Trichome-borne and artificially applied acylsugars of wild tomato deter feeding and oviposition of the leafminer Liriomyza trifolii

Oviposition and adult feeding of the leafminer Liriomyza trifollii (Burgess) (Diptera, Agromyzidae) on Lycopersicon pennellii (Corr.) D'Arcy and its F₁ hybrid with Lycopersicon esculentum (Mill.) was significantly less than that on the cultivated tomato, L. esculentum. The resistance of L. pennellii and the F₁ was reduced following rinsing of foliage with ethanol. Resistant attributes of L. pennellii were transferred to L. esculentum through appression of L. pennellii foliage to L. esculentum leaflets. Application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum significantly decreased feeding and oviposition on L. esculentum leaflets by 61–99%. Therefore the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

Biosynthesis of modified peptidoglycan precursors by vancomycin-resistant Enterococcus faecium

In the presence of bacitracin, vancomycin-resistant Enterococcus faecium (vanA phenotype) accumulate UDP-N-acetylmuramyl(UDP-Mur-NAc)-tetrapeptide and a UDP-MurNAc-depsipentapeptide containing lactate substituted for the carboxy-terminal-D-alanine residue. In an in vitro peptidoglycan polymerization assay, the modified precursors function and confer resistance to vancomycin.     

Comparison of the functional and numerical responses of resistant versus non-resistant populations of the copepod Acartia hudsonica fed the toxic dinoflagellate Alexandrium tamarense

The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from 25 to 500 μgC L⁻¹, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise.     

A genetic and spatial Bayesian analysis of mastitis resistance

A nationwide health card recording system for dairy cattle was introduced in Norway in 1975 (the Norwegian Cattle Health Services). The data base holds information on mastitis occurrences on an individual cow basis. A reduction in mastitis frequency across the population is desired, and for this purpose risk factors are investigated. In this paper a Bayesian proportional hazards model is used for modelling the time to first veterinary treatment of clinical mastitis, including both genetic and environmental covariates. Sire effects were modelled as shared random components, and veterinary district was included as an environmental effect with prior spatial smoothing. A non-informative smoothing prior was assumed for the baseline hazard, and Markov chain Monte Carlo methods (MCMC) were used for inference. We propose a new measure of quality for sires, in terms of their posterior probability of being among the, say 10% best sires. The probability is an easily interpretable measure that can be directly used to rank sires. Estimating these complex probabilities is straightforward in an MCMC setting. The results indicate considerable differences between sires with regards to their daughters disease resistance. A regional effect was also discovered with the lowest risk of disease in the south-eastern parts of Norway.     

Induced resistance during the interaction pathogen x plant and the use of resistance inducers

Plants react to aggressions through different defence responses. Mechanical barriers consist in the increase of production and deposition of substances capable of containing pathogen invasion. Chemical barriers consist in the increase of concentration or activity of defence proteins and synthesis of phenolic compounds and phytoalexins. Elicitor substances have been widely used in plant disease control showing impressive results and a low impact to the environment and man. This review contains information about plant defence mechanisms and shows the use of inducers of resistance in the control of pathogens and prospects of advance towards sustainable agriculture.     

A combined transcriptional,biochemical and histopathological study unravels the complexity of Alternaria resistance and susceptibility in Brassica coenospecies

Alternaria blight is one of the most devastating diseases of rapeseed-mustard caused by a necrotrophic fungus Alternaria brassicae. Lack of satisfactory resistance resource in Brassica is still a main obstruction for developing resistance against Alternaria. In this study, we have selected Brassica juncea, Sinapis alba and Camelina sativa to understand and unravel the mechanism of disease resistance against Alternaria. Histopathological studies showed early onset of necrosis in B. juncea (1 dpi) and delayed in S. alba (2 dpi) and C. sativa (3 dpi) respectively. Early and enhanced production of hydrogen peroxide (H₂O₂) was observed in C. sativa and S. alba (6 hpi) when compared to B. juncea (12 hpi). An increase in catalase activity was observed in both C. sativa (36 % at 6 hpi) and S. alba (15 % at 12 hpi), whereas it significantly decreased in B. juncea at 6 hpi (23 %), 12 hpi (30 %) and 24 hpi (8 %). Gene expression analysis showed induction of PR-3 and PR-12 genes only in C. sativa and S. alba when compared to B. juncea suggesting their vital role for Alternaria resistance. In contrast, SA marker genes were significantly expressed in B. juncea only which provides evidence of hormonal cross talk in B. juncea during Alternaria infection thereby increasing its susceptibility.