Pectinases and cellulases from plum curculio larvae: Possible causes of apple and plum fruit abscission

Plum curculio larvae, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), were assayed for pectic and cellulolytic enzymes. Larvae produce at least five pectic enzymes:pectin methyl-esterase, endo-polymethylgalacturonase, endo-polygalacturonase, pectin methyl-trans-eliminase, and polygalacturonate-trans-eliminase. Larvae also produce cellulase. Enzymes are released as larvae feed and are capable of causing fruit tissue maceration. One or more of these enzymes may be responsible for the premature abscission of plums and apples infested with plum curculio larvae.

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Résumé Les larves de Conotrachelus nenuphar, le Plum curculio ont été testées par la recherche des enzymes pectinolytiques et cellulolytiques. Ces larves produisent au moins cinq enzymes pectinases: pectine methyl-esterase, endo-polymethylgalacturonase, endo-polygalacturonase, pectine methyl trans-eliminase, et polygalacturonate-trans-eliminase. Elles produisent aussi de la cellulase. Les enzymes sont libérées alors que les larves se nourrissent et sont capables de provoquer une macération du tissu des fruits. Une ou plusieurs de ces enzymes peuvent être responsables de la chute prématurée des prunes et des pommes infestées par des larves de Plum curculio.

     

Biotechnological aspects of plum pox virus

Plum pox potyvirus (PPV), the causal agent of a devastating disease that affects stone fruit trees, is becoming a target of intense studies intended both to fight against viral infection and to develop practical applications based on the current knowledge of potyvirus molecular biology. This review focuses on biotechnological aspects related to PPV, such as novel diagnostic techniques that facilitate detection and typing of virus isolates, strategies to implement pathogen-derived resistance through plant transformation, the potential use of genetic elements derived from the virus, and the recent development of PPV-based expression vectors.     

The pectic components of plum fruits

Pectic substances were extracted from plum fruit tissue and the whole pectin, crude pectinic acid, purified pectinic acid and neutral fractions were prepared. Each of the fractions contained galacturonic acid, arabinose, galactose, xylose and rhamnose. High voltage electrophoresis indicated the presence of neutral and negatively charged material, and treatment with pectinesterase showed that the neutral component was completely esterified. The three cultivars of fruits studied showed close similarities. The results are consistent with proposed models of pectin structure and indicate the probable existence of a continuous gradation with respect to degree of esterification and molecular size.     

Host preference of the plum curculio

We assessed host preference of adult plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), based on the total number of mark‐released and wild adults recovered and the total distance moved by mark‐released adults in an orchard whose layout was designed to specifically allow foraging plum curculios to choose among host tree species. Host trees included apple, Malus domestica Borkh.; pear, Pyrus communis (L.); peach, Prunus persica (L.) Batsch; apricot, Prunus armeniaca L.; tart cherry, Prunus cerasus L.; sweet cherry, Prunus avium (L.); European plum, Prunus domestica L.; and Japanese plum, Prunus salicina Lindl. (all Rosaceae). We released 2900 marked adults and recovered 17.7%. We used screen traps to provide a measure of the number of adults that arrived at and climbed up particular host trees and found that significantly greater numbers of marked adults and the greatest number of wild adults were recovered from screen traps attached to Japanese plum. We sampled host tree canopies by tapping limbs to provide a measure of the number of adults within a tree canopy at a particular moment. Again, significantly greater numbers of marked and wild adults were recovered from plum species, with no difference between Japanese and European plum cultivars for marked individuals, but with significantly greater numbers of wild individuals recovered from Japanese plum. The preference index (PI) for Japanese plum based on total distances moved by all marked adults recovered on Japanese plum divided by the total distance moved by marked adults recovered on other host trees indicated that Japanese plum was the most highly preferred host, followed by European plum, peach, sweet cherry, tart cherry, apricot, apple, and pear, respectively.     

