Stephen R. King

Physical barriers to carotenoid bioaccessibility. Ultrastructure survey of chromoplast and cell wall morphology in nine carotenoid-containing fruits and vegetables.

BACKGROUND The ultrastructural characterisation of cellular components is a key element in revealing the bases for differences in nutrient bioaccessibility among fruits and vegetables and their derived products. Together, cell walls and chromoplasts constitute the two major physical barriers to carotenoid release from the food matrix (structure) during digestion. In general, larger cells with thinner cell walls are most likely to fail under mechanical pressure. In relation to chromoplasts, the substructures plastoglobuli, crystals and membranes give decreasing rates of carotenoid solubilisation when exposed to digestive forces. RESULTS This paper describes cell wall and chromoplast structures in nine carotenoid-storing raw fruits and vegetables. Watermelon and melon cells were shown to have the largest cells concomitant with thin, non-fibrous cell walls, while carrot, hypodermal grapefruit and sweet potato cells were smallest with fibrous or dense cell walls. Mango fruit showed the highest proportion of globules to other substructures. Carrot, papaya and tomato contained many crystalline structures. Finally, watermelon, mango and butternut squash developed a high proportion of membranous structures. CONCLUSION A more precise description of the physical characteristics of foods that stand as barriers to bioaccessibility can help in understanding which are more or less inhibitory for particular foods.

Development of a codominant CAPS marker for allelic selection between canary yellow and red watermelon based on SNP in lycopene β-cyclase (LCYB) gene

Flesh color of watermelon is an agronomically important trait that is predominantly determined by a network of the carotenoid biosynthetic pathway, which also contributes to the nutritional value of the fruit through the health-promoting function of carotenoids. We have identified a key gene, lycopene β-cyclase (LCYB) that may determine canary yellow and red flesh color of watermelon and developed a zero-distance molecular marker that identifies a critical single nucleotide polymorphism (SNP) that distinguishes different alleles of the LCYB gene. Analysis of the flesh color inheritance in segregating populations indicated that a single gene determines the color difference between canary yellow and red flesh in watermelon. The sequence comparison of full-length cDNA of LCYB, which was isolated using degenerate PCR and RACE, identified three SNPs in the coding region of LCYB between canary yellow and red. These SNPs showed perfect co-segregation with flesh color phenotypes. One of the SNPs introduces an amino acid replacement of evolutionarily conserved Phe226 to Val, which may impair the catalytic function of LCYB. This SNP was used to develop a cleaved amplified polymorphic sequence (CAPS) marker, which perfectly cosegregated with flesh color phenotype. Our results strongly suggest that LCYB may be the genetic determinant for canary yellow or red flesh color and our CAPS marker will allow breeders to economically distinguish between canary yellow and red watermelon fruit color at the seedling stage.

Genotype × environment interaction for wheat yield in different drought stress conditions and agronomic traits suitable for selection

Wheat cultivars grown in south-eastern Europe are exposed to variable rainfed environments. Climate change predictions indicate that the frequency of dry years will likely increase in the future. This study examined relationships among agronomic traits and some drought indices with grain yield as influenced by genotype and environment. In a 4-year experiment, 100 cultivars and landraces of bread wheat (Triticum aestivum L.) from different countries were tested under 3 watering regimes: fully irrigated, rainfed, and in a rain-out plot shelter. Three selection indices, mean productivity (MP), tolerance (TOL), and stress susceptibility index (SSI), were calculated based on grain yield in irrigated and drought-stressed conditions. The additive main effects and multiplicative interaction (AMMI) models were used to study the genotype × environment effects. Average yield reduction due to drought in the sheltered plots was 37.5%. High-yielding genotypes in each treatment showed high values of MP and high rank for SSI and, particularly, TOL. Conversely, low-yielding genotypes in each treatment had low values of MP and high drought tolerance according to SSI and TOL (i.e. low ranks). MP values were noted as being particularly well suited for predicting performance in this experiment. Total biomass and early vigour were found to be the most important agronomic traits for selecting high-yielding genotypes in a range of stress and non-stress conditions.

