Les effecteurs jouent un rôle fondamental lors des interactions antagonistes plantes-pathogènes en supprimant les défenses de la plante, permettant ainsi aux parasites de se développer. De tels effecteurs ont été caractérisés chez les insectes herbivores mais leur rôle dans la spécialisation à la plante reste méconnu. Les pucerons se nourrissent de la sève du phloème et injectent dans la plante des effecteurs salivaires. L'étude des patrons d’évolution des effecteurs, ainsi que la caractérisation de leurs fonctions sont nécessaires à la compréhension des mécanismes de spécialisation chez les pucerons. Au cours de ces travaux, nous avons cherché à identifier les effecteurs salivaires impliqués dans l'adaptation du puceron du pois, Acyrthosiphon pisum, à ses hôtes.Des approches évolutives, basées sur un nouveau catalogue de 740 effecteurs candidats surexprimés dans les glandes salivaires de A. pisum, ont révélé que certains d'entre eux évoluent rapidement et que l'expansion de familles multigéniques apparaît comme une source importante de diversité des effecteurs. En parallèle, ces travaux ont permis d'optimiser l'expression transitoire médiée par Agrobacterium dans le pois. Ce nouvel outil d'analyse fonctionnelle permet maintenant l'étude des effecteurs candidats afin d'identifier les effecteurs du puceron du pois impliqués dans l'adaptation à la plante hôte. / Effectors play fundamental roles in antagonistic plant-pathogen interactions mainly by suppressing plant defense and allow parasites to multiply on the plant. Some effectors have been characterized in herbivorous insects; however, their role to the evolution in plant specialization remains unknown. Aphids feed from phloem sap and inject salivary effectors into the host plant. Studying evolutionary patterns and characterizing functions of effectors appear as important steps toward unveiling the mechanisms of host plant specialization in aphids. This work sought to identify salivary effectors that are involved in plant specialization of the pea aphid, Acyrthosiphon pisum. Evolutionary approaches based on a new catalogue of 740 putative effectors that are up-regulated in salivary glands of A. pisum revealed that some of them evolve rapidly.Moreover, gene family expansion appear as an important source of novel effectors. In parallel, this work optimized Agrobacterium-mediated transient gene expression in pea to provide a new tool for functional analyses of pea aphid effectors. The construction of a comprehensive catalogue of A. pisum salivary effectors and evolutionary analysis of them provide new candidates in host plant adaptation. By using the gene expression tool now available in pea, functional characterization of candidates will help to identify the effectors that are involved in plant specialization of the pea aphid.

Phloem transport is along hydrostatic pressure gradients generated by differences in solute concentration between source and sink tissues. Numerous species accumulate raffinose-family oligosaccharides (RFOs) in the phloem of mature leaves to accentuate the pressure gradient between source and sinks. In this study, metabolic engineering was used to generate RFOs at the inception of the translocation stream of Arabidopsis thaliana, which transports predominantly sucrose. To do this, three genes, GALACTINOL SYNTHASE, RAFFINOSE SYNTHASE and STACHYOSE SYNTHASE, were expressed from promoters specific to the companion cells of minor veins. Two transgenic lines homozygous for all three genes (GRS63 and GRS47) were selected for further analysis. Sugars were extracted and quantified by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), and 21-day old plants of both lines had levels of galactinol, raffinose, and stachyose approaching 50% of total soluble sugar. All three exotic sugars were also identified in phloem exudates from excised leaves of transgenic plants whereas levels were negligible in exudates from wild type leaves. Differences in starch accumulation or degradation between wild type and GRS63 and GRS47 lines were not observed. Similarly, there were no differences in vegetative growth between wild type and engineered plants, but engineered plants flowered earlier. Finally, since the sugar composition of the phloem translocation stream is altered in these plants, we tested for aphid feeding. When green peach aphids were given a choice between WT and transgenic plants, WT plants were preferred. When aphids were reared on only WT or only transgenic plants, aphid fecundity was reduced on the transgenic plants. When aphids were fed on artificial media with and without RFOs, aphid reproduction did not show differences, suggesting the aphid resistance is not a direct effect of the exotic sugars.

