Aphid resistance

HVlOl Barria, B. N., S. V. Cpaj, and H. M. HV113 Niemeyer. Occurrence of Diboa in wild Hordeum species and its relation to Aphid resistance. Phytochemistry 1992 31(1) 89-91. 

Aphids. Resistance in various species of aphids, especially those transmitting plant virus diseases, remains a serious problem. There are more cases of... 

Li, Y C. Hill S. Carlson B. Diers G. Hartman. Soybean aphid resistance genes in the soybean cultivars. Dowling and Jackson map to linkage group M. Mol. Breed. 2007, 19, 25-34, 2007. 

Birch, A.N.E., Geoghegan, I.E., Majerus, M.E.N., McNicol, J.W., Hackett, C.A., Gatehouse, A.M.R. and Gatehouse, J.A. (1999). Tri-trophic interactions involving pest aphids, predatory 2-spot ladybirds and transgenic potatoes expressing snowdrop lectin for aphid resistance. Mol. Breed. 5,75-83. 

Figure. 1. Nature of glandular trichome-mediated aphid resistance in 5. berthaultiL Key (1) Carboxylic acid sucrose esters (CASE), (2) Viscous type B trichome exudate, (3) Increased aphid movement and attempts to escape, (4) Adhesive aphid tarsi, (5) Enhanced rupture of type A trichome membrane , (6) Polyphenoloxidase + 02 + substrate, (7) Aphid alarm pheromone, E-(B)=famesene, (8) Encasement of tarsi by trichome exudate, (9) Greater effective tarsal size, (10) Decreased aphid mobility, (11) Occlusion of mouthparts by trichome exudate, (12) Starvation and death. Adapted from (38).

Plant Source. Geraniums were maintained in a greenhouse environment using standard cultural practices. The plant line 71-17-7 and its corresponding self-pollinated progeny, family 87-5, had been previously determined to be mite and aphid resistant, and plant line 71-10-1 and its corresponding self-pollinated progeny, families 85-26, 87-13 and 87-14, had previously been determined to be mite and aphid susceptible (Z)- Newly opened... 

Most Nicotiana species have multicellular, glanded leaf trichomes which may produce chemical secretions containing diterpenes and/or sugar esters with C2 to C,o acyl moieties. These components affect tobacco aphids, Myzus nicotianae Blackman, in several ways, including influencing the acceptance or rejection of plants for colonization by alate migrant aphids, and the survival and fecundity of alate and apterous aphids. Cuticular diterpenes and sucrose esters were isolated from the cuticular extracts of aphid resistant and susceptible N. tabacum genotypes. These compounds were applied topically to the backs of apterous aphids. 

For the past 30 years, the U.S. tobacco, Nicotiana tabacum L., and Nicotiana species germplasm collections have been evaluated for tobacco aphid infestations in small field plots in North Carolina, South Carolina, Kentucky, Tennessee and Georgia (7, 75). Aphid resistance observed with some tobacco genotypes may be due to high levels of pyridine alkaloids (8). In 1982 Johnson and Severson (77) reported that chemicsds produced by leaf trichomes played an important role in determining resistance of different tobacco introductions (TI) to the green morph of the tobacco aphid. In this paper we report on the effect of different leaf surface chemistries of N. tabacum germplasm on the colonization of tobacco by the red morph of the tobacco aphid, and discuss studies conducted to determine mechanisms of resistance. We also discuss the effects of specific cuticular isolates on the survival and fecundity of adult tobacco aphids. 

Table I compares the relative field plot aphid ratings with the composition and levels of the trichome-produced cuticular components. The aphid susceptible cultivars NC 2326 (flue-cured) and KY 14 (burley) produced similar levels of DVT-diols. The DVT-diols are the major cuticular components of flue-cured and burley tobacco types (72). The aphid-resistant lines either have nonsecreting trichomes, and very low levels of cuticular components, or glanded trichomes which produce heavy exudates consisting of DVT-ols, and or dj-abienol and labdenediol and or SE (see 72, 74, 18 for structures). The TI 1112 and breeding...

These studies clearly demonstrate a relationship between aphid resistance in V. tabacum and differences in the levels and composition of trichome exudates. Tobaccos which are resistant to the green morph of the tobacco aphid are also resistant to the red form (10, 11, 75). This indicates that both color forms of the tobacco aphid have similar response to plant surface chemistry. It also appears that, as seen in the tobacco budworm and tobacco homworm (72,77-79), the DVT-diols are preference compounds used by alate aphids to identify their host plants. The DVT-ols, cw-abienol, and SE are toxic to the tobacco aphid, and these compounds have potential as contact aphicides. Breeding of commercially acceptable N, tabacum cultivars with high levels of DVT-ols, cw-abienol and/or the SE would greatly decrease the level of tobacco aphid colonization and lessen the need to use conventional insecticides. 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

Metabolic resistance may be the consequence of the appearance of a novel gene on the resistant strain, which is not present in the general population it may also be due to the presence of multiple copies of a gene in different strains or clones as in the example of OP resistance in the peach potato aphid mentioned earlier. 

In the middle of the 1980s in the USSR, approximately 150 species acquired resistance to one of the various OCPs and OPPs used [3], and now require more complicated means of suppression. For example, until the 1950s, weevils and boll weevils were the main pests damaging cotton. After the widespread use of OCP insecticides - DDT, toxafene, and others - cottonworms, tobacco tortricids, tobacco aphids, spider mites and loopers must now be fought as well. Their number jumped after suppression of the first two target species. 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

L. M. Field, A. L. Devonshire, B. G. Forde, Molecular Evidence that Insecticide Resistance in Peach-Potato Aphids (Myzus persicae Sulz.) Results from Amplification of an Esterase Gene , Biochem. J. 1988, 257, 309-312. 

Lettuce is the most pest- and disease-prone member of the Asteraceae. Common pests include slugs, cutworm, leaf aphids, and root aphids. Linder cover, downy mildew and gray mold (botrytis) can be a problem, especially in cool, damp conditions. Cultivars with resistance to aphids, downy mildew, and various physiological disorders are available. For more advice and information, see the A-Z of Plant Problems ipp.320-341). 

Resistance of Cereal Crops to Aphids Role of Allelochemicals... 

In this paper we summarize our work on the role of indole alkaloids and hydroxamic acids on the resistance of cereals to aphids. In addition, we describe the effects of water stress on susceptibility of barley to aphids. 

All these data support the idea that QA may function as chemical defense compounds. We also tested whether this chemical defense is relevant for the survival of a lupin plant. Lupins offer a unique chance to explore this question experimentally plant breeders have selected "sweet" varieties, which have a very low alkaloid content. These varieties can be compared to semi-bitter or bitter ones. We have grown Lupinus albus strains that differ in their alkaloid content in our experimental garden and greenhouse and have monitored their susceptibility to attack by plant pests. As can be seen from Figure 2, "sweet" lupins are preferentially eaten by rabbits (Cuniculus europaeus) or are infested by aphids (Aphidae) or leaf miners (Agromyzidae). Literature data also support the assumption that alkaloid-rich lupins are much more resistant to plant pests than "sweet" varieties (30-32). We conclude therefore, that QA are indeed important for the fitness of a lupin plant and that they constitute a major part of its chemical defense system, in which... 

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