Peach Roots Research Articles

Effects of phytotoxic extracts from peach root bark and benzoic acid on peach seedlings growth, photosynthesis, antioxidance and ultrastructure properties

During growth cycle, the accumulation of autotoxins released from peach root into soil strongly restrains the perennial tree growth in the same soil plot. However, the toxication syndrome on plant developmental physiology and the identities of toxic substances from peach root are still elusive to date. In this study, we used pot trials to investigate the influence of peach root bark extracts (extracted either in water or ethanol) and benzoic acid (a major allelopathic agent in most plant species)on seedling performance. Subsequently, the chemical compounds from peach root extracts were characterized by Gas Chromatography-Mass. Interestingly, in our study, the major toxic cyanide was only detected in the water extracts of root bark not in the root wood part and more cyanide could be detected in the presence of β-glucosidase. After applying exogenous root extracts and benzoic acid, the seedlings physiological growth was inhibited as expected, and lipid peroxidation and the antioxidant enzymes were increased as well. The photosynthetic parameters, including net photosynthetic rate, stomatal conductance and intercellular CO2 concentration, were all significantly reduced by the exogenous root extracts application. At cellular level, transmission electron microscopy showed that most of the organelles were lost in the root tip cells treated by ethanol-based peach root extracts, while the irregular nuclei, amorphous mitochondria in root tip cells, dissolved middle lamella and elongated plastids were observed in benzoic acid treatment. Furthermore, for the first time we identified 49 chemicals from ethanol-based peach root extracts, among which, 2, 4-bis (1, 1-dimethylethyl) -phenol (10.40%), benzoic acid (8.65%) and palmitic acid (7.12%) occurred in the highest amounts. Altogether our comprehensive physiological profile by toxication analysis and the determined major toxins from the root bark extracts could provide critical clues for peach allelopathic studies.

Assessment of various Peach rootstocks for germination and seedling growth

Peach root stocks “Swat local”, “Chitral local” and “Okinawa” were evaluated to assess their performance in nursery at Agricultural Research Institute Mingora, Swat Pakistan during 2013`14. Days to germination, percent seed germination, seedling diameter, number of branches per seedling, number of leaves per seedlings and seedling height were found significant in all the three rootstocks. The indigenous root stock “Swat local” and “Chitral local” performed well for the aforementioned traits. The rootstock “Okinawa” had earlier germination.

Influence of rhizosphere ventilation on soil nutrient status, root architecture and the growth of young peach trees

The peach tree root respiration rate is high, which requires large amounts of oxygen. When the rhizosphere oxygen content is poor, the root respiration and energy metabolism are restrained which will have negative impacts on peach trees growth, fruit quality and yield, especially during high temperature and rainy season. Our objectives were to investigate the relationship between rhizosphere ventilation and orchard soil enzyme activity, nutrient status, root architecture and growth of young peach trees. Two-year-old ‘Chunmei’ peach (Prunus persica L. Batsch) was subjected to various treatments (Treatment 1 [T1]: ventilation every three days; T2: ventilation every six days; T3: natural ventilation; Control: no ventilation) under field cultivation conditions. The soil oxygen content decreased and subsequently increased during the growth period, reaching a minimum in August. The rhizosphere soil oxygen content was higher under ventilation treatment than control, and T1 markedly increased the rhizosphere soil oxygen content. The rhizosphere soil available K and organic matter decreased while the rhizosphere soil available N and available P content increased and the soil enzyme activity was improved under ventilation treatments. The root activity and root nitrate reductase activity increased under ventilation treatments. Under T1, the total root surface area, total root length and number of first lateral root and second lateral root were increased significantly, but the average root diameter and the average length of first lateral root was reduced significantly, the branching angle between first lateral root and vertically downward direction was decreased, the number of small angle was increased. T1improved leaf functions and increased the net photosynthetic rate. Under T1, the leaf chlorophyll content and leaf protective enzyme activity (Superoxide dismutase, Guaiacol peroxidase and Catalase) increased markedly in the middle- and late-growth period and leaf senescence was postponed. The total nitrogen, phosphorus and potassium contents of young peach roots, shoots and leaves, as well as shoot growth, leaf weight and leaf area, increased under T1.