Viability of plum ovules at different temperatures

The viability of ovules was studied in five plum cultivars under laboratory conditions at four constant temperatures: 5°C, 10°C, 15°C and 20°C and under field conditions over two years. During 10 days from the onset of full bloom, ovule viability in cvs ‘?a?anska Rana’, ‘?a?anska Najbolja’ and ‘?a?anska Lepotica’ was between 80–100 % at the temperatures of 5°C, 10°C and 15°C, in both years. In the same period, ovule viability in cvs ‘Wangenheims Frühzwetsche’ and ‘Po?ega?a’ was lower, but never below 50%. At the constant temperature of 20°C, all plum cultivars showed a decline in longevity of ovule viability, which was pronounced in cv. ‘?a?anska Rana’. During the 10 days from the onset of full bloom, ovule viability in all five plum cultivars under field conditions showed a high viability, which approximated to the ovule viability of the cultivars at the constant temperatures of 5°C, 10°C and 15°C, in both years. Determination of the longevity of ovule viability in the mentioned plum cultivars is of great importance due to its effect on the effective pollination period and fertilisation success. This paper deals in detail with the interrelations between the temperature effects on ovule viability, pollen tube growth and fertilisation, as well as on fruit setting.     

Developing a branch-mimicking trap for adult plum curculios

We conducted field and semi-field experiments to determine the most visually stimulating and acceptable version of a branch-mimicking trap (PVC cylinder topped with an inverted screen funnel) to capture adult plum curculios, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) foraging within canopies of host trees. Cylinder traps (25 cm tall × 6 cm diam) coated with different colors of gloss or flat latex paint captured similar numbers of feral adults in field tests. Tall cylinder traps (50 cm tall × 6 cm diam) captured significantly more feral adults in field tests in 1999 than cylinder traps of lesser height and/or different diameter, and significantly more released adults arrived at traps with these dimensions compared to cylinder traps of lesser height in semi-field tests. In field and semi-field tests, respectively, significantly more adults were captured by and numerically more adults arrived at tall cylinder traps (50 cm tall × 6 cm diam) attached in an upright, standard position to a horizontal limb than attached at angles of 45°, 90°, 135°, or 180° to horizontal limbs.     

Bacterial canker of plum trees, caused by Pseudomonas syringae pathovars, as a serious threat for plum production in the Netherlands

In the Netherlands, bacterial canker in plum trees (Prunus domestica) is a serious and recent problem in plum production. It is caused by Pseudomonas syringae pathovars syringae and morsprunorum. The trunks of the affected plum trees are girdled by bacterial cankers resulting in sudden death of infected trees in 3-4 years after planting. Disease incidences can be very high, and sometimes complete orchards have to be removed. Recently, plum cultivation in the Netherlands has changed from a relatively extensive into an intensive cultivation. However, due to the risks of losses of trees due to bacterial canker, growers are reluctant to plant new plum orchards. In general nurseries and fruit growers are not familiar with bacterial diseases and lack knowledge in order to prevent infections. Therefore, control strategies to manage plum decline have to be developed.     

Use of hydrogen cyanamide for apple and plum thinning

Effects of various concentrations of Dormex (a.i. 49% hydrogen cyanamide) on fruit thinning of Rome Beauty apple (Malus domestica Borkh.), Friar and Simka plums (Prunus salicina Lindley) were studied. A full bloom application of Dormex at all tested concentrations decreased Rome Beauty apple fruit set and yield, and increased fruit weight. Dormex at 0.25% (v/v) resulted in adequate apple thinning, indicated by production of an optimum fruit weight (320 g). Prebloom and full bloom applications of Dormex at greater than 0.75% reduced plum fruit set and yield in Friar. Full bloom application of Dormex at 0.50% showed a satisfactory fruit set, yield, and fruit weight in Friar plum. Prebloom Dormex application had no significant effect on `Simka' plum fruit set or yield, but full bloom application decreased fruit set and yield.     

Intra-strain biological and epidemiological characterization of plum pox virus

Plum pox virus (PPV) is one of the most important plant viruses causing serious economic losses. Thus far, strain typing based on the definition of 10 monophyletic strains with partially differentiable biological properties has been the sole approach used for epidemiological characterization of PPV. However, elucidating the genetic determinants underlying intra-strain biological variation among populations or isolates remains a relevant but unexamined aspect of the epidemiology of the virus. In this study, based on complete nucleotide sequence information of 210 Japanese and 47 non-Japanese isolates of the PPV-Dideron (D) strain, we identified five positively selected sites in the PPV-D genome. Among them, molecular studies showed that amino acid substitutions at position 2,635 in viral replicase correlate with viral titre and competitiveness at the systemic level, suggesting that amino acid position 2,635 is involved in aphid transmission efficiency and symptom severity. Estimation of ancestral genome sequences indicated that substitutions at amino acid position 2,635 were reversible and peculiar to one of two genetically distinct PPV-D populations in Japan. The reversible amino acid evolution probably contributes to the dissemination of the virus population. This study provides the first genomic insight into the evolutionary epidemiology of PPV based on intra-strain biological variation ascribed to positive selection.     

