Patterns of aphid resistance in the genus Vicia

The performance of three aphid species, Aphis fubae, Acyrthosiphon pisum and Megoura viciae, was quantified on 22 taxonomically-selected host plant species from the genus Vicia (vetches), using intrinsic rate of increase (r_m) k standard errors. A. pisum proved to be the most successful aphid species, both in terms of highest potential population increase and widest host range; M. viciae was least successful, with most restricted host range and low r_m values on all but the closest relatives of Vicia faba. A wide range of antibiotic resistance was found within the genus, and host resistance to the three aphid species was found to be broadly related to classification patterns based on taxonomy and life-form. Analysis of the components of r_m revealed that nymphal survival rates were the most significant factor limiting host colonisation, not pre-reproductive period which is the most important factor in cultivars of V. faba. The consequences of aphid polyphagy on performance are discussed.     

Taxonomy of the genusGlycine,domestication and uses of soybeans

The genusGlycine has had a stormy taxonomic history. Recent studies of herbarium specimens and cytological and morphological analyses of living collections, coupled with chemotaxonomic investigations, have made it necessary to revise the genus. In the first part of this paper the current taxonomic status of the genusGlycine is reviewed. The soybean was domesticated in China. It is unfortunate that the literature concerned with the antiquity and historical development of the soybean is obscured by legends and myths. In the second section of the paper, the archeological, historical, agricultural and botanical literature is summarized in order to present all the known evidence as to when, where and by whom the soybean was domesticated. The soybean is the world’s premier source of dietary vegetable oil and is nutritionally an excellent and inexpensive source of protein for use either as human food or animal feed. In addition, the soybean has numerous industrial uses. In the last section of this paper the traditional uses of fermented and nonfermented soybeans in the East as well as the high-technology-developed uses of soybeans in the West are summarized.     

The evolution of insecticide resistance in the peach-potato aphid,Myzus persicae

The peach-potato aphid Myzus persicae (Sulzer) can resist a wide range of insecticides, but until recently (1990) the only mechanism identified was the increased production of carboxylesterases (E4 or FE4), which cause enhanced degradation and sequestration of insecticidal esters. We have now identified two forms of target-site resistance involving changes in the acetylcholinesterase (AChE) and sodium channel (kdr) genes. Biochemical and DNA diagnostic methods can be used to identify all three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. Amplified genes underlie the increased production of esterases but their expression is modulated by DNA methylation. Amplification of the E4 gene is in strong linkage disequilibrium with the kdr mechanism. This may reflect strong insecticidal selection favouring aphids with multiple mechanisms, tight chromosomal linkage and/or the prominence of parthenogenesis in many M. persicae populations. The decreased fitness of resistant aphids under winter conditions may be a consequence of the altered sodium-channel gene affecting behaviour and/or the perception of external stimuli.     

Genetic changes under domestication in Vicia faba

Summary The components of variation within each one of two sets of landraces and/or cultivars of Vicia faba, respectively constituted of primitive and advanced morphological types, were studied by means of two sets of 8 × 8 diallel crosses with two repetitions. The results show that primitive and modern forms differ from each other in both the intensity and the kind of selective pressures acting on them, mainly on those characters more modified through the domestication process: i.e., seed morphology and the number of flowers per node. Because of the paramount importance of the additive component in the primitive forms, it is suggested that the most important type of selection on them is the stabilizing one. On the contrary, in the most advanced forms the selection is directional and disruptive : directional towards greater yields, and disruptive separating two morphological types, major and equina. The plant response to these different selective pressures has been to modify the genetic control of different characters: thus the primitive forms generally show only additivity while the most advanced forms show additivity as well as directional and asymmetrical dominance.     

Field evaluation of resistance to black bean aphid, Aphis fabae, in close relatives of the Faba bean, Vicia faba

A field assessment of 26 accessions of Vicia narbonensis and three of V. johannis confirmed previous laboratory studies demonstrating higher levels of resistance to Aphis fabae in these two wild species compared to the closely related crop, Vicia faba. Accessions of V. johannis were significantly more resistant than most accessions of V. narbonensis for all resistance indices measured except survival of aphid nymphs. Plant growth stage significantly affected levels of resistance in both Vicia species, resistance being moderate at pre-bud stage, decreasing on flowering and rising again at pod fill and onset of leaf senescence. Significant intraspecific variability in aphid resistance was found only within the 26 accessions of V. narbonensis, var. serratifolia being more resistant than var. narbonensis. Possible resistance factors and the agronomic potential of these two wild relatives of Faba bean are considered.     