ECOLOGIZATION OF FRUIT CROPS GRAFTED SEEDLINGS GROWING

Cultivation of fruit crops grafted seedlings connect with the application of high doses of nitrogen fertilizers. They have greater mobility in the soil and can contaminate soil and groundwater with nitrates. Using of microbial preparations (MP), which biological agents are nitrogen fixing, phosphate mobilizing and growth promoting bacteria allows reducing the fertilizers doses and improving the nutrition of fruit seedlings. The purpose of our research was to study influence of some biological fertilizers on growth, development and output of seedlings in a fruit nursery with minimal doses of mineral fertilizes. The MP were tested in a small plots field experiment on Calcic Chernozem (Clayic) of southern Ukraine (Crimea). There were Diasofit created on base Agrobacterium radiodacter 204; Azotobacterin was made on the base Azotobacter vinelandii 10702, both of them are nitrogen fixing bacteria; Phosphoenterin (phosphate mobilizing bacteria Enterobacter nimipressuralis 32-3, which also produced physiological active substances) and a complex of microbial preparation (CMP) consist of mix Diasofit, Phosphoenterin and Biopolicid (Bacillus polymyxa P.) with antifungal activity. It is established that the MP promoted strengthening formation of shoots and roots of peach, apricot and cherry-plum seedlings. They improved the growth and development of plants and promoted increasing of the standard seedlings output. The most effective is using Phosphoenterin and CMP for growing of peach seedlings. Application of Azotobacterin at cultivation of cherry-plum and apricot seedlings allowed obtaining the most output of standard seedlings per ha. Application of CMP increased standard seedlings output both of these cultures to 7,200 and 8,200 peaches per ha respectively relative to standard technology.

Emergence of Root-feeding Weevils (Coleoptera: Curculionidae) in Central Georgia Peach Orchards

Injury to peach, Prunus persicae (L.) Batsch, roots is common by several plant pathogen species and by larvae of the peachtree borer, Synanthedon exitiosa Say (Lepidoptera: Sesiidae). External feeding injury to peach roots was observed that was not consistent with S. exitiosa injury but was suspected to be caused by the larvae of root-feeding weevil species (Coleoptera: Curculionidae). Thus, we used conical emergence traps for 3 yr to sample in unsprayed peach orchards (within the dripline of trees and at missing tree sites) to monitor for root-feeding weevils. Fuller rose beetle, Naupactus cervinus (Boheman), whitefringed beetles, Naupactus spp., and the twobanded Japanese weevil, Callirhopalus bifasciatus (Roelofs), (Coleoptera: Curculionidae) were captured at significantly higher numbers within the dripline of the tree than at missing tree sites. Adult N. cervinus emerged from soil year around; whereas, the other 2 species had seasonal emergence. In commercial peach orchards comprised of cultivars with early, mid, and late-season fruit ripening dates, N. cervinus was more abundant than other species. The later a cultivar ripens, the higher the number of insecticide applications it receives; however, we did not detect a difference in N. cervinus emergence between the cultivars. In another sprayed orchard, N. cervinus was again more common than other curculionid species captured. Damage ratings (0 - 5; none to heavy, respectively) on roots revealed a mean rating of 2.79 ± 0.12. Year-long emergence of N. cervinus is likely why it persisted in sprayed orchards. Modification of existing pest management programs will be needed to manage N. cervinus attacking peach roots.

Persistence of Propiconazole in Peach Roots and Efficacy of Trunk Infusions for Armillaria Root Rot Control

