Spatial and temporal distribution of imidacloprid and thiamethoxam in citrus and impact on Homalodisca coagulata populations

Titers of two systemic neonicotinoid insecticides in citrus trees were measured in conjunction with conventional evaluations of their impact on glassy-winged sharpshooter (Homalodisca coagulata (Say); GWSS) populations. Xylem fluid samples were collected at regular intervals and from multiple locations within field-grown citrus trees to determine imidacloprid and thiamethoxam concentrations using commercial ELISA kits. Uptake profiles varied considerably with peak mean titers of imidacloprid occurring 6-8 weeks after application compared with 2 weeks for thiamethoxam. The persistence of each compound also varied as near-peak levels of imidacloprid were sustained for another 6-10 weeks before gradually declining. In contrast, thiamethoxam titers declined more rapidly after the initial peak, possibly reflecting an application rate only one-quarter of that used for imidacloprid. Within-tree distributions were more similar for the two compounds, with no significant effect due to height of the sample (upper or lower half) or to the quadrant location within the tree, with the exception of one quadrant in the thiamethoxam-treated trees. Substantial reductions in GWSS nymphs and adults were observed in imidacloprid-treated trees during the 2001 trial and were sustained for 4-5 months after treatment. Treatment effects on nymphs were not as well pronounced in the 2002 trial, when overall GWSS infestations were much reduced from the previous year. However, consistently lower adult infestations were still observed in 2002 for both treatments compared with untreated trees. Information on the spatial and temporal profiles in citrus trees was obtained for both compounds to complement field impact data and improve understanding of their pest management potential.     

Fungal isolation and identification in 21 cases of guttural pouch mycosis in horses (1998-2002)

This aetiological study of guttural pouch mycosis (GPM) in the horse was based on the retrospective study of 21 horses brought into the National Veterinary School of Lyon (France) between 1998 and 2002. Biopsies were taken from the lesions caused by GPM during endoscopic examination. In 87% of the cases, direct examination gave positive results, whereas 43% of the cultures were found to be negative. The main fungi observed were Aspergillus fumigatus (in three cases), A. versicolor (in two cases, together with other fungi), and A. nidulans and A. niger (one case each). In six cases, the Aspergillus species could not be identified. In two cases, cleistothecia and/or Hulle cells were observed. In three cases, fungi other than Aspergillus were seen, mixed or not with Aspergillus. These results underline the importance of Aspergillus fumigatus in the development of GPM in horses.     

Note: Proline — An inducer of resistance against pearl millet downy mildew disease caused by<Emphasis Type="Italic">Sclerospora graminicola</Emphasis>

In an attempt to find a suitable alternative to the otherwise perilous chemical control strategy of disease management, the amino acid proline was evaluated for its efficiency to elicit resistance in pearl millet (Pennisetum glaucum (L.) R. Br.) against downy mildew disease caused bySclerospora graminicola (Sacc.) Schroet both under greenhouse and field conditions. Proline treatment to seeds at 50 mM concentration for 3 h, significantly enhanced the seed germination and seedling vigor of pearl millet in comparison with the control. The same concentration and duration of seed treatment protected the pearl millet plants from downy mildew by offering 58% protection under greenhouse and 67% protection under field conditions. Studies revealed that 3 days were required for proline-treated plants to develop resistance, which was systemic and was sustained throughout the life of the plants. Apart from disease protection, proline was also found effective in enhancing vegetative and reproductive growth of the plants, as evidenced by the increase in height, fresh weight, leaf area, tillering capacity, 1000-seed weight and grain yield in comparison with the control plants. http://www.phytoparasitica.org posting Oct. 3, 2004.     

水杨酸诱导番茄对灰霉病的抗性研究

[目的]探讨水杨酸(SA)对番茄抗灰霉病的诱导作用。[方法]以SA作为诱抗剂处理番茄幼苗,研究了SA对番茄灰霉病病原菌菌丝生长和分生孢子萌发的影响,并测定了其诱导抗性产生过程中番茄植株体内过氧化氢酶(CAT)、过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)4种防御酶活性及丙二醛(MDA)含量的变化。[结果]SA在其浓度范围内对番茄灰霉病病原菌的孢子萌发和菌丝生长无抑制作用,而相对诱导效果在处理后也有不同程度的提高,其中用150 mg/L SA处理番茄植株后间隔3 d挑战接种灰霉病病原菌产生的诱导效果最好,且抗性持续期在10～15 d。经SA处理后,CAT、POD、PPO、PAL在番茄灰霉病系统诱导抗性中均呈先上升后下降的趋势,且明显高于对照,同时MDA含量以波浪线形式呈上升趋势。[结论]SA在一定浓度范围内使用是安全的;CAT、POD、PPO、PAL活性与番茄对灰霉病的诱导抗性呈正相关,MDA含量的增加与抗病性的提高也密切相关。     

