Synergistic effects of geographical strain, temperature and larval food on insecticide tolerance in Callosobruchus maculatus (F.)

This study investigated the multifactorial interaction of various environmental factors including 17 geographical strain (Brazil, Cameroon and Yemen strains), temperature, dose and larval food 18 (cowpea and mungbean) on the response of Callosobruchus maculatus adult to insecticide. All 19 the main factors, their two-way interactions and the four-way interaction had significant effects 20 on C. maculatus response to malathion (an organophosphate insecticide). However, the three-21 way interactions were not statistically significant (except strain x food x dose, P = 0.002). The 22 2 Brazil strain was the most responsive to temperature irrespective of the larval food type. The 23 impact of food type differs from one strain to the other, for instance, the food that imparts higher 24 tolerance in a strain might reduce the tolerance in another. Likewise, the hierarchy of tolerance 25 among the cowpea-reared strains (Brazil > Cameroon > Yemen) was totally different from the 26 mungbean-reared strains (Cameroon > Yemen > Brazil). The reasons for these differences were 27 discussed in the light of their impact on C. maculatus management. The management of both C. 28 maculatus and development of resistance could be complex, hence, the states of a variety of 29 environmental factors need to be considered. This is necessary in order to maximize management 30 success of this bruchid especially in tropical/subtropical developing countries.

Thiamine plays a critical role in the acid tolerance of Listeria monocytogenes

Understanding the molecular basis of acid tolerance in the food-borne pathogen Listeria monocytogenes is important as this property contributes to survival in the food-chain and enhances survival within infected hosts. The aim of this study was to identify genes contributing to acid tolerance in L. monocytogenes using transposon mutagenesis and subsequently to elucidate the physiological role of these genes in acid tolerance. One mutant harboring a Tn917 insertion in the thiT gene (formerly lmo1429), which encodes a thiamine (vitamin B1) uptake system, was found to be highly sensitive to acid. The acid-sensitive phenotype associated with loss of this gene was confirmed with an independently isolated mutant, from which the thiT gene was deleted (ΔthiT). Cells of both wild-type and ΔthiT mutant that were thiamine depleted were found to be significantly more acid sensitive than control cultures. Thiamine-depleted cultures failed to produce significant concentrations of acetoin, consistent with the known thiamine dependence of acetolactate synthase, an enzyme required for acetoin synthesis from pyruvate. As acetoin synthesis is a proton-consuming process, we suggest that the acid sensitivity observed in thiamine-depleted cultures may be owing to an inability to produce acetoin.

Characterization of a Listeria monocytogenes Scott A isolate with high tolerance towards high hydrostatic pressure

An isolate of L. monocytogenes Scott A that is tolerant to high hydrostatic pressure (HHP), named AK01, was isolated upon a single pressurization treatment of 400 MPa for 20 min and was further characterized. The survival of exponential- and stationary-phase cells of AK01 in ACES [N-(2-acetamido)-2-aminoethanesulfonic acid] buffer was at least 2 log units higher than that of the wild type over a broad range of pressures (150 to 500 MPa), while both strains showed higher HHP tolerance (piezotolerance) in the stationary than in the exponential phase of growth. In semiskim milk, exponential-phase cells of both strains showed lower reductions upon pressurization than in buffer, but again, AK01 was more piezotolerant than the wild type. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella, were elongated, and showed slightly lower maximum specific growth rates than the wild type at 8, 22, and 30°C. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H2O2 compared with the wild type. The difference in HHP tolerance between the piezotolerant strain and the wild-type strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wild type had identical in situ lipid melting curves as determined by Fourier transform infrared spectroscopy. The demonstrated occurrence of a piezotolerant isolate of L. monocytogenes underscores the need to further investigate the mechanisms underlying HHP resistance of food-borne microorganisms, which in turn will contribute to the appropriate design of safe, accurate, and feasible HHP treatments.

Control of final moisture content of food products baked in continuous tunnel ovens

There are well-known difficulties in making measurements of the moisture content of baked goods (such as bread, buns, biscuits, crackers and cake) during baking or at the oven exit; in this paper several sensing methods are discussed, but none of them are able to provide direct measurement with sufficient precision. An alternative is to use indirect inferential methods. Some of these methods involve dynamic modelling, with incorporation of thermal properties and using techniques familiar in computational fluid dynamics (CFD); a method of this class that has been used for the modelling of heat and mass transfer in one direction during baking is summarized, which may be extended to model transport of moisture within the product and also within the surrounding atmosphere. The concept of injecting heat during the baking process proportional to the calculated heat load on the oven has been implemented in a control scheme based on heat balance zone by zone through a continuous baking oven, taking advantage of the high latent heat of evaporation of water. Tests on biscuit production ovens are reported, with results that support a claim that the scheme gives more reproducible water distribution in the final product than conventional closed loop control of zone ambient temperatures, thus enabling water content to be held more closely within tolerance.

The influence of geographic origin and food type on the susceptibility of Callosobruchus maculatus (Fabricius) to Piper guineense (Schum and Thonn)

The tolerance of Callosobruchus maculatus from different geographical locations reared on two cowpea varieties, pale brown Ife Brown (IFBV) and dark brown IAR48 (IAR48V), to seed powder of Piper guineense (Schum and Thonn) was investigated. C. maculatus populations were collected from nine different locations across Osun state in the South Western part of Nigeria. The main and interactive effects of cowpea variety, population origin and dose on C. maculatus tolerance to P. guineense were explored. It was observed that bruchids that emerged from IAR48V had greater tolerance of P. guineense than bruchids reared on IFBV. There were significant effects (P < 0.001) of cowpea variety, population and dose, and significant interactions among these factors (except variety � dose, P > 0.05) on the response of bruchids to P. guineense. When reared on IAR48V, bruchid populations from the North-Eastern part of the state show greater tolerance to P. guineense than their counterparts from the SoutheWest. This study underscores the importance of knowledge of the origin of the population and the cowpea variety on which C. maculatus developed when managing bruchids damage using P. guineense

Field phenotyping of potato to assess root and shoot characteristics associated with drought tolerance

Aims Potatoes are a globally important source of food whose production requires large inputs of fertiliser and water. Recent research has highlighted the importance of the root system in acquiring resources. Here measurements, previously generated by field phenotyping, tested the effect of root size on maintenance of yield under drought (drought tolerance). Methods Twelve potato genotypes, including genotypes with extremes of root size, were grown to maturity in the field under a rain shelter and either irrigated or subjected to drought. Soil moisture, canopy growth, carbon isotope discrimination and final yields were measured. Destructively harvested field phenotype data were used as explanatory variables in a general linear model (GLM) to investigate yield under conditions of drought or irrigation. Results Drought severely affected the small rooted genotype Pentland Dell but not the large rooted genotype Cara. More plantlets, longer and more numerous stolons and stolon roots were associated with drought tolerance. Previously measured carbon isotope discrimination did not correlate with the effect of drought. Conclusions These data suggest that in-field phenotyping can be used to identify useful characteristics when known genotypes are subjected to an environmental stress. Stolon root traits were associated with drought tolerance in potato and could be used to select genotypes with resilience to drought.

Plastic and evolutionary responses to heat stress in a temperate dung fly: negative correlation between basal and induced heat tolerance?

Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source 4 population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot-acclimation or non-acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat-shocked flies, but in the absence of heat stress hot-acclimated flies had reduced life spans relative to nonacclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness-related traits.