Trunk infusion of peach with propiconazole has been suggested as a potential strategy to protect roots from colonization by Armillaria species. In the present study, we investigated the persistence of propiconazole in peach roots following fall infusions and its potential for Armillaria root rot control in a commercial peach orchard. Four 12-year-old trees were infused with either 2 liters of a propiconazole solution at 0.4 mg ml-1 or water in September 2007. Bark tissue collected from primary roots of propiconazole-infused trees 48 hr and 6 and 12 months after infusion and analyzed using gas chromatography-mass spectroscopy contained 6.4, 1.4, and 0.9 μg propiconazole per gram fresh bark, respectively. Asymptomatic trees adjacent to trees that had died from Armillaria root rot (protective treatment) and symptomatic but alive trees (curative treatment) were infused with 1 liter of a propiconazole solution (0.4 mg ml-1) in spring and fall of 2008 and 2009 at a commercial peach orchard planted in 2005. Trees were rated for Armillaria root rot severity 6, 12, 24, and 36 months post-infusion. In the protective treatment, the survival rate in both non-infused and infused trees was 80% 36 months post-infusion. However, more (60%) of the propiconazole-infused trees remained asymptomatic compared to the control trees (30%). A significant difference was observed between the non-infused and propiconazole-infused trees following curative treatment. None of the control trees were alive after 36 months compared to 40% of propiconazole-infused trees. We conclude that fall infusion of peripheral trees of infection centers with propiconazole can slow the expansion of Armillaria root rot infection centers in commercial peach orchards.

Expression of Genes Involved in Nitrate Signaling and Metabolism in Peach Roots in Response to Elevated Levels of Nitrate

Nitrate is a major source of nitrogen, and it also acts as a signaling molecule that has an impact on gene expression associated with nitrogen uptake, metabolism and organ development. During fertilization, plants need to adapt to increased levels of available nitrogen. In this study, we have analyzed gene expression changes during this process using seedlings from peach trees, an important horticultural model plant. The results show that nitrate affects a broad range of genes. Except for carbon metabolism, nitrate affects genes associated with many biological plant processes, such as the biosynthesis of secondary metabolites and plant–pathogen interactions, amongst others. Overall, 1,247 genes were downregulated, 460 genes were upregulated by 10 mM nitrate in roots and 32,296 candidates for new transcripts were found. These results suggest that peach gene transcripts may not have been fully predicted. In this study, we found 12 nitrate transporters, 13 DNA-binding single-finger transcription factors, 6 sucrose non-fermenting-1-related protein kinase 1 and 2 isopentenyl transferase homologous genes. Most of these were repressed by 10 mM nitrate in root tissue compared with 0.5 mM nitrate. These results differed from earlier studies in other plants that showed some genes did not have significant sequence similarity. Future studies will need to characterize the functional roles of the genes with unknown functions, and the results obtained in this work will need to be validated using other expression analysis tools.

EFFECT OF WHITE CLOVER (TRIFOLIUM REPENS 'HUIA') COVER CROP ON AGRONOMIC PROPERTIES AND SOIL BIOLOGY IN AN ORGANIC PEACH ORCHARD

In orchards, cover crops are interesting alternative strategies to tillage or chemical herbicides for managing weeds in the tree row. However, little is known about the effect of cover crops on agronomic properties and soil biology in organic orchards. To fill this gap, the effects of two weed managements, a White clover cover crop (CC) versus classical tillage practice (T) on the tree row, were assessed in an irrigated organic Peach orchard. White clover was sown in 2004, 2006 and 2009 in the tree row and ploughed in 2006 and 2008. Root density, earthworm density, water infiltration rate, nitrogen content and water availability were measured in the soil, in the tree row. In 2009, peach root density observed in the superficial layers was higher in CC treatment. Sampling dates and treatment have a significant effect on total earthworm density with higher abundance observed in CC. However, no difference was observed between CC and T anecic earthworm groups known to make large and vertical burrows. Infiltration rate measured with the simplified Beerkan method was higher in CC treatment. This could be explained by the thick superficial root mat which was associated to a significant higher epigeic earthworm density in CC. Whereas nitrogen supplies were twice lower in CC treatment since 2005, soil nitrogen availability was equivalent in both treatments. These results demonstrate the agronomic interest of nitrogen-fixing plants used as a cover crop in organic peach orchards.

