Ayalsew Zerihun

Effect of site-specific irrigation management on grapevine yield and fruit quality attributes

Spatial variation in yield and fruit composition has been observed in many vineyards, leading to low productivity. In this study, site-specific irrigation was applied in a commercial vineyard (Vitis vinifera L. cv. Shiraz) block in the Sunraysia region of Australia to improve production in low-yielding areas of the block and decrease differences in yield and quality between irrigation management zones. Data collected under uniform irrigation management showed that spatial variation in canopy cover, yield and fruit composition across the vineyard block was substantial. Normalised difference vegetation index (NDVI) and canopy temperature data supported delineation of three irrigation management zones and decisions regarding irrigation strategy. Water use efficiency and yield improvements were achieved by implementing site-specific irrigation. Fruit composition results were varied; pH and titratable acidity showed increased similarity between zones, but other parameters maintained differences between zones. These results lend support to the use of NDVI to determine irrigation management zones.

Exposure of grapes to smoke of vegetation with varying lignin composition and accretion of lignin derived putative smoke taint compounds in wine.

Smoke taint in wines from bushfire smoke exposure has become a concern for wine producers. Smoke taint compounds are primarily derived from pyrolysis of the lignin component of fuels. This work examined the influence of the lignin composition of pyrolysed vegetation on the types of putative smoke taint compounds that accrue in wines. At veraison, Merlot vines were exposed to smoke generated from five vegetation types with differing lignin composition. Smoke was generated under pyrolysis conditions that simulated bushfire temperature profiles. Lignin and smoke composition of each fuel type along with putative smoke taint compounds in wines were determined. The results showed that, regardless of fuel type, the commonly reported guaiacyl lignin derived smoke taint compounds, guaiacol and 4-methylguaiacol, represented about 20% of the total phenols in wines. Quantitatively, syringyl lignin derived compounds dominated the total phenol pools in both free and bound forms. The contributions of p-hydroxyphenyls were generally similar to the guaiacyl sources. A further unexpected outcome of the study was that pine smoke affected wines had significantly elevated levels of syringols compared to the controls although pine fuel and its smoke emission lacked syringyl products.

Deconvoluting effects of vine and soil properties on grape berry composition

BACKGROUND Grape berry composition is influenced by several factors including grapevine and soil properties and their interactions. Understanding how these factors interact to determine berry composition is integral to producing berries with desired composition. Here we used extensive spatio-temporal data to identify significant vine and soil features that influence Shiraz berry composition. RESULTS The concentrations of berry flavonoids (anthocyanins, tannin and total phenolics), total soluble solids and pH were typically negatively associated with canopy, crop and berry size factors whereas titratable acidity was positively associated. The strengths of the associations, however, were generally greater with the crop and berry size factors than with the canopy size factor. The analyses also resolved separate influences of berry and crop size on berry composition. Soil properties had significant influences on berry composition; however, when influences of soil factors on vine-attributes were accounted for, the apparent effects of soil factors on berry composition were largely non-existent. CONCLUSION At each site, variations in berry composition were more strongly associated with crop and berry size than with canopy size factors. Apparent influences of soil properties on berry composition are indirect, being mediated via their effects on vine attributes (canopy, crop and berry sizes).

A GC-MS Based Analytical Method for Detection of Smoke Taint Associated Phenols in Smoke Affected Wines

