Hybrid performance and heterosis in spring bread wheat, and their relations to SSR-based genetic distances and coefficients of parentage

Development of hybrids is considered to be a promising avenue to enhance the yield potential of crops. We investigated (i) the amount of heterosis observed in hybrid progeny, (ii) relative importance of general (GCA) versus specific (SCA) combining ability, and (iii) the relationship between heterosis and genetic distance measures in four agronomic traits of spring bread wheat. Eight male and 14 female lines, as well as 112 hybrids produced in a factorial design were grown in replicated trials at two environments in Mexico. Principal coordinate analysis based on Rogers' distance (RD) estimates calculated from 113 SSRs revealed three different groups of parents. Mid-parent heterosis (MPH) for grain yield averaged 0.02 t ha⁻¹ (0.5%) and varied from −15.33% to 14.13%. MPH and hybrid performance (F1P) were higher for intra-group hybrids than for inter-group hybrids, with low values observed in inter-group crosses involving two non-adapted Chinese parents. Combined analyses of variance revealed significant differences among parents and among hybrids. Estimates of GCA variances were more important than SCA variances for all traits. Tight correlations of GCA with line per se performance, and mid-parent value with F1P were observed for all traits. In contrast, correlations of MPH with RD and coefficient of parentage were not significant. It was concluded that the level of heterosis in spring wheat was too low to warrant a commercial exploitation in hybrids. SSRs proved to be a powerful tool for the identification of divergent groups in advanced wheat breeding materials.     

Genetic diversity of maize inbred lines in relation to downy mildew

A major emphasis in maize breeding in Asian countries has been the improvement for resistance to downy mildew, a serious disease that causes significant yield losses. A total of 102 inbred lines, including lines from Asian breeding programs, Mexico, USA and Germany, were analyzed with 76 SSR markers to measure diversity and investigate the effect of selection for downy mildew resistance. A mean polymorphism information content of 0.59, with a range of 0.14 to 0.83, was observed. Diversity at the gene level showed an average of 5.4 alleles per locus and a range of two to 16 alleles per locus, with a total of 409 alleles. About half of the alleles in the Asian lines had frequencies of 0.10 or less, and only 2% had frequencies > 0.80, indicating the presence of many alleles, and thus a high level of diversity. Some of the high-frequency alleles were in chromosomal regions associated with disease resistance. However, the frequencies of alleles in three SSR loci that are linked to a QTL for resistance to downy mildews in Asia were not significantly different in the subtropical/tropical Asian lines as compared to all the lines in the study. Lines from the US, Germany, and China, comprised three clusters of temperate maize(GS = 0.31), while those from India, Indonesia, Philippines, Thailand, Vietnam and CIMMYT comprised seven indistinct clusters of subtropical and subtropical maize (GS = 0.29). We conclude that maize breeding activity in Asia has not caused a decline in the overall amount of diversity in the region. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic characterization of 218 elite CIMMYT maize inbred lines using RFLP markers

Characterization of genetic diversity among maize inbred lines can facilitate organization of germplasm and improve efficiency of breeding programs. A set of 218 phenotypically diverse inbred maize lines developed at CIMMYT for hybrid production was characterized using 32 RFLP markers to: (1) analyze the genetic diversity present; (2) define potential heterotic groups based on clusters formed with marker data; and (3) identify the most representative testers for each potential heterotic group. Lines were clustered using five different genetic distance measurements to find consensus non-hierarchical clusters. Dendrograms were produced to study hierarchical classification within smaller groups of lines. A very high average allelic diversity was seen in this germplasm. Lines did not cluster based on phenotype, environmental adaptation, grain color or type, maturity, or heterotic response (as determined based on hybrid performance with testers), but lines related by pedigree usually did cluster together. Previously defined testers from opposite heterotic groups were not genetically differentiated, and did not represent well their heterotic group. Discrete clusters were difficult to find; thus, potential heterotic groups will be difficult to suggest using RFLP markers alone. However, suggestions on how to use molecular markers and cross performance information to refine heterotic groups and select representative testers are presented.     

Developmental changes in structure and polypeptide profile of the androgenic gland of the freshwater prawn Macrobrachium rosenbergii

Although the mechanism of sex-differentiation in crustaceans has yet to be defined, the androgenic gland (AG) is thought to be the exclusive organ that produces the androgenic hormone (AH) which induces male sexual development. This paper presents results of light and transmission electron microscopy and total protein analysis of androgenic glands from three male morphotypes (orange-claw, orange-blue-claw and blue-claw) of the freshwater prawn, Macrobrachium rosenbergii. Highest protein content (76 µg//AG) was found in the blue-claw morphotype as compared to the orange-blue-claw (45 µg/AG) and the orange-claw morphotype (19 µg/AG). Sodiumdodecyl sulfate polyacrylamide gel electrophoresis (SDS-page) analysis of the cell free extract of the AG from the three morphotypes revealed four polypeptides (16, 18, 23 and 26 Kd) which quantitatively increase from the sexually immature orange-claw to the sexually mature blue-claw morphotype. The 16 and 18 Kd polypeptides could be the AHs.     