Genetic analysis of wheat domestication and evolution under domestication

Wheat is undoubtedly one of the world's major food sources since the dawn of Near Eastern agriculture and up to the present day. Morphological, physiological, and genetic modifications involved in domestication and subsequent evolution under domestication were investigated in a tetraploid recombinant inbred line population, derived from a cross between durum wheat and its immediate progenitor wild emmer wheat. Experimental data were used to test previous assumptions regarding a protracted domestication process. The brittle rachis (Br) spike, thought to be a primary characteristic of domestication, was mapped to chromosome 2A as a single gene, suggesting, in light of previously reported Br loci (homoeologous group 3), a complex genetic model involved in spike brittleness. Twenty-seven quantitative trait loci (QTLs) conferring threshability and yield components (kernel size and number of kernels per spike) were mapped. The large number of QTLs detected in this and other studies suggests that following domestication, wheat evolutionary processes involved many genomic changes. The Br gene did not show either genetic (co-localization with QTLs) or phenotypic association with threshability or yield components, suggesting independence of the respective loci. It is argued here that changes in spike threshability and agronomic traits (e.g. yield and its components) are the outcome of plant evolution under domestication, rather than the result of a protracted domestication process. Revealing the genomic basis of wheat domestication and evolution under domestication, and clarifying their inter-relationships, will improve our understanding of wheat biology and contribute to further crop improvement.     

Feeding responses of an oligophagous bean aphid, Megoura crassicauda, to primary and secondary substances in Vicia angustifolia

The feeding behaviour of the aphid Megoura crassicauda Mordivilko (Homoptera: Aphididae), which feeds selectively on plants in the genus Vicia (Fabaceae), was studied. The aphids deposited proteinaceous stylet sheaths intercellularly towards the phloem tissues of host plants. Similar stylet sheaths were formed on a Parafilm membrane when host‐specific acylated flavonoid glycosides [two 2″‐O‐(E)‐p‐coumaroyl esters of quercetin 3‐O‐diglycosides] present in the extracts of the narrow vetch, Vicia angustifolia L., were supplied in the solution covered by the membrane. In contrast, their corresponding deacyl analogues, present more abundantly in the host plant tissues, were not stimulatory, which suggested specificity in the structural requirements of the probing stimulants. While the aphids imbibed an artificial diet composed of primary nutrients (e.g., sucrose and amino acids) and produced a large quantity of honeydew, acylated flavonoids alone and non‐acylated flavonoids supplied with the nutrients more or less suppressed honeydew production. These findings implied that the acylated flavonoids serve as a cue to navigate the stylet sheath towards the phloem prior to sap‐sucking, whereas non‐acylated flavonoids may serve as a negative stimulus to refrain from sucking during tissue penetration before tapping the phloem, although the distribution of these compounds in the plant tissues remains unknown. Thus, the feeding behaviour of M. crassicauda appears to be controlled by multiple chemical stimuli in the process of the settling on its host plant.     

Epicuticular wax composition in relation to aphid infestation and resistance in red raspberry (Rubus idaeus L.)

Epicuticular waxes from the aphid-resistant red raspberry (Rubus idaeus) cultivar Autumn Bliss and the aphid-susceptible cultivar Malling Jewel were collected from the newly emerging crown leaves, and also from the group of four more mature leaves immediately below the crown. Resistance and susceptibility status of the leaves to infestation by the large raspberry aphid, Amphorophora idaei, were determined by bioassay with the insect just prior to collection of the wax. Analysis showed the waxes to consist of a complex mixture of free fatty acids; free primary alcohols and their acetates; secondary alcohols; ketones; terpenoids including squalene, phytosterols, tocopherol and amyrins; alkanes and long chain alkyl and terpenyl esters. Compositional differences which may relate to A. idaei-resistance status were noticeably higher levels of sterols, particularly cycloartenol, together with the presence of branched alkanes, and an absence of C₂₉ ketones and the symmetrical C₂₉ secondary alcohol in wax from the resistant cultivar Bliss. There were also differences between the cultivars in the distribution of individual amyrins and tocopherols and in the chain length distribution for homologues of fatty acids, primary alcohols and alkanes, and these may also be related to resistance to A. idaei. Emerging leaves had lower levels of primary alcohols and terpenes, but higher levels of long-chain alkyl esters, and in general, more compounds of shorter chain-length than the more mature leaves. During bioassay A. idaei displayed a preference to settle on the more mature leaves. This may be due to greater wax coverage and higher levels of the compounds of shorter chain length found in the newly emerged younger leaves at the crown of the plant.     

