Tamara Méndez

Bio: Tamara Méndez is an academic researcher from University of Talca. The author has contributed to research in topics: Gene & Gene expression. The author has an hindex of 1, co-authored 2 publications receiving 7 citations.

Variation in resistance mechanisms to the green peach aphid among different Prunus persica commercial cultivars.

Abstract: Peaches and nectarines are frequently attacked by the green peach aphid Myzus persicae (Sulzer), with significant negative impacts on fruit production. The genetic variability of resistance to this aphid among commercial cultivars of Prunus persica (L) Batsch and Prunus persica variety nectarina was evaluated in this study. In total, 16 cultivars of P. persica were selected to evaluate the occurrence and population growth rate of M. persicae in commercial orchards, as well as in no-choice and probing behavior laboratory assays. The results showed variability between cultivars in resistance and susceptibility to M. persicae, with three cultivars exhibiting different signatures of resistance. The peach cultivar ‘Elegant Lady’ exhibited a low occurrence of aphids in the orchard, a low rate of growth, moderate leaf-rejection in a no-choice test and a higher number and longer period of salivation into sieve elements, suggesting resistance at the phloematic level. The nectarine cultivar ‘August Red’ also exhibited low aphid occurrence in the orchard, a low rate of growth, and resistance at the prephloem and phloem levels. Finally, the nectarine ‘July Red-NS92’ exhibited a low occurrence of aphids in the orchard, a higher number of rejections in no-choice assays and no ingestion of phloem during the probing behavior experiments, suggesting prephloematic resistance. The rest of the cultivars studied exhibited clear susceptibility. Hence, different resistance mechanisms are apparent among the studied cultivars. The information gathered in this study regarding the resistance to M. persicae may assist breeding programs aimed at increasing aphid resistance to peaches and nectarines.

Induction of PrMADS10 on the lower side of bent pine tree stems: potential role in modifying plant cell wall properties and wood anatomy.

Abstract: The molecular mechanisms underlying inclination responses in trees are unclear. In this study, we identified a MADS-box transcription factor differentially expressed early after inclination in the stems of Pinus radiata D. Don. PrMADS10 has a CDS of 582 bp and encodes a group II MADS-box transcription factor. We measured highest accumulation of this transcript on the lower side of inclined pine stems. In an effort to identify putative targets, we stably transformed Arabidopsis thaliana with a 35S::PrMADS10 construct. Transcriptome analysis revealed 1,219 genes differentially-expressed, with 690 and 529 genes up- and down-regulated respectively, when comparing the transgenic and wild-type. Differentially-expressed genes belong to different biological processes, but were enriched in cell wall remodeling and phenylpropanoid metabolic functions. Interestingly, lignin content was 30% higher in transgenic as compared to wild-type plants consistent with observed changes in gene expression. Differentially expressed transcription factors and phenylpropanoid genes were analyzed using STRING. Several MYB and NAC transcription factors showed interactions with genes of the phenylpropanoid pathway. Together, these results implicate PrMADS10 as a regulatory factor, triggering the expression of other transcription factors and genes involved in the synthesis of lignin.

Localised laccase activity modulates distribution of lignin polymers in gymnosperm compression wood.

Abstract: The woody stems of coniferous gymnosperms produce specialised compression wood to adjust the stem growth orientation in response to gravitropic stimulation. During this process, tracheids develop a compression-wood-specific S2 L cell wall layer with lignins highly enriched with p-hydroxyphenyl (H)-type units derived from H-type monolignol, whereas lignins produced in the cell walls of normal wood tracheids are exclusively composed of guaiacyl (G)-type units from G-type monolignol with a trace amount of H-type units. We show that laccases, a class of lignin polymerisation enzymes, play a crucial role in the spatially organised polymerisation of H-type and G-type monolignols during compression wood formation in Japanese cypress (Chamaecyparis obtusa). We performed a series of chemical-probe-aided imaging analysis on C. obtusa compression wood cell walls, together with gene expression, protein localisation and enzymatic assays of C. obtusa laccases. Our data indicated that CoLac1 and CoLac3 with differential oxidation activities towards H-type and G-type monolignols were precisely localised to distinct cell wall layers in which H-type and G-type lignin units were preferentially produced during the development of compression wood tracheids. We propose that, not only the spatial localisation of laccases, but also their biochemical characteristics dictate the spatial patterning of lignin polymerisation in gymnosperm compression wood.

The arbuscular mycorrhizal fungus Rhizophagus irregularis affects arthropod colonization on sweet pepper in both the field and greenhouse

Abstract: In the present study sweet pepper plants, Capsicum annuum, were planted in greenhouse and open field conditions to test the effect of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis on phytophagous and predatory arthropod populations. Furthermore, we tested the hypothesis that AMF may increase the crop yield (number of fruits and their weight) and activity level of polyphenol oxidase (PPO) and peroxidase (POD), enzymes that seemingly decrease infestation by arthropod pests. The most abundant arthropod species found were the peach-potato aphid, Myzus persicae, western flower thrips, Frankliniella occidentalis, and the seven-spot ladybird, Coccinella septempunctata. Sweet pepper mutualism with AMF significantly reduced colonization by the peach-potato aphid under greenhouse conditions. Aphid density increased, however, on two of four pepper varieties tested under open field conditions. The density of ladybird predators did not appear directly influenced by AMF under greenhouse conditions, whereas a significantly higher predator density was found on three out of four pepper plant varieties with fungal mutualism tested under field conditions. Crop yield was significantly higher on plants with AMF mutualism under greenhouse conditions, but no clear effects were detected under field conditions. Both PPO and POD activity increased significantly and remained higher than controls until day 14 of the experiment under mutualism with AMF, although only in the greenhouse. The results suggest that under greenhouse conditions, pepper plant mutualism with AMF can increase pepper yield by reducing the numbers of the key pest, peach-potato aphid.

