5 and 5°C and after AA at 45°C for 72 hours. Field emergence after an early sowing was also evaluated. The three cold test temperatures significantly lowered the germination of almost all seed lots, with the magnitude of the decrease depending on the cold temperature used. The interaction treatments × seed lots was also significant owing to differences in vigour among seed lots. Despite the early sowing, the field environment was benign and almost all seed lots had a good emergence. However, standard germination still showed a poorer correlation (r = 0.51**) with field emergence than all the vigour tests (r = 0.75 to 0.79**). There were good correlations (r > 0.80) among all the laboratory vigour tests, while slightly lower correlations with standard germination were shown by the cold test at 10°C and AA test (r = 0.71** and r = 0.63**, respectively). A low correlation with standard germination was shown by both the 7.5 and 5°C cold tests (r = 0.42**). The AA test is likely to be as effective as the 10°C cold test for assessing maize seed lot vigour. However, for cool tolerant varieties, a cold test at 7.5 or 5°C may be necessary to detect vigour differences among seed lots
Expression of Protein L-Isoaspartyl Methyltransferase in sunflower seeds as affected by ageing and priming
No full textIn orthodox seeds, non-enzymatic protein damage occurring during dehydration and storage is hypothesized to be a main cause of deterioration. Therefore, for vigorous germination dry seeds should be equipped with protein repair mechanisms. One of these involves protein L-isoaspartyl methyltransferase (PIMT) which counteracts protein misfolding by catalyzing the conversion of abnormal L-isoaspartyl residues to their regular form. PIMT activity is primarily localized in seed tissues during and after maturation desiccation, suggesting its involvement in restoring the functional conformation of the seed proteome. This study was initiated to assess the putative role of PIMT repair pathway on seed vigor in Helianthus annuus whose seeds are rather sensitive to deterioration during storage. A sunflower homolog of Arabidopsis PIMT1 was isolated and characterized, and its expression in seeds was measured by qRT-PCR on a panel of 16 inbred lines subjected to ageing, priming, and priming after-ageing. The wide variability in the physiological response observed among the lines and the considerable interactions between factors produced a rather complex picture. Considered separately, ageing and priming had expected, although only modest, effects on final germination, i.e. negative the former (-2.4%) and positive the latter (+4.7%). More marked were the effects on germination rate, with an 8.3% increase in T50 after ageing and a 30.6% reduction after priming. On average PIMT transcript levels were highest in quiescent seeds and reached the minimum after ageing, with a 38% drop; also after priming PIMT mRNA decreased 26%, while in primed after-ageing seeds its abundance was variously affected. Therefore PIMT expression pattern in sunflower resembles that of other protein transcripts with protective role in dry seeds. Correlations between transcript levels and germination percentage and rate were not found in control and aged seeds; on the contrary, correlations were negative and significant when priming was applied, perhaps indicating either an attempted repair response or a reduced degradation in damaged tissues. For the complexity of the responses observed, further studies on gene expression and enzyme activity will be necessary to assess the role of this repair mechanism in maintaining seed vigor in sunflower
Nuovi strumenti per la tracciabilità e la protezione della proprietà intellettuale in ambito sementiero
No full textIntroduzione
La costituzione di varietà migliorate ha contribuito considerevolmente agli incrementi produttivi ed ai
miglioramenti qualitativi registrati nel corso dell’ultimo secolo ed il seme è il mezzo mediante il quale tale
innovazione ha potuto essere efficacemente diffusa. Il breeding richiede investimenti cospicui e deve essere
remunerativo, e per questo si è affermato un sistema internazionale di tutela delle novità vegetali. Inoltre, a seguito
della globalizzazione, si è sviluppata l’esigenza di tracciare le filiere produttive anche a valle del seme per
valorizzare i prodotti e garantire gli utilizzatori. La relazione fa il punto sulle applicazioni delle tecniche molecolari
in ambito sementiero.
Metodologia
Il quadro presentato è il risultato da un lato di una disamina della letteratura scientifica e di documenti di
organizzazioni del settore, dall’altro dell’esperienza diretta del LaRAS nel campo dei servizi analitici su aspetti
varietali.
Risultati e conclusione
Nel corso degli ultimi decenni si è assistito ad un boom nelle applicazioni delle tecniche di indagine molecolare in
campo vegetale sia per la ricerca che per lo sviluppo varietale. Da subito sono risultate evidenti le
potenzialità dei marcatori molecolari (MM) nell’ambito della protezione e registrazione delle nuove varietà,
tradizionalmente basate sulla verifica dei requisiti di distinguibilità, uniformità e stabilità (DUS) per caratteri
morfologici. Per la loro capacità discriminante ed indipendenza da effetti ambientali i MM consentono procedure di
valutazione semplificate e notevole precisione delle determinazioni, ma la loro adozione nella pratica è ancora
limitata e procede con prudenza. Per alcune specie i MM sono già utilizzati per la scelta delle varietà con
cui le nuove costituzioni dovranno essere comparate nelle prove di campo; in altri casi marcatori strettamente
associati a geni che controllano descrittori DUS sono analizzati in alternativa e con maggiore efficienza rispetto ai
descrittori stessi; tuttavia, al fine di non indebolire l’attuale sistema di tutela, ad oggi i polimorfismi genetici non
collegati al fenotipo non sono ritenuti prove sufficienti di distinguibilità.
