Stone Fruit Trees Research Articles

Effect of calcium and nitrogen fertilization on bacterial canker susceptibility in stone fruits

Introduction . Bacterial canker, caused by Pseudomonas syringae pv. syringae , is a destructive disease where stone fruit trees are cultivated. The efficacy of nitrogen and calcium fertilization on bacterial canker susceptibility was evaluated in stone fruits. Materials and methods . Field experiments were conducted to study the efficacy of foliar applications of calcium nitrate, and ground fertilization with CAN-17 plus low-biuret urea foliar spray on bacterial susceptibility in ‘Riegel’ peach, ‘French’ prune and ‘Nonpareil’ almond growing in ring nematode-infested and nematicide-fumigated soils. Host susceptibility was evaluated by measuring the length of lesions developed following inoculation with P. syringae pv. syringae . Results and discussion . Foliar applications of Ca(NO3 )2 significantly increased leaf nitrogen and bark calcium concentrations in peach trees growing in both fumigated and nonfumigated areas. Peach trees growing in nonfumigated areas developed significantly longer lesions than trees growing in fumigated areas. However, Ca(NO3 )2 foliar applications had no effect in decreasing peach susceptibility to bacterial infection in both nonfumigated and fumigated areas. After inoculation, diseased prune trees developed significantly longer lesions than healthy trees. Leaf and bark calcium concentrations of diseased prune were significantly increased after Ca(NO3 )2 foliar sprays, but again the treatments did not significantly affect prune susceptibility to bacterial infection. However, nitrogen fertilization with CAN-17 and urea significantly increased the bark nitrogen concentration of almond trees, and these trees had significantly smaller lesions than those not receiving nitrogen fertilization. Foliar application of calcium (Nutri-Cal) did not affect almond susceptibility to bacterial canker. Collectively, these data support the previous hypothesis that increased susceptibility of stone fruits to P. syringae pv. syringae under nematode infestation conditions is mediated by both nitrogen effects and nitrogen-independent effects, and application of ammonium nitrogen may have some beneficial effects in reducing stone fruit susceptibility to bacterial canker where ring nematode infestation prevails.

Class 1 non-symbiotic and class 3 truncated hemoglobin-like genes are differentially expressed in stone fruit rootstocks (Prunus L.) with different degrees of tolerance to root hypoxia

Root hypoxia produced by flooding or over-irrigation limits stone fruit tree development, particularly in orchards established on soils with restricted drainage. To overcome this problem, stone fruit trees are usually grafted on rootstocks (species or hybrid of the Prunus L. genus) with different degrees of tolerance to root hypoxia. However, the molecular base of such variability is largely unknown. In Arabidopsis thaliana (Heynh.), as well as in a number of crops and tree species, hemoglobin (Hb)-like genes stand out among hypoxia-related genes, but no such studies have been done with the Prunus species used as rootstocks. In this study, we analyzed the expression pattern of class 1 non-symbiotic Hb-like (nsHb) and class 3 truncated Hb-like (trHb) genes in Prunus rootstock roots with different responses to this stress. We observed that the putative Prunus nsHb and trHb genes were induced by root hypoxia in all analyzed Prunus genotypes, independently of their tolerance to hypoxia. However, Prunus nsHb and trHb genes had higher expression levels in roots of tolerant rootstocks. Prunus nsHb and trHb genes were also regulated by other abiotic stresses, such as salt stress and low temperatures. Our results suggest that changes in nsHb and trHb expressions could be part of the adaptive mechanisms that have evolved in the Prunus species to survive under hypoxia or other types of environmental stress that commonly challenge stone fruit tree orchards.

EVALUATION OF SOME BACTERIAL ANTAGONISTS FOR BIOLOGICAL CONTROL OF FIRE BLIGHT DISEASE

Antagonistic activities of 120 epiphytic bacterial isolates against Erwinia amylovora were evaluated under laboratory and orchard conditions. Samples were collected at three stages of plant growth during 2009. The hosts were chosen from diseased and healthy pome fruit and stone fruit trees in Alborz, Isfahan and Neishabur regions of Iran. Two in vitro tests including antibiosis and immature fruit assay were performed to identify effective bacterial antagonists. Out of 21 strains, four representative strains encoded Kgh1, Abp2, E11 and E10 showed maximum growth inhibition, growth rate and stability in inhibition. Identification of four bacterial antagonists was confirmed by sequencing their 16S rDNA and performing common biochemical tests. These strains were identified as Pseudomonas fluorescens (E10), Pantoea agglomerans (Abp2), Pseudomonas putida (E11) and Serratia marcescens (Kgh1). Some complementary tests were then conducted to check their antagonistic activity against Erwinia amylovora on pear blossom. In all evaluation procedures, biocontrol effects of Pantoea agglomerans Abp2 and Pseudomonas fluorescens E10 were more promising than those afforded by Pseudomonas putida E11 and Serratia marcescens Kgh1. A one-year field experiment was also carried out on a partially susceptible domestic pear cultivar in an infested orchard in the Karaj region of Iran. The selected bacteria were applied twice at 20% and 80% of blooming. The results showed 46.9% disease occurrence in control plants, while the antagonistic bacteria reduced the disease between 23 and 60%. The field trial the most effective antagonist was P. agglomerans Abp2, while the least effective was S. marcescens Kgh1.

