Resistant Apricot Research Articles

Distribution and Etiology of Gummosis Syndrome Associated with Apricot Fruit Trees of Gilgit-Baltistan, Pakistan

Gummosis syndrome is a serious disease of apricot trees in Gilgit Baltistan (GB), Pakistan. The symptoms of gummosis syndrome on branches, twigs, and the trunk of apricot trees include oozing of a gummy or resinous material, lesions or cankers, bark discoloration, and the disintegration of bark integrity. The disease can weaken branches and twigs, making them more susceptible to breakage. In severe cases, affected branches can die back. In this study, we investigated the fungal species associated with gummosis syndrome in apricots across four districts in GB: Nagar, Hunza, Gilgit, and Ghizer. We recovered a total of 40 isolates from different locations of above four districts, and the most frequently isolated fungal species was Botryodiplodia theobromae. Fusarium solani was also isolated from several locations, and Neoscytalidium spp. were isolated from a few locations in Nagar and Hunza. The spatial distribution of gummosis syndrome in apricots in GB is not uniform. The disease is more prevalent in the northern and western parts of GB, and in areas with higher elevations and cooler temperatures. The Nagar district is the most affected by gummosis syndrome, followed by Ghizer District. Our findings suggest that Botryodiplodia theobromae is the major fungal pathogen associated with gummosis syndrome in apricots in GB. Fusarium solani and Neoscytalidium spp. may also play a role in the disease. The spatial distribution of gummosis syndrome in GB suggests that environmental factors, such as elevation and temperature, may contribute to the disease. Further research is needed to develop effective control measures for gummosis syndrome in apricots in GB. This research should focus on identifying resistant apricot varieties, developing new and more effective fungicides, and developing integrated pest management (IPM) programs.

Identification of key gene networks related to the freezing resistance of apricot kernel pistils by integrating hormone phenotypes and transcriptome profiles

BackgroundApricot kernel, a woody oil tree species, is known for the high oil content of its almond that can be used as an ideal feedstock for biodiesel production. However, apricot kernel is vulnerable to spring frost, resulting in reduced or even no yield. There are no effective countermeasures in production, and the molecular mechanisms underlying freezing resistance are not well understood.ResultsWe used transcriptome and hormone profiles to investigate differentially responsive hormones and their associated co-expression patterns of gene networks in the pistils of two apricot kernel cultivars with different cold resistances under freezing stress. The levels of auxin (IAA and ICA), cytokinin (IP and tZ), salicylic acid (SA) and jasmonic acid (JA and ILE-JA) were regulated differently, especially IAA between two cultivars, and external application of an IAA inhibitor and SA increased the spring frost resistance of the pistils of apricot kernels. We identified one gene network containing 65 hub genes highly correlated with IAA. Among these genes, three genes in auxin signaling pathway and three genes in brassinosteroid biosynthesis were identified. Moreover, some hub genes in this network showed a strong correlation such as protein kinases (PKs)-hormone related genes (HRGs), HRGs-HRGs and PKs-Ca2+ related genes.ConclusionsCa2+, brassinosteroid and some regulators (such as PKs) may be involved in an auxin-mediated freezing response of apricot kernels. These findings add to our knowledge of the freezing response of apricot kernels and may provide new ideas for frost prevention measures and high cold–resistant apricot breeding.

Transmissible tolerance to European stone fruit yellows (ESFY) in apricot: cross-protection or a plant mediated process?

European Stone Fruit Yellows (ESFY) is an emerging disease caused by ‘Candidatus Phytoplasma prunorum’ (‘Ca. P. prunorum’) affecting stone fruits, as apricots. Resistant apricot cultivars are unknown, but it has been demonstrated that individual plants can recover from the disease, behaving as completely tolerant to ESFY. The status of tolerance is transmissible by grafting to successive apricot individuals, but it is not clear whether recovery corresponds to a transmissible tolerance that depends on a plant–mediated reaction or if it is due to a cross-protection promoted by a transmissible protective agent i.e. hypovirulent strain/s of ‘Ca. P. prunorum’. Results achieved after prolonged field experiments support the first hypothesis. Two groups of apricot plants derived from a common recovered mother (one ‘Ca. P. prunorum’-free after heat-treatment and the second not heat-treated, i.e. harbouring potential protective strain/s of the phytoplasma), behaved similarly: no plants from either of the two groups developed stable ESFY symptoms after natural infections. Corresponding groups of plants, derived from symptomatic mothers, developed a high percentage of diseased plants after natural infection. No potential protective ‘Ca. P. prunorum’ hypovirulent strains were detected in the asymptomatic apricot plants. The summarized evidence supports a host-defence induction, likely of epigenetic feature. The present long-term study in apricot represents an uncommon empiric proof supporting the theory of inducible resistance to pathogens in plants.

