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1.
Citrus huanglongbing (HLB) reduces an affected orchard’s economic life. This work aimed to characterize yield loss due to HLB for different sweet orange cultivars and determine the relationship between disease severity and yield. Disease severity and yield were assessed on 949 individual trees distributed in 11 different blocks from sweet orange cultivars Hamlin, Westin, Pera and Valencia. In each block, plants showing a range of HLB severity levels and asymptomatic plants were selected. Total yield (weight of harvested fruit), mean weight of asymptomatic and symptomatic fruit, relative yield (symptomatic tree yield/mean yield of asymptomatic trees from the same block) and relative number of fruits (fruit number from symptomatic tree/mean number of fruits from asymptomatic trees from the same block) were determined. The weight of symptomatic fruit was lower than the weight of asymptomatic fruit, but the weights of asymptomatic and symptomatic fruit were not correlated with disease severity, indicating that the effects of HLB were restricted to symptomatic branches. The relationship of the relative yield with HLB severity can be satisfactorily described by a negative exponential model. The rates of yield decrease as a function of disease severity were similar for all assessed cultivars. A relative yield (up to 19%) was observed even for trees where disease severity was 100%. The strong linear relationship between relative number of fruits per tree and the relative yield per tree suggested that the yield reduction was due primarily to early fruit drop or lack of fruit set on affected branches.  相似文献   

2.
Citrus Black Spot (CBS), caused by Guignardia citricarpa, was detected for the first time in Ghana and in West Africa. The disease was first observed in the Eastern Region in 1999 with typical disease symptoms including hard spot, virulent spot and false melanose were observed on several citrus species. A survey revealed that the disease has reached epidemic levels in the citrus-producing areas of the Eastern and Ashanti regions and is spreading rapidly within these areas and to other regions of the country. Currently, CBS is the most important fruit disease of citrus in Ghana, causing about 22% crop loss. Although the disease does not cause postharvest decay and the internal quality of the fruit is not affected, significant amounts of blemished fruit are discarded at the markets. Disease incidence and severity was found to be higher on mature than on young citrus trees. Pycnidia were found on fruit with hard spot symptoms, and pycnidia and pseudothecia typical of Guignardia spp. were found on decomposing leaves. Two species, G. citricarpa and G. mangiferae, were isolated from 15% of the samples collected and identified using the Oatmeal Agar test and by PCR with species-specific DNA primers. Isolates of G. citricarpa produced CBS symptoms after 80 to 233?days on 75% of the artificially inoculated young fruit of Valencia Late sweet orange. The fungus was re-isolated from symptomatic, inoculated fruit completing Koch’s postulates. Isolates of the endophyte G. mangiferae did not induce symptoms in the pathogenicity tests. In epidemiological studies, infections were detected from November to February for the minor cropping season and from May to November for the major season. Fruit of Valencia Late sweet orange were susceptible to G. citricarpa infection for up to 7?months after petal fall. Knowledge of the disease cycle in Ghana will improve methods for disease control.  相似文献   

3.
Citrus black spot (CBS) may cause substantial yield loss in sweet orange orchards. Severity and distribution of CBS symptoms on fruit may be variable and not all affected fruit may fall. However, the relationship between CBS symptoms and yield loss has not yet been investigated. This study aimed to determine CBS characteristics associated with premature fruit drop. A set of fruit was removed from the tree to measure the detachment force and another set of dropped fruit was collected from Pera and Valencia sweet orange orchards in three municipalities in Sao Paulo state, Brazil. CBS severity, distance of the nearest lesion from the peduncle, and fruit peel colour were assessed in both fruit sets. CBS severity was consistently related with the force to remove fruit and hence associated to the premature fruit drop, irrespective of the cultivar and location. The segmented linear regression showed that the fruit detachment force was reduced abruptly, at a rate of 7% for every 1% increase in disease severity up to 4.2 ± 1.0% CBS severity and, above this breakpoint, the force decreased slightly at a rate of 1.5%. Taking into account all orchards, the proportion of dropped fruit with CBS severity higher than the breakpoint was approximately 90%. This study provides a better understanding of the relationship between CBS severity and premature fruit drop of sweet orange. CBS severity breakpoint may be used as a reference to anticipate harvest and reduce CBS-related yield loss in orchards intended for juice processing.  相似文献   

4.

