Author: Tamara Baumann

With its positive contribution to aroma, Metschnikowia pulcherrimais emerging as a valuable yeast in winemaking. The trial conducted suggests that bioprospection is an effective strategy for leveraging local microbial biodiversity.

In 2021, a campaign for the isolation and genetic identification of microorganisms was conducted in four Swiss Cantons by taking samples from the vineyard and the cellars. Seven yeast genera were isolated, among which Metschnikowia pulcherrima (Mp) accounted for 24% of the total population (Figure 1). After isolation and the establishment of a biobank, these strains were tested during fermentation to assess their biochemical parameters and their ability to produce volatile compounds. The aim was to select a low-fermentation-strength yeast capable of producing an abundance of higher alcohols while generating only low amounts of undesirable compounds (acetic acid or acetaldehyde). The results showed a wide variability between the isolates. Ultimately, the Mp strain isolated in the Canton of Vaud (UASWS2926 VBI-A02) was retained for vinification testing of Chasselas must in the laboratory (2021) and afterwards in an experimental cellar (2022) owing to its outstanding production of 2-phenylethanol and its low levels of undesirable compounds. The aim was to discover whether this yeast could contribute to the creation of new aromas to enrich the aromatic profile of Chasselas wine.

Wide microbial variability in the cellar

In the laboratory, two conditions were compared: a classic fermentation (CC) with a commercial Saccharomyces cerevisiae (Sc) strain, and a sequential fermentation (SF) in which Mp was inoculated five days before Sc. Microbiological monitoring of alcoholic fermentation (AF) was performed via flow cytometry (FCM) to measure cell concentration and activity using fluorescent markers. In addition, samples were taken to determine biochemical parameters via high-performance liquid chromatography (HPLC). A trial was then conducted in the cellar in which three conditions were tested: CC, SF and pied de cuve (PDC) using a starter prepared from grapes one week before the harvest. The results of the cellar trial (Figure 2) show that Mp exhibits low fermentation activity before the inoculation of Sc.  Moreover, the results obtained via FCM indicate that Mp remains active, albeit in low amounts, until the addition of Sc, which corroborates the observations made in the laboratory.

Samples were taken at different stages of AF (must in cellar, 1/3 into AF, 2/3 into AF, end of AF), to enable DNA extraction, amplification and sequencing with the aim of identifying the microbial communities present in the Chasselas must. The results highlighted a wide variability between the three conditions tested (Figure 3). It was observed that after inoculation of Mp into the must, the relative abundance of autochthonous yeasts such as Hanseniaspora uvarum and fungi such as Aureobasidium pullulans decreased with respect to the PDC condition. By contrast, H. uvarum and other yeasts persisted in the presence of Sc throughout AF in the PDC condition. The wines underwent malolactic fermentation, chemical stabilisation and filtration before being bottled to await tasting.telles que Hanseniaspora uvarum et des champignons tels qu’Aureobasidium pullulans a diminué par rapport au PDC. Dans ce dernier, en revanche, H. uvarum et d’autres levures ont persisté en présence de Sc tout au long de la FA. Les vins ont subi une fermentation malolactique, une stabilisation chimique et une filtration avant d’être mis en bouteille en attendant d’être dégustés.

Mp contributes an aromatic note

Biochemical analysis of the wines revealed no major differences between the different conditions. Nevertheless, the sensory analysis revealed a slightly more floral character in the SF wine than in the PDC wine, although the difference was not statistically significant. By contrast, the SF wine exhibited a significantly stronger lactic character, and the wines from the CC and SF conditions were preferred to those of the PDC condition.

Although there is enormous microbial diversity in blueberry substrate, there is no strong correlation between diversity and yield, according to a new Agroscope study examining the interaction of soil biology and cropping system.

In recent decades blueberry crops have become increasingly important at both national and international level. In Switzerland, around 700 tonnes of blueberries were produced and marketed in 2024.