Evaluation of Turkish apricot germplasm using SSR markers: Genetic diversity assessment and search for Plum pox virus resistance alleles

Apricot (Prunus armeniaca L.) is an important fruit crop in Turkey, where a rich diversity of apricot cultivars and seedlings is prevalent. The genetic diversity of the Turkish apricot germplasm was investigated. The profiles of 18 simple sequence repeat (SSR) loci of 239 accessions in the genetic source collection of the country as well as those of European and Pakistani accessions were obtained. Eleven SSRs were selected from the apricot molecular linkage group 1 (LG1), and these are located close to the major Plum pox virus (PPV) resistance locus. The remaining seven SSRs represent the other six linkage groups. A high level of genetic diversity (He=0.74, Ho=0.63) was observed. Stark Early Orange (SEO)/Harlayne-type resistance alleles of three SSR loci (PGS1.21-240, PGS1.23-161 and PGS1.24-119) were found to be rare in the Turkish accessions (1.7%) but were abundantly found in the Pakistani accessions (41.7%). The genetic clustering analyses, the neighbor-joining tree constructed from the genetic distances of the proportions of shared alleles and the population genetic structure did not distinguish the European accessions from the Turkish accessions. However, ‘Harlayne’, ‘SEO’ and the putative resistant apricot accessions were grouped together, indicating a common heritage for the resistant accessions. SSR profiles of the accessions will improve the management of apricot gene banks, and information on the genetic variation in Turkish apricots will assist the international research community.

电导法测定寒地杏种质资源的抗寒性

对国家果树种质公主岭寒地果树圃保存的10份寒地杏种质资源进行抗寒性的鉴定评价，通过切片镜检观察和电导法测定等方法，筛选出一批抗寒杏资源，为杏抗寒性育种提供有价值的亲本材料。结果表明：麦黄杏、龙垦2杏、眉杏、鸡西早熟甜仁、大叶大白杏、铃铛杏和桦甸杏可抗−35℃的低温，但眉杏、大叶大白杏和铃铛杏可能出现4级的冻害；同发杏、桦甸红杏、鸡西粉花可抗−40℃的低温。We identified and evaluated cold resistances of 10 apricot accession germplasm resources which were conserved in National Field Genebank for Hardy Fruits of Gongzhuling in China. We screened a batch of cold resistant apricot germplasm resources through microscopical section examination and conductivity determination method and these resources would be the valuable parent materials for cold resistant apricot breeding. The results show that Maihuang Apricot, Longken 2 Apricot, Mei Apricot, Jixi Zaoshu Tianren Apricot, Daye Dabai Apricot, Lingdang Apricot, and Huadian Apricot are resistant to −35˚C low temperature. But Daye Dabai Apricot and Lingdang Apricot may show the forth level freezing injury. Tongfa Apricot, Huadian Hong Apricot, and Jixi Fenhua Apricot can be resistant to −40˚C low temperature.

Different responses of sensitive and resistant apricot genotypes to artificial Monilia laxa (Aderh. & Ruhl.) infection

Blossom blight caused byMonilia laxa(Ehr.) is the most important fungal disease in Hungarian apricot orchards. The cultivars traditionally grown in the country are susceptible toMonilia laxa(Ehr.) to various extents. In this study the shoots of one tree each of the varieties Zard and Korai Zamatos and 48 hybrids from their cross were artificially infectedin vivowithMonilia laxa(Ehr.). The results indicated that when artificial infections are made to evaluate pathogen resistance, this should be carried out on one-year-old shoots, since this is the natural infection point ofMonilia. It also appears that, due to the great variability in the size of destroyed tissues, the microscopic analysis of the infections could provide a more reliable evaluation of progeny resistance than comparing the sizes of destroyed shoot areas.

