Giacomo Cocetta

Biostimulants and crop responses: a review

Agricultural growing practices have been evolving towards organic, sustainable or environmental friendly systems. The aim of modern agriculture is to reduce inputs without reducing the yield and quality. These goals can be achieved by breeding programmes but would be species specific and time consuming. The identification of organic molecules able to activate plant metabolism may allow an improvement in plant performance in a short period of time and in a cheaper way. Biostimulants are plant extracts and contain a wide range of bioactive compounds that are mostly still unknown. These products are usually able to improve the nutrient use efficiency of the plant and enhance tolerance to biotic and abiotic stresses. In this review, the state of the art and future prospects for biostimulants are reported and discussed. Moreover, particular attention has been paid to intensive agricultural systems such as horticultural and floricultural crops. In vegetables, the application of biostimulants allowed a reduction in fertilizers without affecting yield and quality. In leafy vegetables susceptible to nitrate accumulation, such as rocket, biostimulants have been able to improve the quality and keep the nitrates under the limits imposed by EU regulations. Moreover in leafy vegetables, biostimulants increased leaf pigments (chlorophyll and carotenoids) and plant growth by stimulating root growth and enhancing the antioxidant potential of plants. In floriculture, biostimulants used in bedding plant production stimulated the growth of plants, which reached the blooming and commercial stages earlier, thus optimizing space in the greenhouse.

Ascorbic acid metabolism during bilberry (Vaccinium myrtillus L.) fruit development

Bilberry (Vaccinium myrtillus L.) possesses a high antioxidant capacity in berries due to the presence of anthocyanins and ascorbic acid (AsA). Accumulation of AsA and the expression of the genes encoding the enzymes of the main AsA biosynthetic route and of the ascorbate-glutathione cycle, as well as the activities of the enzymes involved in AsA oxidation and recycling were investigated for the first time during the development and ripening of bilberry fruit. The results showed that the AsA level remained relatively stable during fruit maturation. The expression of the genes encoding the key enzymes in the AsA main biosynthetic route showed consistent trends with each other as well as with AsA levels, especially during the first stages of fruit ripening. The expression of genes and activities of the enzyme involved in the AsA oxidation and recycling route showed more prominent developmental stage-dependent changes during the ripening process. Different patterns of activity were found among the studied enzymes and the results were, for some enzymes, in accordance with AsA levels. In fully ripe berries, both AsA content and gene expression were significantly higher in skin than in pulp.

Evaluation of borage extracts as potential biostimulant using a phenomic, agronomic, physiological and biochemical approach

Biostimulants are substances able to improve water and nutrient use efficiency and counteract stress factors by enhancing primary and secondary metabolism. Premise of the work was to exploit raw extracts from leaves (LE) or flowers (FE) of Borago officinalis L., to enhance yield and quality of Lactuca sativa ‘Longifolia,’ and to set up a protocol to assess their effects. To this aim, an integrated study on agronomic, physiological and biochemical aspects, including also a phenomic approach, has been adopted. Extracts were diluted to 1 or 10 mL L–1, sprayed onto lettuce plants at the middle of the growing cycle and 1 day before harvest. Control plants were treated with water. Non-destructive analyses were conducted to assess the effect of extracts on biomass with an innovative imaging technique, and on leaf photosynthetic efficiency (chlorophyll a fluorescence and leaf gas exchanges). At harvest, the levels of ethylene, photosynthetic pigments, nitrate, and primary (sucrose and total sugars) and secondary (total phenols and flavonoids) metabolites, including the activity and levels of phenylalanine ammonia lyase (PAL) were assessed. Moreover, a preliminary study of the effects during postharvest was performed. Borage extracts enhanced the primary metabolism by increasing leaf pigments and photosynthetic activity. Plant fresh weight increased upon treatments with 10 mL L–1 doses, as correctly estimated by multi-view angles images. Chlorophyll a fluorescence data showed that FEs were able to increase the number of active reaction centers per cross section; a similar trend was observed for the performance index. Ethylene was three-fold lower in FEs treatments. Nitrate and sugar levels did not change in response to the different treatments. Total flavonoids and phenols, as well as the total protein levels, the in vitro PAL specific activity, and the levels of PAL-like polypeptides were increased by all borage extracts, with particular regard to FEs. FEs also proved efficient in preventing degradation and inducing an increase in photosynthetic pigments during storage. In conclusion, borage extracts, with particular regard to the flower ones, appear to indeed exert biostimulant effects on lettuce; future work will be required to further investigate on their efficacy in different conditions and/or species.