For both biological and physicochemical reasons, soil and substrate are decisive factors for blueberry production. Of particular importance are mycorrhizal fungi, which live on the roots and help blueberry plants absorb nutrients that are in short supply, such as nitrogen and phosphorus.

Agroscope conducted a study on nine blueberry plantations to determine the influence of mycorrhizal fungi on plant yield and vegetative growth. The aim was to gain a better understanding of the role of soil microbiology in blueberry cultivation and to develop potential optimisation strategies for sustainable production.

Several thousand species groups of bacteria and fungi

The study revealed an immense variety of bacteria and fungi in the substrates of all plantations. Several thousand microbial species groups were identified, highlighting the biological complexity and the potential of these substrates.

Although the plantations examined clearly differed in terms of the prevalence and composition of microbial diversity, no significant difference in the prevalence of mycorrhizal fungi was found between organic production and integrated production (IP). This suggests that the production system affects these specific microorganisms less than previously assumed.

No significant effect of microbial diversity on yield

In addition, although no significant correlation was found between the microbial diversity of the substrate and agronomic performance, previous studies showed that mycorrhizal fungi and other soil microorganisms may be crucial for plant health and nutrient uptake. This suggests that other factors such as nutrient availability or management practices play a more important role on the plantations studied.

Targeted pH management pays off

Substrate pH also proved to be a key factor in agronomic performance. True, blueberries require an acid environment for optimal growth, but too low a pH can negatively affect growth and yields. The significantly positive correlation between pH and yield underscores how important targeted pH management is for high-yielding, sustainable blueberry production.

The results of this study highlight the importance of holistic substrate management that not only takes into account the microbial population but also focuses on physicochemical parameters such as pH and nutrient supply.

Agroscope researchers tested three natural antagonists of the tomato leafminer on six tomato genotypes. Of the three genotypes displaying a degree of resistance, two were found to be compatible with the natural enemies of the pest.

The combination of host-plant resistance and biological control methods represents a promising strategy for the sustainable management of the tomato leafminer Phthorimaea (Tuta) absoluta, an invasive pest from Latin America that poses a threat to tomato crops worldwide. Combination trials of this sort are conducted because the tomato plants themselves can have a negative impact on the pest’s natural enemies, and can thus adversely affect the efficacy of the pest-control method used. In an Agroscope study, experts therefore investigated the performance of three natural enemies on six tomato genotypes with differing levels of reistance to the tomato leafminer P. absoluta.

Performance of natural antagonist only declined in one case

First, the effectiveness of the egg parasitoid Trichogramma achaeae was evaluated on the eggs of P. absoluta raised on various tomato genotypes. Next, the performance of the larval parasitoid Necremnus tutae was studied on tomatoes harbouring P. absoluta larva. Lastly, the predatory behaviour of the predatory bug Macrolophus pygmaeus towards P. absoluta eggs and larva was evaluated.

Neither tomatoes heavily infested with the pest nor the resistant domesticated tomato Corona F1 or the resistant wild tomato Solanum neorickii negatively affected parasitisation rates or the survival of the antagonist. By contrast, the resistant wild tomato S. arcanum reduced the performance of the two parasitoids and the efficacy of the predatory bugs.

Two tomato genotypes compatible with all of the natural antagonists

In summary, the study shows that the tomato genotypes Corona F1 and S. neorickii are compatible with all of the natural enemies, while S. arcanum is incompatible. One reason for these differences might be the dense glandular hairs in S. arcanum, which limit the mobility of the antagonists. In particular, the glandular hairs inhibit effective parasitisation by T. achaeae and N. tutae as well as the predation and survival of the predatory bug. Currently, it is unclear whether chemical constituents of the tomato plant have a toxic effect on the natural antagonists; further studies aim to discover whether this is the case.

A study led by Agroscope has deepened our understanding of the genetic mechanisms responsible for grape skin colour. New findings have led to a revision of the genealogy of the Rouge du Pays cultivar (Cornalin du Valais) and contributed to a better understanding of the genetic diversity of the grapevine.