The efficacy of pest control of three different oil formulations in multiple low-concentration spray programmes on sweet orange and pummelo were compared with unsprayed and normal farmer-treatments over three years. Phytotoxicity of sprays was assessed in terms of fruit and leafdrop, fruityield and external fruitquality. Trees sprayed with any type of oil had lower pest numbers than unsprayed trees. On sweet orange, the heaviest oil was better than the normal farm practice at controlling chaff scale on fruit and red mite and whitefly on leaves. On pummelo it provided the best control of red mite on leaves. All three oils were as effective as the normal farm practice in control of rust mite on sweet orange fruit and leaves and red mite, rust mite and red scale on pummelo fruit. On sweet orange trees there was no evidence of phytotoxicity, and the external quality of fruit generally improved over time. On pummelo trees, oil sprays were unable to improve the external fruitquality. The number of pummelo per tree was reduced in three of the oil spray schedules in 1995 and one in 1996, but the total weight of fruit harvested per tree was unaffected.  相似文献   

5.

The deficiency of micronutrients, particularly zinc (Zn) and boron (B) has affected vegetative growth, yield and fruit quality of sweet orange in many citrus growing areas of Pakistan. The present study was conducted in 2015 and 2016 to determine the impact of Zn and B supplementation on growth and quality of sweet orange cv. ‘Blood red’. Pre-harvest foliar application of variant Zn and B levels was done at different phenological stages of fruit growth and development, i.e., full bloom, fruit set and premature stage. Results have concluded that pre-harvest foliar application of Zn and B augmented phosphorous, Zn, B, potassium, iron, and manganese contents in leaves, particularly Zn and B content from deficient to optimal level. Moreover, the combined application of Zn and B has also significantly enhanced vegetative characters such as tree height and spread along with reproductive characters, i.e., incremented numbers of fruit, fruit weight, total soluble solids, titratable acidity and ascorbic acid contents. However, among stage comparison, outcomes depicted that foliar application of Zn and B at full bloom?+?fruit set?+?premature stage resulted in maximum production with high quality fruits.

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6.
A 303-nucleotide viroid was isolated from an apple tree (Malus × domestica, ‘Fuji’) cultivated in Japan. The viroid had 84.9% overall nucleotide sequence homology to Apple dimple fruit viroid (ADFVd), a member of Pospiviroidae, reported from Italy. This viroid differed from the Italian variant by 47 mutations (38 substitutions, six deletions and three insertions), and most of these mutations occurred on either side of the central conserved region. The leaves and branches of the infected trees did not have any disease symptoms, but the fruits were dimpled and yellow. The infected scions were top-grafted onto a healthy ‘Fuji’ apple tree, which tested positive for this viroid in a northern hybridization analysis, and yellow dimple fruits were produced in the second growing season. We propose that this viroid is a new variant of ADFVd and causes yellow dimple fruit formation in ‘Fuji’ apple trees.  相似文献   

7.
柑桔体细胞杂种对柑桔脚腐病的抗病性研究   总被引：2，自引：0，他引：2  
 三七[Panax notoginseng(Burk) F.H.Chen,1945]是我国的名贵药材之一,与三七有关的各种病害的研究报道较多,但根结线虫危害三七,引起三七根结线虫病尚未见报道。  相似文献   