安徽省李品种资源考察与优良资源评价

1995～2000年,我们对安徽省李树主要产地的品种资源进行了实地调查与品种对比研究。安徽省李树品种资源主要分布区为淮北平原的宿州市、阜阳市,江淮之间的淮南市、滁州市、合肥市,长江以南的铜陵市、芜湖市、黄山市等地。考察收集到:安农美李、海棠李、清香李、丁香李、鸡血李、八月李、林檎李、水胭脂李、黄     

Factors affecting adventitious regeneration from in vitro leaf explants of 'Improved French' plum, the most important dried plum cultivar in the USA

An adventitious shoot regeneration protocol from in vitro leaves of the most important dried plum cultivar in the USA, ‘Improved French’, has been established. Factors affecting regeneration were studied in order to optimise regeneration. The proliferation medium in which the shoots, used as the source of leaf explants, were cultured had a strong influence on subsequent regeneration. Shoot regeneration was observed at a mean frequency of 52% when a Murashige-based and Skoog-based shoot culture medium with 3 μM N⁶-benzylaminopurine and 0.25 μM indole-3-butyric acid (IBA) was employed compared with shoot regeneration frequencies of less than 5% for a Quoirin-based and Lepoivre-based shoot culture medium, with 8.9 μM N⁶-benzylaminopurine and 0.49 μM IBA. The shoot regeneration medium contained α-naphthaleneacetic acid at 2.0–6.0 μM and thidiazuron at 4.5–15.0 μM. 2,4 Dichlorophenoxy-acetic acid at 9.0 μM was included in the medium but only for the first 4 days of culture. Shoot regeneration frequencies were positively related to thidiazuron concentration and significantly greater (P < 0.05) for 9–15 μM thidiazuron than for the media with 4.5 μM thidiazuron. Leaf explants, incubated in a 16-h-light/8-h-dark photoperiod or in the dark for 1 week followed by exposure to light, showed significantly more organogenic activity (P < 0.01) than was observed for leaves cultured in the dark for 2 or 3 weeks before they were transferred to the light. The utilisation of Bacto agar (0.7%) as the gelling agent increased organogenesis compared with media gelled with TC Agar (0.7%), or an agar–gellan gum blend (Agargel™) (0.45%). The addition of the ethylene inhibitor silver thiosulphate at 60–120 μM also improved organogenesis. When all the studied factors were optimised, a regeneration rate of 65% was achieved. Rooting frequency of regenerated shoots was significantly increased (P < 0.05) by the use of full-strength Murashige and Skoog salts (40%) or 100 mg L⁻¹ phloroglucinol (53%) to the rooting medium.     

Labile anion binding by roots of two plum clones

The anion-exchange capacities (AEC) of roots of intact plants of two plum clones [Marianna 2624 (Prunus cerasifera × P. munsoniana) and Myrobalan 3-J (P. cerasifera)] were assessed with an anionic dye, eosin Y. The positively charged eosin-specific adsorption sites were metabolically dependent and also affected by nutrient status. Myrobalan 3-J roots adsorbed twice as much exchangeable NO₃ as did Marianna 2624. Since we previously showed that net nitrate uptake by Myrobalan 3-J persisted at half the ambient nitrate concentration as that characteristic of Marianna 2624, the data provide circumstantial support for a functional role of labile anion binding in active uptake at dilute concentrations of ambient nitrate.     

