两类柑橘杂种砧木对脐橙幼树生长及若干生理生化指标的影响

以体细胞杂种红橘+枳、红橘+粗柠檬和有性杂种Swingle枳柚、Troyer枳橙(对照)作砧木的脐橙幼树为试材,以盆栽试验研究砧木对幼树的影响。结果表明,体细胞杂种砧木处理和有性杂种Swingle枳柚的树体生长势总体上强于对照;叶片可溶性糖含量较高的是红橘+粗柠檬处理和对照;叶绿素含量最高的是红橘+粗柠檬处理。两年中叶片POD活性分别与当年树冠体积呈负相关。     

橘园中重要天敌具瘤神蕊螨与其主要猎物的生态位

研究了柑橘园中具瘤神蕊螨(Agistemus exsertus)与其主要猎物柑橘皱叶刺瘿螨(Phyllocoptruta oleivora)、柑橘全爪螨(Panonychus citri)、柑橘粉虱(D ialeurodes citri)、黑刺粉虱(Aleurocanthus spiniferus)的生态位宽度、重叠和比例相似性。具瘤神蕊螨与其主要猎物相比,其时间和空间生态位宽度均最大,而其猎物中则以柑橘皱叶刺瘿螨的时间和空间生态位宽度最大,这表明具瘤神蕊螨和柑橘皱叶刺瘿螨的发生期较长,空间分布较广。具瘤神蕊螨与其猎物的生态位重叠在空间上与柑橘全爪螨的重叠值最大,在时间上与柑橘粉虱的重叠值最大。与其猎物相比,具瘤神蕊螨的时—空二维生态位宽度最大,在时空上占有明显的优势。     

Crystal structures of Xanthomonas small heat shock protein provide a structural basis for an active molecular chaperone oligomer

Small heat shock proteins (sHsps) are ubiquitous low-molecular-weight chaperones that prevent protein aggregation under cellular stresses. sHsps contain a structurally conserved α-crystallin domain (ACD) of about 100 amino acid residues flanked by varied N- and C-terminal extensions and usually exist as oligomers. Oligomerization is important for the biological functions of most sHsps. However, the active oligomeric states of sHsps are not defined yet. We present here crystal structures (up to 1.65 Å resolution) of the sHspA from the plant pathogen Xanthomonas (XaHspA). XaHspA forms closed or open trimers of dimers (hexamers) in crystals but exists predominantly as 36mers in solution as estimated by size-exclusion chromatography. The XaHspA monomer structures mainly consist of α-crystallin domain with disordered N- and C-terminal extensions, indicating that the extensions are flexible and not essential for the formation of dimers and 36mers. Under reducing conditions where α-lactalbumin (LA) unfolds and aggregates, XaHspA 36mers formed complexes with one LA per XaHspA dimer. Based on XaHspA dimer-dimer interactions observed in crystals, we propose that XaHspA 36mers have four possible conformations, but only XaHspA 36merB, which is formed by open hexamers in 12mer-6mer-6mer-12mer with protruding dimers accessible for substrate (unfolding protein) binding, can bind to 18 reduced LA molecules. Together, our results unravel the structural basis of an active sHsp oligomer.     

Effect of the rootstock on the occurrence of lime-induced chlorosis of potted Vitis vinifera L. cv. ‘Pinot blanc’

The chlorosis susceptible Vitis vinifera L. cv. Pinot blanc was grafted on two hybrid rootstocks with different iron efficiency, as follows: V. Berlandieri × V. rupestris 140 Ru (iron-efficient) and V. riparia × V. rupestris 101-14 (iron-inefficient). The grafted vines were grown in pots of a calcareous and a non-calcareous soil. The shoot growth was periodically checked and leaves, selected at two different times (at the middle of the annual growing period), were assayed for total chlorophyll, ferrous iron, ash alkalinity, percentage of dry matter and chlorosis score. At the end of the growing cycle the roots were oven-dried and weighed. The most significant findings of the trial were: (a) the soil strongly affected the shoot growth, with canes about twice as long in the non-calcareous soil; (b) the iron-efficient rootstock (140 Ru) did not induce chlorosis when growing on the calcareous soil, while the opposite occurred with the iron-inefficient rootstock (101=14); and (c) a high ash alkalinity occurred in light chlorotic leaves compared to green ones, under the same iron concentration.     

3个桃砧木品种对淹水的光合生理响应特征

以生产中常用的3个桃砧木品种毛桃、山桃和列玛格幼苗为试材,以正常供水为对照,采用模拟水涝试验研究了淹水对其光合特性的影响,探讨桃砧木耐涝的光合机理.结果显示:淹水胁迫下,3个桃砧木叶片净光合速率(Pn)、相对含水量(RWC)、水分利用效率(WUE)、蒸腾速率(Tr)、气孔导度(Gs)、表观量子效率(AQY)、羧化效率(CE)和最大电子传递速率(Jmax)等均显著低于对照,而丙二醛(MDA)含量显著高于对照.试验后期,淹水胁迫下列玛格叶片的叶绿素含量增加显著高于毛桃和山桃,MDA含量显著低于毛桃和山桃,且Pn、RWC、Tr、WUE和Gs下降幅度最小,光合能力最强,而毛桃次之,山桃下降幅度最大;3个桃品种的耐涝性表现为列玛格＞毛桃＞山桃.研究表明,淹水使桃砧木叶片膜脂过氧化加剧,气孔开度减小,水分代谢机能降低,光合电子传递和光合碳同化能力下降,光合机构受损,光合作用效率降低;而列玛格品种在淹水胁迫下叶绿素合成加强,叶片RWC下降缓慢,光能吸收、传递和水分代谢能力以及抗光抑制和光氧化能力最强,膜脂过氧化程度最轻,从而保持最高的光合能力.     

