The WD-40 repeat protein PkwA of Thermomonospora curvata is associated with rapid growth and is localized in the tips of growing hyphae

The PkwA protein of the thermophilic actinomycete Thermomonospora curvata has already been reported as the first instance of a WD-40 module-containing protein of prokaryotic origin. This protein is composed of an N-terminal eukaryotic-type protein kinase domain and of seven C-terminal WD-40 repeats. PkwA is a peripheral membrane protein that is linked to the early exponential growth phase of the bacterium. Its intracellular concentrations are extremely low. We have shown that the protein forms high molecular weight complexes and is localized mainly in the tips of the young Thermomonospora vegetative hyphae.     

Activity and mode of action against fungal phytopathogens of bovine lactoferricin-derived peptides

AIM: To evaluate the activity against fungal phytopathogens of two synthetic peptides derived from the protein bovine lactoferricin: the antibacterial active core of six amino acid residues (LfcinB(20-25)) and an extension of 15 amino acids (LfcinB(17-31)). METHODS AND RESULTS: In vitro activity against fungal pathogens was determined and compared with that against model micro-organisms. Activity was demonstrated against fungi of agronomic relevance. Distinct antimicrobial properties in vitro were found for the two peptides. LfcinB(17-31) had growth inhibitory activity higher than LfcinB(20-25). However, LfcinB(17-31) was not fungicidal to quiescent conidia of Penicillium digitatum at the concentrations assayed, while LfcinB(20-25) killed conidia more efficiently. Microscopical observations showed that the mycelium of P. digitatum treated with LfcinB(17-31) developed alterations of growth, sporulation and chitin deposition, and permeation of hyphal cells. In experimental inoculations of mandarins, both peptides showed limited protective effect against the disease caused by P. digitatum. CONCLUSIONS: LfcinB(20-25) and LfcinB(17-31) peptides were shown to have antimicrobial activity against plant pathogenic filamentous fungi, with distinct properties and mode of action. SIGNIFICANCE AND IMPACT OF THE STUDY: LfcinB(20-25) and LfcinB(17-31) peptides offer novel alternatives to develop resistant plants by molecular breeding.     

Molecular Typing and Genetic Characterization of Pathogenic Variants of Xanthomonas axonopodis pv. citri in Taiwan

Molecular typing was applied and optimized for genetic characterization for three pathogenic variants of Xanthomonas axonopodis pv. citri (Xac) from Taiwan. These three novel variants of atypical symptom–producing X. axonopodis pv. citri were designated as Xac‐A^f, Xac‐A^p and Xac‐A^r. Based on polymerase chain reaction (PCR) with primers specific to X. axonopodis pv. citri, leucine‐responsive regulatory protein (lrp) gene assay and DNA fingerprintings generated by repetitive‐sequence PCR (rep‐PCR) and amplified fragment length polymorphism (AFLP) were used to compare strains including the three types of atypical symptom–producing strains Xac‐A^f, Xac‐A^p and Xac‐A^r, and additional reference strains from pathotypes Xac‐A, Xac‐A*, Xac‐A^w, X. axonopodis pv. auruantifolii and X. axonopodis pv. citrumelo. These three types of X. axonopodis pv. citri variants can be detected with six sets of primer specific for X. axonopodis pv. citri. Cluster analyses by lrp sequence assay, AFLP and combing the band patterns of rep‐PCR clearly grouped the atypical symptom–producing variants in types Xac‐ A^f, Xac‐A^r and Xac‐A^p into the same cluster with typical symptom‐producing strains in pathotype Xac‐A. These three types of X. axonopodis pv. citri variants could be excluded from strains of Xac‐A* and Xac‐A^w in these genotypic analyses. Strains of Xac‐A* and Xac‐A^w were closely related to Xac‐A strains in our results. No Taiwan isolate was related to X. axonopodis pv. auruantifolii or X. axonopodis pv. citrumelo. The results further confirmed the atypical symptom–producing variants of X. axonopodis pv. citri in Taiwan belong to pathotype Xac‐A.     

Field efficacy of Ceratitis capitata (Diptera: Tephritidae) mass trapping technique on clementine groves in Spain

Mass trapping is being used in Mediterranean regions to control Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in citrus. The technique is based on placing a high density of traps with an attractant (Ferag CC D TM^®, a three‐membrane dispensers of trimethylamine, ammonium acetate and diaminoalkane), and a toxicant, aiming to capture the highest numbers of adults in the grove. From 2006 to 2008, field trials were conducted in commercial Clementine (Citrus reticulata Blanco) groves to evaluate the efficacy against medfly of using different trap densities, 25, 50, 75 and 100 traps per ha. Based on the number of adults captured, fruit maturity parameters and medfly fruit damage, a 25 trap per ha density appears to be a valid stand‐alone method to protect mid‐season varieties (Clemenules) from the attack of C. capitata, because <0.5% of fruits on average were damaged at harvest. For early‐season varieties (Loretina and Marisol), mass trapping technique alone did not offer a satisfactory medfly control, because medfly populations were higher in the warmer months of the early‐season variety production, which led to a higher percentage of attacked fruits, even when increasing the trap density from 50 to 100 per ha. However, using 50 traps per ha density combined with chemical treatments only to the perimeter row of the grove gave good results, because <2% of fruits in average were damaged at harvest.     