Experience with the diagnostics and purification of plum pox virus

Some diagnostic methods devised for the demonstration of the presence of plum pox virus in plum (Prunus domestica L.) and apricot (Armeniaca vulgaris Lam.) leaves were examined. The method of radial diffusion in agar can be recommended as the simplest and the least time consuming method which can be used during the entire vegetation period. In order to obtain antisera, some preparation methods of PPV antigen were verified. The best preparation method was a modification of Van Oosten’s method in which HEPES buffer pH 6.7 was used for the homogenization-of leaves from infectedNicotiana clevelandii Gray plants and for the solution of sediments after ultracentrifugation. In this way, antigens with titre up to 1: 2048 and during the immunization of rabbit antisera with titre 1: 512 to 1: 1024 were obtained. After the saturation of antisera according to Uyemoto, the titre of the antisera was 1: 64 to 1: 256. Antisera were used for agar preparation in transparent plastic boxes. 0.2 to 1 g portions of leaf material were homogenized with 0.05 M Tris-HCl buffer pH 7.2, 3% pyrrolidine and 1 % polyvinylpyrrolidone in the ratio of 1: 3 for the determination of PPV in plum and apricot leaves.     

Identification and genetic diversity of plum cultivars grown in Belarus

A study of the collection of sour cherry, sweet cherry, common plum, diploid and tetraploid types of plums, and apricots grown in Belarus carried out using 20 SSR markers showed that they are characterized by high genetic diversity. Among 106 genotypes, 524 polymorphic alleles were identified. The average number of alleles was 15.4 in common plum samples, 11.3 in diploid and tetraploid plum, 9.3 in sour cherry, 6.0 in apricot, and 4.9 in sweet cherry. The greatest genetic diversity is characteristic of common plum cultivars (PD = 0.811). The genetic diversity decreases as follows: diploid plum (PD = 0.741), sour cherry (PD = 0.721), apricot (PD = 0.673), and sweet cherry (PD = 0.655). Cluster analysis shows that the degree of intraspecific divergence in sour cherry and sweet cherry cultivars is less than that of common plum, diploid plum, and apricot plum. Although apricots and plums belong to the subgenus Prunophora, according to the results of SSR analysis, apricot cultivars form a cluster that is more distant from both Cerasus and Prunophora. A set of seven SSR markers (EMPA001, EMPA005, EMPA018, EMPA026 and BPPCT025, BPPCT026, BPPCT039) was selected for DNA identification of cultivars of sour cherry, sweet cherry, common plum, diploid plum, and apricot, as well as species and interspecies hybrids.     

Location of independent root-knot nematode resistance genes in plum and peach

Prunus species express different ranges and levels of resistance to the root-knot nematodes (RKN) Meloidogyne spp. In Myrobalan plum (Prunus cerasifera), the dominant Ma gene confers a high-level and wide-spectrum resistance to the predominant RKN, Meloidogyne arenaria, Meloidogyne incognita, Meloidogyne javanica and the isolate Meloidogyne sp. Florida which overcomes the resistance of the Amygdalus sources. In Japanese plum (Prunus salicina), a similar wide-spectrum dominant resistance gene, termed R _jap , has been hypothesized from an intraspecific segregating cross. In peach, two crosses segregating for resistance to both M. incognita and M. arenaria were used to identify single genes that each control both RKN species in the Shalil (R _Mia557 ) and Nemared (R _MiaNem ) sources. Localisation of these genes was made possible using the RFLP and SSR- saturated reference Prunus map T×E, combined with a BSA approach applied to some of the genes. The Ma1 allele carried by the Myrobalan plum accession P.2175 was localised on the linkage group 7 at an approximate distance of 2 cM from the SSR marker pchgms6. In the Japanese plum accession J.222, the gene R _jap was mapped at the same position in co-segregation with the SSR markers pchgms6 and CPPCT022. The peach genes R _Mia557 and R _MiaNem , carried by two a priori unrelated resistance sources, were co-localized in a subtelomeric position on linkage group 2. This location was different from the more centromeric position previously proposed by Lu et al. (1999) for the resistance gene Mij to M. incognita and M. javanica in Nemared, near the SSR pchgms1 and the STS EAA/MCAT10. By contrast, R _Mia557 and R _MiaNem were flanked by STS markers obtained by Yamamoto and Hayashi (2002) for the resistance gene Mia to M. incognita in the Japanese peach source Juseitou. Concordant results for the three independent sources, Shalil, Nemared and Juseitou, suggest that these peach RKN sources share at least one major gene resistance to M. incognita located in this subtelomeric position. We showed that plum and peach genes are independent and, thus, can be pyramided into interspecific hybrid rootstocks based on the plum and peach species.Communicated by H.C. Becker