8.
Petroleum oils sprays are used as pesticides on citrus in South Australia to control California red scale (Aonidiella aurantii Maskell), but may have phytotoxic effects on trees and fruit. As part of a programme to establish improved specifications for spray oils for South Australia, three oils with different 50 %-distillation temperatures were applied to trees each month from October to May for two seasons in order to observe their effects on fruit quality. The 50 %-distillation temperatures of the three oils were 211, 224 and 240°C at 10 mmHg (in order of increasing molecular weight) and the oils are subsequently referred to as the 211, 224 and 240 oils. The 224 and 240 oils significantly reduced the amounts of sugar and acid in the juice, and delayed and inhibited colouring. These effects increased in severity, the closer to harvest the trees were sprayed and the higher the distillation temperature of the oil. The 240 oil prevented full colour development, and caused ‘re-greening’ if sprayed later than February. Oil sprays applied to the same trees in the following season caused similar effects. However, if oil sprays were omitted in the following season, there was no residual effect, of the previous season's spray, on the sugar and acid contents or the colour of the fruit. Individual fruit weight was not affected in the first spraying season, but there was an increase in the average individual fruit weight in the second season, regardless of whether a second spray was applied that season or not. The effect was more severe, the closer to harvest the trees were sprayed and the greater the distillation temperature of the oil. The effects on yield resulted from a change in the number of fruit per tree.  相似文献   

9.
The huanglongbing (HLB) disease of citrus trees, caused by Candidatus Liberibacter asiaticus and Ca. Liberibacter americanus, was first reported in Brazil in March, 2004. The presence of the disease has caused serious concerns among growers. Pruning experiments were conducted to determine if removal of symptomatic branches or the entire canopy (decapitation) would eliminate infected tissues and save HLB-affected trees. Pruning was done in five blocks on a total of 592 3- to 16 year-old ‘Valência’, ‘Hamlin’ or ‘Pêra’ sweet orange trees showing no symptoms or with two levels of symptom severity. Ten decapitated trees per block were caged and all trees were treated with insecticides to control the psyllid vector, Diaphorina citri. Mottled leaves reappeared on most symptomatic (69.2%) as well on some asymptomatic (7.6%) pruned trees, regardless of age, variety, and pruning procedure. Presence of the pathogen (Ca. Liberibacter americanus) in all symptomatic trees was confirmed by PCR. In general, the greater the symptom severity before pruning the lower the percentage of trees that remained asymptomatic after pruning.  相似文献   

10.
Two surveys (2005/2006 and 2009) were conducted in the state of São Paulo, Brazil, to investigate the incidence of ‘Candidatus Liberibacter asiaticus’ and ‘Ca. L. americanus’, two liberibacters associated with citrus huanglongbing (HLB) disease and both transmitted by Diaphorina citri, in orange jasmine (Murraya exotica), a widespread ornamental tree in cities and villages. The graft‐transmissibility of the two species, and their DNA relatedness to citrus‐associated liberibacters, were also investigated. Quantitative PCR was applied to PCR‐positive orange jasmine and HLB‐positive citrus growing in backyards and orchards to assess their inoculum source potentials. Liberibacters were detected in 91 of 786 sampled orange jasmine plants in 10 of 76 sampled locations. PCR‐positive trees exhibited yellow shoots and/or dieback symptoms indistinguishable from those on PCR‐negative trees. ‘Candidatus Liberibacter americanus’ was more common in 2005/2006 (96·6%) and ‘Ca. L. asiaticus’ in 2009 (84·8%). rplJ nucleotide sequences were identical within all populations of either species. Graft transmission succeeded only in homologous host combinations, including ‘Ca. L. americanus’ (2/10) from/to orange jasmine and ‘Ca. L. americanus’ (5/18) and ‘Ca. L. asiaticus’ (5/9) from/to citrus. Symptoms were mild and developed less rapidly in orange jasmine than in citrus, probably as a result of lower liberibacter multiplication rates. Respective titres of ‘Ca. L. americanus’ and ‘Ca. L. asiaticus’ in orange jasmine averaged 4·3 and 3·0 log cells g?1 tissue, compared with 5·5 and 7·3 in citrus. The results indicate that orange jasmine does not favour liberibacter multiplication as much as citrus. However, its importance in HLB epidemics should not be underestimated as it is a preferred host of D. citri and is not under any strict tree‐eradication programme or measures for insect control.  相似文献   

