Germplasm Assessment Research Articles

The role of botanic gardens as resource and introduction centres in the face of global change

One of the consequences of global change, especially demographic and climatic, will be a demand for novel plant germplasm of all kinds suited to the new ecoclimatic conditions predicted and plant introduction will assume a new importance. As a consequence, botanic gardens will face an unprecedented opportunity to regain their role as introduction centres and become major actors in the assessment of new germplasm, both of ornamentals as well as other economically important plants. Plant introduction has remained largely unchanged over the past 400 years and is as often ad hoc, poorly organized and insufficiently collaborative, but if it is to meet the needs of today’s situation it needs to be overhauled. In particular: (1) the basis of plant introduction needs to be broadened; (2) closer cooperation with agricultural genebanks should be established; (3) agreement should be reached between botanic gardens and the agricultural sector on their respective responsibilities (4) the quality and sampling of the accessions should be more strictly controlled; (5) proper evaluation of the introductions before they are disseminated; (6) information on the accessions of introduced plants and their fate needs to be more effectively maintained and disseminated; and (7) full cognizance should be taken of policies to protect against invasive species and care should be taken to evaluate the risks that new introductions might represent. Finally, consideration should be given to preparing a set of guidelines or even a code of conduct for plant introductions by botanic gardens in association with other agencies.

Characterization of gene expression profiles in developing kernels of maize (Zea mays) inbred Tex6

AbstractMaize inbred Tex6 is resistant to several pests. The objectives of this study were to characterize gene expression profiles in Tex6 kernels and identify unique genes that expressed up‐ or down‐ward in developing kernels in the later stages. Because of the resistance of Tex6 kernels, we reasoned that it would be an interesting candidate for microarray study. By using maize microarray, we analysed gene expression profiles in developing kernels from 25 DAP (days after pollination) to 45 DAP. A total of 8497 positive array spots were detected with unique IDs, in which 4247 genes were detected in all samples. The trends of total expressed genes were decreasing when kernels were maturing. Expression patterns of some genes in several metabolic pathways, including starch, lipid and storage proteins, were analysed. In comparison with 25 DAP, expressions of 211 gene features were significantly different at 45 DAP (P < 0.05), which will be used to produce a macroarray for germplasm assessment and evaluation. The real‐time qRT‐PCR was used to validate microarray study.

Genetic diversity and relationships among Dutch elm disease tolerantUlmus pumilaL. accessions from China

Elm breeding programs worldwide have relied heavily on Asian elm germplasm, particularly Ulmus pumila, for the breeding of Dutch elm disease tolerant cultivars. However, the extent and patterning of genetic variation in Asian elm species is unknown. Therefore, the objective of this research was to determine the extent of genetic diversity among 53 U. pumila accessions collected throughout the People's Republic of China. Using 23 microsatellite loci recently developed in the genus Ulmus, a total of 94 alleles were identified in 15 polymorphic and 4 monomorphic loci. The average number of alleles per locus was 4.9, with a range of 1-11 alleles. Gene diversity estimates per locus ranged from 0.08 to 0.87, and the non-exclusion probability for the 15 polymorphic loci combined was 0.7 x 10(-9). Nineteen region-specific alleles were identified, and regional gene diversity estimates were moderately high (0.48-0.57). The genetic relationships among accessions and regions were estimated by UPGMA and principal coordinate analysis. Both techniques discriminated all accessions and regions. Two microsatellite markers (UR175 + UR123 or Ulm-3) were sufficient to discriminate up to 99.7% of the accessions studied. This research provides useful information for DNA-based fingerprinting, breeding, ecological studies, and diversity assessment of elm germplasm.

Isolation and characterization of Ty1- copia retrotransposon sequences in the blue agave ( Agave tequilana Weber var. azul) and their development as SSAP markers for phylogenetic analysis

Agave tequilana Weber variety “azul” is the only variety of blue agave which is accepted for the production of tequila, but the phylogenetic relationships between this variety and other agave germplasm is still poorly understood. Retrotransposon-based molecular markers have proven to be highly informative in determining phylogenetic relationships in other crop systems. We report the isolation of a population of Ty1- copia retrotransposon terminal sequences from A. tequilana and develop three of these as sequence-specific amplification polymorphism (SSAP) molecular genetic markers. SSAP analysis shows high levels of retrotransposon polymorphism throughout agave varieties and species and identifies the tequila agaves as a distinct phylogenetic group. The retrotransposon SSAP markers presented here represent a powerful new tool for germplasm assessment in the agaves.

In vitro culture response of apical and axillary shoot-tips excised from crisphead lettuce cores depends on head maturity, not storage time

Successful lettuce (Lactuca sativa L.) breeding requires assessment, selection, and reseue of germplasm from field-grown plants during a limited period of time. Tissue culture methods have proved successful in rescuing selected lettuce genotypes and producing seeds in a disease-free environment. The present study was conducted to determine the response of the apical and axillary shoot-tips of lettuce to storage duration prior to in vitro culture. The study focused on core length as a source of variation between maternal explants. Advanced maturity was obtained by applying an agrotextile row cover over lettuce plants. Apical and axillary buds were derived from covered lettuce with long cores (46±0.8 mm) and from non-covered lettuce with short cores (30±0.7 mm). The cores were stored at 2°C for 0,2, or 13d. Apical and axillary shoot-tips were removed from the cores and placed onto MS medium. After 3 mo. of growth culture, twice as many leaf primordia (6.6 leaves) developed from the apical shoot-tip as compared to those from the axillary shoot-tip (3.0 leaves). More shoot-tips survived when excised from short cores (83%) than when excised from long cores (71%). Root formation was affected by the source of shoot-tip and the size of donor explant. Three times more explants from apical shoot-tips and short cores rooted (71%) than did explants from apical shoot-tips and long cores (27%) or explants from axillary shoot-tips (long cores, 14%; short cores, 19%). Storage of cores for up to 13 d had no effect on the survival rate of shoot-tips, nor on shoot or root formation, suggesting that cores of lettuce plants can be stored prior to in vitro micropropagation without significant loss of regeneration efficiency.

