Pat Bowen

How distinct are arbuscular mycorrhizal fungal communities associating with grapevines

Grapevines form associations with arbuscular mycorrhizal (AM) fungi. These root-dwelling fungi have the potential to contribute to crop vigor, productivity, pathogen protection, and nutrient content in grapes. In this study the arbuscular mycorrhizal fungal communities of grapevines and the surrounding interrow and native vegetation are compared. We found over 40 different taxa associating with both vines and interrow vegetation, but these communities differed based on host plant identity. These differences were apparent even after accounting for differences in soil chemical properties and differences in host plant diversity between vinerows and interrows, indicating that Vitis preferentially interacts with a subset of the viticultural fungal community. Since AM fungal communities play a major role in grapevine health, our results suggest that host identity and the diversity of AM fungal hosts in a vineyard can have strong effects on arbuscular mycorrhizal fungi community structure. In this paper, we used high throughput sequencing of the large subunit rDNA to analyze the diversity of AM fungi growing in a vineyard.

Effects of Irrigation and Crop Load on Leaf Gas Exchange and Fruit Composition in Red Winegrapes Grown on a Loamy Sand

Effects of reducing irrigation from fruit set to veraison or harvest combined with crop-load adjustment by cluster or shoot thinning were determined for Merlot and Cabernet Sauvignon grapevines cultured on a coarse loamy sand. Geographic information system tools were used to develop maps of moisture distribution in the soil profile, which revealed reductions in total moisture levels and increased spatial variation in response to reduced emitter density. Stomatal conductance and leaf gas exchange decreased in response to reduced irrigation but also declined across all treatments during the lag phase of berry development and then increased postveraison. Pruning mass was affected little by treatments in Merlot but was reduced by either shoot or cluster thinning in Cabernet Sauvignon. Berry mass and anthocyanin and tannin contents were affected little and inconsistently by irrigation and crop-load adjustment and varied mostly among years, indicating a dominant influence of seasonal climate on berry development and composition.

Cover crops to increase soil microbial diversity and mitigate decline in perennial agriculture. A review

Commercial perennial agriculture is prone to declining productivity due to negative plant-soil feedback. An alternative to costly and environmentally harmful conventional treatment such as soil fumigation could be to manipulate soil microbial diversity through careful selection and management of cover crop mixtures. Although cover crops are already used in these systems for other reasons, their capacity to influence soil biota is unexploited. Here, we examine the role of plant diversity and identity on plant-soil feedbacks in the context of perennial agriculture. We identify key microorganisms involved in these feedbacks and explore plant-based strategies for mitigating decline of perennial crop plants. We conclude that (1) increasing plant diversity increases soil microbial diversity, minimizing the proliferation of soil-borne pathogens; (2) populations of beneficial microbes can be increased by increasing plant functional group richness, e.g., legumes, C4 grasses, C3 grasses, and non-leguminous forbs; (3) brassicas suppress fungal pathogens and promote disease-suppressive bacteria; (4) native plants may further promote beneficial soil microbiota; and (5) frequent tillage, herbicide use, and copper fungicides can harm populations of beneficial microbes and, in some cases, contribute to greater crop decline. Non-crop vegetation management is a viable and cost-effective means of minimizing crop decline in perennial monocultures but is in need of more direct experimental investigation in perennial agroecosystems.

Impacts of using polyethylene sleeves and wavelength-selective mulch in vineyards. II. Effects on growth, leaf gas exchange, yield components and fruit quality of Vitis vinifera cv. Merlot

Response of Merlot vines to wavelength-selective polyethylene mulch in the planted row and clear polyethylene enclosures (sleeves) around canes or cordons for 7 wk in the spring was studied in three Okanagan Valley vineyards. The mulch had no detectable effects on vine development, yield components and fruit quality. The sleeves advanced budbreak by 3 to 6 d, depending on the vineyard site, and increased the early growth rate of shoots. Time of budbreak and shoot growth rate were better predicted by cumulative daily mean temperature than by cumulative degree days (base 10°C). On the day sleeves were removed or opened at top, photosynthesis rates were higher in open-top sleeves than under ambient conditions due to higher mesophyll and stomatal conductances. Sleeves advanced the date of 50% bloom in all vineyards by approximately 10 d. Time of bloom, onset of veraison and the rate of fruit maturation were predictable from degree day accumulation. Sleeves advanced fruit maturation by 7 to 26 d, depending on ...

