Previous Research Highlights (1996-2002)

Use of Light Energy and Implications on Photosynthetic Rates

Work completed from 1998 to 2001 provided essential information on the seasonal changes in pigment concentrations (i.e., chlorophyll and carotenoid concentrations) that occur during the sprout and cropping years of production. This coincided with information collected during 2000 and 2001 on the functional status of the pigments under non-illuminated (i.e., dark) and illuminated (i.e., full sunlight) conditions. Results from these studies indicated that the wild blueberry has chlorophyll concentrations that are equivalent to other members of the Vaccinium family (e.g., high bush cultivars), and the overall concentrations of the pigments do not decrease throughout the course of a growing season to the order of magnitude expected from a shade-adapted plant species. The mechanisms associated with this protection of the underlying pigments is probably in the form of the carotenoid pigments, and also potentially in the form of the anthocyanin pigments. The anthocyanin pigments within the leaf tissue were not originally (i.e., in 1997) expected to provide a significant level of protection for the phytochemsitry of the wild blueberry. However, studies completed on bilberry have indicated that these compounds do provide a rapid and effective protection against environmental stresses including high light intensities and excessive levels of ultraviolet radiation. This protection is provided by absorbing and/or dissipating the excess light energy and subsequently reducing the over-taxation (i.e., over-charging) and subsequent photoinhibition (i.e., reduction in the light reaction of photosynthesis) processes.

In addition, the examination of the seasonal carbon acquisition and allocation within the wild blueberry indicated that (i) the wild blueberry has a relatively low photosynthetic rate, (ii) there is a strong demand for the photoassimilates (i.e., carbohydrates produced via photosynthesis) within the roots, shoots, and rhizomes, and (iii) the maintenance of an effective leaf area is important for not only maintaining the growth within the present season but also in subsequent growing seasons. Therefore, further research activities were initiated to examine the use of anti-desiccants to assist in shedding excess light loads and reducing water losses, and evaluating the use of multiple fertilizer applications within a season to maintain a photosynthetically efficient leaf area.

Seasonal Growth Dynamics

A four-year whole-plant study examining the growth and carbohydrate dynamics of the wild blueberry was conducted from 1998 to 2001. Results from this study indicated that depending on the stage of the seasonal and production cycle, 70 to 100% of the dry matter within a plant can be in the form of roots and rhizomes. Overall, it has been found that the rhizomes are a critical component to the growth dynamics of the wild blueberry with early season root and shoot growth being reliant upon the rhizome carbohydrate content. Furthermore, a cumulative decline in rhizome dry weight, and more specifically carbohydrate content, will result in hindering season to season carryover effects that will result in reduced plant growth, vigor, and yield.

Very interesting wild blueberry growth responses to temperature have been observed over 3 growing seasons, 1998-2001. Upon examining the temperature range at which wild blueberry root growth occurs, it has been observed that root growth occurs at very low temperatures, and that the physiological activity within the plant occurs for a far longer duration than was initially expected. This was apparent with measurable stem and root respiration rates, changes in rhizome dry matter allocation, and shoot and rhizome carbohydrate composition changing throughout the growing season and until the end of November.

Nutrient Assimilation and Allocation

In addition to examining seasonal growth and carbohydrate dynamics, the previously mentioned experiment also examined the seasonal nutrient assimilation and allocation dynamics of the wild blueberry during the sprout and cropping years of production. Results from these studies have indicated that with the exception of supplying adequate nitrogen levels for the initial two months of the sprout phase of production, the wild blueberry is under nitrogen deficient conditions throughout the remainder of the sprout and cropping phases of production, the deficiencies in nitrogen are present throughout the roots, shoots, and rhizomes, and these deficiencies are particularly apparent during the cropping phase of production.

The net results of these findings have been implementation of additional trials to examine the influence of different nitrogen forms (e.g., ammonia versus nitrate formulations), application dates, and application frequencies (1, 2 or 3 times during the 2-year production cycle). From the nitrogen formulation perspective, results have indicated that ammonium sulphate is the most favorable form of nitrogen to use in wild blueberry production with minimal effects on the mycorrhizal association of the wild blueberry, improved phosphorous uptake, improved stem vigor (the stems are less spindly), increased leaf tissue nitrogen levels, and increased yields. The effect of applying multiple nitrogen applications at various intervals throughout the season has indicated the impact of developmental stage, and frequency of application on growth, development, and yield. Results indicated that the optimal timing for nitrogen application consists of an initial application of a broad spectrum fertilizer in the spring of the sprout year (e.g., a 14-18-10), followed by an additional application of nitrogen in late July (i.e., after black-tip has commenced). Depending on the soil type (i.e., light textured soils) and inherent plant vigor, there may continue to be a need for crop-year applications of nitrogen. In addition, the net impact of different nitrogen application methods (i.e., soil-applied fertilizer versus foliar-applied urea) need to be examined to determine the proportion of nitrogen that is being used (i.e., nitrogen use efficiency), the influence of these treatments on the various yield components (i.e., stem densities arising from the rhizomes or improved floral bud quality attributed to increased carbohydrate and nitrogen content within the floral bud), and the most economically feasible means of applying the additional nitrogen applications.