11.
In February 2007, sweet orange trees with characteristic symptoms of huanglongbing (HLB) were encountered in a region of S?o Paulo state (SPs) hitherto free of HLB. These trees tested negative for the three liberibacter species associated with HLB. A polymerase chain reaction (PCR) product from symptomatic fruit columella DNA amplifications with universal primers fD1/rP1 was cloned and sequenced. The corresponding agent was found to have highest 16S rDNA sequence identity (99%) with the pigeon pea witches'-broom phytoplasma of group 16Sr IX. Sequences of PCR products obtained with phytoplasma 16S rDNA primer pairs fU5/rU3, fU5/P7 confirm these results. With two primers D7f2/D7r2 designed based on the 16S rDNA sequence of the cloned DNA fragment, positive amplifications were obtained from more than one hundred samples including symptomatic fruits and blotchy mottle leaves. Samples positive for phytoplasmas were negative for liberibacters, except for four samples, which were positive for both the phytoplasma and 'Candidatus Liberibacter asiaticus'. The phytoplasma was detected by electron microscopy in the sieve tubes of midribs from symptomatic leaves. These results show that a phytoplasma of group IX is associated with citrus HLB symptoms in northern, central, and southern SPs. This phytoplasma has very probably been transmitted to citrus from an external source of inoculum, but the putative insect vector is not yet known.  相似文献   

12.
Transgenic Citrus sinensis ‘Hamlin’ and ‘Valencia’ plants containing Citrus tristeza virus (CTV)-derived sequences were propagated and inoculated with CTV. For propagation, selected buds from transgenic and non-transgenic control plants were grafted onto C. aurantium and C. limonia rootstock plants. CTV inoculation was performed via viruliferous aphids (Toxoptera citricida), and viral detection post-inoculation was performed through DASI-ELISA or RT-qPCR. After four inoculations, none of the transgenic lines tested showed complete resistance. However, viral multiplication was undetectable in some of the propagated clones. These resistant clones mainly came from transgenic ‘Valencia’ sweet orange plants grafted onto C. limonia rootstock containing the pCTV-CS gene construct. Although the tested viral inoculation method represents natural field infection conditions, the results did not differ significantly from those previously reported when the same transgenic lines were bud-graft inoculated. This finding indicates that the difficulties in producing CTV-resistant transgenic citrus lines may be unrelated to the inoculation method. Transgene expression level was quantified by RT-qPCR analysis and it was not possible to relate transgene mRNA level with resistance to the pathogen.  相似文献   

13.
Qualitative and quantitative changes of individual and total phenolics induced by Colletotrichum coccodes fungal infection have been studied in two susceptible sweet pepper cultivars ‘Soroksari’ and ‘Bagoly’, and the role of soluble phenolic compounds in plant's defence mechanism has been evaluated. Three distinct parts were analysed on pepper fruit: healthy tissue, anthracnose lesion, and bordering tissue, and individual phenolic compounds have been identified with the use of HPLC-MS system. In pepper fruit pericarp 21 phenolic compounds have been determined; the prevalent apigenin, quercetin and luteolin glycosides, chlorogenic acid and one chrysoeriol glucoside. C. coccodes infection increased the accumulation of chlorogenic acid, chrysoeriol glucoside, quercetin and luteolin glycosides in infected bordering tissue of both analysed pepper cultivars compared to healthy pepper tissue or symptomatic spot. Total apigenin derivatives did not show a significant increase in bordering tissue compared to the healthy pepper fruit in contrast to other groups of phenolics. This suggests a lesser role of apigenin glycosides in pepper plant defence against the Colletotrichum fungus. Intense phenolic synthesis was characteristic for the bordering zone between the healthy and infected plant tissue resulting in higher total phenolic content which might hinder the fungus to spread from the infected cells into the healthy tissue.  相似文献   