Guaiacol and 4-methylguaiacol are routinely used as markers to determine extent of smoke impact on winegrapes and wines. However, smoke contains a complex group of compounds that may contribute to smoke taint in winegrapes and wine. In this study, a gas chromatography-mass spectrometry (GC-MS) based analytical method was developed and validated for the profiling of various smoke taint compounds in wines made from smoke affected fruit. A total of 22 analytes were separated and identified in the GC-MS chromatogram, all of which were selected to evaluate the samples and precision of the method. The GC-MS method showed good repeatability/reproducibility with intra- and inter-day relative standard deviation (RSD) of ±14%. The method was used to demonstrate that the smoked grapes and resultant wines, compared to unsmoked wines, contained significantly enhanced levels of guaiacol and 4-methylguaiacol along with other lignin derived phenols such as cresols and syringol. In smoke affected grapes and young wines, volatile phenols exist as glyco-conjugates (potential taint), which hydrolyse slowly leading to unacceptable levels of taint accumulation in wine during storage. The GC-MS method reported here, in conjunction with the optimised acid hydrolysis of phenol glycoconjugates, was successfully used to determine potential levels of smoke taint compounds in wines. Thus, the method can be used for screening smoke exposed grapes for potential taint levels prior to wine making. The results presented here highlight the need to include an array of smoke derived phenols to develop a complete picture of smoke taint and associated aroma in affected grapes and wines.

Evaluation of a semi-empirical model for predicting fine root biomass in compositionally complex woodland vegetation

We used measures of plant size, distribution and root core data to evaluate capability of the model of Ammer and Wagner [2] for spatially explicit prediction of fine root biomass (FRB) in Eucalyptus populnea-dominaied woodlands from xeric and mesic regions of Australia. Tree diameter and height were tested as proxy variables for plant size. For the xeric site, which had no understorey grass cover, both the height- and diameter-based models gave reasonable estimates of FRB. However, the height-model provided a better match to the measured data than the diameter-model. For the mesic site, which had a substantial ground cover dominated by C4-grasses whose contribution to FRB could not be captured by the model, neither the height- nor the diameter- model was able to predict FRB satisfactorily. This was also the case even when the contribution of the C4-grasses to FRB was estimated and accounted for after δ13C analysis of fine root samples. Overall, while it is evident that the model can be a useful tool for estimating FRB from aboveground stand inventory in both even-aged plantations and compositionally complex natural vegetation, it is also clear that it does not always provide satisfactory prediction, e.g., the mesic site. Thus, to improve the wider applicability of the model further work is needed to identify why it fails and situations it is likely to be useful.RésuméNous avons utilisé des mesures de dimensions des plants, de distribution et de carotte de racine pour évaluer la capacité du modèle de Ammer et Wagner [2] pour une prédiction spatiale explicite de la biomasse des fines racines (FRB) dans des zones boisées où Eucalyptus populnea est dominant, dans les régions très sèches et mésoïques d’Australie. La hauteur et le diamètre des arbres ont été testés comme des variables de procuration de la dimension du plant. Pour le site sec qui n’avait pas de sous-bois herbeux, l’un et l’autre des modèles basés sur la hauteur et le diamètre donnent une estimation raisonnable de FRB. Cependant, le modèle hauteur fourni une meilleure adéquation aux données mesurées que le modèle diamètre. Pour le site mésoïque, qui a une couverture herbeuse importante dominée par des espèces en C4 et dont la contribution à FRB ne peut pas être prise en compte par le modèle, ni l’un ni l’autre du modèle hauteur et du modèle diamètre était capable de prédire FRB correctement. C’était aussi le cas même quand la contribution des herbes en C4 à FRB a été estimée et justifiée par des analyses de δ13C de fines racines. En général, quoiqu’il soit évident que le modèle peut être un outil utile pour estimer FRB à partir d’un inventaire au-dessus du sol dans les deux plantations équiennes et dans la végétation naturelle composite, il est aussi clair que cela ne permet pas toujours une prédiction satisfaisante, par exemple pour le site moyennement sec. Alors, pour améliorer une plus large applicabilité du modèle davantage de travail est nécessaire pour identifier pourquoi il ne convient pas et les situations où il est possible de l’utiliser.

