Victor O. Sadras

Metabolic effects of elevated temperature on organic acid degradation in ripening Vitis vinifera fruit

Summary Experiments conducted under controlled conditions in vineyards and growth chambers demonstrated day- and night-specific responses of grape berry organic acid levels through altered TCA cycle and amino acid metabolism.

Elevated temperature and water stress accelerate mesocarp cell death and shrivelling, and decouple sensory traits in Shiraz berries

Both water deficit and elevated temperature are likely to accelerate shrivelling in Shiraz berries with consequences for fruit yield and quality. The process of shrivelling is partially related to mesocarp cell death and it has been proposed that enhancement of berry flavour and aroma also correlates with mesocarp cell death. However, the combined effects of water deficit and elevated temperature on berry shrivelling, mesocarp cell death and berry sensory traits are unknown. We tested the hypotheses that (1) the effects of water deficit and elevated temperature on the dynamics of mesocarp cell death and shrivelling are additive, and that (2) faster cell death, as driven by warming and water deficit, negatively contributes to grape sensory balance. Using open-top chambers to elevate day and night temperature, we compared heated vines against controls at ambient temperature. Thermal regimes were factorially combined with two irrigation regimes, fully irrigated and water deficit, during berry ripening. The dynamic of cell death was characterised by a bilinear model with three parameters: the onset of rapid cell death and the rate of cell death before and after the onset of rapid cell death. Statistical comparison of these three parameters indicated that there was not interaction between water and temperature on the dynamics of berry mesocarp cell death. Warming advanced the onset of cell death by ~9xa0days (Pxa0=xa00.0002) and water stress increased the rate of cell death in the period post onset (Pxa0=xa00.0007). Both water stress and elevated temperature increased the proportion of cell death and shrivelling at harvest. An interaction between water deficit and elevated temperature was found whereby the onset of berry net water loss was advanced by elevated temperature under water deficit but not in the fully irrigated treatment. Sensory traits typical of ripened berries were associated with higher cell death; however, warming and water deficit hastened ripening and altered the balance of berry sensory traits.

Whither Crop Physiology

In crop physiology, as in many other disciplines, the degree of understanding varies across fields. Patchiness in the coverage of any particular field becomes more obvious as the limits of the selected field are broadened, and judgments as to relative progress when comparing fields can become highly subjective. Some of this patchiness results from an inherent difficulty in methods but most of it stems from current perceptions of the relative importance of different fields in plant and crop sciences. Crop simulation models improved to incorporate new knowledge about soils, crop physiology, and atmospheric processes continue to act as powerful tools for integrating information about the many processes underlying the formation and realization of yield. Also, these models continue to prove irreplaceable in exploring new situations (such as the one that can arise from alterations in agronomic practice) and in providing multiyear and multienvironment perspectives impossible to obtain by direct experimentation.

Light-mediated self-organization of sunflower stands increases oil yield in the field

Significance Self-organization in biological systems spans from molecular to ecosystem levels. In plant populations and communities, only a primitive mode of self-organization has been described, which involves changes in demography (survival of individuals affected by the availability of resources). Here, we show that sunflower plants cultivated in high-density stands perceive light signals from their immediate neighbors, adopt alternate positions of their single stem along the crop row, and collectively increase production per unit land area. This process is a case where a communicative sensory network leads to self-organization in plants, without changes in demography. Agronomic and genetic adaptations will be necessary to capture the increased oil production of self-organized stands. Here, we show a unique crop response to intraspecific interference, whereby neighboring sunflower plants in a row avoid each other by growing toward a more favorable light environment and collectively increase production per unit land area. In high-density stands, a given plant inclined toward one side of the interrow space, and the immediate neighbors inclined in the opposite direction. This process started early as an incipient inclination of pioneer plants, and the arrangement propagated gradually as a “wave” of alternate inclination that persisted until maturity. Measurements and experimental manipulation of light spectral composition indicate that these responses are mediated by changes in the red/far-red ratio of the light, which is perceived by phytochrome. Cellular automata simulations reproduced the patterns of stem inclination in field experiments, supporting the proposition of self-organization of stand structure. Under high crop population densities (10 and 14 plants per m2), as yet unachievable in commercial farms with current hybrids due to lodging and diseases, self-organized crops yielded between 19 and 47% more oil than crops forced to remain erect.

