Screening of onion seed sets for resistance against new Iranian isolates of Fusarium oxysporum f. sp. cepa

Root and basal rot disease (RBR) of onion, Fusarium oxysporum f. sp. cepa (FOC), is one of the most important diseases, which cause tremendous losses in onion-growing areas worldwide. In this survey, various onion genotypes, including eight main and dominant Iranian seed sets and two exotic ones, were tested against FOC incidence in greenhouse and field conditions of various growing stages. The incidence of the RBR was determined at three stages, such as early, flowering and seed-setting stages, on the basis of disease severity. The genotypes reacted differentially to FOC within and between various stages with a very high significant level. The genotypes were classified in five scoring scales, accordingly. Highly infected ones tended to be associated with the highest mean scores of 75–100% severity and the least infected genotypes had the lowest scores of 0–10%. Moreover, the examined genotypes were ranked from 1 to 10 according to their markedly differing reactions to FOC at various stages. Variance and cluster analysis also showed similar results among the genotypes with various levels of infections. There was a direct, positive and enhancing correlation for every genotype to infection as the growing stages were reaching to the maturing stage.     

Definition and Application of a Histopathological Scoring Scheme for an Animal Model of Acute Mycoplasma pneumoniae Pulmonary Infection

A histopathological scoring system was developed to assess the pathology of acute Mycoplasma pneumoniae pulmonary infection in a hamster model. A final score per animal (ranging 0–26) is obtained by averaging scores from each lung which have been accumulated by the addition of subscores from the assessments of quantity and quality of peribronchiolar and peribronchial infiltrates, luminal exudates, perivascular infiltrates, and parenchymal pneumonia. The scoring scheme was then applied to test the ability of a heat-killed inoculum to induce pulmonary pathology and to the trial of a 43 kDa protein-associated antigen as a vaccine immunogen. A heat-killed inoculum delivered by both intratracheal and intranasal routes did not induce pulmonary pathology compared to a live inoculum (respective mean scores 0.1, 6.7; P<0.01). Animals prevaccinated with the 43 kDa antigen developed an accentuated pathological response after live challenge compared to those unvaccinated (respective mean scores 16.8, 5.8; P=0.00007). Hypersensitization to growth medium components may, however, have contributed to the accentuated disease since the lungs of vaccinated animals challenged with culture-negative media also were affected (mean score 5.4). Reproducibility of the scoring system was measured by duplicate reading of histology slides which were randomized to the observer upon the second reading (r=0.93; P=0.000009). The scoring system has the ability to differentiate disease severity in small groups of animals.     

Is floristic quality assessment reliable in human-managed ecosystems?

The Floristic Quality Analysis (FQA) is a method to assess the quality of a flora based on the assignment of scores to plant species and subsequent calculation of indices. This method is widely applied, but inadequate investigation has been devoted to test its potential problems due to human factors. This work is aimed to specifically test how the human factor can affect the calculation of the FQA indices, by addressing three questions: (i) Are the scores given to plant species consistent among different experts?; (ii) Are the floristic quality indices calculated by different experts consistent in ordering individual sites?; and (iii) Does the use of an appropriate statistics change the ordering of individual sites? To answer these questions, a list of species obtained in 136 plots in central Italy was submitted to nine experts, who scored each species. The FQA indices were then calculated from the scores of each of the experts. The results showed that: (i) the scores given to the species by the experts were not consistent and the derived floristic quality indices were statistically different; (ii) the floristic quality indices calculated for each plot were significantly different among experts, but the ranking of these plots based on their floristic quality was rather consistent; and (iii) the use of ordinal statistics, which is more adequate for this type of data, did not change the results. This study demonstrated that the Floristic Quality Analysis does not provide reliable and objective tools to assess the quality of the flora in a human-managed ecosystem. The application of these indices should be preceded with resolution of the methodological problems associated with the use of inappropriate statistics, and by procedures to reduce the degree of subjectivity in assigning the CC scores.     

The effect of weather on the life cycle of the speckled wood butterfly Pararge aegeria

ABSTRACT.

