Influence of Experimental Warming on the Rate and Duration of Fruit Growth and Oil Accumulation in Young Olive Trees (cvs. Arbequina, Coratina)

Olive tree cultivation in new warmer areas and climate change have increased the global interest in understanding how air temperature affects both fruit growth and oil accumulation. The aims of this study were to evaluate the rate and duration of fruit growth and oil accumulation in response to experimental warming (+3) in a semiarid region of Argentina; and assess how warming affected fatty acid composition. Young, potted olive trees (cvs. Arbequina, Coratina) were warmed (T+) or maintained near ambient temperature (T0) inside open top chambers in the field during oil accumulation in 2014-2015 or 2015-2016 using different trees in each season. Warming reduced the rate of both fruit growth and oil accumulation in T+ compared to T0 in both cultivars. These rate reductions under T+ led to large decreases in final fruit dry weight and oil concentration. In contrast, the durations (i.e., days) of fruit growth and oil accumulation were most often not affected. Cultivar x temperature interactions were observed in 2014-2015 with warming decreasing oleic acid and increasing linoleic acid in cv. Arbequina, while cv. Coratina showed no response to warming. However, no interactions were found in 2015-2016. Studying how fruit growth and oil accumulation respond to adaptation strategies against increasing air temperatures should be a priority in both young and mature olive trees of numerous cultivars given crop expansion to new regions and future climate scenarios.

Influence of environmental growth temperature on tocopherol and sterol oil concentrations in olive fruit

BACKGROUND

Tocopherols and sterols are minor components of virgin olive oils that contribute to oil quality. Based on observations at different geographical locations, it has been suggested that environmental temperature during fruit growth affects tocopherol and sterol oil concentrations in olive fruit. However, controlled experiments have not been conducted to directly assess their responses to temperature. In this study, a manipulative experiment using open-top chambers (OTCs) was performed in the field to evaluate the responses of these oil components to a moderate air temperature increase during oil accumulation in young trees of two olive cultivars (Arbequina, Coratina). The two temperature levels in the OTCs were a control about 1 °C above ambient temperature (T0) and a heated treatment (T+) with a target temperature of 4 °C above T0.

RESULTS

Total tocopherol and sterol oil concentrations in olive fruit were generally higher in the T+ temperature treatment than in the control at the end of the oil accumulation period. The increase in total tocopherols in T+ appeared to be related to a decrease in fruit oil concentration with heating. Individual sterols showed both significant increases and decreases due to T+, and some differences in response occurred between the two cultivars.

CONCLUSION

These findings provide evidence that growth temperature affects tocopherol and sterol oil concentrations in olive fruit at the end of the oil accumulation period. Cultivars should be carefully chosen for new olive-growing regions, and the results could be relevant for global warming scenarios in existing growing regions. © 2021 Society of Chemical Industry.

Effects of prolonged elevated temperature on leaf gas exchange and other leaf traits in young olive trees

Despite the economic importance of long-lived crop species in the Mediterranean Basin and their expansion to new warmer regions, their potential responses to prolonged temperature increases have not been adequately addressed. The objectives of this study were to: (i) assess leaf gas exchange responses to prolonged elevated temperature in young olive trees; (ii) evaluate some additional leaf traits such as stomatal density and size under these same conditions; and (iii) determine whether photosynthetic acclimation to temperature was apparent. A field experiment with two temperature levels was conducted using well-irrigated, potted olive trees (cvs. Arbequina, Coratina) grown in open-top chambers during the summer and early fall in two growing seasons. The temperature levels were a near-ambient control (T0) and a heated (T+) treatment (+4 °C). Maximum photosynthetic rate (Amax), stomatal conductance (gs), transpiration (E) and chlorophyll fluorescence were measured. Stomatal size and density and trichome density were also determined. The Amax, gs and chlorophyll fluorescence were little affected by heating. However, leaf E was higher at T+ than T0 in the summer in both seasons due in large part to the moderate increase in vapor pressure deficit that accompanied heating, and consequently water-use efficiency was reduced in heated leaves. When reciprocal temperature measurements were conducted in mid-summer of the second season, Amax values of T0 and T+ leaves were higher under the temperature level at which they grew than when measured at the other temperature level, which suggests some thermal acclimation. Stomatal size and density were greater in T+ than in T0 grown leaves in some cases, which was consistent with a greater E in T+ leaves when measured at both temperature levels. These results suggest that acclimation to long-term changes in temperature must be carefully considered to help determine how olive trees will be influenced by global warming.