14.
Tree canopies are architecturally complex and pose several challenges for measuring and characterizing spatial patterns of disease. Recently developed methods for fine-scale canopy mapping and three-dimensional spatial pattern analysis were applied in a 3-year study to characterize spatio-temporal development of pre-harvest brown rot of peach, caused by Monilinia fructicola, in 13 trees of different maturity classes. We observed a negative correlation between an index of disease aggregation and disease incidence in the same tree (r?=??0.653, P?<?0.0001), showing that trees with higher brown rot incidence had lower aggregation of affected fruit in their canopies. Significant (P?≤?0.05) within-canopy aggregation among symptomatic fruit was most pronounced for early-maturing cultivars and/or early in the epidemic. This is consistent with the notion of a greater importance of localized, within-tree sources of inoculum at the beginning of the epidemic. Four of five trees having >10 blossom blight symptoms per tree showed a significant positive spatial association of pre-harvest fruit rot to blossom blight within the same canopy. Spatial association analyses further revealed one of two outcomes for the association of new fruit rot symptoms with previous fruit rot symptoms in the same tree, whereby the relationship was either not significant or exhibited a significant negative association. In the latter scenario, the newly diseased fruit were farther apart from previously symptomatic fruit than expected by random chance. This unexpected result could have been due to uneven fruit ripening in different sectors of the canopy, which could have affected the timing of symptom development and thus led to negative spatial associations among symptoms developing over time in a tree.  相似文献   

15.
Citrus black spot (CBS) is a fungal disease, caused by Guignardia citricarpa, that has a high economic impact on citrus. Although G. citricarpa has been associated with black spot of citrus, an adequate pathogenicity test is still not available. Thus, our objective was to develop and evaluate a simple, safe, and practical pathogenicity test. We used fruits from Pera-Rio and Valencia sweet orange trees from two different orchards, located in the State of São Paulo, Brazil. Inoculation was performed by placing six disks colonized by G. citricarpa, onto the peel of healthy fruits, previously bagged. In the Pera-Rio sweet orange grove, initial symptoms of the false melanose type resulting from the inoculations were observed 55 days after inoculation (dai). In the Valencia grove, initial symptoms also of the false melanose type resulting from the inoculations occurred 73 dai. A total of 92.8% and 86.6% of the Pera Rio and Valencia fruits inoculated, respectively, showed symptoms of CBS. Citrus black spot symptoms were not observed in any of the control fruits.  相似文献   

16.
The polyphagous shot hole borer (PSHB), Euwallacea nr. fornicatus (Coleoptera; Scolytinae) has become a serious threat to the avocado industry and several shade tree species in Israel. Branch wilting and tree mortality is the outcome of PSHB galleries. Understanding the relationship between avocado trees and the PSHB is required for considering management strategies. In Israel, 52 tree species from 26 botanical families were attacked by the PSHB, but only 12 species were suitable for beetle reproduction. All examined avocado cultivars were attacked, but ‘Hass’ most severely. Large and medium diameter avocado branches were more resistant to PSHB, compared to thin branches. Effectively, gallery density increased as branch diameter decreased. Concomitantly, in large and medium diameter branches, extensive sugar exudation occurred and beetle attack rarely progressed to the formation of natal galleries, whereas minimal sugar exudation was observed in thin branches. This was more evident in those that were weakened by repeated attacks followed by successful beetle colonization. PSHB prefers and successfully colonized branches that had been previously attacked by its conspecifics, and reproduction was much higher in these branches, as opposed to initial attacks. Lesion frequencies increased from late spring (April) until late summer (September). Avocado branches at the early stages of beetle colonization may be identified by sugar exudation at the base of the thin branches. The main approach for reducing damage caused by the PSHB is sanitation, achieved by the removal of colonized branches and intact infested pruned slash.  相似文献   

17.
The province of Murcia (Murcia Region) is the one of the most important apricot growing regions in Europe. In recent years a fruit disorder named by growers as “degeneración” has been detected in apricot commercial orchards of this region, mainly in the variety Velázquez Fino. Affected fruits are characterized by changes in their external appearance involving rugosity and a loss of organoleptic characteristics, which leads to an unmarketable product. In order to identify the causal agent of this disorder, the presence of the most important viruses affecting stone fruit trees and Hop stunt viroid (HSVd) was tested. While negative results were obtained for all viruses analysed, the viroid was detected in all the symptomatic trees. Within a single tree, the viroid was restricted to branches bearing fruits with the characteristic symptoms but was usually absent from the rest of the tree. Sequence analysis of several isolates of HSVd obtained from these affected trees revealed the presence of two variants previously detected in other apricot cultivars. Taken together, these results suggest that degeneration is associated with HSVd.  相似文献   

