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.      

Biological studies upon Enchytraeus variatus Bouguenec & Giani 1987 in breeding cultures

The life history of an enchytraeid worm, Enchytraeus variatus, was studied under laboratory conditions at 18–22 °C. This species can reproduce simultaneously by asexual (architomy) or sexual reproduction. The number of ova per cocoon varies from 5 to 20 (x = 10.9). The generation period (from cocoon to next cocoon) varies from 14 to 39 days (x = 26.1) according to the period of the year. The number of generations per year is between 7.3 and 26.1 (x = 14). A mature worm can lay between 23.7 and 25.8 cocoons during its life (254 days as maximum observed) at a mean rate of 0.12 cocoon worm^–1 day^–1. Experimental cultures were carried out to determine the structure, density and biomass of the populations. A maximal density of 1 396 314 worms was recorded after 85 days of culture. Net production reached 21.48 g m^–2 day^–1 after 26 days in a culture initiated from cocoons.     

New variation and biosystematic patterns detected by allozyme and morphological comparisons inLimnanthes sect.Reflexae (Limnanthaceae)

Sixty-one populations ofLimnanthes sect.Reflexae were surveyed for variation at 19 allozyme loci and reassessed for their morphological diversity and biosystematic relationships. Cluster analysis of allozyme data at individual population level provided evidence for a fairly good fit with the earlier systematic work on this genus but both morphological and allozyme data together defined some new clusters as well as exceptional entities. For example, only var.rosea of the fourL. douglasii varieties described byMason (1952) on the basis of geographical distribution, flower color and leaf morphology, remained as a distinct entity; the others were realigned along new geographic boundaries.L. striata appeared to have two well-developed subgroups, one of which was closely related to theL. douglasii complex. Further ecogeographic and hybridization studies are needed to fully describe these new phenetic findings in the context of phylogenetic inference. SectionInflexae was readily distinguished from sect.Reflexae by several diagnostic loci, thus supporting the validity of this division. Interspecific variation levels and population differentiation inLimnanthes were high when compared to other plant taxa, possibly indicating highly dynamic evolutionary processes for which variable habitats and extreme subdivision within species have been suggested as explanations.     

Improving nitrogen fixation in legumes by plant breeding; the relevance of host selection experiments in red clover (Trifolium pratense L.) and subterranean clover (T. subterraneum L.)

Summary This paper reviews (i) basic studies on the genetics of symbiosis in red clover (a self-sterile species) and subterranean clover (cleistogamous) and (ii) work on selection and plant breeding to increase nitrogen fixation in these hosts.Symbiotic effectiveness in red clover is influenced by many major and minor genes. The highly effective phenotype is inherited in a complex manner associated with early nodulation and the formation of large amounts of persistent bacteroid-containing tissue. Lines bred to fix more nitrogen with one strain ofRhizobium trifolii do so with most but not all other strains examined. They also show slightly increased vigour when grown on nitrate. The highly effective response is correlated with abundant nodulation and an early flowering habit, the evidence from breeding studies indicating that this correlation is not absolute. Normally effective and highly effective nodules have the same specific nitrogenase activities. The expression of the highly effective response is relatively little affected by environmental factors (temperature, light intensity, day length, supplementary carbon-di-oxide). Inbreeding substantially degrades the symbiotic response.Heterosis is shown in crosses between cultivars of subterranean clover but otherwise selection to increase effectiveness in this host was unsuccessful.The relevance of these results (and their physiological aspects) for the improvement of grain legumes is discussed.     

Genetic structure, relatedness and helping behaviour in the yellow mongoose in a farmland and a natural habitat

The yellow mongoose Cynictis penicillata is a facultatively social species and provides an opportunity to study the evolution of social behaviour. We examined genetic structure, relatedness and helping behaviour in the yellow mongoose in natural habitat in the Kalahari Desert, where the species lives in small family groups of up to four individuals and shows no cooperative breeding; and in farmland in the Western Cape Province of South Africa, where they live in larger groups of up to 13 individuals, engage in numerous social interactions and show cooperative breeding. The farmland population showed significant inbreeding, and lower genetic variability than the desert population, but there was no evidence of a recent population bottleneck. The genetic relatedness between individuals within social groups and that between future potential helpers and pups were higher in the farmland population than in the desert population. However, based on a limited sample, helping effort (in the farmland population) was not preferentially directed towards kin. Thus, the origin of helping in the farmland population is consistent with kin selection, but in the absence of kin discrimination, future research should investigate whether long-term breeding opportunities or group augmentation contribute to maintaining cooperative breeding in this population.     