Study of long-distance movement of Plum pox virus (Sharka) as an alternative resistance-evaluation method in Prunus

During the breeding programs for Plum pox virus (PPV, Sharka) resistance in Prunus, the evaluation of the new releases through symptoms observation on leaves has been contradictory and represents one of the main handicaps in these programs. In order to increase the accuracy of this traditional evaluation method, we here analyze an alternative method based on the study of the ability of a genotype to allow the long-distance movement of the virus through its vascular vessels. Two different plant models have been assayed: (a) in Model I, the inoculation was performed in the ‘GF305’ rootstock with a later grafting of the genotype under evaluation and a scion of healthy control ‘GF305’, to evaluate the long-distance movement through the studied genotype from the rootstock to the scion (xylem transport), and (b) in Model II, the inoculation with ‘GF305’ diseased scions was performed by grafting these diseased scions onto the studied genotypes, which were grafted onto healthy ‘GF305’ peach seedlings, to evaluate the long-distance movement through the studied genotype from the scion to the rootstock (phloem transport). The results show that, regardless of the presence of symptoms, susceptible genotypes allowed the movement of the virus through their vascular vessels in both directions studied. However, the resistant apricot ‘Stark Early Orange’ did not allow this movement. We propose the study of the ability of a genotype to allow the long-distance movement of the virus as an alternative and more accurate method for the evaluation of PPV resistance. However, this protocol is much more tedious than the traditional one and could be used mainly in the evaluation of a reduced number of more interesting genotypes.

CONSTRUCTION OF A GENETIC MAP FOR APRICOT WITH MOLECULAR MARKERS AND IDENTIFICATION OF MARKERS ASSOCIATED WITH PLUM POX VIRUS RESISTANCE

Plum pox virus (PPV) causes serious damage in apricots and breeding and growing of PPV-resistant apricot cultivars are the only way of its efficient control. An integrated genetic linkage map for apricot (Prunus armeniaca L.) was obtained using a BC 1 progeny 'LE-3246' x 'Vestar'. A total of 316 molecular markers (290 AFLPs, 26 SSRs) and the resistance to PPV were assigned to 8 linkage groups covering 574 cM of the apricot genome. The average distance between adjacent loci is 2.5 cM. A PPVres1 locus conditioning resistance to PPV was mapped in linkage group 1. Several AFLPs and an SSR tightly linked to PPVres1 locus were identified. The construction of a genetic map for apricot and identification of molecular markers linked to PPV resistance will facilitate the breeder to obtain resistant apricot cultivars.

The apoplastic antioxidant system in Prunus: response to long-term plum pox virus infection

This work describes, for the first time, the changes taking place in the antioxidative system of the leaf apoplast in response to plum pox virus (PPV) in different Prunus species showing different susceptibilities to PPV. The presence of p-hydroxymercuribenzoic acid (pHMB)-sensitive ascorbate peroxidase (APX) (class I APX) and pHMB-insensitive APX (class III APX), superoxide dismutase (SOD), peroxidase (POX), NADH-POX, and polyphenoloxidase (PPO) was described in the apoplast from both peach and apricot leaves. PPV infection produced different changes in the antioxidant system of the leaf apoplast from the Prunus species, depending on their susceptibility to the virus. In leaves of the very susceptible peach cultivar GF305, PPV brought about an increase in class I APX, POX, NADH-POX, and PPO activities. In the susceptible apricot cultivar Real Fino, PPV infection produced a decrease in apoplastic POX and SOD activities, whereas a strong increase in PPO was observed. However, in the resistant apricot cultivar Stark Early Orange, a rise in class I APX as well as a strong increase in POX and SOD activities was noticed in the apoplastic compartment. Long-term PPV infection produced an oxidative stress in the apoplastic space from apricot and peach plants, as observed by the increase in H2O2 contents in this compartment. However, this increase was much higher in the PPV-susceptible plants than in the resistant apricot cultivar. Only in the PPV-susceptible apricot and peach plants was the increase in apoplastic H2O2 levels accompanied by an increase in electrolyte leakage. No changes in the electrolyte leakage were observed in the PPV-inoculated resistant apricot leaves, although a 42% increase in the apoplastic H2O2 levels was produced. Two-dimensional electrophoresis analyses revealed that the majority of the polypeptides in the apoplastic fluid had isoelectric points in the range of pI 4-6. The identification of proteins using MALDI-TOF (matrix-assisted laser desorption/ionization-time of flight) and peptide mass fingerprinting analyses showed the induction of a thaumatin-like protein as well as the decrease of mandelonitrile lyase in peach apoplast due to PPV infection. However, most of the selected polypeptides showed no homology with known proteins. This fact emphasizes that, at least in Prunus, most of the functions of the apoplastic space remain unknown. It is concluded that long-term PPV infection produced an oxidative stress in the leaf apoplast, contributing to the deleterious effects produced by PPV infection in leaves of inoculated, susceptible Prunus plants.

