Carolyn F. Scagel

Application of ectomycorrhizal fungi in vegetative propagation of conifers

In forestry, vegetative propagation is important for the production of selected genotypes and shortening the selection cycles in genetic improvement programs. In vivo cutting production, in vitro organogenesis and somatic embryogenesis are applicable with conifers. However, with most coniferous species these methods are not yet suitable for commercial application. Large-scale production of clonal material using cuttings or organogenesis is hindered by rooting problems and difficulties in the maturation and conversion limit the use of somatic embryogenesis. Economically important conifers form symbiotic relationship mostly with ectomycorrhizal (ECM) fungi, which increase the fitness of the host tree. Several studies have shown the potential of using ECM fungi in conifer vegetative propagation. Inoculation with specific fungi can enhance root formation and/or subsequent root branching of in vivo cuttings and in vitro adventitious shoots. Germination of somatic embryos and subsequent root growth can also be improved by the use of ECM fungi. In addition, inoculation can increase the trees ability to overcome the stress related to ex vitro transfer. A specific interaction between a fungal strain and tree clone occurs during root induction and germination of somatic embryos. Multiple rooting factors exist in this interaction that complicate the predictability of the response to inoculation. Fungal-specific factors that influence rooting responses to inoculation may include plant growth regulator production, modification of the rooting environment, and interactions with beneficial microbes. A combination of these factors may act synergistically to result in positive responses in tree genotypes that are compatible with the fungus.

Modification of root IAA concentrations, tree growth, and survival by application of plant growth regulating substances to container-grown conifers ∗

Tree survival after planting ispartially a function of the trees capacity toproduce new roots. In a field trial we assessedthe potential to modify the IAA concentrationin roots, root growth responses, and plantsurvival by root application of plant growthregulators (PGRs) such as IBA, NAA, andethylene, or alginate, a moisture retentionmaterial. Container-grown Douglas-fir,Englemann spruce, and lodgepole pine werelifted before and during prescribed liftingwindows and treated with Stim-root®, Ethrel®,Hormogel®, or alginate before or aftercold-storage, then planted in a clearcut.Lifting trees outside of the prescribed liftingwindow decreased IAA concentrations in roots ofDouglas-fir, Englemann spruce, and lodgepolepine. Treating plants with different PGRs aftercold storage increased root IAA concentrationsand root growth after planting compared totreating plants prior to cold storage. Rootgrowth and above ground plant growth andsurvival were well correlated to IAAconcentrations in roots of Douglas-fir andEnglemann spruce. IAA concentrations in rootsof lodgepole pine correlated with root growth,but did not correlate with survival. A costanalysis of treatment effects on growth andsurvival showed that certain post-cold storagePGR treatments can decrease the cost necessaryto attain target stocking and increase the sizeof the trees. Our results suggest thatapplication of PGRs or other root-promotingmaterials to tree roots before planting has thepotential to be a cost-beneficial method forincreasing root growth and tree survival.

Spring growth of almond nursery trees depends upon nitrogen from both plant reserves and spring fertilizer application

Summary June-budded ‘Nonpareil’/‘Nemaguard’ almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mM) from July to September. The trees were sprayed with either water or 3% urea in October, then harvested bareroot after natural leaf fall, and stored at 2°C. One set of trees was destructively sampled for total N content; the remaining trees were transplanted into N-free media in the spring after cold storage. After budbreak, these trees were supplied for 70.d with either N-free Hoagland’s solution or Hoagland’s solution containing 15N-NH4NO3. Nitrogen concentrations in both stem and root tissues were positively correlated with the N-fertigation concentration. Fall foliar urea applications increased levels of stem and root N regardless of the N-fertigation concentration. During the first 70 d of spring growth, the trees utilized nitrogen from both their reserves and spring fertilizer applications. The amount of N reserves used for growth of new shoots and leaves was proportional to the total amount of reserves. Trees with low N reserves relied primarily on the spring fertilizer as their source of nitrogen. We conclude, therefore, that both reserve N and spring-applied N fertilizers are important for enhancing the regrowth of bareroot almond nursery trees during establishment after transplanting. Nitrogen fertilization in the spring can especially improve the performance of trees with low N reserves.

