Comparative Influence of Radopholus similis and Pratylenchus coffeae on Citrus

Pratylenchus coffeae was as pathogenic as Radopholus sirnilis to commercial citrus rootstocks. No rootstock resistant to R. similis was resistant to P. coffeae. Both nematodes stunted citrus in three soil types. Seedling damage by P. coffeae and R. similis was greatest in fine- and coarse-textured soils, respectively. Reproduction and survival on citrus were greater for P. coffeae than for R. similis. Mixed inoculations with R. similis and P. coffeae resulted in lower populations of each species than did separate inoculations.     

GC-MS-SIM analysis of abscisic acid and indole-3-acetic acid in shoot bark of apple rootstocks

Concentrations of abscisic acid and indole-3-acetic acid were measured by GC-MS-SIM in the shoot bark of clonal apple rootstocks (M.27, M.9, MM.106 and MM.111) when the rootstocks were growing actively in the UK. These rootstocks are known to exhibit a wide range of control of tree size when grafted to a common scion. Shoot bark of the dwarfing rootstocks (M.27 and M.9) contained higher concentrations than the more vigorous rootstocks (MM.106 and MM.111) of ABA. Concentrations of ABA increased from May to July, followed by a decline in August. Only the month of sampling showed any significant influence on the concentration of IAA in shoot bark; however, there was a general increase, although not significant statistically, in IAA concentration with the increasing invigoration-capacity of the rootstock. At each sampling date the dwarfing rootstocks showed greater ratios of ABA:IAA than the invigorating rootstocks and generally the ratio for each rootstock increased from May to July, except for M.27 which showed the smallest ratio in June and the largest ratio in August. The results are discussed in relation to the generally accepted control exerted by the rootstocks on tree size and the possible influence of ABA on polar auxin transport.     

Evaluation of Resistance of Stone Fruit Rootstocks to Phytophthora Crown Rot*

The pathogenicity of Phytophthora citrophthora, Phy‐tophthora cactorum and Phytophthora megasperma strains was confirmed on 2‐year‐old stone fruit rootstocks artificially inoculated in the field. Phytophthora mega‐sperma was not virulent or less virulent than P. cactorum or P. citrophthora. The rootstocks Damas and AN 1/7 were resistant whereas the rootstocks Jl, Titan x Nemaguard 5/1, GF 677, Myrandier 613, Italian x Nemaguard 1 and Myrandier 617 were susceptible to P. citrophthora. The rootstocks Tsukuba 9, Tit‐an x Nemaguard 4/7, AN 1/2, AN 1/3, St. Mien 655/2 and Bl showed medium susceptibility to this species. The isolates of P. cactorum induced more extensive necrosis in Myrandier 617 and Italian x Nemaguard than in Myr‐andier 613, GF 677, Jl (ADAFUEL), Tsukuba 9 and St. Julien 655/2. Among seven rootstocks, Tsukuba 5 and St. Julien 655/2 were more resistant than Myrandier 613, Myrandier 617, Jl (ADAFUEL), Tsukuba 9 and St. Julien 655/2.     

苹果砧木SH40 MdNCED1基因克隆与表达分析

9-顺式-环氧类胡萝卜素双加氧酶基因是脱落酸合成途径的关键基因。本试验通过RT-PCR结合RACE技术从苹果SH40(Malus domestica×Malus Honanensis)茎尖组织中克隆了1条NCED基因,命名为MdNCED1(GenBank登录号为KC816734)。该cDNA序列全长2179 bp,包含1个编码606个氨基酸的开放阅读框。氨基酸同源性分析表明,MdNCED1与已报道的其他植物物种的氨基酸序列具有63.7%~93.0%的相似性。构建MdNCED1基因的原核表达载体pDEST15-MdNCED1,转入大肠杆菌(DE3),用IPTG诱导。SDS-PAGE分析表明,MdNCED1基因在大肠杆菌中被诱导表达的蛋白质分子量与预期结果一致。荧光定量结果表明,MdNCED1基因在SH28、M26、SH40及其嫁接品种嘎啦的表达趋势均呈先上升后下降的趋势,同时与其矮生程度呈正相关。     

Characterization of the tolerance to iron chlorosis in different peach rootstocks grown in nutrient solution

Iron chlorosis is an important problem in peach trees, but differences exist between peach rootstocks in their tolerance to Fe chlorosis in calcareous soils. The purpose of this investigation was to characterize the tolerance of different rootstocks to Fe chlorosis induced by bicarbonate in nutrient solution. The rootstocks studied included peach (Nemaguard), plums (Brompton, San Julian A and Puebla de Soto 101) and almond × peach hybrids (Adafuel and GF677). Young plants obtained from rooted cuttings or from in vitro culture techniques were grown individually, under controlled conditions, in flasks with 700 mL of aerated nutrient solution low in iron and with or without 10 mM bicarbonate or 10 mM phosphate. Susceptiblity to bicarbonate-induced chlorosis was inversely correlated with both the Fe content in young leaves and the reducing capacity of roots, but not with the phosphorus content in young leaves. The plum Puebla de Soto 101 and the hybrid GF677 showed the lowest degree of chlorosis and the highest reducing capacity. Phosphate did not induce chlorosis.     