Unravelling the Prunus/Plum pox virus interactions

Plum pox virus (PPV) belongs to the genus Potyvirus that contains the largest number of virus species infecting plants. Its virus genome has been extensively characterised and sequenced. However, few data are available on its interactions with woody host plants. We therefore focused, in the past 4 years, both on the cellular and molecular aspects of the compatible and incompatible Prunus/PPV interactions. GFP (Green fluorescent protein)‐tagged PPV and in situ hybridisation were used to compare the localization of viral particles in stems and leaves of susceptible and resistant apricot cultivars. In parallel, molecular tools were developed through the cloning and characterization of polymorphic, homologous resistance genes and of candidate genes involved in the expression of Prunus/PPV interactions. Candidate genes are currently used to target genomic regions involved in resistance or susceptibility and to identify molecular markers indispensable for further marker assisted selection for resistance to sharka disease.

Plum pox virus induces differential gene expression in the partially resistant stone fruit tree Prunus armeniaca cv. Goldrich

We investigated the changes in the expression profiles of the partially resistant apricot ( Prunus armeniaca L.) cultivar Goldrich following inoculation with Plum pox virus (PPV) using cDNA-amplification fragment length polymorphism (AFLP). Altered expression patterns were detected and twenty-one differentially expressed cDNA had homologies with genes in databases coding for proteins involved in metabolism, signal transduction, defense, stress and intra/intercellular connections. Seven of the modified expressed patterns were further investigated by semi-quantitative RT-PCR or Northern blotting. The expression patterns of five of these genes were confirmed in the partially resistant P. armeniaca cv. ‘Goldrich’ and assessed in a susceptible genotype. One of these cDNAs, coding for a putative class III chitinase, appeared to be repressed in infected plants of the partially resistant genotype and expressed in the susceptible one which could be related to the partially resistant phenotype. On the contrary, the expression patterns of the genes coding for a transketolase, a kinesin-like and an ankyrin-like protein, were clearly linked to the susceptible interaction. These candidate genes could play a role either in the compatible interaction leading to virus invasion or to the quantitative resistance of apricot to PPV.

PPV long-distance movement is occasionally permitted in resistant apricot hosts

The interactions between Plum pox virus (PPV), a member of the Potyvirus genus, and Prunus host plants are, up to now, poorly understood. In the current paper, fluorescence stereomicroscopy, in situ hybridisation and immunogold detection were performed in order to evaluate the virus transport and cellular distribution. The behavior of PPV in several susceptible (cv. ‘Moniqui’ and ‘Screara’) and resistant apricot genotypes (cv. ‘Harlayne’, ‘Henderson’, ‘Harcot’, ‘Goldrich’, ‘Stella’ and ‘Stark Early Orange’) were compared. Viral RNA was detected by in situ hybridisation in stem tissues close to the inoculation point, irrespective of the resistance status of the variety. Systemic infection was evidenced by virus immunodetection and by fluorescence detection of a GFP-tagged PPV in distant leaf sections. The signal obtained by in situ hybridisation colocalised with the fluorescence produced by GFP-tagged PPV in the same plant material but did not colocalise with the signal obtained by immunostaining. Intensity of the PPV infection in susceptible apricot cultivars varied depending on genotypes. The behavior of PPV in systemic leaves was clearly distinct between susceptible and resistant cultivars. While PPV was spreading widely around the major and minor veins in susceptible leaves, in the resistant apricot genotypes it was restricted to isolated spots consisting of few cells embedded in the mesophyll tissue. In summary, differences in the ability of PPV to systemically infect susceptible and resistant apricot cultivars were evident but nevertheless, long-distance transport of PPV occured in resistant apricot scions.