Root damage affects nitrogen uptake and growth of young Fuji/M.26 apple trees

Summary Effects of root damage during the transplant process on growth and nitrogen (N) uptake were studied with one-year-old bench-grafted Malus domestica Borkh ‘Fuji’ on M.26 rootstock apple nursery plants. Plants were potted after grafting and grown outside for one season. At the end of the season uniform trees were selected and randomly divided into four groups. One group of plants were moved into a 2°C cold room with soil and container intact (IR Treatment). Plants in other groups were removed from pots and stored as bareroot in the same cold room for three months. In the spring, bareroot plants were either: (1) transplanted with about 10% of the root system damaged during transplant (TP Treatment and Control-CK); or (2) root pruned by 25% (by volume) prior to transplant (RP treatment). Five trees from each treatment received 1 g of 15NH415NO3 at 12, 41 and 76 d after repotting. Control (CK) trees received no N. Trees were harvested 10 d after each N application, and plant growth and total N and 15N content of different tissues were determined. Root pruning reduced plant total biomass and root biomass at the first two harvests, but the plants from the RP treatment had highest total plant biomass and root biomass at the third harvest. There was no significant difference in the new stem and leaf growth among IR, RP and CK treatments at harvests but the TP treatment reduced new shoot biomass. Plants with intact roots (IR) had the higher total N content while control plants (CK) had the lowest. Root pruning reduced 15N uptake rate at the first two harvests but promoted it at the third harvest. Our results suggest that plant growth and nutrient uptake was suppressed by root pruning/damage during transplanting only in the early season, and the negative effects on growth and N uptake were offset later in the season by compensative root regeneration.

N, P, and K Supply to Pinot noir Grapevines: Impact on Berry Phenolics and Free Amino Acids

Understanding the direct role that macronutrient supply (N, P, and K) has on berry chemistry was evaluated in Pinot noir grapevines grown in sand culture. Self-rooted Pinot noir vines were grown for three years with either full nutrition (Control) or three reduced levels of either N, P, or K supply while holding all other nutrients constant. Vines were managed to minimize differences in vine water status (altering irrigation to achieve similar daily soil moisture content) and fruit cluster solar exposure (altering leaf pulling to achieve similar cluster irradiance) due to varying nutrient supply so that indirect effects on berry chemistry could be largely eliminated. Berry chemistry was evaluated in the second and third years after different nutrient supply treatments were imposed. Results showed that low N, but not low P or K, altered berry free amino acid (FAA) and phenolic profiles. Low N supply reduced FAA and yeast assimilable nitrogen (YAN) in both years by up to 70% and altered certain FAAs more than others, thus changing berry FAA profile. The concentration of sugars, anthocyanins, and flavonol-glycosides increased in low N vines during the third season, but the increase in sugars and anthocyanins was attributed to the decline in berry size that year. Condensed tannins and total phenolic acids were increased in low N vines across both years, independent of changes in berry size. Results indicated that low N supply altered YAN to the greatest degree, while anthocyanin enhancement did not occur until yield and berry size were also reduced. Increased concentrations of tannins and phenolic acids in berries occurred in response to low N supply independent of reductions in yield and berry size.

Soil and foliar nitrogen supply affects the composition of nitrogen and carbohydrates in young almond trees

Summary June-budded ‘Nonpareil/Nemaguard’ almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mM) in a modified Hoagland’s solution from July to September. In October, the trees were sprayed twice with either water or 3% urea, then harvested after natural leaf fall and stored at 2°C. Trees were destructively sampled during winter storage to determine their concentrations of amino acids, protein, and non-structural carbohydrates (TNC). Increasing N supply either via N fertigation during the growing season or with foliar urea applications in the fall increased the concentrations of both free and total amino acids, but decreased their C/N ratios. Moreover, as the N supply increased, the proportion of nitrogen stored as free amino acids also increased. However, protein was still the main form of N used for storage. The predominant amino acid in both the free and the total amino-acid pools was arginine. Arginine N accounted for an increasing proportion of the total N in both the free and the total amino acids as the nitrogen supply was increased. However, the proportion of arginine N was higher in the free amino acids than in the total amino acids. A negative relationship was found between total amino acid and non-structural carbohydrate concentrations, suggesting that TNC is increasingly used for N assimilation as the supply of nitrogen increases. Urea applications decreased the concentrations of glucose, fructose, and sucrose, but had little influence on concentrations of sorbitol and starch. We conclude that protein is the primary form of storage N, and that arginine is the predominant amino acid. Furthermore, the synthesis of amino acids and proteins comes at the expense of non-structural carbohydrates.

Method of Nitrogen Application in Summer Affects Plant Growth and Nitrogen Uptake in Autumn in Young Fuji/M.26 Apple Trees

