Genetic transformation of sweet orange with the coat protein gene of <Emphasis Type="Italic">Citrus psorosis virus</Emphasis> and evaluation of resistance against the virus

Citrus psorosis is a serious viral disease affecting citrus trees in many countries. Its causal agent is Citrus psorosis virus (CPsV), the type member of genus Ophiovirus. CPsV infects most important citrus varieties, including oranges, mandarins and grapefruits, as well as hybrids and citrus relatives used as rootstocks. Certification programs have not been sufficient to control the disease and no sources of natural resistance have been found. Pathogen-derived resistance (PDR) can provide an efficient alternative to control viral diseases in their hosts. For this purpose, we have produced 21 independent lines of sweet orange expressing the coat protein gene of CPsV and five of them were challenged with the homologous CPV 4 isolate. Two different viral loads were evaluated to challenge the transgenic plants, but so far, no resistance or tolerance has been found in any line after 1 year of observations. In contrast, after inoculation all lines showed characteristic symptoms of psorosis in the greenhouse. The transgenic lines expressed low and variable amounts of the cp gene and no correlation was found between copy number and transgene expression. One line contained three copies of the cp gene, expressed low amounts of the mRNA and no coat protein. The ORF was cytosine methylated suggesting a PTGS mechanism, although the transformant failed to protect against the viral load used. Possible causes for the failed protection against the CPsV are discussed.     

黄山贡菊的挥发油成分

The volatile oil in flowers of Dendranthema morifolium (Ramat) Tzvel. cv. Gongju was extracted with steam distillation, the constituents and contents of volatile oil were analyzed by means of GC-MS-DS techniques. The result shows that the principle constituents of the volatile oil are bicyclo[3.1. 1]hept-2-en-4-ol, 2,6,6-trimethyl-, acetate (39.64%); benzene, 1-( 1,5-dimethyl-4-hexenyl)-4-methyl-,2-heptene (5.24%);n-hexadecanoic acid (4.77%); cis-lanceol (4.73%) ; acetic acid,1,7, 7-trimethyl-bicyclo [2.2.1] hept-2-yl-ester (3.95%); (-) spathulenol (3.38%) ; 2, 4, 6-trimethyl-3-cyclohexene-1-carboxaldehyde(3.22%) ; caryophyllene oxide (2.88%) ; 1,2,3,4, 5,6,7,8-octahydro-1,4-dimethyl-7-(1-methylethenyl)-,azulene (2. 80%); 3-(1, 5-dimethyl-4-hexenyl)-6-methylene, cyclohexaene (2. 50%); decahydro-1, 4a-dimethyl-7-( 1-methylidene)-,1-naphthalenol(2.39%);1,1,2-trimethyl-3,5-bis(1-methylethenyl)-,cyclohexane(2.23% ), etc.     

Comparison of the nutrient ecology of coastal Banksia grandis elfinwood (windswept shrub‐like form) and low trees,Cape Leeuwin‐Naturaliste National Park,Western Australia

Abstract Trees growing along windy coasts often have canopies that are greatly reduced in size by the sculpting effects of wind and salt spray. Trees with environmentally reduced stature are called elfinwood (windswept shrub‐form or krummholz) and are ecologically important because they represent outposts growing at the limit of tree success. The purpose of this study was to assess if Banksia grandis elfinwood growing at Cape Leeuwin had a different nutrient status than normal low‐form (LF) trees growing nearby, and if nutrient deficiencies, toxicities and/or imbalances were among the limiting factors imposed on elfinwood. The concentrations of N, P, K, Ca, Mg, Na, Cl^–, Fe, Mn, Zn, Cu, Mo and B were analysed for mature green foliage, immature foliage, foliage litter, flowers and soil. When the elfinwood and LF trees were compared, the foliar nutrient status was generally similar, except that elfinwood foliage had significantly higher mean concentrations of N, Zn and Cu, while LF trees had higher Fe and Mn contents. Many nutrients were conserved before leaves were shed in both elfinwood and LF trees, including N, P, K, Na, Cl^–, Mn and Cu (LF trees also conserved Ca and Mg). However, elfinwood and LF tree‐litter contained significantly higher Fe concentrations than green foliage (elfinwood litter also had higher levels of Mg and B). It is tempting to suggest that the translocation of Fe into leaves before they were shed is a regulation mechanism to prevent Fe toxicity, or imbalance in the Fe : Mn ratio. Proteoid roots strongly acidify the soil to mobilize P, which also chemically reduces Fe⁺³ to plant‐available Fe⁺². The increased supply of Fe⁺² in the rhizosphere, caused by the action of proteoid roots, might tend to defeat self‐regulation of Fe uptake. It is possible that excess Fe accumulation in the plant might be regulated, in part, by exporting Fe into the leaves before they are shed. The nutrient status of B. grandis elfinwood is compared with mountain elfinwood of North America. The extreme habitat of coastal elfinwood provides many theoretical pathways for nutrient limitation, but B. grandis elfinwood at Cape Leeuwin does not appear to be nutrient deficient.     