Genetic differentiation among natural populations of Gastrodia elata (Orchidaceae) in Hubei and germplasm assessment of the cultivated populations

Genetic differentiation among natural populations of Gastrodia elata (Orchidaceae) in Hubei and germplasm assessment of the cultivated populations

Assessing genetic diversity in the cassava (Manihot esculenta Crantz) germplasm collection in Brazil using PCR-based markers

Knowledge of the origin, organization and nature of the cassava (Manihot esculenta Crantz) germplasm collection in Brazil is incomplete due to lack of critical information on several aspects of the collection. This study verifies the utility of SSR-primed PCR markers for germplasm assessment and then utilizes these markers as well as RAPD's to characterize the Brazilian collection. We specifically address the following questions: 1)what is the relationship of morphologically closely related species to cultivated cassava? 2) What is the genetic diversity of cultivars within and between different habitats in Brazil? 3) Do agronomic traits and molecular markers reveal the same relationship among cassava accessions? 4) How complete is the Brazilian cassava collection and how well is it represented in the Word Core Collection of cassava, maintained by CIAT? Results of the interspecific studies of cassava and its wild relatives confirms the close relationship of cassava, Manihot esculenta ssp. esculenta to Manihot esculenta ssp. flabellifolia as well identifying several other closely related wild species. Next, PCR-based markers indicate a strong grouping of varieties related to the region of cultivation in Brazil. Moreover, important regions such as Cerrados and Amazon are relatively poorly represented in germplasm collections. Interestingly, the relationships of accessions based on agronomic traits are not fully congruent with relationships revealed with RAPD markers. Finally, the genetic diversity of the Brazilian cassava collection is not fully represented in the Core of the Word Core Collection of CIAT.

Comparison of DNA Marker Technologies in Characterizing Plant Genome Diversity: Variability in Chinese Sorghums

Chinese sorghums [Sorghum bicolor (L.) Moench] are reputed to have a narrow genetic base, resulting from infrequent introduction of exotic germplasm into China. We have used several different molecular approaches to evaluate diversity and relatedness in a selection of 34 Chinese sorghums. The results indicated that different DNA marker technologies for germplasm assessment yield comparable results, but that a relatively new technique termed inter‐simple sequence repeat amplification (ISSR) was relatively rapid, reproducible, and inexpensive. Extensive diversity was observed within the Chinese sorghums, and all lines could be easily differentiated. Different lines collected from the same locality were found to exhibit particularly high levels of relatedness. Contrary to expectations, improved varieties were found to contain more diversity and to be more different from each other than were the Chinese landraces studied, suggesting recent introduction of non‐Chinese germplasm into these improved materials.

Using RAPD Markers to Assess Genetic Diversity in Brassica Germplasm and Chinese Breeding Lines

Molecular DNA markers based on the RAPD (random amplified polymorphic DNA) assay are gaining use in germplasm assessment. RAPD markers are simple, relatively inexpensive, and highly informative. We used five primers to assess 26 Brassica oleracea breeding lines from the IVF and nine accessions from the PGRU. The test array included eight subspecies of B. oleracea. We generated 90 RAPD markers and were able to unambiguously discriminate among all 35 test entries, but could not separate subspecies within B. oleracea. Genetic similarity between subspecies ranged from 0.629 to 0.738. Average similarity within accessions was 0.96, confirming the suspected homogeneity of breeding lines. Nevertheless, significant genetic diversity was found among kohlrabi, broccoli, and cabbage accessions. Similarity analysis of breeding lines and hybrids confirmed their pedigree relationships. Interestingly, B. o. subsp. costata `Couve Nabica' showed closer similarity to B. napus subsp. oleifera `Jet Neuf' than to other B. o. materials and B. o. subsp. italica `Packman' showed higher similarity to some cabbages than to other broccolis. Results provide further evidence that diversity assessment using RAPDs is broadly applicable and useful in germplasm conservation and utilization.

Winter Hardiness in New Digitaria Germplasm1

AbstractPortions of the USDA Digitaria collection have been assessed for winter hardiness in previous studies. The objective of this study was to identify additional winter hardy Digitaria germplasm for the purpose of extending its production range as permanent pasture in the southeastern United States. This objective was accomplished by assessing plant survival for winter hardiness of 14 species and two subspecies comprising 230 accessions grown in field trials for 3 years at four locations in Florida and Georgia. Significant differential winter hardiness was exhibited among Digitaria species and among clones within species. Winter hardiness of seven species and two subspecies was significantly superior to that of the remaining seven species. The species of greatest economic value, D. decumbens Stent comprising three cultivars, is among the most winter hardy germplasm. The cultivars ‘Pangola,’ ‘Slenderstem,’ and ‘Transvala’ are among 13 clones which exhibited maximum winter hardiness. The average performance of species masked the superior winter hardiness of individual clones in some instances. These findings substantiate those reported previously and emphasize the consideration that should be given individual clones in the search for, and utilization of winter hardy Digitaria germplasm. The effect of minimum temperature on winter survival was determined. This winter hardy germplasm is being utilized in plant improvement programs, particularly in Florida. These results demonstrate the need for additional field research in an assessment of the elite winter hardy germplasm for adaptation and production capacity.