Morphogenetic responses of embryo culture of wheat related to environment culture conditions of the explant donor plant

Availability of immature embryos as explants to establish wheat (Triticum aestivum L.) by tissue culture can be limited by climatic factors and the lack of high quality embryos frequently hampers experimentation. This study evaluates the effects of rainfall, various temperature-based variables and sunshine duration on tissue culture response (TCR) traits including callus formation (CF), regenerating calli (RC), and number of plants per embryo (PPE) for 96 wheat genotypes of worldwide origin. The objectives of this study were to evaluate the significance of a particular climatic factor on TCR traits and to determine the period of wheat growth during which these factors were the most effective. The genotypes were grown in an experimental field during three seasons differing in meteorological conditions. The relationships between TCR traits and climatic factors within three time periods of wheat growth: 2, 6 and 10 weeks prior to embryo sampling were analysed by biplot analysis. The tissue culture traits were influenced at very different degrees by climatic factors: from 16.8% (RC) to 69.8% (CF). Donor plant environment with high temperatures and low rainfalls reduced (p < 0.05) the tissue culture performance of wheat genotypes. Callus formation was most sensitive to the temperature based factors. The environmental conditions between flowering and the medium milk stage were the most important for CF, while RC and PPE were not particularly related to any period.

Intercropped Watermelon for Weed Suppression in a Low-input Organic System

The inclusion of a smother crop used as a cash crop in an intercropping system may be an effective cultural control strategy for the management of weeds in organic production systems. In addition, a multilayered canopy created when intercropping species with different growth forms may limit germination cues for weed seeds and can allow for a more efficient utilization of resources that reduce competition to target crops from weeds. Watermelon (Citrullus lanatus) was evaluated for its ability to reduce weeds in a low-input organic system in Texas when planted alone or in various intercropping combinations that also included peanut (Arachis hypogaea), okra (Abelmoschus esculentus), cowpea (Vigna unguiculata), and hot pepper (Capsicum annuum). Watermelon significantly reduced total weed biomass when planted in monoculture and in all intercropping combinations compared with peanut, okra, cowpea, and pepper monocultures in year 1 of the 2-year study. Total weed biomass was reduced by 81%, 83%, 88%, and 92% in treatments containing watermelon on average as compared with pepper, peanut, okra, and cowpea grown in monoculture, respectively. Less effective weed suppression was obtained with watermelon in year 2. Pepper grown in monoculture had significantly higher weed biomass than all other treatments in year 2. Broadleaf weeds were effectively suppressed across all intercropping treatments in year 1, but nutsedges (Cyperus sp.) were consistently reduced both years, particularly when compared with monocrops with small leaf area such as pepper. The three and four species intercropping combinations consistently had high leaf area index (LAI) values, whereas pepper monoculture had significantly lower LAI values than all other treatments except for cowpea monoculture. There was a significant negative relationship between LAI and total weed biomass 33 d after last planting (r = L0.51, P < 0.01). There was a significant negative relationship between total weed biomass and total fruit yield in year 1 (r = L0.64, P < 0.01) but no significant relationship in year 2. Although findings were inconsistent in year 2 because of changes in precipitation amounts and in relative planting dates, these findings suggest that incorporating a multifunctional intercropping system that includes a low-growing vining crop such as watermelon or at least an architecturally complex mixture can optimize canopy density to reduce weed pressure from resilient perennial weeds such as nutsedge. This may offer organic producers another management tool for the control of perennial weeds.

Time-Resolved Velocity Measurements in a Matched Refractive Index Facility of Randomly Packed Spheres

Complex geometries and randomly connected void spaces within packed beds have hindered efforts to characterize the underlying transport phenomena occurring within. In this communication, we present our experimental studies on a facility of randomly packed spheres that can be a representative of sections within a reactor core in a nuclear power plant. The results of high-fidelity velocity measurements can be seen using Time-Resolved Particle Image Velocimetry (TR-PIV) at the pore scales and near the wall boundary in the Matched Index of Refraction (MIR) facility. The MIR approach allows for a non-invasive analysis of the flow within packed spheres at the microscopic scales with high temporal and spatial resolution. Flow characteristics obtained from the TR-PIV measurements at various Reynolds numbers are presented. The results include the first- and second-order flow statistics, such as mean velocity, root-mean-square fluctuating velocity and Reynolds stresses. Effects of the wall boundary and Reynolds numbers on flow patterns are currently being investigated. Comparisons of the mean velocities, root-mean-square fluctuating velocities, and Reynolds stress components show the increase of flow mixing and turbulent intensities within the gaps between spheres in the packed bed. Sizes of recirculation regions, however, seem to be independent of the increase of Reynolds numbers.Copyright