Contrasts between Citrus species in response to salinisation: An analysis of photosynthesis and water relations for different rootstock-scion combinations

Leaf gas exchange, water relations and ion content were measured on two-year-old Valencia orange (Citrus sinensis [L.] Osbeck), Washington Navel orange (C. sinensis) and Marsh grapefruit (C. parodisi Macfad) scions budded to either Trifoliata (Poncirus infoliata [L] Raf) or Cleopatra mandarin (C. reticuLua Blanco) rootstoeks. Trees were watered with dülute nutrient solution containing either 0 or 50 _mM NaCl for 77 days. Leaf chloride concentrations (cell sap basis) were higher in all scions budded on “Trifoliata but sodium levels were lower than in equivalent foliage budded on Cleopatra mandarin rootstock. Foliar salt levels also varied according to scion. Leaves of Marsh grapefruit had higher levels of both sodium and chloride than leaves of either Valencia orange or Washington Navel orange on both rootstocks. Accumulation of sodium and chloride in salinised leaves caused a reduction in leaf osmotic potential of 0.2–1.4 MPa. and leaf water potential declined by as much as 0.5 MPa. Turgor pressure in salinised leaves was thus maintained at or above the control level. Osmotic potentials determined by psychrometry compared with pressure-volume curves were taken to imply that some accumulation of sodium or chloride in the apoplast of salinised leaves may have occurred. Despite turgor maintenance both _co2 assimilation and stomatal conductance were reduced by salinity. Following onset of leaf response to salinisation, gas exchange was impaired to a greater extent in scions budded to Cleopatra mandarin compared to those on Trifoliata. Amongst those scions. leaves of salt-treated Marsh grapefruit showed greater reductions in gas exchange than Valencia orange or Washington Navel orange budded on either rootstock. Increased sensitivity of 1Marsh grapefruit was correlated with a higher foliar sodium and chloride content in this scion. Scion differences in sensitivity of leaf gas exchange to solute concentration were independent of rootstock and appeared unrelated to leaf prolinebetaine concentrations. This implies an inherent difference between scion species with respect to salt tolerance, rather than variation in their capacity to acquire that type of compatible solute. In terms of rootstock effects, all scions proved more sensitive to salinity when budded to Cleopatra mandarin compared with Trifoliata. That response was attributed to a disproportionately higher concentration of leaf sodium in scions on Cleopatra mandarin.     

Performance of Galia-type melons grafted on to Cucurbita rootstock in Monosporascus cannonballus-infested and non-infested soils

Galia‐type melons grafted on to the Cucurbita rootstock‘TZ 148’and non‐grafted controls were evaluated for vegetative development under greenhouse conditions. In general, the development of grafted and non‐grafted plants was similar within a cultivar. The horticultural and pathological performances of the Galia‐type melons ‘Carrera’, ‘NUN‐5554’, ‘6003’ and ‘Arava’ were evaluated in experiments conducted in non‐infested and Monosporascus‐infested soils. In non‐infested soil, grafted and non‐grafted ‘Carrera’, ‘NUN‐5554’ and ‘Arava’ had the same yields. The yield of grafted ‘6003’ was significantly higher than that of its non‐grafted control. Responses of grafted and non‐grafted Galia‐type melons to Monosporascus cannonballus were evaluated and compared in the spring and autumn growing seasons. Significant differences in disease incidence were found among cultivars, between grafted and non‐grafted plants, and between growing seasons. Disease reduction and the beneficial effect of grafting on yield were more pronounced in the spring. The results indicate that Galia‐type melons can be grafted successfully, but the cultivation of the grafted plants should be adapted to each growing area and season.     

Relative Resistance of Four Peach Rootstocks to Phytophthora cactorum and Phytophthora megasperma

Shoot samples of four peach rootstocks that are important to the peach industry in Greece: KID I, GF305, GF677, and PR204, were inoculated with Phytophthora cactorum and Phytophthora megasperma in the field and in the glasshouse and were then evaluated with regard to susceptibility. The pathogenicity of P. cactorum and P. megasperma to peach rootstocks was confirmed with an excised twig assay. The peach rootstocks showed differential susceptibility to P. cactorum . GF305 was the least susceptible and KID I was the most susceptible, which suggests that the latter rootstock is unsuitable for orchards in which the conditions are favourable for Phytophthora diseases. GF677 and PR204 were moderately susceptible. The plants that were inoculated with P. megasperma in the field and in the glasshouse showed no sign of infection whereas twigs inoculated in vitro with P. megasperma developed necrosis. GF305 was the most resistant, KID I was the most susceptible and PR204 and GF677 were moderately resistant. The present results demonstrate that none of the four peach rootstocks used in this study was completely resistant to P. cactorum , particularly when rootstocks were flooded periodically to enhance disease development. Therefore an integrated approach including host and resistance cultural practices is recommended to manage diseases caused by P. cactorum in peach orchards in Greece.     

The effect of paclobutrazol on in vitro rooting and growth of GF-677 hybrid peach rootstock

This paper deals with the evaluation of the influence of paclobutrazol (N-dimethylaminosuccinamic acid) and 2-naphtoxyacetic acid on rooting and growth of GF-677 hybrid peach rootstocks. The influence of these substances on the average number of roots per plant, the average length of roots per plant and the height of plants was evaluated as well as the effect of the addition of paclobutrazol before and after media sterilisation. As the obtained results indicate, plants, which were rooted on media with paclobutrazol and without auxin had the lowest number of roots per plant. Paclobutrazol showed a statistically significant negative effect on both the length of roots and the height of plants. It canbe concluded that, for the rooting of GF-677 rootstock it is helpful to use auxin plus paclobutrazol in concentration 0.43 μM. Higher concentrations affect inhibition, mainly in height of plants 14 days after transplant to soil. A part of the results referring to the influence of PP 333 on numbers of roots was presented at the conference “Recent Advances in Plant Biotechnology, 5th International symposium in the series”, Stará Lesná, Slovakia, 7–13 September, 2003.