Long‐term plum pox virus infection produces an oxidative stress in a susceptible apricot,Prunus armeniaca, cultivar but not in a resistant cultivar

The effect of plum pox virus (PPV) infection on the response of some antioxidant enzymes was studied in two apricot cultivars, which behaved differently against PPV infection: cultivar Real Fino (susceptible) and cultivar Stark Early Orange (cv. SEO, resistant). In the susceptible cultivar, PPV produced a decrease inΦPSII,F′v/F′mandQp. PPV infection produced a drop inp‐hydroxy mercury benzoic acid (pHMB)‐sensitive ascorbate peroxidase, dehydroascorbate reductase and peroxidase in the soluble fraction from susceptible plants, whereas in the resistant apricot cultivar, pHMB‐insensitive ascorbate peroxidase, monodehydroascorbate reductase, glutathione reductase and superoxide dismutase increased. However, catalase decreased in the soluble fractions from both infected cultivars. Long‐term PPV infection also produced a decrease in the chloroplastic ascorbate–glutathione cycle enzymes only in the susceptible plants. As a consequence of PPV infection, an oxidative stress, indicated by an increase in lipid peroxidation and in protein oxidation, was produced only in the leaves from the susceptible cultivar which was also monitored by the diaminobenzidine peroxidase‐coupled H2O2probe. The loss ofΦPSII, indicative of activated oxygen species production, and the decrease in the levels of antioxidant enzymes in chloroplasts from susceptible plants could be responsible for the chlorosis symptoms observed. The results suggest that the higher antioxidant capacity showed by cv. SEO could be a consequence of a systemic acquired resistance induced by PPV penetration in stem tissue at the graft site and could be related, among other factors, to their resistance to PPV.

IN SITU LOCALISATION OF PLUM POX PARTICLES IN SUSCEPTIBLE AND RESISTANT APRICOT CULTIVARS

ISHS XIX International Symposium on Virus and Virus-like Diseases of Temperate Fruit Crops - Fruit Tree Diseases IN SITU LOCALISATION OF PLUM POX PARTICLES IN SUSCEPTIBLE AND RESISTANT APRICOT CULTIVARS

Localisation and movement of Plum pox virus in apricot stem tissues

SummaryLocalisation and movement of Plum pox virus (PPV), sharka disease, in stem tissues of susceptible and resistant apricot (Prunus armeniaca L.) cultivars was studied. Two different assays were performed. In the first assay, apricot cultivars were grafted on to a non‐inoculated GF305 peach rootstock and, after two months, the sprouted apricot was inoculated by chip‐grafting. In the second assay, apricot cultivars were grafted on to a previously chip‐inoculated GF305 showing strong PPV symptoms. Localisation of virus was studied in apricot stem by immuno‐tissue printing and sharka symptoms in GF305 and apricot leaves were also observed. Virus was mainly localised in the xylem, and sometimes in the cortex and pith. Results revealed that, while all the cultivars allowed limited virus movement from the inoculation point, only the susceptible cultivars (Screara, Bebeco and Colomer) allowed long distance movement and even showed symptoms in leaves.