Influence of coupled ocean-atmosphere phenomena on the Greater Horn of Africa droughts and their implications

Drought-like humanitarian crises in the Greater Horn of Africa (GHA) are increasing despite recent progress in drought monitoring and prediction efforts. Notwithstanding these efforts, there remain challenges stemming from uncertainty in drought prediction, and the inflexibility and limited buffering capacity of the recurrent impacted systems. The complexity of the interactions of ENSO, IOD, IPO and NAO, arguably remains the main source of uncertainty in drought prediction. To develop practical drought risk parameters that potentially can guide investment strategies and risk-informed planning, this study quantifies, drought characteristics that underpin drought impacts management. Drought characteristics that include probability of drought-year occurrences, durations, areal-extent and their trends over 11 decades (1903-2012) were derived from the Standardized Precipitation Index (SPI).Transient probability of drought-year occurrences, modelled on Beta distribution, across the region ranges from 10 to 40%, although most fall within 20-30%. For more than half of the drought events, durations of up to 4, 7, 14 and 24months for the 3-, 6-, 12- and 24-month timescales were evident, while 1 out of 10 events persisted for up to 18months for the short timescales, and up to 36months or more for the long timescales. Apparently, only drought areal-extent showed statistically significant trends of up to 3%, 1%, 3.7%, 2.4%, 0.7%, -0.3% and -0.6% per decade over Sudan, Eritrea, Ethiopia, Somalia, Kenya, Uganda and Tanzania, respectively. Since there is no evidence of significant changes in drought characteristics, the peculiarity of drought-like crises in the GHA can be attributed (at least in part) to unaccounted for systematic rainfall reduction. This highlights the importance of distinguishing drought impacts from those associated with new levels of aridity. In principle drought is a temporary phenomenon while aridity is permanent, a difference that managers and decision-makers should be more aware.

Host–Multi-Pathogen Warfare: Pathogen Interactions in Co-infected Plants

Studies of plant–pathogen interactions have historically focused on simple models of infection involving single host-single disease systems. However, plant infections often involve multiple species and/or genotypes and exhibit complexities not captured in single host-single disease systems. Here, we review recent insights into co-infection systems focusing on the dynamics of host-multi-pathogen interactions and the implications for host susceptibility/resistance. In co-infection systems, pathogen interactions include: (i) Competition, in which competing pathogens develop physical barriers or utilize toxins to exclude competitors from resource-dense niches; (ii) Cooperation, whereby pathogens beneficially interact, by providing mutual biochemical signals essential for pathogenesis, or through functional complementation via the exchange of resources necessary for survival; (iii) Coexistence, whereby pathogens can stably coexist through niche specialization. Furthermore, hosts are also able to, actively or passively, modulate niche competition through defense responses that target at least one pathogen. Typically, however, virulent pathogens subvert host defenses to facilitate infection, and responses elicited by one pathogen may be modified in the presence of another pathogen. Evidence also exists, albeit rare, of pathogens incorporating foreign genes that broaden niche adaptation and improve virulence. Throughout this review, we draw upon examples of co-infection systems from a range of pathogen types and identify outstanding questions for future innovation in disease control strategies.

The effect of phenol composition on the sensory profile of smoke affected wines

Vineyards exposed to wildfire generated smoke can produce wines with elevated levels of lignin derived phenols that have acrid, metallic and smoky aromas and flavour attributes. While a large number of phenols are present in smoke affected wines, the effect of smoke vegetation source on the sensory descriptors has not been reported. Here we report on a descriptive sensory analysis of wines made from grapes exposed to different vegetation sources of smoke to examine: (1) the effect vegetation source has on wine sensory attribute ratings and; (2) associations between volatile and glycoconjugated phenol composition and sensory attributes. Sensory attribute ratings were determined by a trained sensory panel and phenol concentrations determined by gas chromatography-mass spectroscopy. Analysis of variance, principal component analysis and partial least squares regressions were used to evaluate the interrelationships between the phenol composition and sensory attributes. The results showed that vegetation source of smoke significantly affected sensory attribute intensity, especially the taste descriptors. Differences in aroma and taste from smoke exposure were not limited to an elevation in a range of detractive descriptors but also a masking of positive fruit descriptors. Sensory differences due to vegetation type were driven by phenol composition and concentration. In particular, the glycoconjugates of 4-hydroxy-3-methoxybenzaldehyde (vanillin), 1-(4-hydroxy-3-methoxyphenyl)ethanone (acetovanillone), 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde) and 1-(4-hydroxy-3,5-dimethoxyphenyl)ethanone (acetosyringone) concentrations were influential in separating the vegetation sources of smoke. It is concluded that the detractive aroma attributes of smoke affected wine, especially of smoke and ash, were associated with volatile phenols while the detractive flavour descriptors were correlated with glycoconjugated phenols.

