Integrated Analysis of Growth and Light Interception in Winter Lettuce II. Differences between Cultivars

‘Integrated growth analysis’ (emphasizing aspectsof crop and plant structure) and ‘light conversion analysis’(stressing the efficiency of interception and photosyntheticconversion of light) have been used to investigate the wintergrowth of different cultivars of butterhead and crisphead typesof glasshouse lettuce. Measurements from ‘Ambassador’ (large-framed butterhead),‘Renate’ (medium-sized butterhead) and ‘Cristallo’(crisphead) were made, statistical progressions were fittedto the primary data and hence estimates of all the analyticalcomponents were derived. Curves for crop growth rate, like those for most other components,followed a generally similar pattern for all three cultivars.In integrated growth analysis, the biomass curve for Ambassadorlay above the curves for the other cultivars. The weight advantagewas initially 60 per cent and it persisted with only a smallreduction (to 40 per cent) until the final harvest. Relativegrowth rate varied little between cultivars because differencesobserved in leaf area ratio were complementary to those seenin net assimilation rate. In light conversion analysis, differences in light interceptingefficiency between cultivars were not statistically significant,though Ambassador attained full interception 4 days earlierthan Renate and 6 days earlier than Cristallo. Differences inlight utilizing efficiency were small and non-significant exceptduring the post-rosette stage when the value for Renate waslower than that of either Ambassador or Cristallo. Deviationsaround the fitted curves were correlated with fluctuations inthe light regime. An assessment is made of the utility and limitations of thetwo procedures. It is concluded that both approaches can assistin analyzing the rate of dry matter production in crops or plantstands. Integrated growth analysis is advantageous when theneed arises to treat individual and population-based attributessimultaneously, while light conversion analysis provides a meansof explicitly incorporating the primary environmental variableinfluencing growth. Lactuca sativa L., lettuce cultivars, growth analysis, crop growth rate, relative growth rate, light interception, light utilization     

Light Interception and Photosynthetic Efficiency in Some Glasshouse Crops

Productivity of glasshouse crops is strongly limited by lightreceipt, and efficient interception and use of light in photosynthesisis correspondingly important. Mature row crop canopies of cucumberand tomato intercepted about 76% of the light incident on theirupper surfaces; about 18% was lost through gaps between therows. Light transmitted through the entire depth of the canopywas reflected back by white plastic on the ground, so that thelower surface of the canopy received approximately 13% of thelight incident on the upper surface. The light flux incidenton the sides of these canopies (c. 2m tall and 6m x 16m in area)amounted to some 20–30% of that incident on the uppersurface. About 32% of daylight falling on the glasshouse (c.9m x 18m in area) was intercepted by the glasshouse structureand glazing; of the 68% entering the house, some fell on headlandsoccupying 35% of the glasshouse area. The loss of light to headlands,and the gain from canopy side-lighting, would be relativelysmaller for larger glasshouses. At near-ambient CO₂ concentrations, net photosynthetic ratesof the cucumber canopy were comparable to those of closed canopiesof other glasshouse and field crops which have maximum lightconversion efficiencies of 5–8µg CO₂ J^–1 at50–200 W m^–2 incident light flux density. Efficiencydecreases only slightly with stronger light. Glasshouse cropswith CO₂ enrichment to 1200 vpm achieve conversion efficienciesof 7–10µg CO₂ J^–1. Efficiencies of utilizationof intercepted light, on an energy basis, reach 6–10%in various field and glasshouse crops with near-ambient CO₂,and reached an exceptional 11% for the cucumber canopy. Glasshousecrops with CO₂ enrichment achieve maximum efficiency of lightenergy utilization between 12% and 13%. Key words: Glasshouse cucumber and tomato, light interception and utilization, photosynthetic efficiency, row crops     

The effect of short-term weather fluctuations on temperatures inside lizard nests, and on the phenotypic traits of hatchling lizards

Can short‐term stochastic variation in local weather conditions modify the thermal conditions inside lizard nests, and thus (potentially) the developmental rates, hatching success, and phenotypic traits of hatchlings from these nests? This hypothesis requires that (i) natural nests are poorly buffered thermally, such that ambient regimes affect temperatures inside the nest, and (ii) short‐term thermal variations modify attributes of the offspring. Field data on natural nests of the sub‐alpine skink Bassiana duperreyi confirm the existence of this first effect, and laboratory experiments substantiate the latter. Exposure to warmer‐than‐usual temperatures for 2 wéeks during the 9‐ to 16‐wéek incubation period doubled hatching success, and significantly modified hatchling phenotypes (hatching dates, offspring size and locomotor performance). The proportion of development completed prior to this exposure influenced the degrée of response. Exposure to a brief ‘window’ of higher‐than‐usual temperatures soon after oviposition had more effect on hatching time, egg survival and hatchling phenotypes than if the exposure occurred later in development. Thus, minor variations in weather conditions during incubation may have substantial effects on reptile populations.     