Self domestication and the evolution of language

We set out an account of how self-domestication plays a crucial role in the evolution of language. In doing so, we focus on the growing body of work that treats language structure as emerging from the process of cultural transmission. We argue that a full recognition of the importance of cultural transmission fundamentally changes the kind of questions we should be asking regarding the biological basis of language structure. If we think of language structure as reflecting an accumulated set of changes in our genome, then we might ask something like, “What are the genetic bases of language structure and why were they selected?” However, if cultural evolution can account for language structure, then this question no longer applies. Instead, we face the task of accounting for the origin of the traits that enabled that process of structure-creating cultural evolution to get started in the first place. In light of work on cultural evolution, then, the new question for biological evolution becomes, “How did those precursor traits evolve?” We identify two key precursor traits: (1) the transmission of the communication system through learning; and (2) the ability to infer the communicative intent associated with a signal or action. We then describe two comparative case studies—the Bengalese finch and the domestic dog—in which parallel traits can be seen emerging following domestication. Finally, we turn to the role of domestication in human evolution. We argue that the cultural evolution of language structure has its origin in an earlier process of self-domestication.     

Behavior of bird cherry-oat aphid and green peach aphid in relation to potato virus Y transmission

Potato virus Y is transmitted to potato in a nonpersistent manner by many aphid species, some of which do not colonize this crop. The behavior of bird cherry-oat aphid, Rhopalosiphum padi (L.) on potato, Solanum tuberosum L., a plant species that is not colonized by this aphid, was described and compared with that of the potato-colonizing green peach aphid, Myzuspersicae (Sulzer). A higher proportion of winged morph of R. padi than M. persicae left the plant, but aphids that stayed in contact with the plant took the same mean time to initiate the first probe and it lasted the same mean time compared with M. persicae. Electronic penetration graph technique was used to study the probing behavior of the aphids during Potato virus Y (family Potyviridae, genus Potyvirus, PVY) transmission tests. Transmission rate decreased from 29 to 8% when the acquisition time increased from 5 min of continuous probing to 1 h with M. persicae, but it remained low (2 and 1%) with R. padi. Most of the difference in transmission rate between acquisition time with M. persicae and between aphid species was related to the change in the time and behavior taking place between the last cell puncture of the acquisition phase to the first cell puncture of the inoculation phase. Results presented here clearly demonstrated the importance of host plant selection and probing behavior in the transmission of nonpersistent plant viruses. They also stress the need to consider the behavior of the aphid in the design of laboratory tests of virus vector efficacy.     

Seed dispersal in relation to the domestication of Middle East Legumes

Modification of seed dispersal was perhaps one of the most important steps towards domestication of seed crops. Among the legumes of the Middle East, four patterns of such modification can be distinguished in the process of domestication. The initial stage of domestication of lentil, pea and grass pea was apparently due to a single mutation in a major gene that prevented pod dehiscente. In chick pea the domesticated type was formed by accumulation of several mutations in minor genes that reduced the amount of pod dropping and shattering. From a seed dispersal point of view, fenugreek was preadapted to cultivation since the wild species do not shatter their seeds. In the bitter vetch and common vetch partial seed shattering apparently was tolerable and desirable under cultivation since the seed served merely for sowing the next year crop.     

Cytology of Vicia species. X. Karyotype evolution and phylogenetic implication in Vicia species of the sections Atossa, Microcarinae, Wiggersia and Vicia

Automated karyotype analyses and sequence of rDNA spacers have been analysed for the species belonging to sections Atossa, Microcarinae, Wiggersia and Vicia. Karyomorphological parameters, based on Rec, Syi and TF% indices, have been determined and evidenced that, in term of symmetry, the karyotype of Vicia lathyroides was the most asymmetric one. A multivariate analysis using 34 karyological parameters, in addition to the symmetry indices, has been carried out and the corresponding dendrogram of linkage distances showed six different groups. Molecular investigations on the inclusive group in study by employing ITS DNA sequences indicated a different pattern of relationships. The cladistic analysis combining the molecular data set with karyological parameters evidenced that the species of sections Vicia and Atossa join closely to each other in a paraphyletic group, which includes the monophyletic section Wiggersia. Therefore, our karyological and molecular data provide information about the phylogenetic position of the analysed species inside the subgenus Vicia and are discussed in relation to previous results obtained by morphology, isozymes and ribosomal genes analyses.     