Delving of sandy surfaced soils reduces frost damage in wheat crops

Delving is a farming practice involving the mixing of a deep clayey subsoil layer with a sandy topsoil. One of the many effects of this practice is to reduce soil albedo and increase water-holding capacity of the topsoil, thus increasing the potential for storage and release of heat and potential attenuation of the effects of radiative frost. At Keith, a frost-prone location of South Australia, we investigated the effect of management practices with putative capacity to reduce frost damage, with emphasis on delving. Three field experiments were established on Brown Sodosols with a water-repellent sand topsoil. In relation to crops in untreated control soil, delving increased wheat yield from 1.9 to 3.1u2009t/ha in 2003, and from 0.5 to 1.5u2009t/ha in 2004. This large delving effect contrasted with the minor effects of other treatments including soil rolling, sowing rate, row spacing, and cultivar mixture. Lack of significant interactions between treatments indicated a robust response to delving across a range of management practices. Topsoil and canopy-height minimum temperatures were consistently higher in the delved treatment. The average difference in canopy-height minimum temperature between delved and control treatments was 0.3–0.4°C, with a maximum of 1.6°C in 2003 and 1.2°C in 2004. A single, robust relationship between yield and frost damage fitted the data pooled across treatments and seasons. This, together with the temperature differential between treatments, and significant relationships between minimum canopy-height temperature around flowering and frost damage supported the conclusion that a substantial part of the yield gain attributable to delving was related to reduced frost damage.

Agronomic and environmental drivers of population size and symbiotic performance of Rhizobium leguminosarum bv. viciae in Mediterranean-type environments

Abstract. n The population size and symbiotic performance (ability to fix N2) of rhizobia (Rhizobium leguminosarum bv. viciae) capable of nodulating field pea (Pisum sativum) were assessed in 114 soils from Mediterranean-type environments of southern Australia. All soils were collected in autumn, before the growing season, and had a history of crop legumes including field pea, faba bean, lentil, or vetch. The most probable number (MPN) technique, with vetch as a trap plant, was used to estimate the numbers of pea rhizobia in soils. Of the soils tested, 29% had low numbers of pea rhizobia (<100u2009rhizobia/g), 38% had moderate numbers (100–1000/g), and the remaining 33% had >1000/g. Soil pH, the frequency of a host crop in the rotation, and the number of summer days with a maximum temperature >35°C were strongly correlated with the pea rhizobia population size. Symbiotic performance (SP) of pea rhizobia in soils was assessed for soils with a MPN >100u2009rhizobia/g. An extract of the soils was used to inoculate two field pea cultivars growing in a nitrogen-deficient potting media in the greenhouse. Plants were grown for 5 weeks after inoculation and shoot dry matter was expressed as a percentage of the dry matter of plants grown with a commercial strain R. leguminosarum bv. viciae, SU303. Symbiotic performance ranged from 25 to 125%. One-quarter of the soils assessed had suboptimal SP (i.e. <70%). Soil and climatic variables were weakly associated with SP, with pH and average annual rainfall accounting for 17% of the variance. This research highlights the complexity of factors influencing population size and symbiotic performance of pea rhizobia in soils. Options for the improved management of populations of pea rhizobia in Mediterranean environments are discussed. Specifically, our data indicate that inoculation of pea crops is likely to be beneficial where pH(H2O) <6.6, particularly when summers have been hot and dry and when a host has been absent for ≥5 years, as numbers of rhizobia are likely to be below the thresholds needed to optimise nodulation and crop growth. New inoculation technologies and plant breeding will be required to overcome large populations of pea rhizobia with suboptimal SP.

Hypoxia in grape berries: the role of seed respiration and lenticels on the berry pedicel and the possible link to cell death

Grape berry internal oxygen concentration is dependent upon lenticels on the pedicel, and cell death in the mesocarp is correlated to hypoxia during ripening.

