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The influence of PGPR on the susceptibility of glasshouse cucumber and tomato to spider mites was studied. lt was found that plants treated with PGPR suppressed the development of mile populations on both studied crops. The effect was more evident for cucumber, as compared to tomato plants. Mite population was smaller by more than 40% on the leaves of the susceptible cucumber cultivar, Corona growing in the presence of rhizobacteria, as compared to that without bacteria. The development of spider mile population on the bacterized susceptible tomato cultivar, Romatos was more inhibited on young leaves (43%) than on older ones (34%). As the injury of plants progressed the level of inhibition was decreased.
The purpose of experiments conducted during five years in an apple orchard and indoor conditions was to economise the collection and introduction of predatory mite (Typhlodromus pyri Scheut. Phytoseiidae), the effective predator of spider mites (Tetranychidae) in the orchards. It was found that collecting T. pyri in cloth belts in orchards was the efficient and economical way to gain high amount of predators for introduction. In order to avoid very high winter mortality of predators in Polish conditions the belts were transfered in autumn from the orchard to the room with stable temperature O°C -+ 1°C and high humidity. Keeping the belts with predators in outdoor condition in polivinyl boxes kept in shadow allowed also to avoid high mortality of overwintering T. pyri.
Experimental cucumber and tomato plants were cultivated under glasshouse conditions with or without PGPR. Young plants were infested with spider mites (T. urticae - cucumber and T. cinnabarinus - tomato). Leaves were analysed for protein and amino acid concentration. In infested leaves of the cucumber cultivar, susceptible to spider mites (Corona), an important decrease in protein content occurred in both bacterized and nonbacterized plants. Amino acid content was higher in mile infested leaves and the presence of PGPR did not influence this phenomenon. The content of proteins was also studied in the leaves of the less susceptible cucumber cultivar (Aramis). Spider mile feeding caused a small decrease in their concentration. The presence of bacteria in the root system caused an increase of soluble proteins in the leaves. In infested leaves of the highly susceptible tomato cultivar (Romatos), cultivated without bacteria, an evident increase of amino acid content was found opposite to plants with PGPR. The protein concentration was also increased in injured leaves of this cultivar but the presence of bacteria in the root system of mite infested plants caused a decrease of these compounds in their leaves. lnjured foliage of the less susceptible tomato cultivar (Sionka) had a lower protein concentration in bacterised plants as compared to those nonbacterised and both controls.
Artificial defoliation is often used in studies of induced defense reactions of plants to damage by arthropods. However, little is known about the role of various external factors that may determine the nature of inducible defenses. Here we tested whether light level under which plants grow could affect the natural invasion of two-spotted spider mite (Tetranychus urticae Koch) with a broad range of host plants. For this study we used two host species that differ widely in shade tolerance: shade-adapted Norway maple (Acer platanoides L.) and sun-adapted European mountain ash (Sorbus aucuparia L.). The purpose of this study was to explore mite invasion and to test whether prior simulated defoliation, light conditions and host species differences in secondary defense metabolites (soluble phenolics) play a role in the pattern of invasion. One-year-old maple and ash seedlings growing in pots were placed into two shade houses that produced a treatment with 5% light transmittance, and the second group of seedlings was placed in full sunlight. The experiment was carried out in a location chronically affected by spider mite presence. The defoliation was performed in mid-May by manual removal of 0 (control), 25, 50, 75 and 100% of leaves. Natural two-spotted spider mite invasion took place in mid-July and was observed only on seedlings growing in the shade. Mites were found on leaves of almost all seedlings. However, the intensity of feeding damage to leaves was related to the level of earlier defoliation. Control and slightly to moderately (25–50%) defoliated seedlings of both species were most affected by spider mites. Mite feeding behavior was directly linked to changes in concentration of leaf carbon and phenolic compounds. Carbon content was positively correlated with the percent of seedlings damaged by spider mites in both tree species (R² > 0.80; P <0.05). The highest concentration of phenolic compounds was observed in leaves of seedlings subjected to 50 and 75% defoliation. Our results indicated that two-spotted spider mites preferred plants grown in a shade environment and within these plants favored leaves which are high in carbon and low in phenolic compounds. Both plant species were able to survive early season leaf damage inflicted by spider mites. Inducible phenolic compounds were among defensive secondary metabolites contributing to low spider mite success in plants recovering from artificial spring defoliation.
The present study aimed at finding techniques alternative to chemical control, capable of reducing spider mite density. The experiment was carried out in 7 single-leader and 3 multi-leader training systems. The pest density was compared across the systems and between apple cultivars Elstar and Jonagold showing variable crown densities and trichome cover of leaves. The spider mite mobile stages were more abundant in singleleaders crowns, whereas more eggs were laid in multi-leader crowns. Nevertheless, the egg and the youngest stages survival was reduced in multi-leader crowns probably by the more intensive solar radiation reducing the air RH. The lowest pest abundance was found in the crowns of the V-Gćttingen system, and in the similar, stretched Tatura trellis 2-leader system. These types of crowns should be therefore recommended for integrated and organic apple production.
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