A general approach to the concept of varietal ability for synthetic varieties

Summary Genetic effects for varietal value are defined at the level of the population of k-parent synthetic varieties. A simple expression for the total variance among synthetics arises directly from these definitions. A general expression for the covariance among related synthetics is given. Genetic effects are also defined in a completely general way so as to allow for any system of testing and used to derive an expression for the genetic advance in recurrent selection for varietal value. Covariances between relatives evaluated in the system of testing and in varietal combination are introduced, allowing a direct expression of the genetic advance in varietal development when parents are selected either individually or in groups. Some general implications for plant breeding are outlined.Dedicated to Professor F.W. Schnell on the occasion of his 65th birthday     

Structure,development and function of the branchial sieve of the common bream,Abramis brama,white bream,Blicca bjoerkna and roach,Rutilus rutilus

Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach.     

Mechanisms of embryonic drift in the amphidromous goby,Rhinogobius brunneus

Synopsis We tested the reactions of free embryos of the amphidromous goby, Rhinogobius brunneus, to light under both artificial and ambient conditions along streams in which their downstream migration occurs. The embryos showed a positive phototaxis to 500 1ux light but a negative response to light of more than 5000 lux. They were able to swim at 1.54 cm sec^–1 t in still water and showed positive rheotaxis, but their swimming ability was not sufficient to allow active movement in rapids. Ambient natural light conditions varied among locations in relation to local topographical features. The variation in the diel periodicity of their migration could be explained by the interaction between behavioral reactions of embryos and environmental factors along river courses.     

Fixed effect genetic analysis of a diallel cross in dry beans (Phaseolus vulgaris L.)

Summary A full diallel cross among four diverse homozygous strains of dry edible beans (Phaseolus vulgaris L.) was evaluated for yield, protein content, and culinary quality traits in the F₂ and F₃ generations in two locations. Interpretation of diallel effects [Method 1 Model I] using a fixed-effect genetic model made it possible to combine data from two generations into a single analysis and quantify the relative contributions of additive and dominance genetic effects to general (GCA) and specific (SCA) combining abilities. GCA was found to arise from three potential sources: additive effects, dominance interactions at homozygous loci, and average dominance interactions in hybrids involving the parent in question. SCA was found to be a function solely of dominance. Additive effects were the primary determinant of GCA and were highly significant. Specific dominance interactions were significant for seed yield, cooked bean moisture content, and texture but not for protein content. Texture was the only trait for which the additive-dominance model failed to provide an adequate fit to the data, suggesting that texture is significantly affected by epistatic interaction. One cross (Brazil-2 × Sanilac) was identified that exhibited a large heterotic effect for seed yield although the parents' additive effects were nonsignificant. Such a nicking effect was attributed to complementation between the two parents.Cooperative investigations of the Agricultural Research Service, U.S. Department of Agriculture and Michigan State University, East Lansing, MI 48824. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Michigan State University. Approved for publication by the Michigan Agricultural Experiment Station as Journal Article No. 11791. Research supported by USAID under a Title XII Bean/Cowpea CRSP and cooperative with Washington State University, Pullman, WA99164     

The biology of Butomus umbellatus in shallow waters with fluctuating water level

Butomus umbellatus L. is a plant species typical of littoral communities of river and stream shores. It can form continuous stands in shallow reservoirs with fluctuating water level. Their expansion is promoted by: (a) intensive vegetative reproduction of plants, (b) crowded sprouting from rhizome fragments on emerged pond bottom, (c) shallow water layer in the year following summer drainage. Expansion of B. umbellatus depends on ploidy level: two cytotypes were found in the Czech and Slovak Republics, differing in their reproductive ability. Seed production of triploids is strongly limited (they are self-incompatible within clones), while diploids can be fully fertile. Nevertheless, even in diploids, the efficiency of seed reproduction under natural conditions is low. Triploids spread by intensive vegetative reproduction, which is decisive for clonal growth of populations and their regeneration after scraping of bottom surface. During seasonal development, maximum of aboveground biomass is produced in early summer, while underground biomass increases till autumn. Growth of the plants is limited by cutting before maximum underground biomass is attained, or by duck grazing.     

Springtail postmolt vulnerability to pseudoscorpion predation: Mechanisms and implications

Arthropod prey are expected to be more vulnerable to their predators immediately following molt. The effects of springtail (Isotoma carpenteri) postmolt vulnerability on interactions with a pseudoscorpion predator were examined in the laboratory. Springtails exposed to vials pretreated with pseudoscorpions (Apochthonius minimus) delayed molting compared to those prey that were exposed to vials pretreated only with springtails. Although their escape ability (measured as distance jumped) was unaffected by molt condition, postmolt springtails were more profitable in terms of reduced predator handling time following capture. Despite this,A. minimus did not distinguish between postmolt and intermolt prey presented at either end of a T-maze.     