Thesis (M.Sc. (Agricultural Agronomy)) --University of Limpopo, 2015 / Refer to document / Department of Agriculture Forestry and Fisheries (DAFF)

Thesis (Ph.D. Agriculture (Plant Production)) -- University of Limpopo, 2020 / Worldwide, both root-knot (Meloidogyne species) and sugarcane aphid (Melanaphis sacchari Zehntner), are economic pests on sugarcane and sorghum crops. In most cases, each of the two pests is managed using host plant resistance due to the economic benefits derived from this management strategy. The highly nematode resistant sweet stem sorghum (Sorghum bicolor L.) cv. 'Ndendane-X1' used in ethanol production, is highly sensitive to sugarcane aphid, with some indication that the latter could interfere with nematode resistance in the sorghum cultivar. This study had four objectives which collectively intended to investigate the interactive effects of infection by three Meloidogyne species and infestation by aphid under different conditions on resistance to nematode in a nematode-resistant sorghum cultivar. The research objectives were achieved through four trials. In each trial a 2 × 2 factorial experiment, each with and without nematode and aphid as first and second factors, respectively, were conducted. Treatments were arranged in a randomised complete block design, with six replications, and each experiment validated in time. At 150 days, after emergence, the nematode × aphid interaction significantly reduced sucrose by 17, 74 and 42% in Meloidogyne enterolobii, Meloidogyne incognita and Meloidogyne javanica trials, respectively. Aphid infestation of sorghum significantly increased the reproductive potentials of the three respective Meloidogyne species by 196, 320 and 152%, but significantly, reduced plant growth variables from 20-44 and 48-51% in two respective trials. The mineral nutrients S and Zn were reduced in leaf tissues of the test cultivar in Trial 1, whereas Ca and Zn were respectively reduced by 24 and 51% in Trial 2 and by 52 and 51% in Trial 3. Since the reproductive potential values for Meloidogynqe species on the test sorghum cultivar were greater than unity and nematode infection reduced the plant variables, cv. 'Ndendane-X1' lost resistance to xx the test Meloidogyne species. In achieving Objective 2, procedures were similar to those in Objective 1 except that the study was conducted under field conditions under mixed nematode populations of M. enterolobii, M. incognita and M. javanica. Sorghum seedlings were raised at 0.3 m × 0.3 m inter and intra row spacings. Soon after emergence, plants were thinned to one per station, randomly selected for nematode and nematode-aphid treatments. Mixed populations of Meloidogyne species (M. enterolobii, M. incognita and M. javanica) at approximately 1:1:1 (v/v) ratio were applied at 300 eggs + J2 per plants after thinning at the five plants which were used as nematode alone treatments. The latter were also infested with 20 sugarcane aphids to constitute a nematode + aphid treatments. Buffer zone plants separating the treatments were monitored for aphids and stock borer, which were sprayed when necessary. At 150 days after infestation, relative to nematode alone, nematode-aphid significantly reduced degrees Brix from 13% to 61%, but significantly increased the reproductive potential of mixed Meloidogyne species and root galls by 279 and 199%, respectively. Also, the combined effect significantly reduced plant growth variables from 35 to 55% and the mineral nutrient elements in leaf tissues of the cultivar from 33 to 73%. At 150 days after the treatment, the second and first order interaction (Nemarioc-AL × Nemafric-BL × Mordica and Nemafric-BL × Mordica) had significantly increased sucrose content from 48 to 66%, increased plant growth variables from 49 to 163%, increased accumulation of certain nutrient elements from 164 to 206%. The terpenoid-containing phytonematicides could have potential future application in the husbandry of ethanol-producing sweet stem sorghum cultivars in relation to increasing sucrose above the 16% minimum for premium delivery fees and increased plant growth. Under field conditions, in pest-free condition (Objective 3), drenched terpenoid-containing phytonematicides significantly increased sucrose content at xxi middle and bottom part of SSS cv. 'Ndendane-X1' by 66 and 48%. However, these products did not significantly increase plant variables, except tiller number, which was increased by 163 under first order interaction from Nemafric-BL and Mordica phytonematicides. Similarly, nutrient elements variables had generally not been increased by the interaction of these products, except Ca and K, which were increased by 206 and 164%. In achieving Objective 4, a 2 × 2 × 2, with the first, second and third factor being Nemarioc-AL (with and without), Nemafric-BL (with and without) and Mordica (with and without) phytonematicides, respectively. on sorghum cultivar infected with a mixture of Meloidogyne species and infested with aphids, under microplot conditions, untreated control sucrose content remained below the standard of 16 degrees Brix, whereas the second order interaction increased the variable far above the standard, along with various plant growth variables also increased. However, both nematode and aphid population densities were significantly reduced by the interactions. Findings in this thesis constituted the first report where aphid infestation broke resistance to Meloidogyne species in sweet stem sorghum cv. 'Ndendane-X1'. Therefore, the successful use of nematode resistance in the cultivar in areas with high nematode population densities would depend upon the effective management of the sugarcane aphid population densities. Also, the three terpenoid-containing phytonematicides would when combined or used alone have the potential future in the husbandry of sweet stem sorghum cultivars intended for ethanol production and suppression of nematode population densities / National Research Foundation (NRF)