The red colouration of plant tissue is mainly caused by a class of pigments called anthocyanins. In the grapevine, the presence or absence of these pigments in the skin determines the colour of the berry. This colour is a key criterion in ampelography (the study of grapevine varieties) which enables thousands of different cultivars to be classified in two main categories: those with white grapes and those with red grapes (black).

Berry colour is determined genetically by a major locus; in other words, a specific location on the grapevine genome. The main gene involved in this mechanism is called MybA1; inactivation of this gene causes the absence of pigmentation in white cultivars. Each gene occupies a precise position on a chromosome and can exist in several different forms, called alleles. Each cultivar has two variants (alleles) of each gene, one from each parent.

An allele of the MybA1 gene is considered functional if it enables the synthesis of anthocyanins, and non-functional if it does not. The black skin pigmentation is a dominant characteristic, whereas the white colour is recessive.

The SUB allele is present in the red cultivars of Valais and the Aosta Valley …

This study focusses on a specific allele of the MybA1 gene called SUB because it has some unusual characteristics. It is expressed in both red and white cultivars, which raises questions about its capacity to activate anthocyanin synthesis. In addition, the role of this allele is still poorly understood. Indeed, classic genetic models are unable to predict berry colour when this allele is present.

As part of this study, the SUB allele was identified in several red grape cultivars originating from Valais and the Aosta Valley (Val d’Aoste) (Figure 1). These cultivars belong to a group of closely related genotypes. Early ampelographers had noted similarities between certain Valaisian and Valdotian cultivars at the start of the 20th century. In 2003, genetic analysis suggested that Rouge du Pays (Cornalin du Valais) was the product of a natural crossing between Petit Rouge and Mayolet, two red cultivars from the Aosta Valley. However, our results invalidate this hypothesis definitively. Rouge du Pays carries two red alleles for the MybA1 gene (SUB and ALF), excluding the possibility that it originated from two parents that carry only SUB and ITA, as is the case with Petit Rouge and Mayolet.

… as well as some white cultivars

The cultivars grown today are the result of a domestication process from Vitis sylvestris – the wild ancestor of the cultivated grapevine, which has black-skinned berries.  Although white cultivars have been known since antiquity, until now it was thought they were the result of a single mutation. However, our results suggest the presence of a second mechanism involving the SUB allele, found in several white cultivars such as Sultanina, Khusaine Belyi and Otcha Bala (Figure 2). The mechanism highlighted in our study now completes the genetic model controlling berry pigmentation in the grapevine.

A study on Chasselas grapevines shows that yield regulation by cluster thinning after foliar fertilisation does not increase grape nitrogen concentration but does encourage N accumulation in the perennial parts of the vine.

In viticulture, nitrogen excess and deficiency can both impair grape yield and quality. Nitrogen affects plant vigour, plant susceptibility to disease and fruit ripening. It also plays a key role in wine fermentation and aroma due to its impact on the yeast-assimilable compounds. Nevertheless, our understanding of the relationship between plant nitrogen status and fruit nitrogen composition remains incomplete. Plant nitrogen assimilation depends on several factors: environmental conditions, plant material and cultivation practices. Fruit-load regulation is a practice that aims to limit fungal diseases and encourage grape ripening; however, its effect on the amount and composition of nitrogen in the berries and in the plant remains unknown.  

In 2017-2018 a study was conducted on the Chasselas grape variety using a large fruit-load gradient obtained by grape removal at the ‘cluster closure’ stage (0.5-5.0 kg per plant). The study analysed the effect of crop load and N fertilisation on vegetative growth, fruit composition and the distribution of N in the vine over a two-year period. For this, 20 kg/ha of nitrogen in the form of urea was applied to the canopy in four passes around veraison. The isotopic labelling of nitrogen (10% ¹⁵N) allowed us to quantify the nitrogen assimilated by the vine and to follow its distribution among the leaves, fruits, trunk and roots as a function of yield.