Organic fertilization leads to increased peach root production and lifespan

We evaluated the effects of mineral and organic fertilizers on peach root dynamics in the growing season from 2003 to 2006 in a nectarine (Prunus persica L.) orchard, planted in 2001 and located in the Po valley, northeastern Italy. Very few studies have conducted long-term investigations of root dynamics of fruit crops. Our main objective was to determine whether organic fertilizers affect root dynamics differently than mineral fertilizers. The experiment was a completely randomized block design with four replicates of three treatments: unfertilized, mineral fertilized and composted with municipal waste. Mineral fertilizers included P (100kgha(-1)year(-1)) and K (200kgha(-1)year(-1)) applied only at planting and N (70-130kgha(-1)year(-1)) split into two applications, one at 40 days after full bloom (60%) and the other in September (40%) each year. The compost fertilization represented a yearly rate of 10 metric tons (t) dry weightha(-1), which approximates (in kgha(-1)year(-1)) 240 N, 100 P and 200 K, split similarly to that described for the mineral fertilization of N. Both root growth and survival were evaluated at 20-day intervals during the growing season by the minirhizotron technique. Compost increased the production of new roots compared with the other treatments (P<0.01). Roots were mainly produced at a depth of 41-80cm and from March to May and in late summer. An analysis of covariance indicated no significant effect of soil nitrate on root production (P=0.47). The root lifespan was longer in compost-treated trees than in mineral-fertilized or unfertilized trees (P<0.01) and it was strongly affected by time of birth; roots born later in the summer lived longer than those born in the spring. Across years and treatments, the average root lifespan was positively correlated with soil nitrate (r=0.60; P<0.001). Variation in root lifespan with method of fertilization could be accounted for by variation in soil nitrate concentration as indicated by no effect of fertilizer treatment on root lifespan when soil nitrate was included as a covariate. These results reveal how shifting from mineral to organic fertilizers may shift both soil properties and nutrient availability, leading to changes in both root production and lifespan.

NITROGEN ABSORPTION AND RESPIRATION IN WHITE AND BROWN PEACH ROOTS

The relationship between root age and root physiology is poorly understood, despite its importance for nutrient absorption. In peaches, roots are white when they first appear and then become brown with age, which corresponds to a number of physiological changes. We related root browning to nitrogen (N) absorption and respiration in order to provide a better understanding of how color changes as typically observed using minirhizotrons relate to changes in root physiology. The experiment was conducted on peach seedlings (Prunus persica cv. ‘Guardian’) grown in 30-L pots in a greenhouse. Brown roots showed lower respiration rates than white roots. White roots showed a higher 15N uptake than brown roots and higher concentration of N, potassium (K), magnesium (Mg), manganese (Mn), iron (Fe) and copper (Cu), no significant differences were observed regarding calcium (Ca), and zinc (Zn) concentration.

Seasonal pattern of net nitrogen rhizodeposition from peach ( Prunus persica (L.) Batsch) trees in soils with different textures

Rhizodeposition plays an important role in nitrogen (N) cycling within ecosystems, but it is understudied in agroecosystems, especially in orchards. In this study, we quantified N flux from peach root to soil in two soils with different texture. Seedlings were grown for 1 year in sand and fertilized with 15N-enriched ammonium nitrate. Trees were then transplanted into pots filled with a coarse-textured (CT) or a fine-textured (FT) soil with natural 15N abundance. The isotopic mass balance technique was applied to quantify the uptake and the release of N by roots. At the end of the experimental year tree growth was 431 g tree −1 in CT soil and 188 g tree −1 in FT soil, and root N concentration was 0.98% in CT soil and 0.73% in FT soil. Leaf chlorophyll was always higher in trees grown in CT than in FT soil. Nitrogen uptake in CT soil was more than double that in FT soil (4471 mg tree −1 vs. 2106 mg tree −1), but its allocation was not affected by soil texture (57% aboveground and 43% belowground). Nitrogen flux from roots to soil was 453 and 412 mg N tree −1 year −1 for trees in CT and in FT soil, respectively, 70% of which transferred in the winter. Our data suggest that root mortality is more important than root exudation in N transfer from roots to soil. Rhizodeposition was similar for both soils but tree growth was greater in CT soil than in FT soil. As a consequence, trees in FT soil allocated belowground (root biomass and rhizodeposition) a higher proportion of the absorbed N compared to trees in CT soil. Data also indicate that rhizodeposition can account for a major fraction (25–41%) of the photosynthate flux to the root system and therefore it should be considered to accurately estimate BNPP. A deeper knowledge of the belowground orchard processes is necessary to understand a balanced tree nutrient uptake. Rhizodeposition can also contribute to nutrient mobilization, heavy metal detoxification, root exploitation of soil, and drought tolerance. This work can thus provide information enabling horticulturists to develop management practices to optimise tree growth.