植物保护剂防治害虫效果的评价方法

在以作用因子组建的生命表和干扰作用控制指数(IIPC)的基础上建立植物保护剂的研究方法和综合评价指标,以表示驱避成虫选择寄主,干扰成虫的产卵行为,对卵孵化的影响,以及干扰幼虫的行为,包括逃避、拒食、幼虫特别是初孵幼虫中毒死亡的作用.采用所建立的研究方法和评价指标的试验结果表明,菜田附近大多数非寄主植物的乙醇抽提物(干重1g·100ml^-1)如大叶桉(Eucalytus rubusta)、蟛蜞菊(Wedelia chinensis)等对保护十字花科蔬菜免受小菜蛾为害起着明显的作用.印楝油对小菜蛾幼虫的防治效果相当显著.机油乳剂(CAL TEX产品)对桔全爪螨具有明显的控制效果.     

Effect of host deprivation on the foraging behavior of the Asian citrus psyllid parasitoid Tamarixia radiata: observations from the laboratory and the field

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a significant citrus pest and the parasitoid Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) has been released in various citrus‐producing areas in classical biological control programs targeting D. citri. We investigated the effect of host deprivation on the foraging behavior and patch utilization by T. radiata. In the laboratory, females deprived of hosts for 3 days tended to leave patches of 12 nymphs without parasitizing hosts during the ca. 30 min they spent in the patch before leaving. Moreover, half of these females failed to host feed, and those that did host feed, on average, needed more than 15 min to complete feeding. Conversely, non‐host‐deprived females parasitized on average three nymphs before leaving patches without host feeding during the ca. 39 min they spent in the patch. These laboratory observations were compared to mass‐reared female T. radiata that were released onto colonies of D. citri nymphs infesting citrus in the field. Release vials were provisioned with honey and these females had no opportunities to host feed over the 1‐ to 2‐day containment period prior to release. When introduced onto D. citri colonies, 68% T. radiata females abandoned D. citri patches prior to probing hosts, in part, because Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), tending colonies disturbed searching parasitoids. These results from laboratory and field studies are discussed in the context of classical biological control, with the aim of understanding how to manipulate host availability and ant activity so establishment rates and impact of T. radiata can be improved.     

Effect of different ground cover management on spider mites (Acari: Tetranychidae) and their phytoseiid (Acari: Phytoseiidae) enemies in citrus orchards

We determined the effect of ground cover on phytoseiid predatory mite populations and the potential biological control of Panonychus citri (McGregor). Results showed that citrus trees with ground cover contained higher population densities of predatory mites and provided better regulation of P. citri than trees in bare soil. The ground cover Ageratum conyzoides L. performed better than Palspalum notatum Flugge in sheltering phytoseiid mites.     

Solution structure of ApaG from Xanthomonas axonopodis pv. citri reveals a fibronectin-3 fold

ApaG proteins are found in a wide variety of bacterial genomes but their function is as yet unknown. Some eukaryotic proteins involved in protein-protein interactions, such as the human polymerase delta-interacting protein (PDIP38) and the F Box A (FBA) proteins, contain ApaG homology domains. We have used NMR to determine the solution structure of ApaG protein from the plant pathogen Xanthomonas axonopodis pv. citri (ApaG(Xac)) with the aim to shed some light on its molecular function. ApaG(Xac) is characterized by seven antiparallel beta strands forming two beta sheets, one containing three strands (ABE) and the other four strands (GFCC'). Relaxation measurements indicate that the protein has a quite rigid structure. In spite of the presence of a putative GXGXXG pyrophosphate binding motif ApaG(Xac) does not bind ATP or GTP, in vitro. On the other hand, ApaG(Xac) adopts a fibronectin type III (Fn3) fold, which is consistent with the hypothesis that it is involved in mediating protein-protein interactions. The fact that the proteins of ApaG family do not display significant sequence similarity with the Fn3 domains found in other eukaryotic or bacterial proteins suggests that Fn3 domain may have arisen earlier in evolution than previously estimated.     

红壤旱坡地桔园覆盖的生态效应及经济效益评价

柑桔是南方红壤地区栽培的主要果树种类,栽培面积达1126×106ｈｍ2。柑桔是一种常绿果树,生长量大,挂果期长,周年需要消耗大量的水分。我国南方红壤地区虽然雨水充沛,但降水季节分布不均,柑桔果实迅速生长的7～10月正是该地区雨水少、蒸发量大的伏秋干旱季节。经常性的伏秋干旱是制约我国柑桔产量和质量进一步提高的主要障碍因素之一。桔园夏秋进行秸秆覆盖可以降温[1]、保水[2]、防止杂草生长[3]等,但桔园应用地膜覆盖及常年连续覆盖对桔园的生态效应方面的研究较少,为此我们开展了这方面的工作,并通过连续3ａ的产量及产值分析覆盖桔园的经…     

Protection of plants from frost using hydrophobic particle film and acrylic polymer

Frost damage to potatoes, grapevine and citrus plants was assessed following treatment with either an acrylic polymer (Antistress?) or with a hydrophobic particle film (CM‐96–018). In large freezing tests, the application of the hydrophobic particle film consistently led to less damage whilst the acrylic polymer led to the same amount or more damage when compared to control plants. Detailed examination of the freezing of leaves of all three species using infrared thermal imaging revealed that the hydrophobic particle film delayed the entry of ice from a frozen water droplet containing ice nucleating active bacteria and in some cases for the complete duration of the frost test. In contrast, the acrylic polymer was only able to influence the time of ice nucleation of the leaves of citrus plants. It was concluded that the hydrophobic particle film shows considerable promise as a frost protectant applied to susceptible crops just prior to a freezing event.