D’altra parte i MM sono considerati indispensabili per identificare, mediante stime di distanza genetica, varietà
essenzialmente derivate da altre preesistenti protette, dalle quali le prime differiscono per uno o pochi caratteri; le
biotecnologie, infatti, rendendo più semplice la derivazione, hanno aumentato i rischi di abuso nell’impiego di
materiali protetti.
Nell’ambito della moltiplicazione sementiera, l’automazione delle procedure analitiche e la diminuzione dei costi
rendono oggi realizzabili controlli di qualità genetica (identità e purezza varietale) di routine nella produzione di
semente ibrida di elevato valore commerciale, oppure più specifici e mirati al mantenimento di elevati livelli di
purezza nelle prime generazioni, quali il nucleo del costitutore o il seme prebase.
I medesimi strumenti molecolari permettono l’accertamento della rispondenza varietale delle partite alle esigenze
delle filiere di trasformazione, siano esse relative a produzioni convenzionali legate a determinati parametri
qualitativi, oppure a produzioni biologiche o tipiche a marchio di qualità ed aderenti a specifici disciplinari. Infine,
la resistenza del DNA ai trattamenti utilizzati nei processi di trasformazione consente in genere di estendere la
tracciabilità ai prodotti finali e di verificarne le dichiarazioni riportate in etichetta, contribuendo a mantenere la
fiducia del consumatore
Population structure and long-range linkage disequilibrium in a durum wheat elite collection
No full textA collection of 134 durum wheat accessions, mainly including cultivars (cvs.) representative of the major gene pools, was assembled and characterized with 70 SSRs for genetic diversity and level of long-range linkage disequilibrium (LD). Results of both a distance-based and a model-based (Bayesian) cluster analysis evidenced the presence of a structured diversity. In the model-based analysis, six to eight main distinct subpopulations were identified based on the molecular data. Only a relatively small portion (20%) of the molecular variation was accounted for by the geographical origin of the accessions. Major differences were detected between the North American and the Mediterranean cvs., while a considerable overlap characterized the cvs. from CIMMYT-ICARDA and Italy. The North American cvs. showed the highest within group mean genetic similarity (GSm = 0.68). French cvs. revealed sizeable similarities with both the North American as well as the Italian and CIMMYT-ICARDA pools. Considering the germplasm as a whole, high levels of LD were found both at locus pairs with an intrachromosomal distance <50 cM as well as at those with distances more than 50 cM and independent (86, 52 and 54% of SSR pairs at p < 0.01, respectively). After re-evaluating LD within each of the three main subgroups identified through the analysis of the germplasm structure, the LD level remained high for tightly to moderately linked locus pairs (<20 cM apart), but was greatly reduced in the loosely linked (more than 50 cM apart) and independent locus pairs. The implications of these findings as to the possibility of using association mapping for gene/QTL discovery in durum wheat are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A RAPID IDENTIFICATION TOOL FOR ITALIAN LANDRACES AND OLD VARIETIES OF TRITICUM
No full textGenetic diversity is one of the key factors for the future of agriculture and food security,
making continuous crop improvements possible. Also in this perspective, EU legislation promotes
landrace conservation through the use of ‘Protected Designation of Origin’ (PDO) labels on derived
products and by allowing the production and exchange of landrace seed in their area of origin,
derogating from the requirements for variety registration. The availability of molecular marker
systems efficient in assessing genetic diversity is relevant for the safeguar of ‘varieties adapted to
the local and regional conditions and threatened by genetic erosion’, supporting their maintenance
and exploitation over the long term. In this work, 17 accessions of Triticum turgidum, belonging to
both durum and turanicum subspecies, and 14 of T. aestivum, including landraces and old cultivars,
were analyzed with two multiplex SSR sets made up in total of 12 markers. The two marker sets
had been previously used to characterize two larger panels including the most prominent durum and
bread wheat varieties presently commercialized in Italy. Heterogeneity was observed in most of the
landraces, with several non-fixed loci (up to 5 alleles per locus were scored), whereas accessions of
T. turanicum as well as old improved varieties of T. aestivum turned out basically uniform. In total,
70 alleles were detected in T. turgidum and 87 in T. aestivum accessions; of them 31 and 22 had not
been previously encountered in current varieties of the two respective species, indicating a
considerable loss of variability over time, particularly for the former. The greater allelic richness
found in T. aestivum compared to T. turgidum was also reflected by the higher mean level of
informativeness (PIC values of 0.72 and 0.56, respectively). Interestingly, the two SSR sets
allowed the distinction of all T. aestivum accessions, except two old varieties, whereas in T.
turgidum four were those undistinguishable. In conclusion, the two marker sets appear suitable for a
rapid assessment of wheat germplasm collections, and could be useful for the management of
specialty products, ensuring traceability over the whole production chain thus increasing their value
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