Low pesticide rates may hasten the evolution of resistance by increasing mutation frequencies

At very low pesticide rates, a certain low proportion of pests may receive a sublethal dose, are highly stressed by the pesticide and yet survive. Stress is a general enhancer of mutation rates. Thus, the survivors are likely to have more than normal mutations, which might include mutations leading to pesticide resistance, both for multifactorial (polygenic, gene amplification, sequential allelic mutations) and for major gene resistance. Management strategies should consider how to eliminate the subpopulation of pests with the high mutation rates, but the best strategy is probably to avoid too low application rates of pesticides from the outset.     

Induction of Systemic Resistance in Cucumber against Several Diseases by Plant Growth-promoting Fungi: lignification and Superoxide Generation

Five fungal isolates (Trichoderma, Fusarium, Penicillium, Phoma and a sterile fungus) from zoysiagrass rhizosphere that promote plant growth were tested for their ability to induce systemic resistance in cucumber plants against Colletotrichum orbiculare. Roots of cucumber plants were treated with these fungal isolates using barley grain inocula (BGI), mycelial inocula (MI) or culture filtrate (CF). Most isolate/inoculum form combinations significantly reduced the disease except BGI of Trichoderma. These fungal isolates were also evaluated for induction of systemic resistance against bacterial angular leaf spot and Fusarium wilt by treatment with BGI. Penicillium, Phoma and the sterile fungus significantly reduced the disease incidence of bacterial angular leaf spot. Phoma and sterile fungus protected plants significantly against Fusarium wilt. Roots treated with CFs of these fungal isolates induced lignification at Colletotrichum penetration points indicating the presence of an elicitor in the CFs. The elicitor activity of CFs was evaluated by the chemiluminescence assay using tobacco callus and cucumber fruit disks. The CFs of all isolates elicited conspicuous superoxide generation. The chemiluminescence activity of the CF of Penicillium was extremely high, and its intensity was almost 100-fold higher than that of other isolates. The chemiluminescence activity was not lost following treatment with protease or autoclaving or after removal of lipid. The MW 12,000 dialyzed CF fraction was highly effective in eliciting chemiluminescence activity. Chemiluminescence emission from cucumber fruit disks treated with Penicillium was the same as that obtained from tobacco callus, except that the lipid fraction also showed a high activity. Both the MW 12,000 fraction and the lipid fraction induced lignification in the epidermal tissues of cucumber hypocotyls.     

利用诱导因子抗新疆甜瓜疫霉病的田间效果

用化学诱导因子和灭活的生物诱导因子在田间自然条件下诱导了新疆甜瓜产生对疫霉病的整体抗性。1996年的试验结果表明，用化学诱导因子诱导处理，最高诱抗效果可达79．40％，平均诱抗效果在40％以上；生物诱导因子诱导处理，最高诱抗效果为68．2％，平均诱抗效果为30％以上。1997年的试验基本上验证了1996年的结果，化学诱导因子最高诱抗效果可达60％，平均诱抗效果为35．86％，经t测验分析，诱抗效果显著。     

草酸诱导紫花苜蓿对霜霉病的抗性

为确定外源草酸(OA)对紫花苜蓿(Medicago sativa)抗霜霉病(Peronospora aestivalis)的诱导作用,本研究采用喷雾法将10、20、30、40 mmol·L-1的草酸喷洒在十叶期紫花苜蓿幼苗上,喷雾后7 d测定苜蓿霜霉病苗期病情指数,并分别于喷雾后1、3、5、7和9 d测定叶片过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)和超氧化物歧化酶(SOD)的活性。结果表明,喷雾10~40 mmol·L-1草酸溶液均可降低苜蓿霜霉病的病情指数,且随着草酸浓度升高,病情指数由31.1%下降到19.6%,下降了11.5百分点,相对诱导抗病效果呈上升趋势,最高诱抗效果达到50.8%,苜蓿叶片中POD、PAL和SOD的活性增强。     

氧化塘深度对猪场厌氧消化液后处理的影响

采用小试装置对3个不同深度氧化塘处理猪场厌氧消化液的效果进行了研究,结果表明:当平均气温为21.9℃,停留时间在80 ～110天,进水负荷为0.05 m3·m-2d-1的条件下,氧化塘对NH4-N的去除率达到了90％以上,CODcr,TP的去除率分别为50％,40％.硝化作用和藻类的吸收是氧化塘去除NH4-N的主要方式,沉淀作用则是CODcr和TP的主要去除方式,在较长停留时间下,微生物对于溶解性CODcr的分解和同化也能提供一定的去除效果.当平均气温为21.9℃,在表面负荷为0.05 m3·m-2d-1的条件下,有效深度为0.3m和0.7m的氧化塘面积去除负荷分别为1.41 g·m-2d-1,1.49 g·m-2d-1,容积去除负荷分别为4.7g·m -3d-1,2.8g·m-3d-1.虽然较深氧化塘具有较高的面积去除负荷,但较浅的氧化塘却有更高的容积去除负荷.     