桔园内多种天敌对桔全爪螨的控制作用

本文应用二次回归旋转组合实验设计统计方法,对桔园内主要天敌食螨瓢虫(Stethorus che-ngi)、长须螨(Agistemus exsertus citri)、尼氏钝绥螨(Amblyseius nichols)和普通钝绥螨(Amb-lyseius vulgaris)对桔全爪螨(Panongchus citri)的控制作用,以及天敌与天敌之间、天敌与害螨之间的相互作用进行了研究。得出了这4种天敌对桔全爪螨的捕食量模型。并对模型进行主效分析,表明桔全爪螨自身密度的大小对天敌的总捕食量影响最大。在这4种天敌中对总的捕食量影响最大的是食螨瓢虫,其次为长须螨,尼氏钝绥螨再次之,普通钝绥螨的影响最小。对各天敌间交互作用的分析表明,天敌个体大、活动能力强、捕食量大,他们的种内种间干扰程度也大,特别是食螨瓢虫种内种间干扰十分明显。其次为长须螨,而尼氏钝绥螨和普通钝绥螨的种内种间干扰较弱,在密度较低时,他们还表现出相互促进的作用。最后本文还讨论了这4种天敌能有效地控制桔全爪螨的最大密度,以及在该密度下各种天敌密度的最佳组合。     

Morphology,life cycle and management of two invasive subspecies of Papilio demoleus (Lepidoptera: Papilionidae): A review

Papilio demoleus L., also known as the citrus butterfly or chequered swallowtail, is a common species in the Asia-Pacific region, with two of its subspecies (P. d. demoleus and P. d. malayanus) posing significant threats to the citrus industry in Asia and other regions of the world. Its predominant natural host plants are the Rutaceae for the invasive northern subspecies and Fabaceae for the southern subspecies. The morphology and development of this species are reasonably well studied, although further information is required on its natural mortality rates and environmental tolerance in order to accurately predict its future potential spread throughout the Middle East and Central Americas. Synthetic pyrethroids such as deltamethrin are highly effective for the control of P. demoleus larvae. However, better control is likely to be found using an integrated approach to pest management, incorporating techniques such as biocontrol agents, microbial pesticides and phytopesticides, in conjunction with synthetic pesticides where required.     

Argovin,a novel natural product secreted by the fungus Meira argovae,is antagonistic to mites

A metabolite of the fungus Meira argovae Boekhout, Scorzetti, Gerson & Sztejnberg (Exobasidiomycetidae) was assayed as an antagonist of mites. Separation of extracted fungal metabolites by reversed phase liquid chromatography (RPLC), with subsequent testing of the obtained fractions, allowed us to isolate a single mite‐antagonistic fraction (also active against a bacterium) that primarily includes one major component. This active compound (herein termed ‘argovin’) was identified by analyzing its spectral characteristics as 4,5‐dihydroxyindan‐1‐one, which has previously only been described as a product of chemical reactions. The growth rate of the fungus was higher at a neutral pH than at an acidic one. Meira argovae adjusts the pH of its media to values optimal for its colony growth and toxic secretions. RPLC‐cleaned argovin at 0.2 mg ml^?1 killed 100% of a population of the citrus rust mite, Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae). This trait may be used to control citrus rust mites in the field, as well as for toxin production for industrial and pharmaceutical uses.     

An analysis of the feeding behavior of three stages of Toxoptera citricida by DC electrical penetration graph waveforms

With the purpose of studying the feeding behavior of the brown citrus aphid pest, Toxoptera citricida (Kirkaldy) (Hemiptera: Aphididae), we compared stylet probing behaviors of third and fourth instars and adults on Citrus unshiu Marc (Rutaceae) seedlings using the electrical penetration graph (EPG) technique. EPG waveforms exhibited the full suite of stylet behaviors – stylet pathway, intracellular stylet puncture, phloem salivation (E1), sieve ingestion (E2), and xylem sap ingestion activities, plus the non‐penetration (Np) waveform. Before the phloem phase, the number of probes was significantly higher for third‐instar nymphs than for adults. Overall duration of Np events by adults was significantly lower than the duration of third and fourth instars. The number of short probes of the fourth instars was significantly higher than that of the adults. In the phloem phase, adults made more frequent and longer E1 events than the third and fourth instars. Third instars made more frequent but shorter E2 events, whereas adults made fewer but longer events. These results showed adults gained nutrients by increasing feeding time during phloem ingestion. Thus, the probability of phloem‐associated virus acquisition and transmission of T. citricida was higher in adults than in nymphs.     

Status of biological control by egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae) in citrus in Florida and Puerto Rico

Eggs of Diaprepes abbreviatus (L.) were routinely monitored in citrus groves at ten locations in Florida during 1997 and 1998 to study egg parasitism. One citrus location was studied in Puerto Rico. No native parasitoids were recovered from 1,337 D. abbreviatus egg masses studied in Florida citrus. In contrast, an average of 35.5% (range 12.5 to 68.8%) parasitism of egg masses was reported in Puerto Rico. The parasitoids Aprostocetus gala, Horismenus spp, and Quadrastichus haitiensis were recovered from the eggs of D. abbreviatusfstudied in Puerto Rico. The Horismenus parasitoids were suspected hyperparasitoids. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were initiated during 1998 at each of the Florida research sites. By the end of 1998, C. etiennei had been recovered from D. abbreviatus eggs at two of nine locations in Florida citrus. The parasitoid was recovered from 1 of 34 egg masses at one of these locations during the month of September and from 3 of 34 egg masses at the other location during the month of November. Whether or not C. etiennei establishes itself at one or more locations in Florida remains to be seen.