Nuclear DNA contents, rDNAs, and karyotype evolution in Vicia subgenus Vicia: II. Section Peregrinae

Summary. Nuclear DNA contents, automated karyotype analyses, and sequences of rDNA spacers have been determined for the species of Vicia belonging to sect. Peregrinae, as well as for V. mollis. The phylogenetic data generated from the comparison of rDNA sequences and karyomorphological results would both indicate that Vicia mollis is a sister group to sect. Peregrinae. The relationships among the species belonging to the Peregrinae section and species enclosed in sections Faba, Narbonensis, and Bithynicae have been also investigated: a clade including V. mollis and sect. Peregrinae is a sister group to a clade including V. bithynica and sect. Narbonensis. With our choice of outgroup, Vicia faba (including subsp. paucijuga) is external to the above mentioned inclusive group. Correspondence and reprints: Dipartimento di Agrobiologia ed Agrochimica, Università della Tuscia, via San Camillo de Lellis, 01100 Viterbo, Italy.     

The identification of an aphid juvenile hormone, and its titre in relation to photoperiod

ABSTRACT. Whole body extractions from larval and adult apterous forms of Megoura viciae , and from adult Aphis fabae , were analysed for the known insect juvenile hormones (JHs) by a gas chromatography-mass spectrometric method. Low levels of JH III were detected in both aphid species, the first identification of a juvenile hormone from an homopteran insect. Although the mean titre in adult M. viciae is higher in long-day than in short-day reared insects (0.12±0.03 v. 0.04±0.01 ng/g), titres were variable and measurements overlapped. The results are discussed in the context of the hormonal control of aphid polymorphism and the question of identity of homopteran and hemipteran JH.     

Parallel domestication, convergent evolution and duplicated gene recruitment in allopolyploid cotton

A putative advantage of allopolyploidy is the possibility of differential selection of duplicated (homeologous) genes originating from two different progenitor genomes. In this note we explore this hypothesis using a high throughput, SNP-specific microarray technology applied to seed trichomes (cotton) harvested from three developmental time points in wild and modern accessions of two independently domesticated cotton species, Gossypium hirsutum and G. barbadense. We show that homeolog expression ratios are dynamic both developmentally and over the several-thousand-year period encompassed by domestication and crop improvement, and that domestication increased the modulation of homeologous gene expression. In both species, D-genome expression was preferentially enhanced under human selection pressure, but for nonoverlapping sets of genes for the two independent domestication events. Our data suggest that human selection may have operated on different components of the fiber developmental genetic program in G. hirsutum and G. barbadense, leading to convergent rather than parallel genetic alterations and resulting morphology.     

Study on inheritance of resistance to root aphid, Pemphigus bursarius, in lettuce

The inheritance of resistance to lettuce root aphid, Pemphigus bursarius, was studied in lettuce using the Wellesbourne cultivars Avondefiance and Avoncrisp as resistant parents and Borough Wonder and Webb's Wonderful as aphid-susceptible parents. All four cultivars were crossed in all possible combinations including reciprocals and the response to root aphid of plants in the P₁F₁F₂ and BC generations was assessed using apterae of P. bursarius from the lettuce cv. Iceberg. Resistance to attack was clearly inherited and the parents appeared to be homozygous for their resistance or susceptibility. In the F₁ generation, however, in all crosses between resistant and susceptible parents, segregation into susceptible, resistant and some slightly less resistant plants occurred. This and the highly significant differences in segregation between pairs of reciprocal crosses in the F₁ and other generations indicate that the inheritance of resistance to root aphid is controlled by extra-nuclear factors. Modifying genes might also be involved but there appears to be no linkage of root aphid resistance with resistance to downy mildew, for which the Wellesbourne lettuces were bred.     

Inheritance of resistance to the cowpea aphid in cowpea

Summary Inheritance of resistance to cowpea aphid, Aphis craccivora Koch, in three resistant cultivars of cowpea, Vigna unguiculata (L.) Walp, was studied. The parents, F₁ and F₂ population were grown in an insect-proof screenhouse. Each 3-day-old seedling was infested with 10 apterous adult aphids. Seedling reaction was recorded when the susceptible check was killed. The segregation data revealed that the resistance of ICV11 and TVU310 is governed by single dominant genes. All the F₂ seedlings of the cross ICV10xTVU310 were resistant, indicating that they have the same gene for resistance. However, the F₂ populations from the crosses ICV10xICV11 and ICV11xTVU310 segregated in a ratio of 151, indicating that the dominant genes in ICV11 and TVU310 are non-allelic and independent of each other. The resistance gene of ICV10 and TVU310 is designated as Ac₁ and that of ICV11 as Ac₂.