Investigations of the Plum pox virus in Chile in the past 20 years

Sharka disease, which is caused by Plum pox virus (PPV), is one of the most serious diseases affecting stone fruit trees around the world. Identified in Bulgaria in 1931, it was restricted to the European continent until 1992 when the virus was identified in Chile. It was subsequently verified in the USA, Canada, and Argentina. After 20 years since first detecting PPV in Chile, it seems clear that the disease cannot be eradicated in spite of various measures. Considering the seriousness of this problem for the domestic industry, a series of studies have been conducted to determine the distribution and degree of transmission of the disease, its biological and molecular characterization and epidemiological aspects, etc. The available information has allowed national phytosanitary control agencies to take steps to decrease the effects of the virus. However, there is a lack of data with respect to epidemiological factors for a more accurate understanding of the performance of the virus under Chilean conditions.

First Report of Cherry necrotic rusty mottle virus on Stone Fruit Trees in China.

During the growing seasons of 2010 through 2012, leaf tissues from 206 stone fruit trees, including one flowering cherry, three sour cherry, six nectarine (Prunus persica L. var. nucipersica Schneider), 14 apricot, 24 plum (P. domestica L.), 41 sweet cherry, and 117 peach [P. persica (L.) Batsch] trees, grown in six provinces of China, were randomly collected and tested for the CNRMV infection by RT-PCR. Out of those sampled trees, 37 showed shot holes and vein yellowing symptoms. Total RNA was extracted from leaves using the CTAB protocol reported by Li et al. (2). The primer pair CGRMV1/CGRMV2 (1) was used to amplify a fragment of 949 bp from CNRMV genome, which includes the CP gene (804 bp). PCR products with the expected size were detected in one sweet cherry, one apricot, one peach, one plum, and two sour cherry plants. However, no correlation between PCR data and symptom expression could be found. PCR products were cloned into the vector pMD18-T (TaKaRa, Dalian, China). Three independent clones from each isolate were sequenced by Genscript Corp., Nanjing, China, and sequences were deposited in the GenBank under accession nos. JX491635, JX491636, JX491637, JX648205, and JX648206. Results of sequence analysis showed that sequences of the five CNRMV isolates shared the highest nt (99.0 to 99.6%) and aa (98.9 to 100%) similarities with a cherry isolate from Germany (GenBank Accession No. AF237816). The sequence of one isolate from a peach tree (JX648205) was divergent and shared only 84.7 to 86.1% nt and 94.4 to 95.1% aa similarities with those cp sequences. Clones intra each isolate shared more than 99% nt similarities. To confirm CNRMV infection, seedlings of peach GF 305 were graft-inoculated with bud-woods from a peach and a sweet cherry tree, which was positive to CNRMV and also two other viruses: Cherry green ring mottle virus (CGRMV) and Plum bark necrosis stem pitting-associated virus (PBNSPaV), as tested by RT-PCR. Grafted seedlings were kept in an insectproof greenhouse and observed for symptom development. In May of the following year, some newly developed leaves of inoculated seedlings showed vein yellowing, ringspot, and shot hole symptoms. Results of Protein A sandwich (PAS)-ELISA using an antiserum raised against the recombinant CP of a CNRMV isolate (unpublished) and RT-PCR confirmed CNRMV infection in inoculated trees. In addition to CNRMV, tested seedlings were also found to be infected with CGRMV and PBNSPaV by RT-PCR. To our knowledge, this is the first report on the occurrence of CNRMV on stone fruit trees in China, and also the first record of the CNRMV infection in peach and plum plants. Given the economic importance of its hosts and the visible symptoms of the viral disease, it is important to prevent the virus spread by using virus-tested propagation materials.

Fusarium spp., Cylindrocarpon spp., and Environmental Stress in the Etiology of a Canker Disease of Cold-Stored Fruit and Nut Tree Seedlings in California.