• 1 Pararge aegeria (L.) is a very unusual butterfly of Britain, having a long period of adult activity, from April to October, without discrete flight periods. In central Britain it overwinters in two stages: pupae and third instar larvae, both being the progeny of late summer adults. Other larval stages die at the onset of cold winter weather. The overwintering stages give rise to the first adult generation in spring, split into two parts.
• 2 Different temperature regimes affect development rates in larvae and pupae differently. Late larval development is more rapid than that of pupae at low temperatures, thus in cool spring weather the overlap of the two parts of the first generation is greater than in warm spring weather.
• 3 Adults emerge continuously throughout the summer because larval development rates are variable. When summer is warm there is a partial third generation but when cool only two.
• 4 The timing of the end of the flight period is consistent with the hypothesis that both temperature and photoperiod are important in determining whether individuals enter diapause or develop directly. In warm summers larvae develop beyond a sensitive stage before critical daylength is reached and develop directly, but in cool summers individuals enter diapause because they are at the sensitive stage when critical daylength is reached.
• 5 It is suggested that variable development rates can facilitate parasite escape in autumn and increase the probability of adult success when weather is unpredictable, and this strategy is maintained because these benefits are greater than the cost of winter mortality of larvae.

     

Development of powdery mildew on leaves of several barley varieties at different growth stages

On detached leaves and intact plants of several barley varieties at different growth stages, lower percentages of germinated conidia of Erysiphe graminis f.sp. hordei penetrated the host and initiated infection on the abaxial than adaxial surface. More and larger E. graminis colonies developed on the adaxial surface and these comprised more densely packed hyphae and produced more conidiophores than did colonies on the abaxial surface. These results are consistent with the observation that there is usually more powdery mildew on the adaxial than abaxial surface of barley leaves in the field. Smaller proportions of germinated E. graminis conidia penetrated and infected the host on leaves of adult or near-adult plants than on those of seedlings or juvenile plants. Older plants also supported fewer, smaller and less dense colonies with less sporulation than young plants. The effects of growth stage of the host plant on development of powdery mildew were much greater in some barley varieties, and with some E. graminis isolates, than others.     

Studies on Entomophthora in populations of Aphis fabae on field beans

The population of Aphis fabae on field beans at a site in Highfield, Rothamsted in 1973 reached its peak 1 wk earlier than that at an equivalent site in Mill Dam Close, Woburn, 29 km NW of Rothamsted. Epizootics of Entomophthora caused weekly maximum mortalities of adult apterae of 71% at Highfield and 67% at Mill Dam Close. These epizootics and the periodicity of Entomophthora conidia in the air closely paralleled the development of the aphid population. There was little evidence of a consistent relationship between Entomophthora infection and any of the weather factors considered. At both sites most mortality was caused by E. planchoniana though many aphids were killed by E. aphidis and E. obscura. E. fresenii and E. virulenta killed very few aphids. Most conidia in the air were of the E. aphidis-type. Up to 44% of alatae emigrating from bean crops were infected with Entomophthora, confirming that aphid migration is an important means of distributing the fungi. Aphid numbers rose to more than 1600/plant at both sites, in spite of the action of Entomophthora, and would probably have been less had the fungi been more abundant earlier in the season.     

崇明东滩湿地芦苇种群内功能性状及生态对策变异分析

植物种群功能性状及生态对策变异对其自身环境适应能力及群落结构具有重要影响。该文基于崇明东滩湿地芦苇(Phragmites australis)种群内3个小种群不同发育时期分株集合的多项性状指标,分析了其性状及生态对策变异,并基于CSR、LHS生态对策体系,对各小种群的生态对策进行了排序。结果表明, 3个芦苇小种群的21项性状指标及C、R对策得分均存在显著差异。在LHS体系中,以比叶面积(11.5 mm2/mg)、株高(175 cm)和花序干质量(4 g)为分界线,可对3个小种群进行区分。处于生殖生长期的芦苇分株具有更大的植株大小、更高的叶片干物质含量及S对策得分,而处于营养生长期的分株则具有较小的植株大小、较大的比叶面积及R对策得分。总体而言,崇明东滩湿地3个芦苇小种群间及各小种群内处于不同生长发育阶段的分株集合间,都存在显著的性状差异及生态对策差异,且二者的差异模式基本吻合。芦苇种内性状及生态对策变异特征,可为该区芦苇种群的生态保育和恢复实践提供重要的理论参考和技术支撑。     