过量表达OsNPR1基因稳定提高水稻对白叶枯病的抗性

在拟南芥中,NPR1是系统获得抗性SA信号传导途径中的一个重要的调节因子,在水稻中已克隆到与之同源的OsNPR1基因。构建OsNPR1基因水稻过量表达载体,并将其转化粳稻TP309得到转基因植株;通过自交纯合,得到17个纯合株系;对T3、T4代纯合株系进行PCR鉴定,证实转基因纯合株系中外源伪OsNPR1基因具有遗传稳定性;检测了T1、T2代转基因株系和T3代转基因纯合株系对水稻白叶枯病病原细菌Xanthomonas oryzae pv．oryzae的抗病性,结果表明,在T1、T2代中70％以上的株系对水稻白叶枯病的抗性显著提高,T3代中约67％的株系对水稻白叶枯病的抗性显著提高,说明这种抗病性的提高具有遗传稳定性。OsNPR1基因可作为选育水稻抗白叶枯病新种质的一个良好的候选基因。     

FCV-VBS isolated from cats with typical symptoms caused VSD in experimental cats

Commercially available vaccines have been used widely to prevent feline calicivirus infection (FCI). However, with their widespread use, field strains, which are weakly cross-reactive with the live-virus vaccine strain F9, have posed the problem of vaccine breakdown. Recently the existence of FCV—associated virulent systemic disease (VSD) has been published. But their molecular diversity, antigenic mutations and physicochemical property have not been sufficiently clarified. Thus, we experimentally gave the vaccine breakdown strain (VBS) H10 to cats that had been inoculated with an F9 live vaccine. After the administration of strain H10, vaccinated cats (1 through 4) had no respiratory symptoms, whereas the non-vaccinated cat 5 showed clinical symptoms such as a fever of over 40°C, loss of vitality, decreased appetite, diarrhea, and nasal discharge after receiving strain H10, and died. Lethal FCV is rare, and may be a virulent systemic disease (VSD)—inducing strain. This is the initial report on VSD in Japan. It has been reported that symptoms of VSD were similar in vaccinated and nonvaccinated cats on experimental infection. However, no VSD-like symptoms developed, and the incidence of the disease varied depending on the presence or absence of vaccination, suggesting that there are two mechanisms of vaccine breakdown: one is associated with the vaccine immunity level, and the other is not. The characteristics of the VBS revealed were: (1) the duration of virus excretion was short when the originally carried antibody titer before virus challenge was high, (2) the excreted viral molecular species varied daily, not being limited to a specific species with time, and (3) the acquired physicochemical properties did not persist, and altered daily. FCV-VBS alters the molecular species and physicochemical properties daily due to the reduction of host immunity, which may lead to VSD.     

Evidence of Migration and Endophytic Presence of Agrobacterium tumefaciens in Rose Plants

Agrobacterium tumefaciens was isolated from stem tumors of several rose cultivars showing that the bacterium is the causal agent of aerial galls in rose plants. No differences were observed in the characteristics of the Agrobacterium isolates from crown or aerial galls. Stem inoculation of ten rose cultivars showed that all of them were susceptible to A. tumefaciens but differences in the size of the resulting tumors were observed. The movement of A. tumefaciens in rose plants was demonstrated using two wild type strains and two antibiotic resistant mutants. Three months after inoculation, the inoculated strains were recovered in the roots, crown and below and above the inoculation site but low numbers of pathogenic Agrobacterium cells were isolated. New tumors appeared in 5% of the noninoculated wounds. A. tumefaciens was isolated from the stem at different distances from the tumor in naturally infected plants. In symptomless commercial plants, the isolation from the roots, crown and at different stem levels demonstrated the existence of systemic and latent infections in rose. Direct isolation using a nonselective and selective media with or without a previous enrichment step were efficient methods for isolating tumorigenic Agrobacterium from the different parts of rose plants.     

磷酸盐诱导黄瓜系统抗病中主要酶活性的变化

黄瓜幼苗第２叶喷施７５ｍｍｏｌ／ＬＫ２ＨＰＯ４溶液之后,叶片中几丁质酶、β－１,３－葡聚糖酶和过氧化物酶活性明显升高,并诱导第３,４,５叶片中几丁质酶、β－１,３－葡聚糖酶活性增强,从而抵制以后炭疽菌（Ｃｏｌｅｔｏｔｒｉｃｈｕｍｌａｇｅｎａｒｉｕｍ）的侵入。但过氧化物酶活性仅在叶片受到直接诱导时才增强。上述结果表明,几丁质酶、β－１,３－葡聚糖酶活性与诱导系统抗病直接相关,而过氧化物酶活性仅与局部诱发抗病有关。喷施７５ｍｍｏｌ／ＬＫ２ＨＰＯ４溶液能安全、有效地诱导黄瓜抵抗炭疽病。