Crop load influenced nitrogen distribution

Plant crop load strongly influenced the leaf-to-fruit ratio, which ranged from 0.4 to 3.0 m²/kg (Table 1). Crop-load regulation improved grape ripening by encouraging sugar accumulation (+1.3 Brix) and reducing titratable acidity (‒0.8 g/L) compared to the high-yield condition but had no impact on the concentration of assimilable nitrogen in the must at harvest (Table 1). Conversely, although fertilisation did not affect ripening it increased the concentration of assimilable nitrogen in the must (+34 mg N/L) compared to the non-fertilised control. Foliar fertilisation at the veraison stage did not have a significant effect on either vine growth or yield (Table 1).

Fertilisation encouraged nitrogen accumulation in the grapes (+24 mg N/L) without modulating plant vigour or total biomass. However, foliar N assimilation varied as a function of crop load (34% of the applied N on average in the high-yield conditions versus just 25% in the low-yield conditions (Figure 1). In other words, limiting yield reduced fertilisation efficiency. N uptake was higher for the fruits than for the canopy and perennial parts (roots and trunk).

Crop load influenced nitrogen distribution between the fruits and the perennial parts of the vine (Figure 2): 40% of the nitrogen fertiliser was found in the fruits at harvest in high-yield conditions, as against just 24% in low-yield conditions. Nitrogen distribution remained constant in the canopy. The amount of nitrogen exported from the vineyard was linked to the amount of grapes harvested. Consequently, the nitrogen reserves in the perennial parts at the time of harvest were lower in high-yield conditions (17% of total assimilated N) than in low-yield conditions (31%).

An Agroscope study shows that pre-flowering removal of the main leaves instead of the lateral shoots appears to be a viable practice with a moderate effect on both yield potential and must composition.

Leaf removal (LR) is a common practice in viticulture for limiting fungal attack and promoting grape ripening. The timing of leaf removal is critical and must be adjusted to regional climatic conditions and the winegrower’s objectives. When performed after berry set, LR does not usually affect yield. When done before flowering, it can influence grape composition and the sensory profile of the wine, particularly the aromas and polyphenols. However, pre-flowering leaf removal also reduces yield by 40 to 50% by limiting the carbon source necessary for berry set. The effects of leaf removal are thus a function of factors such as grape variety, climatic conditions, and LR timing and intensity. The choice of which leaves to remove – main leaves or lateral shoots – in the cluster area is also a key consideration for adjusting LR intensity.

A trial was conducted from 2016 to 2021 at Agroscope’s experimental vineyard in Leytron, Switzerland to highlight the physiological effects of pre-flowering leaf removal in the cluster area of the Swiss white-grape variety ‘Petite Arvine’. The experimental design followed a randomised complete four-block format with four treatments, each involving different combinations of main-leaf and/or lateral-shoot removal from the cluster area (from the base of the shoot to the sixth leaf), all applied in May at the phenological stage of ‘separated flower buds’ (Figure 1).

Effect of pre-flowering LR intensity

Pre-flowering leaf removal significantly affected vine performance, reducing berry-set rate and yield in particular. Complete removal of the lateral shoots and main leaves in the cluster area led to an average yield loss of 37% (Figure 2). By comparison, removal of 50% of the main leaves limited yield losses to 5–21%, demonstrating that moderate pre-flowering leaf removal can limit the risk of excessive yield losses. The trial also highlighted the important role played by environmental factors in yield formation.

Intensive pre-flowering leaf removal had a negligible effect on the accumulation of sugars in the grapes (23.7 ± 0.3 Brix) but increased tartaric acid concentration (Figure 3). Wine composition showed negligible differences following intensive pre-flowering LR, except for a higher concentration of polyphenols associated with the smaller size and thicker skins of the berries and their greater exposure to light. It is worth noting that removing all the leaves and lateral shoots from the cluster area tended to reduce concentrations of Cys-3MH (a thiol precursor) (-21%; p < 0.10) with respect to the control.

