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Abstract
The root system of woody perennial crops exists in an extremely complex environment. We as horticulturists and problem solvers need to improve our understanding of the role of the interactions of soil microrganisms, soil media, and the root rhizosphere. It is for this purpose that several ASHS Working Groups—Rootstocks and Compound Genetics, Citrus Crops, Mycorrhiza, Pomology, Nursery Crops, and Viticulture and Small Fruits—have combined to help sponsor this symposium. Plant pathologists and soil microbiologists were invited to elucidate on the impact of pathogenic and beneficial soil bacteria, fungi, and nematodes. As brought out by authors in the following papers, practices employed in managing horticultural crops often discourage the development of plant growth-stimulating microorganisms. Such practices as fumigation and high application rates of fertilizers can alter the composition of the rhizosphere. Conversely, the bacteria, fungi, and nematodes can also alter the rhizospheres by producing substances such as antibodies and toxic metabolites. In citrus, mycorrhizae can alter the nutrient balances, which can indirectly suppress pathogenic fungi.
Abstract
The widely varying soil and climatic conditions of the apple and peach growing areas of the United States and Canada have resulted in serious problems with the adaptability of the rootstocks currently available to the fruit industry. Growers in each area are searching for the most efficient rootstocks adaptable to their region. In the past, it has taken 20 to 30 years to test rootstocks adequately and to develop the database on which to make sound recommendations to growers. In the interim, many costly mistakes were made; current economic conditions make these mistakes no longer tolerable.
One of the main problems facing organic horticulture is orchard ground floor management. Several works report that ground floor management affects root architecture of fruit trees, changing the position and depth of the roots. The purpose of this work is to study the effects of orchard ground floor management systems (GFMS) in an apple orchard under organic protocol in Michigan. The research was conducted at the Clarksville Horticultural Experimental Station of Michigan State University, in the organically certified (by OCIA) orchard of `Pacific Gala' grafted on M9 NAKB 337, established in May 2000. The GFMS being studied are: 1) mulch (MU) made of alfalfa hay on the tree rows, with a width of 2 m; 2) “Swiss Sandwich System” (SSS) that consists in superficial tillage of two strips 90 cm wide at each side of the tree row, leaving a 40-cm strip in the middle (under the canopy) where volunteer vegetation is allowed to grow; 3) flaming (FL) of the weeds in a 2-m strip underneath the tree canopy by a propane burner. Root architecture was studied in Sept. 2005 through the frequency of roots by the profile wall method. Trenches (3.36-m long × 1.32-m deep) were dug in the soil 45 cm from the tree trunk. Two 158 cm × 130 cm metal grid frames divided by strings into a 28 cm × 22 cm grid were placed against the profile faces to facilitate the counting and mapping of the root distribution. The GFMS did affect the root distribution of the two classes of roots under study (<2 mm and >2mm). In the FL and MU treatments, roots were noticed to be superficial and their frequency was higher close to the tree. In SSS, root frequency was similar until 80 cm deep in the soil profile and they extended farther from the tree.
Abstract
The influence of two rootstocks on leaf nutrient concentrations of ‘Montmorency’ sour cherry (Prunus cerasus L.) was studied at two locations for 4 years. Trees on Mazzard (Prunus avium L.) rootstocks were generally higher in leaf K, Ca, B, N, and Mn concentrations, but lower in leaf Mg than trees on Mahaleb (Prunus mahaleb L.) rootstocks. Differences due to rootstocks did not appear to be related to crop load or tree vigor.
Soil organic matter is a critical component which is fundamental in plant growth. Several soil factors are influenced by organic matter such as slow release of nutrients, increased water holding capacity, improved soil physical characteristics and improved environment for soil microorganisms. The aim of this work is to investigate the physical effect of organic matter content in the soil on apple root growth and development. Twenty five two-year old apple trees (Malus domestica, Borkh) cv. `Buckeye Gala' on M.9 NAKB 337 rootstock were planted in completely transparent acrylic boxes. Plants have been grown in a green house to avoid external rain in a complete randomized design. Trees were planted in a sandy-mix soil amended with soil high in organic matter, “muck”, at four incremental levels. Treatments compared were a control (sandy soil with 0% organic matter) and 1%, 2%, 4% and 8% soil organic matter. The amount of water applied by automatic drip irrigation was comparable for all the treatments to avoid high fluctuation of soil moisture on root dynamics. All treatments have been fertilized with the same amount of mineral fertilizer to avoid the nutrition effect on root dynamics. Digital photos of roots were taken to study their dynamics every one to two weeks during a period of five months. Roots have been highlighted with Photoshop and then analyzed with WinRhizo to measure root length, area, lifespan and dynamics. At the end of the growing period plants have been harvested and fresh and dry weight was evaluated to asses the root/shoot ratio. The effects of the treatments on root length, area, lifespan and dynamics, and root/shoot ratio will be discussed.