Unravelling the resistance mechanism of lettuce against Nasonovia ribisnigri

Abstract: Aphids are serious pests of crop plant species, and host plant resistance is often the most effective and environmentally friendly control strategy to control these pests. One of these aphid pests is the black currant - lettuce aphid, Nasonovia ribisnigri (Mosely), an economically important pest of cultivated lettuce, Lactuca sativa L. Host plant resistance has been used since 1982 to control this aphid species and is mediated by the Nr-gene, originating from wild lettuce Lactuca virosa L. However, this resistance is not effective anymore, since N. ribisnigri aphids virulent to the Nr-resistance have been reported since 2007. The aim of this thesis was to unravel the mechanism of resistance mediated by the Nr-gene against N. ribisnigri, by behavioural studies on the aphids on both resistant and susceptible lettuce, to allow lettuce breeders to accelerate their resistance breeding programmes. Although the exact mechanism of Nr-mediated resistance remains unknown, the data in this thesis provide insight into this mechanism. The active site of the Nr-mediated resistance is mainly located in the phloem and some resistance might be encountered by the aphids along the pathway to the phloem. The inability of the avirulent aphids to feed from the resistant plant could be caused by the failure of aphids to suppress the wound response of the sieve element. The resistance factor(s) are only produced in the shoot, because grafts with resistant shoots and susceptible roots were resistant, whereas grafts with susceptible shoots and resistant roots remained susceptible. An intact vascular system is needed for full resistance, because both detached leaves and leaf disks of resistant lettuce plants were less resistant. Variation in virulence was observed among populations of different geographical origin. Aphids from a highly virulent population performed equally well on both resistant and susceptible lettuce plants, whereas semi-virulent aphids performed better on susceptible lettuce plants. Both short-term and long-term virulence loss were observed for virulent aphid populations differing in virulence level, which indicates this virulence is associated with fitness costs. A possible mechanism underlying virulence in N. ribisnigri to the Nr-resistance is the presence of an effector protein in the salivary secretion of the aphids suppressing resistance. Virulent aphids seemed to actively suppress the resistance in lettuce against the avirulent aphids. The original donor or the Nr-resistance, L. virosa accession IVT 280, was tested as possible source of new resistance against the virulent biotypes of N. ribisnigri and was foundfully resistant against virulent aphids, and can be exploited as a source of resistance in breeding for new resistance in cultivated lettuce.

A review on the complexity of insect-plant interactions under varying levels of resources and host resistance: the case of Myzus persicae-Prunus persica

Abstract: La complexite des interactions insectes-plantes en fonction de differents niveaux de ressources et de resistance de l’hote : le cas de Myzus persicae-Prunus persica (synthese bibliographique) Introduction. Les interactions plantes-insectes sont influencees directement ou indirectement par plusieurs facteurs de stress. Dans cette synthese bibliographique, l’effet de la disponibilite des ressources sur ces interactions est en premier lieu aborde au sens large, suivi d’une analyse ciblee des relations impliquant le modele puceron, en particulier le puceron vert du pecher Myzus persicae et son hote principal, Prunus persica. Litterature. Les defenses des plantes envers les insectes se manifestent de deux facons : la resistance et la tolerance, toutes deux influencees par des facteurs abiotiques. Les informations recueillies a partir d’etudes (n = 29) concernant l'effet de la diminution de la disponibilite en eau sur les defenses contre les insectes, ont montre que dans 41,4 % des etudes, le stress hydrique induit la resistance. Dans 34,5 %, 20,1 % et 3,4 %, les effets sur la resistance etaient respectivement moindres, absents et conditionnels. Conclusions. Le stress hydrique provoque des effets mitiges sur la resistance des plantes aux pucerons. Toutefois, la revue bibliographique suggere egalement un role des pratiques culturales dans les interactions pecher-puceron, tandis que le developpement de modeles predictifs visant a assister les systemes de gestion des bio-agresseurs necessite la collecte de davantage de donnees.

Host plant and competitor identity matter in genotype × genotype × environment interactions between vetch and pea aphids

Abstract: 1 Selection does not only operate in a genotype (G) × environment (E) context, but can also be modulated by the activities of organisms interacting with their environment (G × G × E) 2 The influences of aphid clonal identity and host plant (Vicia faba) intraspecific genetic variation on the performance of five genotypes of pea aphid (Acyrthosiphon pisum) were investigated – with and without interaction with a competing heterospecific clone of vetch aphid (Megoura viciae) – across three cultivars of V faba 3 Pea aphid performance in the presence of a competing vetch aphid clone (G × G × E) compared with the absence of competition (G × E) revealed strong context-dependent, genotype-specific shifts in performance, influenced by plant cultivar, competitor presence and their interaction 4 The performance of vetch aphid in competition with each pea aphid clone was also compared Here, competitor's genotype and abundance underlay a remarkably varied response by vetch aphid across interactions 5 The study shows that aphid genotypes exhibit a varying degree of risk spreading, contingent on competitor identity and the patterns of aggregation across three plant cultivars Owing to feedback loops between species activities and selective forces acting on them, our findings suggest that there are context-dependent responses by competitors that are shaped via the interplay of the co-occurring species and their biotic environment 6 This work highlights the complexity of species interactions and the importance of investigating reciprocity between competition and intraspecific genetic variation A better understanding of the eco-evolutionary interactions between phloem-feeding insects and their host plants can potentially be used to enhance crop protection and pest control