Analysis of the nexus between population, water resources and Global Food Security highlights significance of governance and research investments and policy priorities: Governance and research investments as priorities for food security

BACKGROUND Analyses of sensitivity of Global Food Security (FS) score to a key set of supply or demand factors often suggest population and water supply as being the most critical and on which policies tend to focus. To explore other policy options, we characterized the nexus between GFS and a set of supply or demand factors including population, agricultural and industrial water uses, agricultural publications (as a surrogate for investment in agricultural research and development (R&D)) and corruption perception index (CPI), to reveal opportunities for attaining enduring GFS. RESULTS We found that despite being the primary driver of demand for food, population showed no significant correlation with FS scores. Similarly, agricultural water use was poorly correlated with GFS scores, except in countries where evaporation exceeds precipitation and irrigation is significant. However, FS had a strong positive association with industrial water use as a surrogate for overall industrialization. Recent expansions in cultivated land area failed to yield concomitant improvements in FS score since such expansions have been mostly into marginal lands with low productivity and thus barely compensated for lands retired from cropping in several developed economies. However, FS was positively associated with agricultural R&D investments, as it was with the CPI scores. The apparent and relative strengths of these drivers on FS outcome amongst countries were in the order: industrial water-use ≈ publication rate ≈ corruption perception ≫ agricultural water use > population. CONCLUSIONS We suggest that to enshrine enduring food security, policies should prioritize (1) increased R&D investments that address farmer needs and (2) governance mechanisms that promote accountability in both research and production value chains.

Real-Time PCR for Diagnosing and Quantifying Co-infection by Two Globally Distributed Fungal Pathogens of Wheat

Co-infections – invasions of a host-plant by multiple pathogen species or strains – are common, and are thought to have consequences for pathogen ecology and evolution. Despite their apparent significance, co-infections have received limited attention; in part due to lack of suitable quantitative tools for monitoring of co-infecting pathogens. Here, we report on a duplex real-time PCR assay that simultaneously distinguishes and quantifies co-infections by two globally important fungal pathogens of wheat: Pyrenophora tritici-repentis and Parastagonospora nodorum. These fungi share common characteristics and host species, creating a challenge for conventional disease diagnosis and subsequent management strategies. The assay uses uniquely assigned fluorogenic probes to quantify fungal biomass as nucleic acid equivalents. The probes provide highly specific target quantification with accurate discrimination against non-target closely related fungal species and host genes. Quantification of the fungal targets is linear over a wide range (5000–0.5 pg DNA μl-1) with high reproducibility (RSD ≤ 10%). In the presence of host DNA in the assay matrix, fungal biomass can be quantified up to a fungal to wheat DNA ratio of 1 to 200. The utility of the method was demonstrated using field samples of a cultivar sensitive to both pathogens. While visual and culture diagnosis suggested the presence of only one of the pathogen species, the assay revealed not only presence of both co-infecting pathogens (hence enabling asymptomatic detection) but also allowed quantification of relative abundances of the pathogens as a function of disease severity. Thus, the assay provides for accurate diagnosis; it is suitable for high-throughput screening of co-infections in epidemiological studies, and for exploring pathogen–pathogen interactions and dynamics, none of which would be possible with conventional approaches.