Main and Interactive Effects of Nitrogen, Phosphorous, and Potassium

Upon realizing the significant effect that nitrogen formulation could have on the uptake of phosphorous at the end of the 1998 growing season, research was initiated in 1999 to examine the main and interactive effects of nitrogen, phosphorous, and potassium in wild blueberry production. These trials involved the use response surface techniques to examine the main and interactive responses of sprout and cropping year applications of nitrogen, phosphorous, and potassium. These trials were completed at 4 sites for the sprout year applications, 2 sites for the cropping year applications, and an additional 3 sites (i.e., 2 sites consist of sprout applications and one site consists of a cropping year fertilizer application).

Results from the sprout year nitrogen, phosphorous, and potassium trials have indicated that (i) there have been beneficial effects observed at all sites from the addition of phosphorous, (ii) the leaf tissue phosphorous levels at all sites are in a deficiency position at the start of the sprout year, and (iii) the beneficial effects of phosphorous are augmented with the presence of nitrogen. In addition, since switching from a urea (an ammonia formulation of nitrogen that is fairly prone to nitrogen losses through volatilization) to an ammonium sulphate formulation of nitrogen (urea was initially used to specifically look at nitrogen effects and not a combination of nitrogen and sulphur), improvements in plant growth and development and yield increases have also been observed. The other interesting feature observed in these trials has been the minimal effect observed with potassium applications (i.e., only a slight increase in fruit set observed at 1 location that was also exposed to a moderate frost during bloom).

The cropping year applications of nitrogen, phosphorous, and potassium fertilizer have indicated that there may be beneficial effect of using cropping-year applications of nitrogen, phosphorous, and potassium fertilizers. Most of the beneficial effects have been observed with nitrogen applications, and the only interesting feature from a fruit composition perspective is that addition of phosphorous can increase anthocyanin levels within the blueberry fruit.

Improving Phosphorous Availability

Concerns have been raised over the use of phosphorous in wild blueberry production as a result of increasing total phosphorous levels in the soil and the increasing cost of phosphorous fertilizers. Phosphorous (P) deficiencies are encountered in wild blueberry soils as a result of P adsorption to the cation exchange sites of clay minerals which results in P becoming predominately in a bound form and unavailable for plant growth and development. One possible mechanism to improve phosphorous availability in blueberry soils is through the use of organic materials known as humates. Humates are decomposed organic materials that are void of sugar, fiber, cellulose, lignin, or protein, and are resistant to further decomposition. The benefits that have been observed with humic acids include increased water holding capacity, improved soil aeration, the retention of mobile nutrients such as nitrogen, increased ion exchange capacities, and increased assimilation and allocation of inorganic nutrients including phosphorous, calcium, and magnesium, stimulated cell growth and division, and increased biomass production and yield.

Trials were initiated in 2000 in cooperation from the Potash and Phosphate Institute to examine the impact of humic acid substances and included five foliar and soil applied humic acid amendments at two locations in Nova Scotia. Unfortunately, no beneficial effects have been observed on the soil characteristics, plant nutrition, growth, development, or yield with any of the humic acid treatments. Therefore, research activities that commenced in 2001 consisted of attempting to improve phosphorous availability through the use of phosphorous solubilizing endophytes (i.e., phosphorous soil-applied innoculants). These endophytes have been proven effective with the production of agronomic, nursery, and ornamental crops, and have been acquired from Philom Bios (Saskatoon, Saskatchewan).

Studies examining the impact of water availability (i.e., supplemental irrigation and drought stress) on the photochemistry, leaf gas exchange (i.e., photosynthesis and transpiration), growth, development, and yield of wild blueberries were initiated in 1997 at the Nova Scotia Wild Blueberry Institute. In addition, the impact of one and two years of irrigation and drought stress treatments, and the impact of supplemental irrigation and drought stress treatments applied either during the sprout or cropping years of production have also been examined. Overall, results have indicated that the wild blueberry is extremely tolerant to drought stress with the wild blueberries remaining physiologically active at extremely low soil moisture levels (i.e., less than 5% available soil moisture). In addition, it has been observed that the plants have adaptive mechanisms in the form of rhizotomous tissue and the feeder roots (i.e., roots that extend up to 1 m in depth) which ensures that there is a very efficient horizontal and vertical distribution of water within a blueberry clone (i.e., it is very effective at mocing water from an area of source to sink). Furthermore, the vast carbohydrate stores present in the rhizomes of the wild blueberry the wild blueberry with the ability to endure severe and prolonged periods of drought stress. However, being a source limited plant (i.e., a plant with an extensive root and rhizome system and a limited photosynthetic capacity), the combination of drought stress and a significant crop load can have a negative impact on plant growth, development, and yield. It is for this reason that results have indicated that the provision of supplementary irrigation in both the sprout and cropping years of production and the maintenance of an effective leaf area (i.e., leaf area duration) are critical to optimizing the yield potential of wild blueberries.