Effects of geolocator attachments on breeding parameters of Lesser Kestrels

ABSTRACT Light level geolocators, also known as GLS loggers, are electronic devices intended for tracking the location of wide‐ranging animals using ambient light to estimate latitude and longitude. Miniaturized geolocators that can be used on relatively small migratory birds have recently become available, but little is known about the potential harmful effects of geolocators on birds. We examined the possible effects of 1.5‐g geolocators (dimensions: 21 × 6.5 × 9 mm) on the breeding success and survival of migratory Lesser Kestrels (Falco naumanni). During the 2007 breeding season, kestrels were fitted with geolocators using two attachment methods (Teflon wing harnesses and darvic bands), and geolocators were removed in 2008 after the birds returned to the breeding grounds. We found no differences in the breeding success of control and tagged pairs during the 2007 breeding season, but tagged pairs had greater fledgling mortality in the following breeding season. Furthermore, nestlings of tagged individuals had higher triglyceride and uric acid concentrations in their blood than control nestlings during the breeding season following tagging. As for return rates, 75% of tagged birds came back to the colony after the nonbreeding period, a proportion similar to that reported in previous studies. Although back‐mounts are slightly heavier and require more skill to attach, we recommend their use on small migratory raptors because most leg‐mounted geolocators in this study were damaged or rendered useless by dirt obscuring the light sensor.     

Local breeding experience and the reproductive performance of Tree Swallows

ABSTRACT The potential advantages of repeated breeding at a particular location should improve reproductive performance in long‐lived species of birds. However, for short‐lived species, natural selection should favor individuals that most quickly develop competency in reproduction. Therefore, we hypothesized that local breeding experience beyond the first breeding attempt at a particular location would have little effect on subsequent reproductive performance of Tree Swallows (Tachycineta bicolor), a species where about 50% of adults breed only once in their lives. We tested this hypothesis using data collected from Tree Swallows in Michigan from 1993 to 2002. Because we were specifically interested in examining the effects of local breeding experience on reproductive performance, we restricted our analyses to after‐second‐year (ASY) females and their mates that we first encountered as breeders. Consistent with our hypothesis, we found no relationship between repeated local breeding experience and the reproductive performance of ASY female Tree Swallows and their mates as measured by clutch size and number of fledged young. However, pairs with more combined total local experience tended to lay eggs earlier in the season. These results suggest that Tree Swallows may benefit from breeding site fidelity, not because repeated local experience improves reproductive performance as measured by the production of fledglings, but because returning individuals acquire nest cavities earlier and are able to begin breeding earlier, providing time to renest in case of early nest failure.     

圆唇苣苔属(Gyrocheilos)花柱侧偏弯折现象及其传粉适应机制

圆唇苣苔属(Gyrocheilos)是苦苣苔科的中国特有属,有5种,全部狭域分布在我国西南及广东的高海拔山区。圆唇苣苔属所有物种的花柱侧偏且花柱顶端呈90°弯折,使得柱头位于花开口的中央位置。这种独特的侧偏弯折花柱结构,说明圆唇苣苔属可能有着特殊的演化历史和适应机制。为揭示这种特殊的花柱侧偏弯折现象的发生范围、发育过程及其传粉适应机制,该研究在圆唇苣苔(Gyrocheilos chorisepalus)、折毛圆唇苣苔(G. retrotrichus)和微毛圆唇苣苔(G. microtrichus)3个物种中开展了花部综合征观察,并研究了广东大雾岭保护区内的折毛圆唇苣苔花发育过程、花部特征和繁育系统以及传粉过程。结果表明:(1)微毛圆唇苣苔只有花柱左偏弯折现象,而圆唇苣苔和折毛圆唇苣苔虽然大部分花是花柱左偏弯折,但在部分个体中出现了少量的花柱右偏弯折现象(占种群总花数的2%～3%)。(2)传粉观察发现,折毛圆唇苣苔在花蕾期即出现了花柱弯折现象,2个可育雄蕊的花药合生、位于花冠筒喉部中央位置,与侧偏花柱不存在左右镜像对称关系。(3)折毛圆唇苣苔的花粉胚珠比(P/O)为456.98±15.55,属于兼性异交繁育系统。折毛圆唇苣苔存在一定的传粉限制,自交授粉可以结实,但异交种子萌发率更高,可能存在近交衰退。(4)折毛圆唇苣苔的访花昆虫较少,访花频率较低,主要访花昆虫有隧蜂、熊蜂、食蚜蝇等; 熊蜂体型较大,访花时降落在弯折花柱和花瓣下唇,胸部侧面及下部能有效接触到柱头。(5)反射率结果显示,折毛圆唇苣苔花瓣反射波长范围集中在紫光和蓝紫光区域,花冠的反射波长范围与蜂类视觉范围一致且花冠筒外侧和花瓣下唇的反射强度最大,更容易吸引蜂类落置在花冠宽大的下唇; 圆唇苣苔属的花柱侧偏弯折现象可能来自近缘的长蒴苣苔属(Didymocarpus)的花柱下弯现象或镜像花(mirror-image flowers)。综上认为,这种侧偏弯折的花柱,可能通过提供昆虫降落平台,使得柱头位于花开口中央和花瓣下唇的上方位置,提高了柱头接触访花昆虫的概率,是适应高海拔地区低频率访花者的一种机制。