The Antioxidants Changes in Ornamental Flowers during Development and Senescence

The concentration of antioxidant compounds is constitutive and variable from species to species and is also variable considering the development of the plant tissue. In this review, we take into consideration the antioxidant changes and the physiological, biochemical and molecular factors that are able to modulate the accumulation of antioxidant compounds in ornamental flowers during the whole development process until the senescence. Many ornamental flowers are natural sources of very important bioactive compounds with benefit to the human health and their possible role as dietary components has been reported. The most part of antioxidants are flower pigments such as carotenoids and polyphenols, often present in higher concentration compared with the most common fruits and vegetables. The antioxidants content changes during development and during senescence many biochemical systems and molecular mechanisms are activated to counteract the increase of reactive oxygen species and free radicals. There is a tight correlation between antioxidants and senescence processes and this aspect is detailed and appropriately discussed.

Spatial and temporal transcriptome changes occurring during flower opening and senescence of the ephemeral hibiscus flower, Hibiscus rosa-sinensis

Highlight Pathway analysis suggests that identified temporal and spatial transcriptomic changes associated with senescence of the short-lived hibiscus flower are regulated by light/circadian clock-, aquaporin-, cell wall-, and calcium-related gene families.

Identification of innovative potential quality markers in rocket and melon fresh-cut produce

Ready-to-eat fresh cut produce are exposed to pre- and postharvest abiotic stresses during the production chain. Our work aimed to identify stress responsive genes as new molecular markers of quality that can be widely applied to leaves and fruits and easily determined at any stage of the production chain. Stress responsive genes associated with quality losses were isolated in rocket and melon fresh-cut produce and their expression levels analyzed by quantitative real time PCR (qRT-PCR) at different time points after harvest at 20 °C and 4 °C. qRT-PCR results were supported by correlation analysis with physiological and biochemical determinations evaluated at the same conditions such as chlorophyll a fluorescence indices, total, reducing sugars, sucrose, ethylene, ascorbic acid, lipid peroxidation and reactive oxygen species. In both species the putative molecular markers increased their expression soon after harvest suggesting a possible use as novel and objective quality markers of fresh-cut produces.

Comparative physiology during ripening in tomato rich-anthocyanins fruits

Solanum lycopersicum L. (tomato) is a very important fruit vegetable with high economic importance and nutritional impact on the consumers worldwide. Moreover, tomato fruits are an important source of nutraceutical compounds. This work describes the physiological diversity affecting the ripening process that yields variation in fruit pigmentation with regard to anthocyanins compounds for one non-anthocyanin-accumulating (Ailsa Craig) and two anthocyanin-accumulating tomato genotypes (anthocyanin fruit type, low pigment accumulation, and Sun Black, high pigment accumulation). Using tomato fruits obtained by traditional breeding the present study reported modified hormone equilibrium at different ripening stages. This phenomenon can be considered as a consequence of the different pattern in the anthocyanins accumulation in fruits. Moreover, the fruit genotype showing the highest pigment accumulation appear more firm at the commercial stage. Overall, these results showed the considerable potential of exploiting natural genetic diversity to obtain tomatoes with higher levels of anthocyanins, and different quality traits such as colour and firmness.

