A comparison of levels of genetic polymorphism and self-compatibility in geographically restricted and widespread plant congeners

Summary Evolutionary theory predicts low levels of genetic polymorphism and high levels of self-compatibility in plant species with small ranges and few individuals. To test these predictions, I compared published data on electrophoretically detectable genetic variation and breeding systems for geographically restricted and widespread congeners in eleven genera. The restricted species exhibit significantly fewer polymorphic loci and alleles per polymorphic locus than do their widespread congeners. Although some rare species are genetically impoverished, others are nearly as polymorphic as their widespread congeners. The restricted species and their widespread congeners do not differ consistently with respect to breeding systems.     

Influence of environmental manipulation and nest-box availability on reproductive success of captive cockatiels (Nymphicus hollandicus)

Environmental conditions greatly influenced breeding induced by nest-box presentation in pair-bonded cockatiels. Thirty-six pairs were first held under nonstimulatory environmental conditions for 13 weeks. To provide potential breeding cues, photoperiod, light intensity, ambient temperature, and humidity were then increased over a 12-day period; millet was replaced by a nutritionally adequate, crumbled diet; and nest-boxes were presented. Compared to previous trials performed under more constant conditions, number of pairs laying eggs, pair-day egg production, clutch size, and chick hatch weight were significantly increased. In experiment 2, either millet or crumbled diet was fed to 36 pairs during a 9-week nonstimulatory period. Both groups were then exposed to stimulatory environments, fed crumbled diet, and presented with nest-boxes. Their reproductive performances were not different, indicating that diet change was not required to stimulate breeding. In experiment 3, birds were fed crumbled diet throughout the trial. Nest-boxes were presented to 31 pairs during nonstimulatory conditions (group 1) or to 28 pairs during the transition to stimulatory conditions (group 2). Percent of pairs laying (85.7 v. 16.7), pair-day egg production (0.279 ± 0.036 v. 0.036 ± 0.014), and clutch size (9.1 ± 1.0 v. 4.6 ± 1.2) were greater in group 2, indicating that nest-box presentation is an insufficient stimulus to evoke maximal breeding under nonstimulatory environmental conditions.     

A method of line development using doubled haploids: the single doubled haploid descent recurrent selection

Summary Different methods of line development using doubled haploids in recurrent selection are presented. They are divided into two types: recurrent selection with progeny testing and recurrent selection on the phenotype of lines. It is shown that one of the best methods of line development is based on single doubled haploid descent recurrent selection. Only one line is studied per plant of the population, and the best lines are intercrossed. Using this method it is very easy to extract lines for variety development.     

Transfer of resistance to PLRV titer buildup from Solanum etuberosum to a tuber-bearing Solanum gene pool

Summary Hybrids between Solanum etuberosum and S. pinnatisectum harboring resistance to titer buildup of potato leafroll virus (PLRV) were reciprocally crossed with tuber-bearing wild species S. acaule and S. verrucosum. A total of 47 hybrids with acaule were obtained with the aid of embryo rescue and sterile culturing of embryos from imbibing seeds. All but two hybrids with acaule had low pollen stainabilities or were pollen sterile. Hybrid seeds from crosses with verrucosum were easily obtained, and the triploid progenies were sterile. Hybrid progeny were screened for resistance to PLRV infection by viruliferous green peach aphid and for resistance to titer buildup. Although hybrids did not exhibit resistance to infection, PLRV was not detectable using ELISA. Virus was detected, however, by graft transmission to Datura stramonium. Crosses of fertile acaule-etuberosum-pinnatisectum hybrids with S. phureja, a cultivated diploid, using the latter as pollen parent, produced berries but seed did not complete development and was aborted. Rescue of immature embryos 25 days after pollination by excision from berries and sterile culture produced vigorous, pot-cultured plants. Segregation of susceptible (virus detected) and resistant (virus undetected) progenies suggests simple inheritance.     

Correlations between gametophytic (pollen) and sporophytic (seed) generations for polyunsaturated fatty acids in oilseed rape Brassica napus L.