The principal objective of this study was to determine the etiology of a canker disease in dormant stone fruit and apple tree seedlings maintained in refrigerated storage that has significantly impacted California fruit and nut tree nurseries. Signs and symptoms of the disease develop during storage or soon after planting, with subsequent decline and death of young trees. Isolations from both diseased and healthy almond and apple trees and Koch's postulates using stem segments of desiccation-stressed almond trees as hosts implicated Fusarium avenaceum and F. acuminatum as the primary causal agents. F. solani, Ilyonectria robusta, and Cylindrocarpon obtusiusculum were also capable of causing similar symptoms but were less frequently encountered in isolations of diseased tissue. Loss of bark turgidity in excised almond stem segments, as can occur in cold-stored seedlings, correlated with increased susceptibility to F. acuminatum, with maximum canker development occurring after relative bark turgidity dropped below a threshold of approximately 86%. Healthy almond trees, almond scion budwood, and a wheat cover crop used in fields where tree seedlings were grown and maintained until cold storage all possessed asymptomatic infections of F. acuminatum, F. avenaceum, and C. obtusiusculum as determined by activation following overnight freezing, cold storage, or desiccation.

Unfolding the secrets of plum pox virus: from epidemiology to genomics

Over an approximately 80-year period since the description of the Sharka disease, the plum pox virus (PPV) has been thoroughly studied on various levels of the infection cycle. World-wide distribution of the virus, severity of the disease for the fruit industry with a potential to be further increased and discovery/emergence of new strains make PPV the most epidemiologically important viral pathogen of stone fruit trees. The history of PPV research reflects the development of analytical methods applicable in plant virology. In particular the establishment of molecular biology with reverse genetics and improvement of DNA sequencing technology have further contributed to the increase in knowledge on PPV variability, evolution, replication and interaction with host plants. This review gives a comprehensive summary of PPV data accumulated progressively, from the biological characterization of the disease to recent attempts aimed at using the PPV-based vectors for expression of exogenous proteins in plants.

Using putrescine to increase the rooting ability of hardwood cuttings of the peach × almond hybrid GF677

Abstract GF677 is an interspecific hybrid which has important value in terms of economic and horticultural characteristics. The use of this rootstock for some stone fruit trees including almond and peach has been increased dramatically in recent years. It has some useful characteristics i.e. high tolerance to calcareous soil, a strong root system and suitability for poor soils, but its propagation is difficult. This study aimed to evaluate the effect of putrescine (PUT) on the rooting of GF677 cuttings under mist conditions. Treatments used include PUT concentrations (2 and 4 mM for 5 minutes), indole-3-butyric acid (IBA) using the quickdip method (1500 and 3000 mg l-1 for five seconds), and a commercial rooting powder and control (without any rooting substances). Treatments were applied at the end of the dormant season. Growth data were obtained 120 days after the treatments. The results showed that application of 1500 mg l-1 of IBA and commercial rooting powder improved GF677 rooting, but 3000 mg l-1 of IBA resulted in toxic effects on rooting and foliage of the cuttings. Cuttings treated with PUT solutions showed the best roots and shoots in terms of the number and quality. In conclusion, IBA may be replaced by PUT in the rooting process of GF677 cuttings.

Serological detection of Sharka quarantine disease (Plum pox virus) on stone fruit trees in Golestan province

Sharka disease is one of the most damaging diseases of fruit trees in the world, which is caused by Plum pox virus (PPV) that belongs to the genus Potyvirus in the family Potyviridae. Each year, this virus decreases the yield and causes substantial economic damages to its host plants worldwide. This virus is quarantined in Iran but in recent years, suspicious symptoms of the disease were observed in different grown areas, such as Golestan province. During 2010, 420 samples with mosaic, chlorosis, necrosis, ring pattern, blotches, etc. symptoms were collected from the gardens in Golestan province that included 100 samples from plum, 100 from peach and 240 from nectarine. These samples were evaluated using a double-antibody sandwich-ELISA (DAS-ELISA) method and a polyclonal antibody. The results of this survey indicated that among the total of 420 samples, none of them showed positive reaction in DAS-ELISA test.