Spatial and temporal pattern of colonization of Nabidae (Heteroptera) in alfalfa (Medicago sativa)

Abstract: Six species of Nabidae (Heteroptera) were collected by standardized sweep net sampling in alfalfa fields in Thuringia, Germany, from 1993 to 1995: Nabis pseudoferus , N. ferus , N. brevis , N. major , Nabicula flavomarginata and Aptus mirmicoides . Colonization of a newly cultivated field was studied over a 3-year period. The density of all the studied nabid species was low (less than five individuals per 100 sweeps) and not related to time since colonization started, or to the distance from the margin of the field. Macropterous species were able to colonize the whole field within one season. The density of one macropterous species, N. pseudoferus , varied between the years of study and was mainly affected by the harvest regime. The brachypterous species reached the margin within one season but for density it took three seasons to reach satiated values also in the centre of the field. The abundance of the brachypterous N. brevis was significantly different both between years and sampling sites. This indicates the importance of the surroundings on the succession of this species. Nabis major , a fully winged species, showed a migration pattern intermediate to macropterous and brachypterous nabids. These results suggest that the total abundance of nabid predators cannot be predicted by time or distance from the expansion source (shelter belts). The abundance of brachypterous nabid individuals can be predicted from time since colonization but is best analysed at the species level.     

Use of seedling progeny tests for genetical studies as part of a potato (Solanum tuberosum subsp. tuberosum) breeding programme

A diallel set of crosses, including selfs and some reciprocal crosses, was made between 15 parents chosen for their male fertility from those included in a tetraploid potato (Solanum tuberosum subsp. tuberosum) breeding programme at the Scottish Crop Research Institute. Seedling progeny tests were used to evaluate the progenies for non-race-specific resistance to late blight (Phytophthora infestans) in both foliage and tubers, quantitative resistance to the white potato cystnematode (PCN) (Globodera pallida) and the commercial worth of their tubers as judged by breeders' visual preference. No reciprocal differences were found. Comparisons of the selfs and crosses revealed inbreeding depression for breeders' preference, which varied among the parents from negligible to severe, whilst there were also statistically significant differences for foliage and tuber blight, but not for PCN. When the selfs were omitted from the combining ability analyses, large differences in general combining ability (GCA) were found for all four traits, and smaller differences in specific combining ability for tuber blight and breeders' preference. The only statistically significant correlation between GCAs for different traits was a favourable one of r = 0.56 between foliage and tuber resistance to late blight. It was concluded that prospects were good for simultaneously improving all four traits by multitrait genotypic recurrent selection.     

Line x tester analysis for fixed effect model in cotton (Gossypium hirsutum L.)

Summary The data from an experiment in cotton consisting of three testers and 12 lines selected deliberately have been analysed. The investigation showed higher specific combining ability variance for yield of seed cotton and number of bolls, indicating the predominance of non-additive gene action. Of parental lines, H777 was found to possess high g.c.a. effects for seed cotton yield, number of bolls and number of sympodes. Parent H842 contributed only for boll weight, whereas H655 was good general combiner for number of monopodes. There appeared to be better chances for increasing the yield by exploiting hybrid vigour for the number of bolls and boll weight. The presence of marked non-additive gene effects, in addition to additive gene effects, indicated the need for exploiting both the fixable and non-fixable components of genetic variance for increasing productivity in cotton.     

Combining ability and parental evaluation in five selected clones of sugarcane (Saccharum sp. hybrids)

Summary Five Hawaiian commercial sugarcane (Saccharum sp. hybrids) clones were crossed in a full diallel. Four morphological characters were studied in the progeny: number of millable stalks per plant, stalk diameter, stalk length, and sucrose content. A fifth character, plant volume, was calculated from stalk number, stalk diameter and stalk length. The five selected parental clones were treated as fixed variables in the analysis. General combining ability (gca) was significant for all five characters; specific combining ability (sca) was significant for stalk diameter, stalk length, and plant volume. The variance for gca was large in all progeny populations. However, the variance for sca was large in the progeny of only some clones and/or for some individual characters. Parents were evaluated on the basis of their general combining ability: clone H49-3533 had high gca for sucrose content, while clone H53-5356 had high gca for plant vigor.Published with the approval of the Director as Journal Series Paper No. 455, Experiment Station, Hawaiian Sugar Planters' Association.