Fifteen small grain fields, including eight wheat fields, two barley fields and five oat fields, throughout the grain growing areas of Graham, Greenlee and Cochise counties were surveyed weekly from the third week in March through the second week in June, to document the presence of Russian wheat aphid (RWA), other aphid, parasites and predators. RWA were found in all three counties and in all three grains. Presence of RWA caused chemical pest control applications in approximately 19%, 33% and 90% of the small grain fields in Graham, Greenlee and Cochise counties, respectively. Thirty three percent of the fields had beneficial parasites and predators were found 93% of the fields. Presence of parasites reduced the RWA populations in 80% of the cases and presence of predators had a dramatic effect on other aphids and was felt to be beneficial in controlling RWA.

During 1990 the emphasis on surveying was placed in the southeastern corner of the state, where damage was found to be most severe in previous years. Estimates of the incidence of and damage caused by the Russian Wheat Aphid (RWA) were made for the entire state. These estimates indicate that small grain producers in the state lost $212,000 due to this pest in 1990.

Call number: LD2668 .T4 1948 K7 / Master of Science

Master of Science / Department of Chemistry / Christopher T. Culbertson / The study of aphid salivary secretome has practical importance on understanding interactions of aphids and their host plants. Around 250 species of aphids out of the identified 4000 aphid species are considered as serious pests. The experiments were performed with pea aphids (Acyrthosiphon pisum) that were feeding on bean plants (Vivia fabe). Pea aphids feed on plant phloem sap by probing their stylet into the sieve elements of the plant and secreting saliva for external digestion. In order to collect aphid salivary proteins from the secreted saliva, small scale and large scale sample collection methods were carried out. The small scale sample method was performed in microfluidic devices using 10-25 aphids. Aphids were able to feed on the artificial diet by probing through a stretched ParafilmTM and survived for 2-3 days in the microfluidic devices. The experiments proved that the aphid survival and feeding rate could be improved with the factors such as ventilation, light intensity and increasing diet volume. However it was difficult to collect sufficient amounts of aphid saliva for detection using small scale devices. The large scale sample collection method was performed by feeding 8000 aphids in large screened chamber for 24/48h. The collected salivary samples after undergone a concentration process was capable of collecting detectable aphid salivary secretions. The experimental conditions were adjusted to obtain optimized HPLC separations. Finally, LC/MS/MS followed by peptide sequence database searching were able to identify potential aphid salivary proteins.

Dissertation (PhD (Agric))--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use. / AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van , Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie van Suid-Afrika uitgevoer. Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste femur kon gebruik word om die 2de , 3de en 4de instars van mekaar te onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie onbetroubaar. Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling was by 4.32 en meer as 30°C onderskeidelik. Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in monsters is egter beïnvloed deur die afstand vanaf die stam waarby die monsters geneem is en die teenwoordigheid van wortelmateriaal in die monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief. Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter afgeneem, veral as die winterreënval hoogwas. Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in wortels sonder galle was hoër as in wortelgalle. Talle entomopatogeniese swamme, insluitend spesies van Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot biologiese beheer is nie bekend nie. 'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans in gebruik is, onderdruk.

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