Study on morphology, pathogenicity and genetic diversity of Wilsonomyces carpophilus isolates, the causal agent of shot hole of stone fruit trees based on RAPD-PCR in Iran

Shot hole disease is one of the most important diseases of stone fruit trees in Iran. The disease is wide spread among orchards of Prunus spp. During spring and summer of 2007, 80 monoconidial isolates of the pathogen were recovered from infected leaves, fruits and twigs of different Prunus spp. in West Azerbaijan, Tehran, Ghazvin and Razavi Khorasan provinces of Iran and were studied taxonomically. Based on morphological and physiological characteristics and growth optimal temperature, all isolates were identified as Wilsonomyces carpophilus. Seedlings of stone fruits (apricot, almond, peach, nectarine, plum, sweet cherry and sour cherry) were used for pathogenicity tests. All seedlings were susceptible to the fungal isolates and showed disease symptoms on twigs, leaves, buds and petioles. Genetic diversity of 28 selected fungal isolates was investigated based on DNA fingerprinting by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), using four random primers. Based on cluster analysis of the PCR results from the four primers, 10 fingerprinting groups (clonal lineages) and 27 haplotypes were identified. Clonal lineages “C”, “D” and “E”, each with six haplotypes formed the biggest clonal lineages, but other clonal lineages (“B”, “F”, “G”, “H”, “I” and “J”) included only one isolate. No correlation was detected among clonal lineages with the location of selected isolates and their host species. A correlation was found between the substrate (fruit, twig or leaf) and clonal lineages, particularly in “C” clonal lineage. The results showed that the fungus population had high genetic diversity which is distributed among the different areas of Iran.

Genetic variability of Iranian strains of Pseudomonas syringae pv. syringae causing bacterial canker disease of stone fruits

Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.

Family‐based linkage and association mapping reveals novel genes affecting Plum pox virus infection in Arabidopsis thaliana

Sharka is a devastating viral disease caused by the Plum pox virus (PPV) in stone fruit trees and few sources of resistance are known in its natural hosts. Since any knowledge gained from Arabidopsis on plant virus susceptibility factors is likely to be transferable to crop species, Arabidopsis's natural variation was searched for host factors essential for PPV infection. To locate regions of the genome associated with susceptibility to PPV, linkage analysis was performed on six biparental populations as well as on multiparental lines. To refine quantitative trait locus (QTL) mapping, a genome-wide association analysis was carried out using 147 Arabidopsis accessions. Evidence was found for linkage on chromosomes 1, 3 and 5 with restriction of PPV long-distance movement. The most relevant signals occurred within a region at the bottom of chromosome 3, which comprises seven RTM3-like TRAF domain-containing genes. Since the resistance mechanism analyzed here is recessive and the rtm3 knockout mutant is susceptible to PPV infection, it suggests that other gene(s) present in the small identified region encompassing RTM3 are necessary for PPV long-distance movement. In consequence, we report here the occurrence of host factor(s) that are indispensable for virus long-distance movement.

Apricot latent virus - Review

Apricot latent virus (ApLV) is a definitive species of the Foveavirus genus, the Betaflexiviridae family. Although the virus is not highly prevalent, it was identified in several European and Mediterranean countries thus far. Biological experiments demonstrated that, in addition to the only known natural host, Prunus armeniaca, ApLV can be experimentally graft-transmitted to several Prunus species. Therefore, the eradication of the viral pathogen largely depends on the use of virus-free propagating materials and rootstocks, which should be seriously considered when designing and implementing stone fruit certification schemes. Although ApLV is not present on the list of viruses and other pathogens that require testing in the EPPO certification schemes for the production of healthy stone fruit trees for planting, Peach asteroid spot disease (PAS) causing agent whose occurrence was often justly correlated with ApLV, is included on the list. This review summarises the current available knowledge of ApLV on the biological, morphological, physicochemical and molecular levels and includes the contemporary management approaches.

Mixed infections of pome and stone fruit viroids in cultivated and wild trees in Greece

In a survey during 2006-2009, 947 field samples (bark, fruit and leaves) of cultivated and wild pome and stone fruit trees showing various symptoms, including scar skin, dappling, fruit malformation, leaf mottle and stem canker (Fig. 1)…

Nutrição e manejo do solo em fruteiras de caroço em regiões de clima temperado

The agronomic techniques adopted for stone fruit trees cultivation should be ecologically and economically sustainable. This implies that production processes, apart from improving fruit yield and quality, mantain or increase the value of natural resources, guaranteeng satisfactory incomes to growers. The paper discusses fertilization and soil management aspects for peach, species largely investigated, and other stone fruit species, with emphasis on the Italian fruit industry.