Olive Cultivation in the Southern Hemisphere: Flowering, Water Requirements and Oil Quality Responses to New Crop Environments

Olive (Olea europaea L.) is a crop well adapted to the environmental conditions prevailing in the Mediterranean Basin. Nevertheless, the increasing international demand for olive oil and table olives in the last two decades has led to expansion of olive cultivation in some countries of the southern hemisphere, notably in Argentina, Chile, Perú and Australia. While the percentage of world production represented by these countries is still low, many of the new production regions do not have typical Mediterranean climates, and some are located at subtropical latitudes where there is relatively little information about crop function. Thus, the primary objective of this review was to assess recently published scientific literature on olive cultivation in these new crop environments. The review focuses on three main aspects: (a) chilling requirements for flowering, (b) water requirements and irrigation management, and (c) environmental effects on fruit oil concentration and quality. In many arid and semiarid regions of South America, temperatures are high and rainfall is low in the winter and early spring months compared to conditions in much of the Mediterranean Basin. High temperatures have often been found to have detrimental effects on olive flowering in many olive cultivars that have been introduced to South America, and a better understanding of chilling requirements is needed. Lack of rainfall in the winter and spring also has resulted in an urgent need to evaluate water requirements from the flower differentiation period in the winter to early fruit bearing. Additionally, in some olive growing areas of South America and Australia, high early season temperatures affect the timing of phenological events such that the onset of oil synthesis occurs sooner than in the Mediterranean Basin with most oil accumulation taking place in the summer when temperatures are very high. Increasing mean daily temperatures have been demonstrated to decrease fruit oil concentration (%) and negatively affect some aspects of oil quality based on both correlative field studies and manipulative experiments. From a practical standpoint, current findings could be used as approximate tools to determine whether the temperature conditions in a proposed new growing region are appropriate for achieving sustainable oil productivity and quality.

QTL analysis of fruit antioxidants in tomato using Lycopersicon pennellii introgression lines

Antioxidants present in fruits and vegetables may help prevent some chronic diseases such as cancer, arthritis, and heart disease. Tomatoes provide a major contribution to human dietary nutrition because of their widespread consumption in fresh and processed forms. A tomato introgression line population that combines single chromosomal segments introgressed from the wild, green fruited species Lycopersicon pennellii in the background of the domesticated tomato, Lycopersicon esculentum, was used to identify quantitative trait loci (QTL) for nutritional and antioxidant contents. The concentration of ascorbic acid, total phenolics, lycopene and beta-carotene, and the total antioxidant capacity of the water-soluble fraction (TACW) were measured in the ripe fruits. A total of 20 QTL were identified, including five for TACW (ao), six for ascorbic acid (aa), and nine for total phenolics (phe). Some of these QTL (ao6-2, ao6-3, ao7-2, ao10-1, aa12-4, phe6-2, and phe7-4) increased levels as compared to the parental line L. esculentum. For lycopene content, we detected four QTL, but none increased levels relative to L. esculentum. The two QTL (bc6-2 and bc6-3) detected for beta-carotene increased its levels. The traits studied displayed a strong environmental interaction as only 35% of the water-soluble antioxidant QTL (including TACW, ascorbic, and phenolic contents) were consistent over at least two seasons. Also, only two QTL for phenolics were observed when plants were grown in the greenhouse and none was detected for ascorbic or TACW. The analysis demonstrates that the introgression of wild germplasm may improve the nutritional quality of tomatoes; however regulation appears to be complex with strong environmental effects.