18.
Peach fruit is enriched with natural antioxidants but oxidation caused by biotic and abiotic stresses, reduce these antioxidants and consequently effect the quality and yield of the fruit. Therefore, an experiment was conducted to investigate the role of ascorbic acid to sustain the natural antioxidant activity, improve the fruit quality and yield of peach cultivars (Early Grand and Florida King). The peach cultivars, Early Grand and Florida King were tested against four levels of ascorbic acid (200, 400, 600 and 800?ppm) and compared with control as water spray. The foliar application of ascorbic acid significantly influenced anti-oxidant activity and physico-chemical attributes of peach cultivars. However, the foliar application of ascorbic acid @ 800?ppm significantly increased the fruit weight, fruit yield, fruit firmness, total soluble solids, titratable acidity, antioxidant activity of fruit peel, with least percent infected fruits and fruit juice pH as compared to the rest of the treatments. Similarly, significant variation was recorded for peach cultivars regarding anti-oxidant activity and various physico-chemical attributes. The maximum fruit weight, fruit yield, fruit firmness, total soluble solids, titratable acidity and TSS/TA ratio were noted in fruit of cultivar Florida King. On other side the foliar treated fruit of peach cultivar Early Grand had the highest percent infected fruits, fruit juice pH and antioxidant activity of fruit peel. It is concluded from the significant findings of present research that the peach cultivar Florida King performed better in terms of maximum fruit yield, whereas the cultivar Early Grand produced better quality fruits with high anti-oxidant activity when treated with 800?ppm of ascorbic acid as foliar spray.  相似文献   

19.
Anthracnose fruit rot, caused by Colletotrichum acutatum, is among the most important diseases of blueberries. Most cultivars are susceptible but ‘Elliott’ is resistant. Our objective was to identify possible antifungal compounds that play a role in the resistance response. Chemical fractions from freeze-dried, ripe fruit of ‘Elliott’ and a susceptible cultivar (Jersey) were extracted with methanol and ethyl acetate. Extracts were screened on solid media for suppression of microconidiation of C. acutatum. The methanolic extract was fractionated and the soluble methanolic fraction from ‘Elliott’ was the most biologically active. This fraction was dried, dissolved in water, and screened in vivo by pre-treating ripe ‘Jersey’ fruit with 0.5, 1, 2, and 4% solutions (w/v) and subsequently inoculating the fruit with C. acutatum. An 88% reduction in infection incidence was observed after 12 days with the 4% solution. Anthocyanins and other flavonoids were then quantified in fruit of the two cultivars using HPLC-MS. ‘Elliott’ fruit contained more anthocyanins (4.87 mg/g of freeze-dried tissue) than ‘Jersey’ (3.27 mg/g of freeze-dried tissue); however, the same compounds were found in both cultivars. ‘Elliott’ fruit also contained more non-anthocyanin flavonoids (0.18 mg/g of freeze-dried tissue) than ‘Jersey’ (0.12 mg/g of freeze-dried tissue), including two distinctive compounds in ‘Elliott’. The non-anthocyanin flavonoid fractions of both ‘Elliott’ and ‘Jersey’ significantly decreased the growth of C. acutatum in a liquid bioassay but the effect was more pronounced in the ‘Elliott’ fraction. The two distinctive compounds in ‘Elliott’ were further characterized by MS/MS and were identified as quercetin 3-O-rhamnoside and, putatively, syringetin rhamnoside. Additionally, we evaluated ‘Elliott’ and ‘Jersey’ methanolic extracts for their ability to inhibit lipid peroxidation, and the extract obtained from ‘Elliott’ was almost twice as active at inhibiting peroxidation. These results provide new insights into the role of antifungal compounds in the resistance response of ripe ‘Elliott’ blueberries to infection by C. acutatum.  相似文献   

20.
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