QTLs conditioning early growth in a soybean population segregating for growth habit

 There are both economic and environmental reasons for reducing the use of herbicides for weed control in soybean [Glycine max (L.) Merr.] fields. Optimizing crop competitiveness can reduce reliance on chemical weed control. Fast and vigorous early growth and rapid canopy development can be effective in suppressing weed infestation of crop plants. The purposes of this study were to identify and molecularly map the quantitative trait loci (QTLs) conditioning soybean plant height and canopy width during the early vegetative stages of soybean growth. A restriction fragment length polymorphism (RFLP) linkage map was created using 142 markers and 116 F₂-derived lines from a cross of ‘S100’בTokyo’. The parents and the 116 F₂-derived lines were evaluated in the greenhouse and in the field at Athens, Ga., in 1996 and 1997. Combined over environments, Tokyo averaged 41 and 17% taller plants than S100 at the V7 and V10 stages of development. Transgressive segregation was observed among the progeny at both stages. Based on single-factor analysis of variance (ANOVA), three and four independent RFLP loci were associated with plant height at the V7 and V10 stages, respectively. All three loci detected [on linkage groups (LGs) C2 and F, and unlinked] at the V7 stage were also detected at the V10 stage along with one additional independent locus on LG E. The Tokyo allele contributed to increased plant height at all loci except at the unlinked locus. Three QTLs (on LGs C2, E, and F) were consistent across environments, three (on LGs C2 and F, and unlinked) were consistent across stages of plant development, and two (on LGs C2 and F) were consistent both across environments and stages of plant development. Within each stage of development, there was no interaction among the independent loci, and the respective loci together explained most of the variation in the traits. Three independent RFLP loci were associated with canopy width at the V10 stage, of which one was unique to the trait, while the remaining loci (on LGs C2 and F) were in common with the independent loci for plant height. Canopy width had a strong correlation (r=0.87) with plant height at the V10 stage. However, mature plant height, lodging, or seed weight had no phenotypic or QTL association with early plant height or canopy width. Received: 10 May 1998 / Accepted: 13 July 1998     

Inheritance Characteristics of Microsatellite DNA Loci in Experimental Families of Japanese Flounder Paralichthys olivaceus

Allele segregating patterns of microsatellite DNA loci in 5 experimental families of Japanese flounder Paralichthys olivaceus and genotype frequencies for deviation from Hardy-Weinberg expectations (HWE) in natural P. olivaceus populations were studied to assess inheritability. Of the 12 microsatellite loci examined, 1 locus had a possibility of scoring errors of heterozygous individuals caused by unreproducible polymerase chain reaction amplifications of a particular allele. At the remaining 11 loci, almost all of alleles were segregated according to Mendelian transmission, and observed genotype frequencies in natural populations were consistent with HWE. The results demonstrated here would provide useful information supporting the suitability of these microsatellite loci as inheritable P. olivaceus genetic markers. Received September 25, 2000; accepted March 1, 2001     