Trees of Gala were planted in 1994 on 18 rootstocks at the Clarksville Horticulture Experiment Station as one cooperating site of 26 North American sites organized by the NC-140 Regional Pome and Stone fruit rootstock committee. One tree each of seven rootstock treatments and two on B.9 and B.491 have died since establishment. Death has been caused by wind (brittle union) on most of the trees in replication one, on the western exterior of the plot which is exposed to strong wind. The most vigorous trees in this planting are those on V.1 and M.26 and least vigorous on M.27 and P.22. Cropping in 2003 was highest on Pajam 2, Ottawa 3 and M.9 NAKB 337, yielding an average of between 60 to 70 kg per tree. Cropping over the years has been highest on PJ.2, M.9 EMLA, and O.3. Cumulative yield efficiency in this plot is highest on P.16, followed by P.22 and B.491. Trees on M.26 are the least efficient over the years. Average fruit weight was highest in 2003 on V.1 and PJ.2. M.9 NAKB 337, the dominant international an national standard M.9 clonal rootstock is not as productive and as precocious as many other M.9 clonal stocks in this trial. After 10 years of evaluation, there appears to be no significant difference in cropping, cumulative yield, for `Gala' among the top eight rootstocks led by M.9 Pajam 2. M.9 NAKB 337 is not among the top eight rootstocks at this site. Pajam 2 is impressive from the view that while it is the top cropping stock, it is the rootstock in 2003 which also averaged the largest fruit. Among the M.9 clonal rootstocks, PJ 2 is also the most vigorous which for North American commercial apple orchards, has excellent commercial potential to withstand field and production stresses.
Fine root dynamics, timing of the events, and their relationship with soil conditions are of major interest because the understanding of these phenomena will permit a better synchronicity between nutrients and plant uptake. The goal of this research is to study the effect of different soil conditions, generated from two ground floor management systems, on fine root dynamics of apple trees under organic protocol in Michigan. The research has been conducted at the Clarksville Horticultural Experimental Station (CHES) of Michigan State University (MSU), in the organically certified (by OCIA) orchard of “Pacific Gala” grafted on M9 NAKB 337, established in May 2000. The orchard floor management systems being studied are: 1) a mulch made of alfalfa hay on the tree rows, with a width of 1.8 m and 2) the “Swiss Sandwich System” (SSS) that consists in superficial tillage of two strips 80 cm wide at each side of the tree row, leaving a 40 cm strip in the middle (on the tree row, under the canopy) where volunteer vegetation is allowed to grow. Root dynamics are studied on four replicas of two trees per each of the two ground treatments (16 in total) in a block design. For each tree in the trial four clear butyrate minirhizotrons have been installed (64 in total) at a 45° angle facing the tree, in the summer of 2002. Root dynamics, measured through pictures taken with a Bartz Technology digital camera and analyzed with a new software under development at MSU. During the 2003 season differences between the two systems have been found depending on the parameter taken in consideration. Mulch had different root distribution compared to SSS. Mulch treatment showed shallower roots even if below 90 cm the two systems didn't show any difference.
The effects of short-term soil flooding on gas exchange characteristics of containerized sour cherry trees (Prunus cerasus L. cv. Montmorency /P. mahaleb L.) were studied under laboratory conditions. Soil flooding reduced net CO2 assimilation (A) within 24 hours. Net CO2 assimilation and residual conductance to CO2(gr′) declined to ≈30% of control values after 5 days of flooding. Effects on stomatal conductance to CO2 (gS) and intercellular CO2 (Ci) were not significant during the 5 days of treatment. Apparent quantum yield (Φ) gradually declined to 52% that of controls during these 5 days. In a second experiment, CO2 response curves suggested that, initially, stomatal and nonstomatal limitations to A were of about equal importance; however, as flooding continued, nonstomatal limitations became dominant.
`Imperial Gala' apple trees (Malus ×domestica Borkh.) on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Water relations, gas-exchange parameters per unit leaf area and per tree, chlorophyll fluorescence, and leaf abscisic acid content were determined during each stress and recovery period. Whole-plant calculated gas exchange best indicated plant response to drought stress, with consistent reductions in CO2 assimilation, transpiration, and leaf conductance. Variable and maximal chlorophyll fluorescence and fluorescence quenching were not as sensitive to stress. Other fluorescence parameters showed little difference. The most consistent decreases due to stress for gas exchange per square meter were in transpiration and leaf conductance, with few differences in CO2 assimilation and fewer for mesophyll conductance, internal CO2 concentration, and water-use efficiency. Leaf water potential was consistently lower during drought stress and returned to control values upon irrigation. Leaf abscisic acid content was higher for drought-stressed trees on M.9 EMLA than control trees during the stress periods but inconsistently different for the other rootstock treatments. Trees on M.9 EMLA were least affected by drought stress, MM.111 was intermediate, and Mark was the most sensitive; these results are consistent with the growth data.
`Imperial Gala' apple (Malus domestica Borkh.) trees, trained to two shoots, on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Leaf growth rate, leaf area, leaf emergence, shoot length, and trunk cross-sectional area were measured during each stress and recovery period. Leaf growth rate was reduced during both stress periods but most consistently during the second drought stress. Length of the less-vigorous shoot was reduced most consistently due to drought stress but did not recover upon irrigation. Leaf emergence and trunk cross-sectional area increment were inconsistent in response to stress. Tree growth was reduced by drought stress to the greatest extent for trees on Mark, with MM.111 intermediate and M.9 EMLA least affected. At termination, the plants were separated into roots, current-season shoot growth, previous-season shoot growth, and rootstock, and dry weights were measured. Dry weights confirmed the growth measurements taken during the experiment with a 16%, 27%, and 34% reduction in total plant dry weight for drought-stressed trees on M.9 EMLA, MM.111, and Mark, respectively, compared to corresponding controls. It was concluded that Mark was the most sensitive of the three rootstocks followed by MM.111; M.9 EMLA was the most drought resistant.