COMBINED EFFECT OF THE ANTAGONISTIC POTENTIAL OF SELECTED PSEUDOMONAS SPP. STRAINS AND THE SYNTHETIC PEPTIDE “CAMEL” ON PSEUDOMONAS SYRINGAE pv. SYRINGAE AND P. SYRINGAE pv. MORSPRUNORUM

A set of bacterial isolates originating from tomato rhizosphere was screened for their potential to inhibit the growth of Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. morsprunorum. Isolates P482, P487, T660 and T777 showed the greatest antagonism towards the majority of the tested pathogenic isolates and therefore were selected for further studies. These strains were tentatively identified as Pseudomonas fluorescens (T660 and T777) and Pseudomonas putida (P482 and P487) on the basis of the 16S rDNA sequence analysis. The synthetic peptide CAMEL, an antagonistic factor with proved antimicrobial activity was also tested. The determined value of the minimal bactericidal concentration (MBC) of CAMEL was 1.6 μM towards 5 strains each of both P. syringae pathovars. CAMEL did not influence the growth of the antagonists in concentrations of up to 3.4 μM, therefore a possible synergistic activity of the antagonists and CAMEL towards the tested pathogens was investigated. To this end, spontaneous rifampicin- resistant mutants of the antagonists were selected. The MBC value of CAMEL used against the tested pathogens decreased to 1.13 μM when P. fluorescens T660 was applied simultaneously with the peptide. The selected antagonistic Pseudomonas sp. strains, CAMEL, or the combination CAMEL/P. fluorescens T660 could potentially contribute to the management of P. syringae infections in stone fruit trees based on enhanced antagonistic activity in vitro. Field studies are necessary to substantiate this postulate.

First Report of Apricot pseudo-chlorotic leaf spot virus Infecting Plum (Prunus domestica) in the Czech Republic.

Apricot pseudo-chlorotic leaf spot virus (APCLSV) is a novel, still poorly known Trichovirus in the family Betaflexiviridae. It is most closely related to Apple chlorotic leaf spot virus (ACLSV) (2,4) and infects stone fruit trees of the Prunus genus. Its presence has so far been detected in apricot, plum, Japanese plum, and peach trees in Italy, Spain, France, Hungary, Turkey, Jordan, and Australia (1,2,4). During the summers of 2008 and 2010, leaf samples of old Czech local plum cultivars were obtained from the Holovousy collection and assessed for the presence of viruses belonging to the Capillovirus, Trichovirus, and Foveavirus genera using the polyvalent degenerate oligonucleotides (PDO) nested reverse transcription (RT)-PCR test (3). Following amplification from total RNAs extracts, the amplicons were cloned and several clones were sequenced for each plant sample. In plum (Prunus domestica) cv. Babce, a mixture of amplicons was observed and BlastN and BlastX analyses of the obtained sequences revealed the presence of ACLSV and APCLSV. The 310-bp APCLSV amplicon (GenBank Accession No. JN790294) showed highest identity (82.9% in nucleotide sequence and 97.1% in amino acid sequence) with the Sus2 isolate of APCLSV (4) and clustered with APCLSV isolates in a phylogenetic analysis. APCLSV infection was further confirmed with an APCLSV-specific RT-PCR assay (4), which yielded a product of the expected 205-bp size (GenBank Accession No. JN653070) with closest homology again to the Sus2 APCLSV isolate (83.4 and 94.3% nucleotide and amino acid identity, respectively). To our knowledge, this finding represents the first detection of APCLSV in domestic plums in the Czech Republic, extending our vision of APCLSV diversity and its geographic distribution. For unknown reasons, APCLSV has almost always been reported in mixed infection with ACLSV (1,2,4) and the situation in cv. Babce does not deviate from this trend. This has greatly hindered the analysis of the pathogenicity of APCLSV, a situation further complicated in the current case because the Babce cultivar was also infected by Plum pox virus.

Weed Management in Peach

This revised 6-page fact sheet was written by Peter J. Dittmar and Jeffrey G. Williamson, and published by the UF Department of Horticultural Sciences, January 2012. HS93/WG020: Weed Management in Stone Fruit Tree Crops (Nectarine, Peach, and Plum) (ufl.edu)

Weed Management in Nectarine

This revised 6-page fact sheet was written by Peter J. Dittmar and Jeffrey G. Williamson, and published by the UF Department of Horticultural Sciences, February 2012. HS93/WG020: Weed Management in Stone Fruit Tree Crops (Nectarine, Peach, and Plum) (ufl.edu)

Weed Management in Plum

This revised 6-page fact sheet was written by Peter J. Dittmar and Jeffrey G. Williamson, and published by the UF Department of Horticultural Sciences, February 2012. HS93/WG020: Weed Management in Stone Fruit Tree Crops (Nectarine, Peach, and Plum) (ufl.edu)