BISAP、Ranson和APACHEⅡ评分系统对高脂血症性急性胰腺炎患者病情和预后的评估价值

目的:研究急性胰腺炎床旁指数(BISAP)、Ranson和急性生理与慢性健康状况Ⅱ(APACHEⅡ)评分系统对高脂血症性急性胰腺炎(HLAP)患者病情和预后的评估价值。方法:对2015年3月~2019年3月期间我院收治的160例HLAP患者的临床资料进行回顾性分析,其中轻度患者113例、中度患者26例、重度患者21例、并发症患者14例、死亡患者5例。采用Pearson相关检验三种评分与病情的相关性,分析三种评分与中/重度患者、并发症患者、死亡患者的关系,并通过受试者工作特征(ROC)曲线分析三种评分评估HLAP患者病情及预后的价值。结果:BISAP、Ranson、APACHEⅡ三种评分均随病情的加重呈上升趋势,有显著的正相关关系(P<0.05)。三种评分对HLAP患者病情严重程度具有较高的评估价值,曲线下面积(AUC)均在0.76以上,敏感度和特异度均高于0.7。BISAP评分≥3分、Ranson评分≥3分、APACHEⅡ评分≥8分的中/重度患者、并发症患者及死亡人数占比均分别高于BISAP评分<3分、Ranson评分<3分、APACHEⅡ评分<8分的患者(P<0.05)。三种评分对排除并发症和死亡的预测有较高价值,其特异度均在0.9以上。结论:BISAP、Ranson和APACHEⅡ评分系统应用于HLAP患者的病情和预后评估中均存在一定价值,值得临床推广应用。     

Response of a Native Perennial Grass Stand to Disturbance in California's Coast Range Grassland

To assess the potential for enhancing an existing stand of native perennial grasses on a California Coast Range Grassland site, we experimentally manipulated the seasonal timing and presence of grazing for 3 years (1994 through 1996) and of autumn burning for 2 years (1994 and 1995) and measured species cover for 6 years (1993 through 1998). We subjected the species matrix to classification (TWINSPAN) and ordination (CCA) and tested the ordination site scores as well as diversity indices with linear mixed effects models. Four distinct plant community groups emerged from the classification. Two of these were dominated by annual grasses and two by perennial grasses. No treatment effects were observed on diversity. For composition, temporal and spatial random effects were important mixed effects model parameters, as was the fixed effect covariate, pre‐treatment CCA site score, indicating the importance of random environmental variation and initial starting conditions. Incorporation of these random effects and initial condition terms made for more powerful tests of the fixed effects, grazing season, and burning. We found no significant burning effects. Grazing removal imparted a shift in plant community from more annual‐dominated toward more perennial‐dominated vegetation. Individual perennial grass species responded differently according to genus and species. Nassella spp. increased gradually over time regardless of grazing treatment. Nassella pulchra (purple needlegrass) increase was greatest under spring grazing and N. lepida (foothill needlegrass) was greatest with grazing removal. Danthonia californica (California oatgrass) had little response over time under seasonal grazing treatments, but increased with grazing removal. Under relatively mesic weather conditions it appears that grazing removal from Coast Range Grasslands with existing native perennial grass populations can increase their cover. However if N. pulchra is the sole existing population, spring season‐restricted grazing should be equally effective at enhancing cover of the native grass species.     

Plant defence as a complex and changing phenotype throughout ontogeny

Background and Aims Ontogenetic changes in anti-herbivore defences are common and result from variation in resource availability and herbivore damage throughout plant development. However, little is known about the simultaneous changes of multiple defences across the entire development of plants, and how such changes affect plant damage in the field. The aim of this study was to assess if changes in the major types of plant resistance and tolerance can explain natural herbivore damage throughout plant ontogeny.Methods An assessment was made of how six defensive traits, including physical, chemical and biotic resistance, simultaneously change across the major transitions of plant development, from seedlings to reproductive stages of Turnera velutina growing in the greenhouse. In addition, an experiment was performed to assess how plant tolerance to artificial damage to leaves changed throughout ontogeny. Finally, leaf damage by herbivores was evaluated in a natural population.Key Results The observed ontogenetic trajectories of all defences were significantly different, sometimes showing opposite directions of change. Whereas trichome density, leaf toughness, extrafloral nectary abundance and nectar production increased, hydrogen cyanide and compensatory responses decreased throughout plant development, from seedlings to reproductive plants. Only water content was higher at the intermediate juvenile ontogenetic stages. Surveys in a natural population over 3 years showed that herbivores consumed more tissue from juvenile plants than from younger seedlings or older reproductive plants. This is consistent with the fact that juvenile plants were the least defended stage.Conclusions The results suggest that defensive trajectories are a mixed result of predictions by the Optimal Defence Theory and the Growth–Differentiation Balance Hypothesis. The study emphasizes the importance of incorporating multiple defences and plant ontogeny into further studies for a more comprehensive understanding of plant defence evolution.     