Strategic Conservation of Orchard Germplasm Based on Indigenous Knowledge and Genetic Diversity： a Case Study of Sour Orange Populations in China

To effectively conserve sour orange （Citrus aurantium L.） germplasm on two islands at the estuary of the Yangtze River in China, we estimated genetic variation and relationships of the known parental trees and their proposed descendents （young trees） using the fingerprints of random amplified polymorphic DNA （RAPD）. Results based on RAPD analyses showed considerable genetic diversity in the parental populations （He = 0.202）. The overall populations including the parental and young trees showed slightly higher genetic diversity （He = 0.298） than the parents, with about 10% variation between populations. An unweighted pair group method with arithmetic mean analysis dendrogram based on cluster analysis of the Jaccard similarity among individuals demonstrated a more complicated relationship of the parental and young trees from the two islands, although the young trees showed a clear association with parental trees. This indicates a significant contribution of parental trees in establishing the sour orange populations on the two islands. According to farmers＇ knowledge, conservation of only one or two parental trees would be sufficient because they believed that the whole populations were generated from a single mother tree. However, this study suggests that preserving most parental trees and some selected young trees with distant genetic relationships should be an effective conservation strategy for sour orange germplasm on the two islands.     

Effects of exogenous B supply on growth, B accumulation and distribution of two navel orange cultivars

To investigate the effects of boron (B) on growth, B concentration and distribution of two navel orange cultivars, ‘Newhall’ (Citrus sinensis Osbeck) and ‘Skagg’s Bonanza’ (Citrus sinensis Osbeck) grafted on the rootstock trifoliate orange [Poncirus trifoliata (L.) Raf.], B at five levels was exogenously supplied to 1-year-old grafted plants of both cultivars under greenhouse conditions. Plants were grown in sand:perlite (1:1, v/v) medium and were irrigated every 2 days with half-strength Hoagland’s No. 2 nutrient solutions containing different B, 0.01, 0.05, 0.10, 0.25 and 2.50 mg l⁻¹ (0.25 and 2.50 mg l⁻¹ were considered as control and excess B treatment, respectively, and the other three B levels were considered as low B treatments). After treatments for 183 days, leaves (from basal, middle, upper parts of the shoots), stem of scion, stem of rootstock and root were separately sampled. Our results showed that plant growth (plant height, root volume and dry weights of various parts) was inhibited in response to low or excess B supplies in both cultivars. It was found that B concentrations in the upper leaves of both cultivars were substantially higher than those in the basal leaves when low concentrations (≤0.05 mg l⁻¹) of exogenous B were applied, suggesting that B was preferentially translocated to the upper-younger leaves to support their growth. Analysis of B distribution in different parts indicated that translocation of B from the root to the scion’s shoots (stems and leaves of scion) may be restricted upon exposure to low B conditions. When B was inadequately supplied, growth of ‘Skagg’s Bonanza’ was better than ‘Newhall’, implying that the former cultivar was more tolerant to low B status, which may be due to the higher efficiency of B translocation from the root to the scion’s shoots. However, when the plants were treated with excess B (2.50 mg l⁻¹), both cultivars showed a similar degree of B toxicity. The probability of scion–rootstock interactions in relation to the differential responses of growth and different efficiency of B translocation involved in the two orange cultivars following the long-term low B stress were discussed.     

金丝小枣多糖ZP3c的分离纯化及其组成分析

经DEAE-SepharoseCL-6B、SepharoseCL-6B和Sephadex G-200柱层析,得到一个均一的金丝小枣多糖组分(ZP3c).ZP3c的中性单糖是由鼠李糖、阿拉伯糖和半乳糖组成,其摩尔比为1:2.13:19.3.经红外光谱测定,ZP3c的酯化度为41.85%.     

Post-release survey to assess impact and potential host range expansion by Amitus hesperidum and Encarsia perplexa, two parasitoids introduced for the biological control of the citrus blackfly, Aleurocanthus woglumi in Dominica

Four years after the release of two exotic parasitoids, Amitus hesperidum Silvestri (Hymenoptera: Platygasteridae) and Encarsia perplexa Huang and Polaszek (Hymenoptera: Aphelinidae) for the classical biological control of the citrus blackfly (CBF), Aleurocanthus woglumi Ashby (Hemiptera: Aleyrodidae) in Dominica, a survey was conducted to assess establishment as well as potential nontarget effects especially on Aleyrodidae and other related taxa. CBF populations were low to non-existent in 50 of 51 field sites examined. At the site where CBF was encountered, both E. perplexa and A. hesperidum were present and CBF populations were declining. The two parasitoids were not among the several species collected on nontarget Aleryodidae and Hemiptera. It is concluded that E. perplexa and A. hesperidum have kept CBF populations under effective biological control in Dominica and there is no evidence of any nontarget effects on other Aleyrodidae or their natural enemies. Handling Editor: Dirk Babendreier.     

Enhanced proliferation and efficient transmission of Candidatus Liberibacter asiaticus by adult Diaphorina citri after acquisition feeding in the nymphal stage

We carried out a quantitative detection of Candidatus Liberibacter asiaticus, the bacterium associated with the disease of huanglongbing, in the vector psyllid Diaphorina citri by using a TaqMan real‐time PCR assay. The concentration of the bacterium was monitored at 5‐day intervals for a period of 20 days after psyllids were exposed as fifth instar nymphs or adults to a Ca. L. asiaticus‐infected plant for an acquisition access period of 24 h. When adults fed on Ca. L. asiaticus‐infected plant, the concentration of the bacterium did not increase significantly and the pathogen was not transmitted to any citrus seedlings. In contrast, when psyllids fed on infected plant as nymphs, the concentration of the pathogen significantly increased by 25‐, 360‐ and 130‐fold from the initial acquisition day to 10, 15 and 20 days, respectively. Additionally, the pathogen was successfully transmitted to 67% of citrus seedlings by emerging adults. Our data suggested that multiplication of the bacterium into the psyllids is essential for an efficient transmission and show that it is difficult for adults to transmit the pathogen unless they acquire it as nymphs.