Genetics of resistance to Plum pox virus in apricot

Plum pox virus (PPV) causes serious damage in apricots grown in the Czech Republic and other countries where it is<br />present. The virus spreads in orchards from infected trees by aphids to healthy trees of susceptible cultivars. Chemical<br />control is ineffective from epidemiological point of view. For this reason growing of resistant apricot cultivars is the only<br />way how to solve one of the most significant phytopathological problem. To study PPV resistance in apricot, three crosses<br />between an apricot cultivars or a selection resistant to PPV and an apricot cultivars or a selection susceptible to PPV<br />(LE-3218 × Stark Early Orange, LE-3241 × Vestar and LE-3246 × Vestar) were performed at Faculty of Horticulture<br />of Mendel University of Agriculture and Forestry in Lednice na Moravě in 1999. The BC1 seeds were stratified and the<br />subsequent seedlings were grown in a greenhouse. The seedlings were repeatedly inoculated with PPV-Vegama isolate<br />(PPV-M strain) by an infected chip. The resistance of the plants was evaluated by symptom observing and ELISA in<br />three consecutive growth periods. The χ<sup>2</sup> test was used to analyse the data. It was found that two independent dominant<br />complementary genes conditioned PPV resistance in apricot. The significance of these findings in relation to other reports<br />is discussed. Knowledge of PPV resistance inheritance will help in planning apricot breeding programmes.

Response of antioxidative enzymes to plum pox virus in two apricot cultivars.

Recent evidence has indicated that activated oxygen species (AOS) may function as molecular signals in the induction of defence genes. In the present work, the response of antioxidative enzymes to the plum pox virus (PPV) was examined in two apricot (Prunus armeniaca L.) cultivars, which behaved differently against PPV infection. In the inoculated resistant cultivar (Goldrich), a decrease in catalase (CAT) as well as an increase in total superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR) activities were observed. Ascorbate peroxidase (APX), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) did not change significantly in relation to non-inoculated (control) plants. In the susceptible cultivar (Real Fino), inoculation with PPV brought about a decrease in CAT, SOD and GR, whereas a rise in APX, MDHAR and DHAR activities was found in comparison to non-inoculated (control) plants. Apricot leaves contain only CuZn-SOD isozymes, which responded differently to PPV depending on the cultivar. Goldrich leaves contained 6 SODs and both SOD 1 and SOD 2 increased in the inoculated plants. In leaves from Real Fino, 5 SODs were detected and only SOD 5 was increased in inoculated plants. The different behaviour of SODs (H2O2-generating enzymes) and APX (an H2O2-remover enzyme) in both cultivars suggests an important role for H2O2 in the response to PPV of the resistant cultivar, in which no change in APX activity was observed. This result also points to further studies in order to determine if an alternative H2O2-scavenging mechanism takes place in the resistant apricot cultivar exposed to PPV. On the other hand, the ability of the inoculated resistant cultivar to induce SOD 1 and SOD 2 as well as the important increase of DHAR seems to suggest a relationship between these activities and resistance to PPV. This is the first report about the effect of PPV infection on the antioxidative enzymes of apricot plants. It opens the way for the further studies, which are necessary for a better understanding of the role of antioxidative processes in viral infection by PPV in apricot plants.

Inheritance of resistance to plum pox potyvirus (PPV) in ‘Stella’ apricot seedlings

AbstractResistance to sharka (plum pox potyvirus) was studied in 74 seedlings resulting from open pollination of the resistant apricot cultivar ‘Stella’. Each seedling was inoculated at the base by a chip‐bud from a diseased GF305 peach tree. To follow tlie spread of virus into the scedlings. a Chip‐bud of a healthy GF305 and another from a healthy sensitive Manicot apricot were grafted above the inoculation point in the order described. Six observations of symptoms were made in the leaves of the GF305 used For inoculation, the GF305‐control, the Manicot‐control and the ‘Stella’ seedlings during four growth cycles. An enzyme‐linked immunosorbent assay (ELISA) was applied to the leaves of the ‘Stella’ seedlings. No ‘Stella’ seedling showed symptoms of sharka. Only three seedlings reacted positively to the ELISA. Substantial differences were observed in the speed of virus propagation through the ‘Stella’ seedlings, some of them showing a strong resistance to virus translocation. The possible use of the ‘Stella’ cultivar in apricot breeding programmes to obtain resistant cultivars is discussed.