Mite parasitization on armored scale insects: host suitability

Suitability of three armored scale insects (Homoptera: Diaspididae), their stages, the host plants and their parts, for the parasitic miteHemisarcoptes coccophagus Meyer was investigated. The studied scales were chaff scales,Parlatoria pergandii Comstock andP. cinerea Hadden, infesting grapefruit and orange orchards, latania scale,Hemiberlesia lataniae (Signoret), and oleander scale,Aspidiotus nerii Bouche occurring on acacia (Acacia cyanophylla) branches and leaves. Host suitability was evaluated by mite survival, mean intensity (active mites/attacked scales) and fecundity. It was highest on latania scale, lowest on oleander scale and intermediate on chaff scales. Results of laboratory experiments were consistent with these field findings: while developing on oleander scale, mites suffered 3× higher mortality, and their generation time was twice as long as on latania scale; the full egg clutch on the latter was high whereas on oleander scale it was negligible. Our data suggest that ovipositing females of latania and oleander scales, but not of chaff scales, are more suitable hosts than young scale females and the latter more suitable than immature stages. No direct effects of acacia plant parts on host suitability were detected. Citrus species affected chaff scale suitability for the mite through their effect on host diaspidid size. The ability ofH. coccophagus to control pestiferous diaspidids may depend on the specific host scale, its age structure and the specific host plant. The implications of these findings for the biological control of armored scale insects are discussed.     

On-site growth response of a desert ephemeral plant, <Emphasis Type="Italic">Plantago minuta</Emphasis>, to indigenous arbuscular mycorrhizal fungi in a central Asia desert

Desert ephemeral plants play a key role in desert ecosystem stability and environmental conservation. To determine the effect of indigenous arbuscular mycorrhizal (AM) fungi on the growth and P uptake of the desert ephemeral Plantago minuta, we conducted two on-site experiments in the Gurbantunggut Desert. The co-development of a pre-isolated indigenous AM fungus, Glomus etunicatum, with the ephemeral was also investigated. The results showed that both the single fungus and the indigenous AM fungal community enhanced the growth and P uptake of P. minuta. The phenological phases of P. minuta were highly consistent with the phases of the indigenous AM fungus, G. etunicatum, indicating that both symbiotic partners seem to be able to sense the changes in local weather, which might be an important trait for the survival of both plant and fungus in desert environments. The development of host plant and indigenous AM fungi were interdependent in the desert.     

Incidence of fungal species associated with leaf rot disease of coconut palms in relation to weather and the stage of lesion development

Leaf rot disease (LRD) of coconut occurs in Kerala State, India, and is generally severe during the monsoon, a time of high rainfall and r.h. and low maximum temperature. The pathogenic fungi Colletotrichum gloeosporioides, Exserohilum rostratum, Gliocladium vermoeseni, Fusarium solani, F. moniliforme var. intermedium, Thielaviopsis paradoxa and Rhizoctonia solani were among 14 species isolated from spindles of palms with LRD in multiple samplings of two experiments, each lasting 1 year. Co-occurrence of fungi was observed in 70–76% of spindles although leaf pieces yielded mostly individual fungi irrespective of the stage of lesion development. C. gloeosporioides occurred most frequently on early lesions. The incidence of C. gloeosporioides was most strongly correlated with rainfall and r.h. and, negatively, with maximum temperature and hours of sunshine. It was the fungus isolated most commonly during the monsoon and occurred on early lesions more frequently than on advanced lesions (determined in one experiment). C. gloeosporioides is thus implicated as the principal pathogen involved in initiation of the disease during monsoons. Its relatively low incidence in the dry season suggests a quiescent phase between periods of parasitic activity. E. rostratum was isolated less frequently and its incidence was less strongly or consistently correlated with weather or with the stage of lesion development. Fusarium spp. and R. solani were associated with dryer weather and higher temperatures. The Fusarium spp. were the fungi isolated most commonly during part of the dry season (January-March) and occurred more on early than on advanced lesions at one sample (January) when they may have been primary disease agents. R. solani was also more frequent on advanced lesions and may be principally a secondary coloniser of established lesions. The incidence of other fungi, which occurred less frequently and more sporadically, was not associated with weather or consistently with different stages of lesion development.     