Learning of foraging skills by fish

This chapter outlines the relationships between a number of key factors that influence learning and memory, and illustrates them by reference to studies on the foraging behaviour of fish. Learning can lead to significant improvements in foraging performance in only a few exposures, and at least some fish species are capable of adjusting their foraging strategy as patterns of patch profitability change. There is also evidence that the memory window for prey varies between fish species, and that this may be a function of environmental predictability. Convergence between behavioural ecology and comparative psychology offers promise in terms of developing more mechanistically realistic foraging models and explaining apparently ‘suboptimal’ patterns of behaviour. Foraging decisions involve the interplay between several distinct systems of learning and memory, including those that relate to habitat, food patches, prey types, conspecifics and predators. Fish biologists, therefore, face an interesting challenge in developing integrated accounts of fish foraging that explain how cognitive sophistication can help individual animals to deal with the complexity of the ecological context.     

The value of conserving whales: the impacts of cetacean‐related tourism on the economy of rural West Scotland

• 1. During the tourist season of 2000, interview surveys were conducted with those involved in whale‐watching in West Scotland. The groups included in the study were boat operators (32), visitor‐centre managers (8), tourists on whale‐watching trips (324), general tourists to West Scotland (673) and local residents (189). The latter two groups were interviewed for comparison of responses of those engaged in whale‐watching against the views of the local community and tourists in general. From the data provided by these interviews, estimates for the economic value of this specialist sector of the Scottish tourism industry were calculated.
• 2. Extrapolating from the surveys, in the year 2000, an estimated total of approximately 242 000 tourists were involved in cetacean‐related tourism activities in West Scotland.
• 3. In 2000, 59 full‐time and one part‐time jobs were estimated to be created as the direct result of cetacean‐related tourism, with 38% of these positions being seasonal.
• 4. Cetacean‐related tourism was estimated to account for 2.5% of the total income from tourism in the region. In remote coastal areas, cetacean‐related tourism may account for as much as 12% of the area's total tourism income.
• 5. The direct economic income (i.e. expenditure on excursion tickets) from cetacean tourism activities was estimated to be £1.77 million per annum.
• 6. A 23% of surveyed whale watchers visited West Scotland specifically to go on whale‐watching trips. The associated expenditure (accommodation, travel, food, etc.) from tourists being brought to rural West Scotland solely due to the presence of whales represented £5.1 million in additional tourism income for the region.
• 7. In addition to the above tourists, 16% of surveyed whale watchers stayed in West Scotland an extra night as a result of going on a whale‐watching trip; thus generating a further £0.9 million of additional associated expenditure (extra accommodation, food, etc.).
• 8. The total gross income generated (directly and indirectly) by cetacean‐related tourism in rural West Scotland was estimated at £7.8 million.
• 9. In comparison with established whale‐watching industries (in countries such as the USA, Canada and New Zealand) the total expenditure by tourists on whale watching in West Scotland is low. However, cetacean tourism in West Scotland is still a relatively young industry and still developing.
• 10. The value of the non‐consumptive utilization of cetaceans (i.e. whale‐watching) to rural, coastal communities in West Scotland was three times greater than the value of the consumptive utilization of cetaceans (i.e. commercial whaling) for rural, coastal communities in Norway.
• 11. This study demonstrates that live cetaceans in Scotland can provide notable financial benefits and, therefore, their conservation has an economic value.

Copyright © 2003 John Wiley & Sons, Ltd.     

Comparative evaluation of molecular diagnostic tests for Nucleospora salmonis and prevalence in migrating juvenile salmonids from the Snake River, USA

Nucleospora salmonis is an intranuclear microsporidian that primarily infects lymphoblast cells and contributes to chronic lymphoblastosis and a leukemia-like condition in a range of salmonid species. The primary goal of this study was to evaluate the prevalence of N. salmonis in out-migrating juvenile hatchery and wild Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss from the Snake River in the U.S. Pacific Northwest. To achieve this goal, we first addressed the following concerns about current molecular diagnostic tests for N. salmonis: (1) nonspecific amplification patterns by the published nested polymerase chain reaction (nPCR) test, (2) incomplete validation of the published quantitative PCR (qPCR) test, and (3) whether N. salmonis can be detected reliably from nonlethal samples. Here, we present an optimized nPCR protocol that eliminates nonspecific amplification. During validation of the published qPCR test, our laboratory developed a second qPCR test that targeted a different gene sequence and used different probe chemistry for comparison purposes. We simultaneously evaluated the two different qPCR tests for N. salmonis and foundthat both assays were highly specific, sensitive, and repeatable. The nPCR and qPCR tests had good overall concordance when DNA samples derived from both apparently healthy and clinically diseased hatchery rainbow trout were tested. Finally, we demonstrated that gill snips were a suitable tissue for nonlethal detection of N. salmonis DNA in juvenile salmonids. Monitoring of juvenile salmonid fish in the Snake River over a 3-year period revealed low prevalence of N. salmonis in hatchery and wild Chinook salmon and wild steelhead but significantly higher prevalence in hatchery-derived steelhead. Routine monitoring of N. salmonis is not performed for all hatchery steelhead populations. At present, the possible contribution of this pathogen to delayed mortality of steelhead has not been determined.