Impacts of using polyethylene sleeves and wavelength-selective mulch in vineyards. I. Effects on air and soil temperatures and degree day accumulation

Effects on soil and air temperatures of wavelength-selective polyethylene mulch applied in planted rows, and clear polyethylene enclosures (sleeves) applied around vine canes or cordons for 7 wk in the spring were determined in three Merlot vineyards in the Okanagan Valley, British Columbia. Three sleeve configurations were studied: single-layer and closed at bottom; single-layer with bottom ventilation added after 5 wk; and double-layer with bottom ventilation added after 5 wk. All sleeves were perforated at the top between two supporting trellis catch wires, and were stapled closed at the bottom under the cordon or cane. Sleeve removal was either all at once or in two stages by first opening the top then removing the sides 6 d later. The sleeves increased mean air temperatures by ca. 1 to 2°C and maximum temperatures by ca. 5 to 8°C, and decreased minimum temperatures by ca. 1 to 2 °C, depending on the vineyard, measurement period, and sleeve configuration. Adding bottom ventilation to sleeves increased...

Effects of Converting from Sprinkler to Drip Irrigation on Water Conservation and the Performance of Merlot Grown on a Loamy Sand

Effects of converting from overhead sprinkler to drip irrigation on the growth, leaf gas exchange, and fruit production of Merlot grapevines with and without cluster thinning were determined over four years. Drip or sprinkler irrigation was applied to the loamy sand soil when in-row soil moisture was depleted to <8%. Irrigation frequency averaged 50% higher (27 compared with 18 times per year) under drip than sprinkler irrigation, but 64% less water (574 compared with 1580 L per vine per yr) was applied on average under drip. Maps of moisture in the soil profile revealed differences in moisture distribution and dry-down dynamics in response to irrigation method. Increasing soil dry-down rates over years indicated that roots proliferated within the drip-irrigated soil volume. Converting to drip reduced the growth and survival of floor vegetation. Vine vigor, leaf gas exchange, and crop yield were reduced but crop yield recovered in the second year and vigor recovered by the fourth year. Stomatal conductance and leaf gas exchange remained lower under drip irrigation. Transpirational water-use efficiency was higher under drip than sprinkler irrigation in the first three years. Input water use efficiency averaged 2.5 times higher under drip irrigation over the four years. Fruit maturation was advanced by drip compared with sprinkler irrigation each year and was associated with increased cluster exposure and higher ambient temperatures. Cluster thinning also advanced fruit maturation but reduced crop yield substantially each year and had only minor interactions with irrigation method.

Arbuscular Mycorrhizal Fungal Communities Associated with Vitis vinifera Vines under Different Frequencies of Irrigation

The effects of irrigating daily or every three days on arbuscular mycorrhizal fungal communities associated with grapevine roots were determined in vineyard blocks of Merlot and Syrah on 3309 rootstock. After exposure to treatments for four growing seasons, root samples were analyzed for changes in AM fungal colonization, species richness, and community composition. AM fungal colonization was higher in response to irrigating every three days compared with daily irrigation, indicating a treatment effect on the physiology of the fungal communities. Using a pyrosequencing approach, no difference in AM fungal community composition was found in response to irrigation frequency. Species richness, identity and dispersion were consistent across the two treatments. A difference in AM fungal communities between the two varietal blocks was associated with differences in soil chemistry and plant physiological traits. In particular, soil carbon and extractable copper levels along with vine vigor and photosynthesis were correlated with community variation. This indicates environmental factors other than irrigation frequency influence the fungal community structure in vineyards.