Transgenic tobacco revealing altered bacterial diversity in the rhizosphere during early plant development

The rhizosphere constitutes a complex niche that may be exploited by a wide variety of bacteria. Bacterium–plant interactions in this niche can be influenced by factors such as the expression of heterologous genes in the plant. The objective of this work was to describe the bacterial communities associated with the rhizosphere and rhizoplane regions of tobacco plants, and to compare communities from transgenic tobacco lines (CAB1, CAB2 and TRP) with those found in wild-type (WT) plants. Samples were collected at two stages of plant development, the vegetative and flowering stages (1 and 3 months after germination). The diversity of the culturable microbial community was assessed by isolation and further characterization of isolates by amplified ribosomal RNA gene restriction analysis (ARDRA) and 16S rRNA sequencing. These analyses revealed the presence of fairly common rhizosphere organisms with the main groups Alphaproteobacteria, Betaproteobacteria, Actinobacteria and Bacilli. Analysis of the total bacterial communities using PCR-DGGE (denaturing gradient gel electrophoresis) revealed that shifts in bacterial communities occurred during early plant development, but the reestablishment of original community structure was observed over time. The effects were smaller in rhizosphere than in rhizoplane samples, where selection of specific bacterial groups by the different plant lines was demonstrated. Clustering patterns and principal components analysis (PCA) were used to distinguish the plant lines according to the fingerprint of their associated bacterial communities. Bands differentially detected in plant lines were found to be affiliated with the genera Pantoea, Bacillus and Burkholderia in WT, CAB and TRP plants, respectively. The data revealed that, although rhizosphere/rhizoplane microbial communities can be affected by the cultivation of transgenic plants, soil resilience may be able to restore the original bacterial diversity after one cycle of plant cultivation.     

Differences in nutritional quality of parts of Vitis vinifera berries affect fitness of the European grapevine moth

The European grapevine moth, Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae), is a major grapevine pest in Europe. The larva is polyphagous and able to develop on more than 25 plant species, several of them being more suitable than Vitaceae for the fitness of L. botrana. Larvae normally eat the pulp of the berry, but may also consume the seeds according to the development stage of the berry and the larval density per bunch. Understanding the effect on individual fitness of such feeding behaviour is important to assess how suitable the different berry tissues are for this insect. We offered to the larvae either entire berries, seeds, or pulp with skin of the variety Vitis vinifera cv. ‘Cabernet Sauvignon’ as larval food in order to assess several life history traits from egg hatching to adult death. Two control groups were raised on semisynthetic diets, offering a low (no plant material) or a higher (with corn flour) nutritive value medium. The larvae performed differently when fed on diets containing different parts of berries. The larvae fed on a diet containing grape berry seeds had a prolonged development time and showed higher mortality. The females emerging from these larvae had a lower fecundity and mating success than the females emerging from larvae fed on diets containing other parts of the berries. However, their longevity was greater in comparison to the other groups. We conclude that seeds of Cabernet Sauvignon are not toxic to larvae but affect the reproductive life history traits in L. botrana.     

