Cryptic species identification: a simple diagnostic tool for discriminating between two problematic bumblebee species

Distinguishing between cryptic species is a perennial problem for biologists. Bombus ruderatus and Bombus hortorum are two species of bumblebee, which can be indistinguishable from their morphology. The former species is in decline, whereas the latter is ubiquitous. In the UK, isolated records of B. ruderatus occur amongst many for B. hortorum. For ecological studies of B. ruderatus to be feasible, the two species need to be reliably distinguishable. We present a diagnostic tool for quick and reliable identification of problematic individuals based on a restriction enzyme digest of the cytochrome b region of mitochondrial DNA.     

Influence of environmental conditions on spore dispersal and infection by Septoria nodorum

In field experiments using healthy trap plants it was found that pycniospores of S. nodorum were dispersed from diseased wheat plants whenever rain fell and occasionally in the absence of rain. Of two spring wheats tested, cv. Kolibri seemed a better ‘source’ plant and cv. Maris Butler a better ‘receptor’ when rainfall was light, but this difference was not apparent when rainfall was heavy. On 44 occasions, plants of Kolibri and M. Butler were also exposed to natural conditions immediately following artificial inoculation with S. nodorum. Infection of plants occurred on 10 occasions and was associated with the following minimum conditions: r.h, at inoculation >63%; and in the following 24 h, minimum temperature <6°C, at least 4 h with r.h. >90% and not more than 4 h with r.h. >60%.     

Rate of trypanosome killing by lectins in midguts of different species and strains of Glossina

The activity of lectins in different species of tsetse was compared in vivo by the time taken to remove all trypanosomes from the midgut following an infective feed and in vitro by agglutination tests. Teneral male Glossina pallidipes Austen, G. austeni Newstead and G. p. palpalis R-D. removed 50% of all Trypanosoma brucei rhodesiense Stephens & Fantham infections within 60 h. A 'refractory' line of G. m. morsitans Westwood took 170 h to kill 50% infections while a 'susceptible' line of the same species failed to kill 50%. Agglutination tests with midgut homogenates showed differences between fly stocks which accorded with differences in rate of trypanosome killing in vivo. Flies fed before an infective feed were able to remove trypanosomes from their midguts more quickly than flies infected as tenerals. Increasing the period of starvation before infection increased the susceptibility to trypanosome infection of non-teneral flies. Teneral flies showed little agglutinating activity in vitro, suggesting that lectin is produced in response to the bloodmeal. Feeding flies before infection also abolished the differences in rate of trypanosome killing found between teneral 'susceptible' and 'refractory' G. m. morsitans, suggesting that maternally inherited susceptibility to trypanosome infection is a phenomenon limited to teneral flies. Electron micrographs of midguts of G. m. morsitans suggest that procyclic trypanosomes are killed by cell lysis, presumably the result of membrane damage caused by lectin action.     

A Low-Moisture-Content Limit to Logarithmic Relations Between Seed Moisture Content and Longevity

Seeds of quinoa (Chenopodium quinoa Willd.), sunflower (Helianthusannuus L.) and linseed (Linum usitatissimum L.) showed negativelogarithmic relations between longevity and moisture contentsbetween 4.4 and 15.4, 3.2 and 13.0, and 3.2 and 15.5%, respectively,in hermetic storage at 65 °C. However, between 1.8 and 3.1,1.1 and 1.9, and 1.1 and 2.1%, respectively, longevity did notvary. The critical moisture content, below which further reductionin moisture content no longer increased longevity in hermeticstorage at 65 °C, for each species was 4.1, 2.04 and 2.7%,respectively. Quinoa, Chenopodium quinoa Willd., sunflower, Helianthus annuus L., linseed, Linum usitatissimum L., seed storage, improved viability equation, seed longevity, seed moisture content     

Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Development to Flowering in Four Cultivars of Rice (Oryza sativa L.)