Summary Lipids were extracted from the diploid seed and haploid pollen of Brassica napus L. Two fractions of pollen lipids, namely the diploid-specified pollen-coat and the haploid-specified internal cytoplasmic lipids were obtained. Significant correlations exist between pollen and seed generations for linoleic (182) and linolenic (183) acids. In pollen internal storage lipids, the level of 183 is positively correlated and the level of 182 is negatively correlated with the level of 183 in seed lipids. Evidence is presented that strongly supports the hypothesis that lipid biosynthesis occurs within the pollen and that synthesis is specified by haploid genes. These data support the concept of pollen selection, so that selecting among living pollen grains for superior individuals has potential as a new plant breeding tool for improving seed oil quality.     

Genetic basis of resistance to zonate leaf spot disease in forage sorghum

Summary Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.     

Differentiation Patterns of Reproductive Systems in the Genus Trillium

Abstract The differentiation patterns of reproductive systems, including breeding and pollination systems, and perennation strategies of the genus Trillium were critically studied. The pedicellate- and sessile-flowered species with different floral morphologies and ecological distributions exhibited distinct modes of reproductive systems in relation to their habitat conditions. The pedicellate-flowered species occurring in stable mesic temperate deciduous forests reproduce exclusively by seeds, while sessile-flowered species growing in the alluvial flood plain habitats depend to a large extent on vegetative reproduction to compensate for the insufficient sexual reproduction under ecologically unstable conditions, e.g., frequent disturbance due to flooding. These sessile-flowered species are characterized by low ovule numbers, subsequent low seed outputs and low fecundity levels. In contrast to the sessile-flowered species, the pedicellate-erect-flowered species showed very high seed setting rates of over 50%. Breeding experiments for four Japanese species suggest that, although they substantially possess the capability of both inbreeding and outbreeding, the high fecundity levels are maintained by predominant inbreeding system. Furthermore, resource levels in the stock organs of these species obviously determine fecundity levels. As a consequence the amount of reserved food in the rhizomes transferred to the next season is determined, which gurantees a continuous reproductive activity of a given individual plant.     

Influence of breeding conditions on longevity and fecundity ofRaphitelus maculatus [Hym.: Pteromalidae] reared under standard laboratory conditions

The rearing ofRaphitelus maculatus Walker, which oviposits through the bark onto beetle larvae has been carry out under standard laboratory conditions of 22 ± 2°C, 60% R.H. and photoperiod 16L∶8D. The host (Phloeotribus scarabaeoides Bernard) has been reared by cutting fresh branches of living olive tree on which they overwinter as adults. The effect of several rearing conditions (feeding conditions) on longevity and fecundity has been tested. The time of parasitoid and host development as well as the periods of emergence from the infested cut branches has been determined. It has been noted that both longevity and fecundity are influenced by the feeding conditions, reaching toca. double value when parasitoids were fully fed. Under standard rearing conditionsR. maculatus completes its life cycle in 17–18 days depending on sex, whereasP. scarabaeoides takes about 48 days. Finally 3 emergence periods has been observed from which the 1^st is the most important and the 3^rd is always the less significantly one, provided that the emerging brood cannot oviposits easier than the parents due to a decrease on host larvae proportion as well as on parasitoid fecundity.      

Community structure of benthic invertebrates in interior Alaskan (USA) streams and rivers

Taxonomic composition of benthic invertebrates in interior Alaskan streams and rivers is summarized from published and unpublished data. Diptera dominate the Alaskan stream fauna and constitute a larger proportion of the benthos in Alaskan streams than in streams of temperate North America. Plecoptera and Ephemeroptera are the next most abundant in Alaskan streams with Trichoptera generally very scarce. Several orders that occur regularly in streams of temperate North America are absent (or in very low abundance) in interior Alaskan streams: Hemiptera, Odonata, Megaloptera, Coleoptera. Net-spinning caddisflies, burrowing mayflies, and several families of stoneflies (Pteronarcyidae, Peltoperlidae and Perlidae) are conspicuous by their absence or extreme scarcity. Taxonomic composition varies significantly among hydrologic regions (major watersheds) and among stream types (springs, headwater streams, small rivers, and large rivers). Only two taxa (Chironomidae and Nemouridae) significantly increase in proportional contribution from south to north while many taxa decrease.