The overwintering of cereal aphids on Gramineae in southern England, 1977–1980

Cereal aphids were sampled monthly on graminaceous host plants on farmland in Hampshire, UK from September 1977 to April 1980. Sitobion avenae overwintered anholocyclically on most types of Gramineae, particularly seedling grass crops and small-grain cereals. S. fragariae was probably mainly holocyclic on Rubus spp. Large summer populations of Metopolophium dirhodum were probably derived from holocyclic colonies on roses. M. festucae (subsp. cerealium) appeared to overwinter only anholocyclically, and was found mainly on mature grass crops and grasses in hedgerows. Rhopalosiphum padi was the most numerous species in autumn and overwintered anholocyclically in all three winters studied. R. insertum and R. maidis were rare and did not appear to survive the winter anholocyclically on graminaceous hosts.     

A NEW SPECIES OF THE WOMBAT WARENDJA FROM LATE MIOCENE DEPOSITS AT RIVERSLEIGH, NORTH-WEST QUEENSLAND, AUSTRALIA

Abstract:  A new species of the plesiomorphic wombat Warendja is described. Warendja encorensis sp. nov., the second species to be attributed to this genus, is known from a single fossil locality (Encore Site) at Riversleigh, north-west Queensland. Specimens of W. encorensis are limited to isolated teeth, two mandibular fragments and a maxillary fragment. Two molars preserve the unworn crown morphology. Encore Site has been estimated to be late Miocene in age, making these the only known specimens of Warendja to be clearly older than Pleistocene. Warendja encorensis is also the first described species of wombat from Miocene deposits to which hypselodont teeth have been attributed. It differs from W. wakefieldi in its larger size, distribution of enamel, and in details of the incisor and premolar morphology.     

Identification and characterization of simple sequence repeat markers from Brassica napus expressed sequences

The availability of expressed sequence data derived from gene discovery programs enables mining for simple sequence repeats (SSR), providing useful genetic markers for crop improvement. These markers are inexpensive, require minimal labour to produce and can frequently be associated with functionally annotated genes. This study presents the development and characterization of 24 expressed sequence tags (EST)‐SSR markers from Brassica napus and their cross‐amplification across Brassica species. The markers show reliable amplification, genome specificity and considerable polymorphism, demonstrating the utility of EST‐SSRs for genetic analysis of wild Brassica populations and commercial Brassica germplasm.     

Long-term survival despite low genetic diversity in the critically endangered Madagascar fish-eagle

The critically endangered Madagascar fish-eagle ( Haliaeetus vociferoides ) is considered to be one of the rarest birds of prey globally and at significant risk of extinction. In the most recent census, only 222 adult individuals were recorded with an estimated total breeding population of no more than 100–120 pairs. Here, levels of Madagascar fish-eagle population genetic diversity based on 47 microsatellite loci were compared with its sister species, the African fish-eagle ( Haliaeetus vocifer ), and 16 of these loci were also characterized in the white-tailed eagle ( Haliaeetus albicilla ) and the bald eagle ( Haliaeetus leucocephalus ). Overall, extremely low genetic diversity was observed in the Madagascar fish-eagle compared to other surveyed Haliaeetus species. Determining whether this low diversity is the result of a recent bottleneck or a more historic event has important implications for their conservation. Using a Bayesian coalescent-based method, we show that Madagascar fish-eagles have maintained a small effective population size for hundreds to thousands of years and that its low level of neutral genetic diversity is not the result of a recent bottleneck. Therefore, efforts made to prevent Madagascar fish-eagle extinction should place high priority on maintenance of habitat requirements and reducing direct and indirect human persecution. Given the current rate of deforestation in Madagascar, we further recommend that the population be expanded to occupy a larger geographical distribution. This will help the population persist when exposed to stochastic factors (e.g. climate and disease) that may threaten a species consisting of only 200 adult individuals while inhabiting a rapidly changing landscape.     

Genetic variation and reproductive mode in populations of Simocephalus vetulus (Branchiopoda: Cladocera) from the East Midlands of England

SUMMARY. 1. Five populations of the cladoceran Simocephalus vetulus (O. F. Muller) examined by enzyme electrophoresis at four to five loci revealed high levels of genetic variation.
2. The one intermittent population had genotype frequencies in Hardy Weinberg equilibrium, the three permanent populations showed deviations from equilibrium of varying magnitude. The fifth population was fixed for a single clone, and was possibly recently derived from a single ephippial hatchling.
3. Laboratory breeding experiments confirmed that this species is a cyclic parthenogen.