Gene expression analysis of rocket salad under pre-harvest and postharvest stresses : a transcriptomic resource for Diplotaxis tenuifolia

Diplotaxis tenuifolia L. is of important economic value in the fresh-cut industry for its nutraceutical and sensorial properties. However, information on the molecular mechanisms conferring tolerance of harvested leaves to pre- and postharvest stresses during processing and shelf-life have never been investigated. Here, we provide the first transcriptomic resource of rocket by de novo RNA sequencing assembly, functional annotation and stress-induced expression analysis of 33874 transcripts. Transcriptomic changes in leaves subjected to commercially-relevant pre-harvest (salinity, heat and nitrogen starvation) and postharvest stresses (cold, dehydration, dark, wounding) known to affect quality and shelf-life were analysed 24h after stress treatment, a timing relevant to subsequent processing of salad leaves. Transcription factors and genes involved in plant growth regulator signaling, autophagy, senescence and glucosinolate metabolism were the most affected by the stresses. Hundreds of genes with unknown function but uniquely expressed under stress were identified, providing candidates to investigate stress responses in rocket. Dehydration and wounding had the greatest effect on the transcriptome and different stresses elicited changes in the expression of genes related to overlapping groups of hormones. These data will allow development of approaches targeted at improving stress tolerance, quality and shelf-life of rocket with direct applications in the fresh-cut industries.

Nondestructive Apple Ripening Stage Determination Using the Delta Absorbance Meter at Harvest and after Storage

The delta absorbance (DA) meter is a handheld instrument which noninvasivelymeasures the chlorophyll content in fruits. In the present work, it was used to monitor the ripening process linked to the climacteric phase in apple (Malus ·domestica). The results [index of absorbance difference (IAD)] were correlated to quality attributes at harvest and after commercial scale storage at different conditions. Two cultivars (Red Delicious, Golden Delicious) were analyzed in two different seasons, whereas Morgenduft and Gala were analyzed only in the first and second seasons, respectively. In general, a linear reduction of the IAD values was observed in all apple cultivars along with the progression of ripening and ethylene biosynthesis.When ethylene productionwas inhibited by 1-methylcyclopropene (1MCP) treatment, the decrease of IAD values was markedly reduced. IAD threshold values for each cultivar were identified, delineating the central phase of the ethylene climacteric rise. Predictive models were built by correlating IAD index to the soluble solids concentration (SSC), titratable acidity (TA), and firmness measured at harvest and after removal from different storage regimes. The best model was developed for SSCprediction on ‘RedDelicious’ apple [ratio performance deviation (RPD) = 1.88] and for firmess evaluation in ‘GoldenDelicious’ apple (RPD = 1.84). Moreover, IAD values were consistently associated with the differences in fruit quality as affected by optimal and suboptimal storage conditions. The IAD, due to its acceptable accuracy and speed of assessment, can be a promising tool for assisting in sorting apples before and after storage in warehouses or commercial packing lines. IAD cannot totally replace standard ripening indices, but can effectively supplement data for these parameters.

Use of Spectral and Thermal Imaging Sensors to Monitor Crop Water and Nitrogen Status

High spatial and temporal resolution monitoring methods are the key to improve the efficiency in water and fertilizer input management. In this context, this work presents the set-up and the first results of a greenhouse experiment conducted on two crops with a different canopy geometry (rice and spinach) subjected to four nitrogen treatments. The experiment involves the acquisition of thermal, multispectral and hyperspectral images at three phenological stages for each crop. At each stage, spectral acquisitions are conducted on one-third of the pots, at good water conditions and, later on, at different times after interruption of irrigation. The total number of pots in the experiment is 72 (corresponding to 4 nitrogen levels x 2 crops x 3 phenological stages x 3 replicates). Just after the spectra acquisitions, non-destructive and destructive measurements of variables correlated with the crops nitrogen and water status are conducted. Multivariate regression analysis between the spectra features and measured variables will be used to identify predicting models for the estimation of crop water and nitrogen status. The most significant wavelengths for the detection of water and nitrogen stress could be the subject of a future experimentation in open field conditions using multispectral systems.