Abstract Effects of foliar vs. soil nitrogen (N) application during the summer and the autumn were studied in young Fuji apple trees (Malus domestica Borkh) on Malling 26 (M.26) rootstock. One‐year‐old bench‐grafted trees were potted in 3.8‐liter pots in a mix of perlite, peat moss, and loam soil (1:1:1 by volume) and were treated weekly from late June to early September with 0.5% urea either by foliar or soil application or soil application of water (control). At the end of September, five trees from each treatment were harvested, and shoot and root growth and leaf N concentration were determined. In mid‐October of the same year, trees from each treatment were randomly divided into three subgroups. One group received soil application of water (control), and the other groups received either a foliar or soil application of 3% 15N‐urea. After natural leaf defoliation, trees were harvested, and total N and 15N concentration of stems (all aboveground tissue) and roots was determined. Regardless of application method, N application during the summer promoted plant growth and increased leaf N concentration. Soil N application during the summer stimulated more shoot and extension root growth than foliar N application. In contrast, the foliar N application in the summer promoted more feeder root growth than soil N application. Regardless of application method, autumn N application after terminal bud set had little effect on current‐year growth but increased total plant N concentration. In the autumn, trees that received soil N applications in the summer had more 15N uptake by leaves, while trees receiving foliar N applications in the summer had more 15N uptake by root. These results suggest that the differential influence of N application methods during the summer on growth and partitioning of trees affects tree responsiveness to autumn N applications. The use efficiency of autumn‐applied N depends on the method of N application in the summer.

Effects of copper, zinc and urea on defoliation and nitrogen reserves in nursery plants of almond

Summary ‘Nonpareil’/‘Nemaguard’ and ‘Nonpareil’/ ‘Lovell’ almond (Prunus dulcis (Mill) D. A. Webb) nursery trees were used to study the effects of foliar applications of CuEDTA (Cu), ZnSO4 (Zn) and urea on defoliation and nitrogen (N) reserves. Foliar application of Cu and Zn induced early defoliation, with one spray as effective as two. Trees receiving Cu were defoliated 20–30 d before controls and defoliation on trees sprayed with Zn occurred 10–14 d before controls. Urea increased the efficiency of defoliation by Zn (1.25–2% ZnSO4) and Cu (0.5% CuEDTA). Trees receiving defoliants contained 4–26% less N than naturally defoliated controls, and N reserves were higher in trees given urea than in controls. Trees sprayed with urea plus defoliants contained up to 20% more N than controls. Both CuEDTA and ZnSO4 promoted early defoliation in almond trees, while the addition of urea can assist in maintaining tree N reserves.

Isolate-specific rooting responses of Leucothoe fontanesiana cuttings to inoculation with ericoid mycorrhizal fungi

Summary We assessed whether adding ericoid mycorrhizal fungi (EMF) to the rooting substrate during cutting propagation altered rooting and root growth of Leucothoe fontanesiana ‘Rainbow’. Hardwood cuttings, treated or untreated with rooting hormone prior to sticking into rooting substrate, were grown with one of three isolates of EMF as inoculum or with no inoculum (control). Cuttings were placed under mist in a greenhouse, with no bottom heat, and harvested 63, 84 and 109 d after sticking. Cuttings in substrate inoculated with two of the three EMF isolates showed better rooting than in non-inoculated substrate 63 d after sticking. However, by the end of the experiment, there were no differences in rooting between cuttings in the different inoculation treatments. Only cuttings in pots inoculated with one of the EMF isolates had consistently higher root initiation and weight than non-inoculated cuttings at all harvest dates. Root initiation and weight of cuttings in pots inoculated with either of the other two EMF isolates were greater than non-inoculated cuttings only when the cuttings had been treated with rooting hormone. In general, roots on EMF-inoculated cuttings were less branched and longer than roots on non-inoculated cuttings. Root colonisation was positively correlated with root initiation, length and weight 63 d after sticking; while, at later harvest dates, root colonisation was positively correlated only with root weight. The ability of EMF to increase rooting during cutting propagation of easy-to-root species, may decrease root production time. EMF-induced increases in root initiation during cutting propagation appear to be related to specific plant-fungus interactions and to interactions with rooting hormone. Although there were isolate-specific differences in rooting response, EMF-induced changes in root size and anatomy appear to be time-dependent and may influence the function of the new root system relative to water use and nutrient uptake, as well as survival, during transplanting.

Timing of urea application affects leaf and root N uptake in young Fuji/M.9 apple trees

Summary Leaf and root nitrogen (N) uptake was compared at different times of the season in young apple trees. One-year-old potted Fuji/M.9 trees were supplied with 1% 15N-labelled urea either by foliar or soil applications in May, July and September. Trees receiving only water served as controls. The trees were harvested 10 d after 15N application, separated into shoots (leaves and current-year stems), stem (previous-year wood) and roots. Biomass, total N and 15N contents of all tissues were determined. New shoot biomass and total tree biomass increased as the season advanced, while root biomass peaked in July. Leaf N uptake was higher than root uptake in May and September, while root N uptake was higher than leaf uptake in July. Leaf N uptake increased as the season advanced, while root N uptake was highest in July. The lowest 15N recovery (11%) was obtained in May with soil N application, and the highest 15N recovery (48%) was obtained in September with foliar N application. Our results suggest that foliar application of N early in the season, followed by soil N application in mid-season, then foliar application again late in the season is an efficient N management strategy for young trees.