Comparison of main-leaf versus lateral-shoot removal

The removal of the main leaves alone resulted in a larger exposed leaf area (+15 %) compared to the removal of the lateral shoots, mainly due to the growth of the lateral shoots in the cluster area. The total photosynthetic activity of the canopy was reduced until berry set due to the higher proportion of young leaves and lateral shoots that had not yet reached maximum photosynthetic capacity. This results in a lower yield potential (-14%), mainly due to a lower number of berries per cluster (-11%). The cooler microclimate owing to the greater leaf area – resulting in less abiotic stress – probably contributed to the higher concentration of both malic acid (+0.5 g/L, +12%) and glutathione (+6 mg/L, +11%) in the musts of treatment D (removal of the main leaves) compared to those of treatment A (removal of the lateral shoots). The increase in titratable acidity (+4%), and of malic acid in particular may be desirable in the current global warming context, which strongly influences the ratio of total soluble solids (sugar) to titratable acidity. Treatment D had the lowest concentration of tartaric acid and the highest of malic acid. Removal of the main leaves alone increased the concentration of glutathione in the must with respect to the other treatments (+13%; p < 0.001). Glutathione is an asset for preserving wine aromas and colour. No significant differences were noted in terms of TSS, pH or Cys-3MH in the musts between the lateral-shoot and main-leaf elimination treatments. By contrast, yeast-assimilable nitrogen concentrations increased (+26 mg/L, +10%). The wine produced by treatment D had higher colour intensity and fewer vegetable aromas than the wine from treatment A.

Foliar fertilisation around veraison improves grape nitrogen levels without affecting vigour. A trial shows that the fertilisers ‘Safe N 300’ and ‘Folur’ effectively increase assimilable nitrogen in the grape must; however, their degree of effectiveness depends on climatic conditions.

Foliar fertilisation is an essential practice in agriculture – particularly in viticulture – for optimising rapid nutrient assimilation and preventing grape nitrogen deficiencies. Unlike root uptake, foliar uptake is passive and dependent upon the leaf-surface nutrient concentration gradient. Applying foliar nitrogen in the form of urea around veraison (BBCH 81 stage) increases grape nitrogen levels, thereby preventing stuck alcoholic fermentation and organoleptic deviations during winemaking. Vine vigour was not affected.

A trial was conducted from 2017 to 2019 on a Chasselas plot in Pully, Switzerland to test the efficacy of two mineral foliar fertilisers compared to a non-fertilised control (Table 1). The fertilisers were applied in two treatments of 5 kg N/ha around veraison with no additional fertilisation. The measured parameters included vine vigour, yield, grape quality and levels of assimilable nitrogen in the musts.

Both tested fertilisers shown to be effective

The results show that the climatic conditions of the vintages strongly influenced grape nitrogen levels. The hot, dry 2018 vintage (385 mm precipitation, average temperature of 18.6° C during the April-September growing season), favoured better fruit ripening but limited the accumulation of assimilable nitrogen in the must (89 mg N/L in the non-fertilised control). Conversely, the cooler, more humid 2017 and 2019 vintages led to better plant nitrogen assimilation (average 132 mg N/L in the must) (Figure 1).

Foliar nitrogen application significantly increased the level of assimilable nitrogen in the musts. The two fertilisers tested demonstrated a similar efficacy without affecting yield or grape maturity. Increases in assimilable nitrogen varied according to the year: an average gain of 62mg N/L in 2019 as compared to just 24mg N/L in 2017 and 2018. In 2018, despite fertilisation, nitrogen levels failed to reach the critical threshold of 140mg N/L, jeopardising a potential improvement in wine quality. By contrast, in 2017 and 2019 this threshold was exceeded thanks to fertilisation, ensuring a good nitrogen balance.  

‘Safe N 300’ marginally outperformed ‘Folur’, although the differences between the two over the whole of the three-year period were negligible. The use of several forms of assimilable nitrogen seems to have contributed to greater fertilisation efficacy.

A study conducted on Chasselas vines in Switzerland shows the effects of yield regulation practices on grape ripening and nitrogen composition and suggests a two-year approach for optimising quality and sustainability.