Demonstration of nutrient concentration effects on pineapple sage with the aid of automated crop monitoring

Summary The yield and quality of pineapple sage (Salvia elegans Vahl.) grown in two substrates (sawdust and rockwool) and at two nutrient solution concentrations (electrical conductivities of 1.7 and 4 mS cm–1) were compared in each of two years. No consistent effects of substrate were observed on any of the parameters measured, including plant fresh mass, dry mass, leaf area, chlorophyll content or shelf life. Leaf/stem fresh and dry mass ratios were also largely unaffected by substrate. Electrical conductivity (EC), however, had significant effects on most of these parameters. High EC reduced plant size, with lower plant fresh and dry mass, leaf number and leaf area. However, plant quality was improved as demonstrated by increased leaf/stem fresh mass ratio. In addition, chlorophyll concentrations were higher in high EC-treated plants, and shelf life was improved as shown by a reduction in percent water loss in cold storage. Load cells placed beneath the plants were used to monitor and compare transpiration and 24 h growth of high and low EC-treated plants grown in rockwool over a 90 d period. Daily growth recorded between 2400 and 0200 hours was found to be higher in the low EC-treated plants, supporting the observation of greater harvested fresh mass for those plants. Daily transpiration was found to be higher in the low EC plants, due mostly to their greater leaf area compared with high EC plants. When transpiration was compared on a leaf-area basis, no consistent differences were observed between EC treatments. Adapting the principles of a water-balance lysimeter, load cells were also found to be a useful means to check for relative moisture content of the substrate. Since transpiration and water replenishment (supply minus leachate) could be recorded independently, comparison of the two indicates an increase (replenishment > transpiration), decrease (replenishment < transpiration) or no change (replenishment = transpiration) in water content.

Groundcover management changes grapevine root fungal communities and plant-soil feedback

AimsThe objective of this study was to determine if vineyard groundcover management can mitigate negative plant-soil feedback caused by soil borne pathogens through changes in root fungal communities.MethodsWhole-soil inoculum was collected from a field trial of groundcover identity (exotic grasses, exotic grasses plus legumes, native grasses, and native grasses plus forbs) and irrigation type (drip, sprinkler, and a combination of both) in a modified feedback experiment with grapevine rootstock ‘101–14’ (Vitis riparia x V. rupestris). To see if these groundcovers would differ in their ability to protect vines against negative feedback caused by a soil borne pathogen, we inoculated all pots with the soil-borne root pathogen, Ilyonectria liriodendri (Halleen, Rego & Crous) Chaverri & C. Salgado.ResultsAfter eight months, vines growing with soil trained by exotic grasses had greater above-ground growth response relative to sterilized control than did vines growing with soil trained by native grasses and forbs. These treatments also resulted in compositionally distinct root fungal communities. The intensity of root colonization by arbuscular mycorrhizal fungi did not differ among ground cover treatments.ConclusionsOur results show that soil feedback outcomes for grapevines, including negative effects of black foot pathogens such as Ilyonectria liriodendri, could depend on groundcover vegetation management that alters root-associated fungal communities.

Arbuscular Mycorrhizal Fungi in Viticulture: Should We Use Biofertilizers?

Summary Aim: Arbuscular mycorrhizal (AM) fungi are a group of symbiotic soil fungi known for their role in promoting host-plant growth by improving nutrient uptake, providing pathogen protection, and increasing tolerance to common vineyard soil abiotic stressors such as salinity, extreme pH, and low water availability. Use of commercially produced AM fungal inoculants, known as fungal biofertilizers, is growing in viticulture, but remains untested under field conditions. Here we discuss factors that affect the performance of fungal biofertilizers and scenarios where they may be more, and less, advantageous. Key Themes: Fungal biofertilizer use is increasing globally, but does their use translate to improved grapevine performance under vineyard conditions? What are the key considerations for incorporating AM fungi into vineyard management? Impact and Significance: While the importance of AM fungi for plant performance is well known, inoculation with fungal biofertilizers does not increase plant growth or yield consistently. This may be due to context dependency of the AM symbiosis, which can be affected by vineyard management practices like fertilizer use and tillage. Where AM fungi are not limiting, as in most vineyard soils, adding inoculants when compatible fungi are abundant may be redundant. However, in situations where soil fungi may be limiting, such as in greenhouse propagation nurseries using near-sterile media, or in fields with a history of heavy fertilizer use, AM fungal additions may be warranted.