Population models for threshold-based control of Tetranychus urticae in small-scale Kenyan tomato fields and for evaluating weather and host plant species effects

The spatial distribution of motile life stages of the two-spotted spider mite Tetranychus urticae Koch in Kenyan small-scale tomato fields was described by Taylor’s power law and an enumerative sampling plan was designed for research purposes. The exponential increase of T. urticae populations during three growing seasons permits the development and use of a simple exponential model for the design of a threshold-based chemical control system. For this purpose, a critical threshold of 440 motile mites per sample unit at the end of the growing season (12 weeks after transplanting) was translated into a proportion of 0.83 infested units in sample 3, i.e. five weeks after transplanting. A sequential binomial sampling plan with respect to the proportion of 0.83, five weeks after transplanting, was designed. The exponential model was extended to account for the influence of weather and host plant species. Model development and parameter estimation were based on three data sets (Kenyan tomato fields, Italian and Californian strawberry fields). The model satisfactorily predicted a positive influence on growth rates by (i) changing the host plant from tomato to strawberry, and (ii) temperature, while a negative effect resulted from (iii) rainfall; both (ii) and (iii) are controlled by temperature–rainfall interactions. In contrast, the estimated parameter values did not satisfactorily describe the expected responses at specific temperature and rainfall values. Nevertheless, the model allowed the rating of host plant species in the field. A fourth data set from Swiss apple orchards was used to test the model, and population build-up on the apple host plant appeared to be higher than on tomatoes but lower than on strawberry.     

The microflora of ripening barley grain and the effects of pre harvest fungicide application

Newly-emerged ears of barley soon became colonised by micro-organisms with numbers increasing to 5·8 × 10⁵ viable propagules/g dry weight by harvest. Bacteria were numerically predominant throughout. Yeasts and yeast-like fungi were also numerous during the early stages of grain development but were exceeded by propagules of filamentous fungi during ripening, with Cladosporium spp., Alternaria alternata, Epicoccum purpurascens and Verticillium lecanii most abundant. Numbers of most micro-organisms were greatest in a wet season but Alternaria was equally abundant in hot dry weather. Application of fungicides at or after anthesis modified the grain microflora. Captafol was most effective overall in decreasing numbers of fungi. However, benomyl decreased Cladosporium inoculum more than catpafol but was ineffective against Alternaria which became more numerous on benomyl-treated grain than on untreated. Yield increases of up to 4% were obtained by late fungicide treatment, least in a hot, dry year. Germination was also increased by some treatments by up to 5%.     

Non-random distribution among a guild of parasitoids: implications for community structure and host survival

Abstract 1. Immature stages of the gall midge, Asphondylia borrichiae, are attacked by four species of parasitoids, which vary in size and relative abundance within patches of the gall midge’s primary host plant, sea oxeye daisy (Borrichia frutescens). 2. In the current study, a bagging experiment found that the smallest wasp, Galeopsomyia haemon, was most abundant in galls exposed to natural enemies early in the experiment, when gall diameter is smallest, while the wasp with the longest ovipositor, Torymus umbilicatus, dominated the parasitoid community in galls that were not exposed until the 5th and 6th weeks when gall diameter is maximal. 3. Moreover, the mean number of parasitoids captured using large artificial galls were 70% and 150% higher compared with medium and small galls respectively, while stem height of artificial galls significantly affected parasitoid distribution. Galls that were level with the top of the sea oxeye canopy captured 60% more parasitoids compared with those below the canopy and 50% more than galls higher than the plant canopy. 4. These non‐random patterns were driven primarily by the differential distribution of the largest parasitoid, T. umbilicatus, which was found significantly more often than expected on large galls and the smallest parasitoid of the guild, G. haemon, which tended to be more common on stems level with the top of the plant canopy. 5. Large Asphondylia galls, especially those located near the top of the Borrichia canopy, were more likely to be discovered by searching parasitoids. Results using artificial galls were consistent with rates of parasitism of Asphondylia galls in native patches of sea oxeye daisy. Gall diameter was 19% greater and the rate of parasitism was reduced by almost 50% on short stems; as a result, gall abundance was 24% higher on short stems compared with ones located near the top of the plant canopy. 6. These results suggest that parasitoid community composition within galls is regulated by both interspecific differences in ovipositor length and preferences for specific gall size and/or stem length classes.