不同处理及pH变化对果胶酶诱导抗病性的影响

从不同处理方法、酶液pH变化等方面对果胶酶诱导黄瓜抗黑星病效能的影响进行了研究。结果表明，在果胶酶的4种不同处理试验中，以全株表面喷雾法处理的黄瓜黄化子叶黑星病的病情指数降低最多，浓度100和200U／ml的诱导防病效果分别为56．34％和64．13％；下胚轴注射、灌根和漫种等3种处理方法的诱导抗病效果均不显著。经果胶酶诱导处理的黄瓜绿苗叶片病情明显降低，而处理叶上部的未处理叶片发病情况与相应对照差别不大。该结果表明，果胶酶诱导黄瓜绿苗抗黑星病的作用属于局部诱导。果胶酶处理次数的增加可增强其诱导抗病效果，并延长诱导抗病时间。酶液pH变化对果胶酶的诱导抗病作用影响显著，pH5．5时，2个浓度的诱导效果最好，分别为51．87％和66．42％。     

具有农业生物活性壳寡糖的研究进展

壳寡糖是一类由N-乙酰氨基葡萄糖或氨基葡萄糖通过β-(1,4)-糖苷键连接起来的低聚合度水溶性的糖类,在食品、医药、化妆品等方面具有广泛用途。主要评述了壳寡糖在植物生长调节(诱导抗性)、杀菌作用以及杀虫活性方面的应用,表明壳寡糖是一种对环境友好的、良好的生物源农药。     

The effect of salt stress on Arabidopsis thaliana and Phelipanche ramosa interaction

Salinity and Orobanche or Phelipanche spp. infection are important crop stress factors in agricultural areas. In this study, we investigated the effect of salt stress on Phelipanche ramosa seed germination and its attachment onto Arabidopsis thaliana roots. We also evaluated the effect of both stresses on the expression of genes regulated by abiotic and biotic stresses. According to our results, high concentration of NaCl delayed P. ramosa seed germination in the presence of a strigolactone analogue (GR24). A similar pattern was observed in the presence of A. thaliana plants. Furthermore, we found that salt‐treated A. thaliana seedlings were more sensitive to P. ramosa attachment compared with the untreated plants, indicating that there was a positive correlation between salt sensitivity and the ability of P. ramosa to infect A. thaliana plants. At the molecular level, a synergystic effect of both salt and P. ramosa stresses was observed on the cold‐regulated (COR) gene expression profile of treated A. thaliana seedlings. Our data clarify the interaction between parasitic plants and their hosts under abiotic stress conditions.     

褪黑素诱导小豆抗锈病机理的初步研究

为明确外源褪黑素诱导小豆抗锈性的作用及机理,以感病小豆品种‘宝清红’为材料,采用叶面喷施不同浓度褪黑素激发处理小豆真叶,而后对真叶挑战接种锈菌夏孢子,结果表明,低浓度(11.61 mg/L)褪黑素可显著提升小豆对锈病的抗性。夏孢子萌发试验表明,褪黑素对夏孢子萌发及芽管生长无显著抑制作用,表明褪黑素无抑菌活性。进一步的基因表达分析发现,与对照相比,褪黑素激发诱导了水杨酸(SA)通路关键基因NPR1于接种后24 h显著上调表达,且病程相关蛋白PR1、几丁质酶(CHI)、β-1,3-葡聚糖酶(GLU)及PR5均于接种后24～120 h被显著诱导表达,说明褪黑素可能通过诱导NPR1表达,进而激活下游PR蛋白的高水平应答,使感锈病小豆品种获得对锈病的抗性。     

木霉对植物的促生及诱导抗性研究进展

木霉不仅能够直接抑制植物病原菌的生长,还可通过定殖于植物的根部引起植物新陈代谢的改变。本文综述了木霉在植物根部定殖后,通过产生植物生长调节剂、抑制或降解根际有害物质、增加养分利用率以促进植物生长以及通过产生激发子诱导植物形成胞壁沉积物、合成抗菌物质以诱导植物局部或系统抗性的研究进展,以期为进一步扩大木霉在农业生产中的应用提供参考。