Plant responses to current solar ultraviolet-B radiation and to supplemented solar ultraviolet-B radiation simulating ozone depletion: an experimental comparison

Field experiments assessing UV-B effects on plants have been conducted using two contrasting techniques: supplementation of solar UV-B with radiation from fluorescent UV lamps and the exclusion of solar UV-B with filters. We compared these two approaches by growing lettuce and oat simultaneously under three conditions: UV-B exclusion, near-ambient UV-B (control) and UV-B supplementation (simulating a 30% ozone depletion). This permitted computation of "solar UV-B" and "supplemental UV-B" effects. Microclimate and photosynthetically active radiation were the same under the two treatments and the control. Excluding UV-B changed total UV-B radiation more than did supplementing UV-B, but the UV-B supplementation contained more "biologically effective" shortwave radiation. For oat, solar UV-B had a greater effect than supplemental UV-B on main shoot leaf area and main shoot mass, but supplemental UV-B had a greater effect on leaf and tiller number and UV-B-absorbing compounds. For lettuce, growth and stomatal density generally responded similarly to both solar UV-B and supplemented UV-B radiation, but UV-absorbing compounds responded more to supplemental UV-B, as in oat. Because of the marked spectral differences between the techniques, experiments using UV-B exclusion are most suited to assessing effects of present-day UV-B radiation, whereas UV-B supplementation experiments are most appropriate for addressing the ozone depletion issue.

Solar UV-B radiation affects leaf quality and insect herbivory in the southern beech tree Nothofagus antarctica

We examined the effects of solar ultraviolet-B (UV-B) radiation on plant-insect interactions in Tierra del Fuego (55 degrees S), Argentina, an area strongly affected by ozone depletion because of its proximity to Antarctica. Solar UV-B under Nothofagus antarctica branches was manipulated using a polyester plastic film to attenuate UV-B (uvb-) and an Aclar film to provide near-ambient UV-B (uvb+). The plastic films were placed on both north-facing (i.e., high solar radiation in the Southern Hemisphere) and south-facing branches. Insects consumed 40% less leaf area from north- than from south-facing branches, and at least 30% less area from uvb+ branches than from uvb- branches. The reduced herbivory on leaves from uvb+ branches occurred for both branch orientations. Leaf mass per area increased and relative water content decreased on north- versus south-facing branches, while no differences were apparent between the UV-B treatments. Solar UV-B did lead to lower gallic acid concentration and higher flavonoid aglycone concentration in uvb+ leaves relative to uvb- leaves. Both the flavonoid aglycone and quercetin-3-arabinopyranoside were higher on north-facing branches. In laboratory preference experiments, larvae of the dominant insect in the natural community, Geometridae "Brown" (Lepidoptera), consumed less area from field-grown uvb+ leaves than from uvb- leaves in 1996-97, but not in 1997-98. Correlation analyses suggested that the reduction in insect herbivory in the field under solar UV-B may be mediated in part by the UV-B effects on gallic acid and flavonoid aglycone.

Ozone depletion and UVB radiation: impact on plant DNA damage in southern South America

The primary motivation behind the considerable effort in studying stratospheric ozone depletion is the potential for biological consequences of increased solar UVB (280-315 nm) radiation. Yet, direct links between ozone depletion and biological impacts have been established only for organisms of Antarctic waters under the influence of the ozone "hole;" no direct evidence exists that ozone-related variations in UVB affect ecosystems of temperate latitudes. Indeed, calculations based on laboratory studies with plants suggest that the biological impact of ozone depletion (measured by the formation of cyclobutane pyrimidine dimers in DNA) is likely to be less marked than previously thought, because UVA quanta (315-400 nm) may also cause significant damage, and UVA is unaffected by ozone depletion. Herein, we show that the temperate ecosystems of southern South America have been subjected to increasingly high levels of ozone depletion during the last decade. We found that in the spring of 1997, despite frequent cloud cover, the passages of the ozone hole over Tierra del Fuego (55 degrees S) caused concomitant increases in solar UV and that the enhanced ground-level UV led to significant increases in DNA damage in the native plant Gunnera magellanica. The fluctuations in solar UV explained a large proportion of the variation in DNA damage (up to 68%), particularly when the solar UV was weighted for biological effectiveness according to action spectra that assume a sharp decline in quantum efficiency with increasing wavelength from the UVB into the UVA regions of the spectrum.