The durations of the photoperiod-sensitive and photoperiod-insensitivephases of development to panicle emergence were estimated infour contrasting indica cultivars of rice (Oryza sativa L.)in a reciprocal-transfer experiment. Plants were grown in potsin glasshouses maintained at warmer (32/26 C) or cooler (28/20C) day/night temperatures, and the durations from sowing topanicle emergence were determined for plants moved from relativelyshort (11 h) to relatively long (13.5 h) days and vice versaat various times after sowing. Panicle emergence was delayedby long days in all cultivars, but the traditional cvs Carreonand Peta were much more sensitive to photoperiod than the moderncvs IR8 and IR36 The durations of the photoperiod-insensitivepre-inductive phase (equivalent to some definitions of the basicvegetative phase) varied from 14.4 d in cv. Carreon at 32/26C to 42.0 d in cv. IR8 at 28/20 C. In all cultivars this initialphase was of a longer duration in the cool than in the warmregime. The duration of the photoperiod-insensitive post-inductivephase was also consistently greater, but usually only slightso, at cool than relatively warm temperatures; it varied from6.8 d in cv. IR8 at 32/26 C to 272 d in cv. Carreon at 28/20C. As expected, the length of the intervening photoperiod-sensitiveinductive phase was greater in long days, but the effect oftemperature on these durations was not consistent; for example,these durations were longer in warm than in cool temperaturesin cv. 1R8 but, if anything, they were slightly longer in coolthan in warm temperatures in cv. IR36. This difference is compatiblewith previous findings that cv. IR36 has a warmer optimum temperaturefor rate of progress towards panicle emergence than cv. IR8.A subsequent reciprocal-transfer experiment with cv. Peta providedestimates of the durations of the photoperiod-insensitive andphotoperiod-sensitive phases of pre-flowering development whichwere compatible with our earlier estimates. Furthermore, panicleinitiation was found to occur after about 80% of the photoperiod-sensitiveinductive phase had elapsed. We conclude that although the durationof the photoperiod-insensitive pre-inductive phase in rice isgreater than in many other annual crops, genotypic variationin this duration may well be less than was previously deduced.We also conclude that, despite common assumptions to the contrary,photoperiod-sensitivity during rice plant development does notend at panicle initiation. Oryza sativa L., rice, panicle initiation, panicle emergence, photoperiodism, temperature     

Further studies relating chlorogenic acid concentration in carrots to carrot fly damage

The effects of first generation carrot fly larval damage on chlorogenic acid concentration in carrots was investigated in a field experiment at Wellesbourne in 1985. In a separate experiment carrots grown in the absence of a resident population of carrot fly were also analysed for chlorogenic acid; these carrots maintained low concentrations of chlorogenic acid through the summer and autumn until low ground temperatures occurred from November to January. The relationship between chlorogenic acid concentration and damage by the first generation of carrot fly was described by a similar model to the one derived previously for late-generation damage but without the cultivar dependence. This may have been because first generation damage takes place in mid-summer when soil temperature is not sufficiently low for differential chlorogenic acid production by carrot cultivars. The model supports the hypothesis that carrot fly damage increases chlorogenic acid production which subsequently encourages further attack. The increase in acid production due to the low winter temperature may be the mechanism which, in turn, induced a differential cultivar response in carrots harvested during the winter.     

The Influence of Temperature on Seed Germination Rate in Grain Legumes: II. INTRASPECIFIC VARIATION IN CHICKPEA (Cicer arietinum L.) AT CONSTANT TEMPERATURES

Positive linear relationships were shown between constant temperaturesand the rates of progress of germination to different percentiles,G, for single populations of each of five genotypes of chickpea(Cicer anetinum L.). The base temperature, T_b, at which therate of germination is zero, was 0·0°C for all germinationpercentiles of all genotypes. The optimum temperature, T_o(G),at which rate of germination is most rapid, varied between thefive genotypes and also between percentiles within at leastone population. Over the sub-optimal temperature range, i.e.from T_b to T_o(G), the distribution of thermal times within eachpopulation was normal. Consequently a single equation was appliedto describe the influence of sub-optimal temperatures on rateof germination of all seeds within each population of each genotype.The precision with which optimum temperature, T_b(G), could bedefined varied between populations. In each of three genotypesthere was a negative linear relationship between temperatureabove T_b(G) and rate of germination. For all seeds within anyof these three populations thermal time at supra-optimal temperatureswas constant. Variation in the time taken to germinate at supra-optimaltemperatures was a consequence of normal variation in the ceilingtemperature, T_o(G)—the temperature at or above which rateof progress to germination percentile G is zero. A new approachto defining the response of seed germination rate to temperatureis proposed for use in germplasm screening programmes. In two populations final percentage germination was influencedby temperature. The optimum constant temperature for maximumfinal germination was between 10°C and 15°C in thesepopulations; approximately 15°C cooler than the optimumtemperature for rate of germination. It is suggested that laboratorytests of chickpea germination should be carried out at temperaturesbetween 10°C and 15°C. Key words: Chickpea, seed germination rate, temperature