Propiconazole Inhibits Armillaria tabescens In Vitro and Translocates into Peach Roots Following Trunk Infusion.

Intravascular trunk infusion of propiconazole has been associated with beneficial effects on Armillaria root rot control in Prunus sp. but its basipetal movement has not been verified. Propiconazole, a sterol demethylation inhibitor fungicide, was more effective in inhibiting mycelial growth of Armillaria tabescens isolates in vitro (average effective concentration to inhibit mycelial growth by 50% [EC50 value] of 0.6 μg/ml) compared with fungicides from five other chemical classes (EC50 values ranging from 4.6 to >1,000 μg/ml). The fungicide was infused into the vascular system of peach trees in the spring, summer, and fall of 2005 and 2006. Propiconazole concentration was determined using gas chromatography mass spectrometry in trunk sections above and below the infusion site and in primary roots. Over two experimental years, spring and fall infusions resulted in consistent propiconazole accumulations in primary peach roots. Spring infusions yielded propiconazole concentrations of 1.7 μg/g in 2005 and 5.6 μg/g in 2006, whereas the highest accumulations were detected following fall infusions with 9.2 μg/g in 2005 and 6.7 μg/g in 2006. Propiconazole was also consistently detected in trunk sections collected from above and below the infusion site. The basipetal movement of propiconazole in peach trees and its inhibitory activity against A. tabescens in vitro suggest that propiconazole infusion could be useful for targeted Armillaria root rot management.

Influência da poda de renovação e controle da ferrugem nas reservas de carboidratos e produção de pessegueiro precoce

Este trabalho objetivou verificar a influência da poda de renovação e controle da ferrugem nas reservas de carboidratos não-estruturados em ramos e raízes do pessegueiro cultivar Flordaprince, bem como o possível efeito na produção e qualidade dos frutos. O trabalho foi conduzido no Departamento de Produção Vegetal da ESALQ-USP, em Piracicaba. O delineamento experimental utilizado foi em sete blocos ao acaso, constando de três tratamentos, sendo cada parcela constituída de quatro plantas. O tratamento 1 consistiu na realização da poda de renovação que foi executada 45 dias após a colheita, no mês de outubro de 2003. No tratamento 2, não se realizou a poda de renovação, e foi feito o controle da ferrugem. No tratamento 3, não foi realizada a poda de renovação, tampouco o controle da ferrugem, ocasionando desfolha antecipada. Os dados foram submetidos às análises de variância e à comparação das médias, pelo teste de Tukey. O espaçamento utilizado foi de 3,0 por 1,2 m, correspondendo a 2.777 plantas ha-1. As plantas foram conduzidas em sistema de líder central e receberam as práticas culturais normalmente utilizadas. Foram coletadas amostras de raízes e ramos que foram secos, moídos e submetidos à análise de laboratório para verificação dos teores de carboidratos não-estruturados. Ocorre flutuação na concentração de carboidratos solúveis nas raízes e nos ramos de acordo com a época da coleta, sendo que os teores de carboidratos solúveis nas raízes são sempre superiores àqueles encontrados nos ramos. O tratamento 2 apresentou maior produção de frutos e maior número de frutos por planta. Não houve efeito dos tratamentos nos aspectos qualitativos dos frutos, como diâmetro, comprimento, coloração e teor de sólidos solúveis.