Late pruning impacts on chemical and sensory attributes of Shiraz wine: Late pruning impact on wine

Background and Aims n nWarming has two major effects on the wine industry: compressing harvest duration, thus stressing the current capacity of wineries to process more fruit in a shorter time, and compromising fruit composition and wine style. Late pruning can effectively delay vine development and contribute to decompressing harvest, but its impact on wine is unknown. Our aim was to measure the effects of late pruning on wine chemical and sensory attributes. nMethods and Results n nWe compared wines made from Shiraz vines pruned in winter (Control), and in two late pruning stages, when Controls reached budburst and 2–3 leaves in two vintages. Late pruning consistently increased wine anthocyanin, tannin, pigmented tannin and colour density and altered the wines sensory profiles over two vintages. In 2014, colour intensity, fruit aroma, fruit flavours and body were more intense in wine made from late pruning treatments. In 2015, wine made from late pruning treatments showed more intense savoury flavours with a dryer palate and a smoother texture tannin (roughing sub‐quality). The colour improvement was associated with cooler temperature 1 week after veraison in the late‐pruned vines. nConclusions n nLate pruning consistently improved wine chemical composition and altered sensory profiles of Shiraz under Barossa Valley conditions. nSignificance of the Study n nLate pruning is a cost‐effective tool to decompress harvest, with neutral effects on yield and positive effects on wine chemical attributes with enhancement of fruit and colour intensity perception in an extended vintage (2014), and smoother tannin texture with dryer perception in a short and compressed vintage (2015).

Effect of water stress and elevated temperature on hypoxia and cell death in the mesocarp of Shiraz berries: Berry hypoxia and death under water/heat stress

Background and Aim n nBerry shrivel during ripening is cultivar dependent and is correlated with berry cell death (CD). We hypothesised that under heat stress and water stress, regions of the pericarp in Shiraz berries would become hypoxic depending on berry porosity, and that this would induce CD. nMethods and Results n nWe measured CD and [O2] across the pericarp in berries developed under the factorial combination of two thermal regimes (ambient and heated) and two irrigation regimes (irrigated and non‐irrigated) in the Barossa Valley, South Australia. Heating increased ambient temperature by 0.6°C for irrigated and 1°C for non‐irrigated vines but had no effect on water relations, while non‐irrigation decreased stomatal conductance and stem water potential. Non‐irrigation decreased berry [O2] and increased both CD and ethanol concentration relative to irrigation. An association was established between mesocarp [O2] and CD. Berry respiration and total berry porosity decreased during berry ripening, but relative locule air‐space measured by X‐ray micro‐computed tomography increased late in ripening. Heating had little or no effect on CD or [O2] but decreased berry porosity, which was not affected by irrigation. nConclusion n nWater stress increased berry CD, which was associated with increased hypoxia. nSignificance of the Study n nThe association between berry [O2] and CD provides insights into berry ripening with implications for yield and berry flavour.

Late Pruning and Elevated Temperature Impact On Phenology, Yield Components and Berry Traits in Shiraz

Recent warming has shortened and compressed vintages and has altered enologically relevant berry traits. Late pruning can decompress harvest and preserve fruit quality. Here, we were interested in exploring the interactive effects of late pruning and heating on Shiraz development and composition. We established a factorial experiment that combined two thermal regimes (ambient versus heated) with open-top chambers, and three pruning times (late pruning at budbreak and at two to three leaves, a winter control) in Shiraz vines over three seasons in the Barossa Valley. Late pruning delayed budbreak by up to 23 days, flowering by up to 17 days, and veraison by up to 16 days. Heating advanced flowering in late-pruned vines by up to seven days, with a minor effect in winter-pruned controls. Heating advanced veraison by up to seven days, with greater advances in years with warmer springs. Pruning weights were unaffected by late pruning and were increased by heating. Yield was increased in a single season by late pruning and heating, but it remained unchanged for the pooled three-year data. Late pruning delayed maturity in four of six cases; the largest delay was 17 days in unheated vines pruned when two to three leaves had emerged. Late pruning maintained the anthocyanin-to-sugar ratio, which decreased with heating in two seasons. There was an interaction between the timing of pruning and heating, whereby late pruning enhanced the berry tannin-to-sugar ratio in heated but not in unheated control vines. Late pruning delayed the harvest by shifting the onset and rate of ripening, with a higher degree of response in the warmest season in both ambient and heated treatments.