Nitrogen is an essential element for vine development and yield. It is also involved in the vinification process and substantially influences wine composition. It is therefore essential to monitor and optimise plant nitrogen use to guarantee suitable grape composition at harvest while steering technical choices towards minimising input losses with the aim of supporting sustainability.

In 2017-2018 we tested the combined effects of fertilisation and yield regulation on grape nitrogen composition on Chasselas vines. Two yield levels were implemented: for each level, foliar urea was applied at veraison for comparison with a non-fertilised control. Yield regulation consisted of fruit thinning at the ‘bunch closure’ stage. Vine development and grape composition were evaluated over two years.

Crop thinning influences grape composition over at least two consecutive years

Foliar fertilisation with urea at veraison increased the amount of nitrogen in grapes at harvest in the same year, but had no impact on grape ripeness or carryover effect on year n+1.

Thinning, for its part, encouraged grape maturity in the same year by reducing nitrogen and carbon demand without impacting nitrogen concentration. Thinning also encouraged building reserves of these same nutrients in the roots. The following year, differences were observed from the veraison stage onwards: under low-yield conditions, total soluble sugars (TSS) were higher (+25%), and titratable acidity was lower (−18%) (Figure 1). Conversely, the yeast-assimilable nitrogen concentration was constant in the fruits regardless of plant fruit load. Only the proportion of amino acids varied, allowing the musts to be distinguished according to fruit load (Figure 2).

This experiment highlighted the influence of the previous year’s yield regulation practices on carbon and nitrogen accumulation in the grapes. Consequently, the modulation of grape composition at harvest should be considered over two consecutive years.

The combination of competition by forage plants and herbivory by native root-boring moth larvae can significantly reduce the growth of small broad-leaved dock plants in permanent grasslands.

Broad-leaved dock (Rumex obtusifolius L.) is one of the most problematic weeds in intensively managed grasslands in Europe. Non-chemical control measures are in high demand, especially on organic farms. Two European moths, Pyropteron chrysidiforme and P. doryliforme (Sesiidae), have therefore been proposed as candidates for the biological control of broad-leaved dock, as their larvae are root borers and overwinter in the taproot. So far as is known, however, the impact of the larvae is too small to have a significant control effect on mature broad-leaved dock. Agroscope researchers were therefore looking for ways to enhance the larvae’s effect on the dock plants.

A factorial field experiment was established to investigate the combined effect of the root-boring larvae and competition from common ryegrass (Lolium perenne L.) on dock plants. Because ryegrass is a well-known competitor of broad-leaved dock and suppresses small dock plants in particular, dock plants of differing root size were planted in plots with and without ryegrass competition. The plants were then inoculated with eggs of either P. chrysidiforme or P. doryliforme, while the remaining third of the plots served as an untreated control. A total of 432 R. obtusifolius roots were planted. After one season, the total stem, leaf and root mass of the dock plants were measured. The roots were dissected to quantify the number of larvae and the damage caused by them.

Synergistic effects of ryegrass and larvae on small broad-leaved dock

Although competition from ryegrass significantly suppressed both the stem and leaf mass as well as the root mass of the broad-leaved dock, plants from initially small roots were more strongly suppressed by ryegrass than those growing from large roots. The combination of competition from ryegrass and inoculation with moth eggs strongly reduced the growth of the small plants or caused them to die off. By contrast, broad-leaved dock not subjected to competition from ryegrass suffered almost no negative effects from the larvae. This shows a synergy between ryegrass and moth larvae, with the combined impact being greater than the sum of the individual effects. Competition from ryegrass also affected the herbivores themselves: in the presence of competition, the infestation rate and number of larvae per root mass were higher, resulting in more larvae in the small dock roots.

The results show that plant competition and root-boring larvae synergistically suppress broad-leaved dock, but that they only do so effectively in the case of small dock plants. The competition from grasses reduces available resources, while the dock plants are further weakened by the root-boring larvae. The application of Pyropteron species to control broad-leaved dock in established grasslands thus has potential, but is not at present commercially available owing to the complexity of the cultivation process.