Characterization and Host Range Determination of Soybean Super VirulentAgrobacterium tumefaciensKAT23

Agrobacterium tumefaciens KAT23 isolated from peach root causes crown gall disease in a number of grain legume plants, including the common bean (Phaseolus vulgaris) and soybean (Glycine max). KAT23 caused tumor formation in each of these plants more effectively than strain C58. Biotype determination suggested that this strain is biotype II. KAT23 was able to utilize nopaline as a carbon source. Partial sequence analysis indicated that KAT23 harbors a nopaline-type Ti plasmid, designated pTiKAT23, which was highly homologous with other nopaline-type Ti plasmids (pTiC58 and pTiSAKURA). KAT23 transferred not only the T-DNA of the Ti plasmid but also introduced T-DNA of the binary vector efficiently. The common bean inoculated with KAT23 (pIGFP121-Hm) showed crown galls, and some plants showed beta-glucuronidase (GUS) and sGFP (S65T) gene expression. This virulent ability of KAT23 indicates its potential application to legumes, especially to soybean transformation.

Molecular cloning and expression analysis of cDNAs encoding a putative Nrt2 nitrate transporter from peach

Two cDNA clones encoding a putative high-affinity nitrate transporter (Nrt2) were isolated from a cDNA library of peach (Prunus persica (L.) Batsch) roots. The nucleotide sequences of the clones, named PpNrt2.1 and PpNrt2.2, showed 99% identity in their coding regions, but their 3'-untranslated sequences showed only 40% identity. The deduced amino acid sequences of the clones showed 44-90% homology to NRT2 proteins from other plants. Both clones contained open reading frames encoding polypeptides of 530 amino acid residues, each with a predicted molecular mass of about 57 kDa. Both polypeptides had 12 putative transmembrane domains and a long hydrophilic C-terminal domain like other members of this protein family. Analyses of the genomic structures and of Southern blots suggested that PpNrt2.1 and PpNrt2.2 originated from different loci in the peach genome. In Northern blots, transcripts of PpNrt2.1 and PpNrt2.2 were detected in roots but not shoots of seedlings after nitrate application. They were not detected in leaves, stems, flowers, fruits or seeds of mature trees in the field, indicating root-specific expression of PpNrt2.1 and PpNrt2.2. Application of nitrate to roots of nitrogen-deprived seedlings strongly induced expression of PpNrt2.1 within 0.5 h, and gradually induced expression of PpNrt2.2. Application of ammonium to roots of nitrogen-deprived seedlings repressed expression of PpNrt2.1 and PpNrt2.2. The relationship of PpNrt2.1 and PpNrt2.2 to the inducible high-affinity transport system (iHATS) involved in the uptake of nitrate in peach roots is discussed.

Bioassay and Identification of Root Exudates of Three Fruit Tree Species

AbstractA laboratory bioassay was designed to determine the allelopathic potential of root exudates of three fruit tree species on apple germination. The results showed that root exudates of apple (Malus pumila L.) and peach (Prunus persica L.), each at concentrations of 0.02 and 0.2 mg/L, inhibited germination and radicle growth of apple seeds by 56.7%, 60.7%, 51.5%, and 59.3%, respectively. The corresponding shoot growth inhibition rate was 49.5%, 46.7%, 36.4%, and 44%, respectively. Root exudates of jujube (Ziziphus jujuba Mill.) had no significant effect on apple seeds. Qualitative determination of root exudates of apple, peach, and jujube tree was developed with gas chromatography‐mass spectrometry. The root exudates of apple seedlings mainly contain organic acids, glycol, esters, and benzenphenol derivatives. Peach root exudates contained phenolic acids and benzenphenol derivatives in addition to two unidentified compounds. The root exudates of jujube did not contain any phenolic acids.

Detecting and Measuring Fine Roots in Minirhizotron Images Using Matched Filtering and Local Entropy Thresholding

An approach to automate the extraction and measurement of roots in minirhizotron images is presented. Two-dimensional matched filtering is followed by local entropy thresholding to produce binarized images from which roots are detected. After applying a root classifier to discriminate fine roots from unwanted background objects, a root labeling method is implemented to identify each root in the image. Once a root is detected, its length and diameter are measured using Dijkstra’s algorithm for obtaining the central curve and the Kimura–Kikuchi–Yamasaki method for measuring the length of the digitized path. Experimental results from a collection of peach (Prunus persica) root images demonstrate the effectiveness of the approach.