Vegetation Management Strategies

The vegetation management strategies that have been examined for wild blueberry production have included (i) the use of introduced living mulches as a means of minimizing the detrimental effects of soil erosion, (ii) the net impact of native grasses in wild blueberry production, and (iii) the suppression of native grasses in wild blueberry production through the use of sub-lethal herbicide applications. Results from the introduced living mulch trials have indicated that there are several commercially available species of living mulches that are suitable for wild blueberry production. These include creeping red fescue, hard fescue, sheep’s fescue, and to a lesser extent birdsfoot trefoil. The benefits that have been observed with these living mulches have included the successful establishment in marginal blueberry soils, reduced soil temperatures, increased water retention, reduced weed pressures, and increased rhizome growth and colonization rates. However, in situations where significant native grass stands may already have been present, a more cost-effective means of reducing the negative impact of soil erosion may be through the use of alternative herbicide applications.

The competitiveness of varying native grasses with the wild blueberry was examined during the 2000 and 2001 growing seasons. The native grasses that were examined have included Canada bluegrass, creeping bentgrass, and poverty oatgrass, and the variables that have been examined include the seasonal changes in native grass and wild blueberry growth and biomass production, and the competition for resources (i.e., light and soil moisture) that may be occurring between the wild blueberry and native grass. Results have indicated that with the exception of a slight competition for soil moisture during July of the 2001 growing season with creeping bentgrass, there has been no significant competition between the wild blueberries for light and water. However, there is evidence with all three native grass species that there is competition for physical space within the rootzone, and these native grass species are adapting to environmental conditions conducive to wild blueberry production. Subsequently, over time, this will have a negative effect on wild blueberry growth, development, and yield. Therefore, these results clearly indicate the need for alternative and sublethal herbicide practices in wild blueberry production.

Research conducted by Mr. Peter Burgess (M.Sc. student), Glen Sampson, D. Percival, and Klaus Jensen during the 2000 and 2001 growing seasons has examined the impact of sprout and cropping year applications of alternative herbicides including Fusilade (Venture), Select, Beacon, Poast, and Ultim. The experimental treatments have consisted of examining the impact of various concentration (0, 1/3, 2/3, and full application rate), application dates, and combination with Velpar (0, ½ and full application rates). This study focused on the impact of these various herbicides on poverty oat grass, and results have indicated that with the exception of the herbicide Beacon, these herbicides do offer sublethal control of native grasses with minimal impact on the wild blueberry.

Prevention of Fruit Shatter in Wild Blueberry Production

Studies were initiated during the 2000 growing season to examine the influence of ethylene inhibiting compounds in wild blueberry production. Ethylene is a plant hormone that has been attributed to inducing the ripening of various climacteric (e.g., apples, pears, and bananas) and nonclimacteric (cherries, oranges, and strawberries) fruit crops. Therefore, it was hypothesized that the use of the ethylene inhibiting compounds may retard the ripening process, increase fruit pigmentation, improve berry firmness, reduce fruit shatter, and reduce fruit shrink during processing.

Research trials with the ethylene inhibiting compounds have been conducted during the 2000 and 2001 growing seasons at three commercial wild blueberry fields in Nova Scotia. The treatments consisted of field applications of ReTain (Valent BioSciences, a.i.: aminoethyloxyvinylglycine), and postharvest applications of EthylBloc (i.e., MCPA, BioTechnologies for Horticulture, a.i.: 1-methylcyclopropene). Overall, it has been found that the ripening process and more specifically the climacteric of wild blueberries (the increase in respiration rate associated with the onset of ripening) occurs quite early (i.e., 3 to 4 weeks before harvest), the use of the field applications of ReTain will retard the ripening process, increase anthocyanin content, improve fruit firmness, and reduce fruit shatter. However, the field applications of ReTain are quite expensive (i.e., $65 to $180 per acre), work only on fields with slight to moderate crops, and can increase berry acidity (this was particularly evident during the 2000 season).