Automatic Detection of Fine Roots in Minirhizotron Images

Minirhizotrons and specialized camera equipment have been widely adopted for in situ observation of fine root dynamics in horticultural settings. However, the laborious nature of data collection from minirhizotron images limits the number and size of experiments that can reasonably be analyzed. Here we present an algorithm for the automatic detection and measurement of roots in minirhizotron images, including the discrimination of light-colored roots from bright background objects. First, two-dimensional matched filtering and local entropy thresholding are used to produce binarized images from which roots are detected. Next, a strong root classifier based on geometric and intensity features is used to discriminate roots from unwanted background objects. A labeling algorithm identifies each individual root in the image, and root lengths and diameters are measured using Dijkstra's algorithm and the Kimura–Kikuchi–Yamasaki method for obtaining the length of a digitized path. This approach allows us to identify and measure fine roots as individuals, rather than simply measuring the aggregate root length in an image. Experimental results from a collection of 250 peach (Prunus persica) root images demonstrate the effectiveness of the approach. The algorithm is able to detect and measure a variety of roots of different shapes, sizes, and orientations, with a detection rate of 92%, a false–positive rate of 5%, and an average measurement error of 4.1% and 6.8% for length and diameter, respectively. Current work involves improving the efficiency of the algorithm and incorporating it into an application. We are also exploring algorithms for tracking the location of a root over time as it grows darker in color and blends with the surrounding soil.

Interaction dynamics between saprobic lignicolous fungi and Armillaria in controlled environments: Exploring the potential for competitive exclusion of Armillaria on peach

Armillaria root rot, caused by Armillaria tabescens and Armillaria mellea, is a major cause of premature tree death in peach orchards in the southeastern United States. The root systems of infected trees can become entirely colonized by Armillaria, serving as an inoculum source for adjacent trees and providing massive inoculum levels in replant situations. If dead or dying trees could be colonized by an effective competitor of Armillaria before their removal, the extent of root colonization by the pathogen could be reduced, thus decreasing the threat to adjacent trees and/or subsequent plantings. Interactions between five species of saprobic lignicolous fungi (Ganoderma lucidum, Hypholoma fasciculare, Phanerochaete velutina, Schizophyllum commune, and Xylaria hypoxylon) and the two Armillaria species were examined in controlled conditions to provide proof of concept for competitive exclusion of Armillaria from peach roots. On agar-coated glass slides, all five potential antagonists induced detrimental reactions in >58% of the Armillaria hyphae observed, with the majority resulting in hyphal swelling or granulation. On poplar wood blocks, all antagonists consistently either overgrew Armillaria colonies or—in the case of S. commune—engaged in deadlock reactions; in all cases, the viability of Armillaria colonies was reduced to <30% of that of unchallenged controls. When inoculated simultaneously onto opposite ends of peach root segments, all antagonists consistently reduced growth and viability of Armillaria on and under the bark, whereby reduction of pathogen growth underneath the bark, Armillaria’s primary ecological niche, was most pronounced for G. lucidum, S. commune, and X. hypoxylon. When root segments were allowed to be colonized entirely by Armillaria before being inoculated with the antagonists, the latter were able to overgrow the pathogen on the root surface but unable to pre-empt it from underneath the bark. In summary,G. lucidum, S. commune, and X. hypoxylon caused strong hyphal and mycelial interference reactions and the most pronounced reductions in growth of Armillaria above and below the bark, indicating that they would be the most promising candidates for field-scale evaluations to restrict colonization of dead or dying peach trees by Armillaria in the orchard.

Effect of Nitrogen Fertilization on Primary Xylem Differentiation in Roots of Young Peach Trees

The primary xylem differentiation in new, white roots of differing root diameters in 3-year-old peach Prunus persica (L.) (Batsch) trees supplied different amounts of nitrogen was examined. Primary xylem differentiation as the number of xylem ridges in cross-sections of new, white roots increased significantly with increasing root diameters, irrespective of differing amounts of nitrogen applications. The number of xylem ridges ranged from three to seven in peach roots. These results indicate that the numbers of thick roots having many primary xylem cells increased more in nitrogen fertilized plants than did those in no-nitrogen ones.