Biological Control of Black Rot (Xanthomonas Campestris Pv. campestris) of Brassicas with an Antagonistic Strain of Bacillus Subtilis in Zimbabwe

Biological control efficiency of an antagonistic, endophytic strain of Bacillus subtilis (strain BB) was evaluated against three strains of the black rot pathogen, Xanthomonas campestris pv. campestris (Xcc), in four Brassica crops (cabbage, cauliflower, rape and broccoli) grown during three consecutive growing seasons and on two soil types, in two different areas in Zimbabwe. Strain BB controlled the disease caused by strain Xcc B-147 in all Brassica crops during the dry and short rainy seasons. A similar effect was observed in cabbage using the strain Xcc 33908. Biological control was effective in broccoli, but not in cabbage and rape during the main rainy season in clay loam soil and limited biological control effect was still observed when these crops were grown in sandy loam soil. The endophytic colonisation of cabbage roots by strain BB was confirmed by immuno-blotting during the whole growing season. Biological control of black rot with strain BB is discussed in relation to its effect on Xcc strains, Brassica crops and to the effect of weather and soil conditions.     

Effect of plant extracts and an essential oil on the control of brown spot disease, tillering, number of panicles and yield increase in rice

The effects of essential oils (EO), cold water (CWE), hot water (HWE) and ethanol (ETHE) extracts of Callistemon citrinus L. and Cymbopogon citratus (DC) Stapf on the radial growth of Alternaria padwickii (Ganguly) M.B. Ellis and Bipolaris oryzae (Breda de Haan) Shoemaker, the control of brown spot disease, the tillering, the number of panicles and the yield increase in rice were evaluated under laboratory and field conditions. In vitro, the growth of both fungi was completely inhibited by the EO of C. citrinus and C. citratus at 4,520 μg/ml and 452 μg/ml, respectively. For solvent extracts, the ETHE of C. citrinus was the most active and inhibited 80–85 % of the fungal growth followed by the CWE of C. citratus with 77 % and 36 % diameter reduction against B. oryzae and A. padwickii, respectively at 10 000 μg/ml. Under laboratory conditions, seed treatment with the EO of C. citrinus reduced the incidence of B. oryzae in seeds by 85–100 % compared to the non-treated controls. Similarly, the seed treatment increased the germination of an irrigated rice cultivar by 10.6 %, whereas the percentage of germinated seeds of upland rice was not significantly affected. The highest germination (85–94 %) was found in the non-treated and treated samples with a low incidence (0–4 %) of B. oryzae. Under field conditions, the combined use of the essential oil of C. citrinus as a seed treatment and spraying the plants with 2 % ethanol followed by 2 % (w/v) aqueous extracts of C. citrinus or C. citratus increased the emergence, tillering, panicles/plant and the grain yield by 25–55 % of the irrigated rice. In addition, the brown spot severity was reduced by 36–42 %. For the upland rice, the treatments led to similar results with the grain yield increase of 54–137 % and 20–80 % reduction in the brown spot severity. From our results, we concluded that the EO and solvent extracts of C. citrinus and C. citratus have potential as control agents against brown spot and other seed-borne fungal diseases in rice under both conventional and organic farming.     

棉田旋幽夜娥的发生特点与防治技术

旋幽夜蛾[Discestra trifolii(hüfnagel)]属夜蛾科,过去曾称三叶草夜蛾.在我国辽宁、河北、内蒙古、陕西、甘肃、宁夏、青海、新疆、西藏等省、自治区均有分布.该虫在新疆各甜菜产区均有发生,是为害新疆甜菜的重要害虫之一.进入20世纪90年代以后.随着棉花种植面积的迅速扩大,开始进入棉田,但是,为害面积及造成的损失不大.     

电场对白沙蒿和沙蒿瘦果粘液粘附功能的影响

用不同强度的电场处理沙生植物白沙蒿(Artemisiasphaerocephala)和沙蒿(Artemisiaarenaria)果实,在自然环境下研究电场作用后粘液物质将沙粒粘附于瘦果周围后瘦果重量的变化情况、果实水合与脱水情况、粘液果实及剔除粘液层的果实萌发情况。结果表明:适宜的电场使粘液瘦果吸附沙粒多,果实吸水快,脱水慢,粘液果实发芽率高于对照组,而电场对剔除粘液层果实发芽率无影响。     

近45年宁夏极端气温与太平洋海温的遥相关

利用1961-2005年标准化宁夏极端气温、SST和北半球500 hPa环流特征量资料,采用REOF、小波分析、最大熵谱、Mann-Kendall检验等方法,分析了极端气温的时空变化特征及其与SST和同期北半球500 hPa环流特征量的遥相关。结果表明:宁夏极端气温的年代际气候特征表现为一致的上升趋势,异常敏感区在宁夏北部和六盘山区;极端最低气温在1984年前后发生突变,突变后气温转暖,中部半干旱带增温最明显,有显著的2.32年和4.40年周期;极端最高气温的增暖过程经历了2个阶段,其中1976年的增暖趋势最显著,突变后宁夏中北部增温最明显,有显著的3.14年周期;虽然突变后高温日数明显增加,但仍有异常的低温事件发生;当前一年1~6月加利福尼亚西岸海区温度偏高、同期冬季西太平洋副高西升北抬、面积增大、强度增强、亚洲区极涡面积收缩、青藏高原500 hPa位势高度增高时,极端最低气温偏高;当前一年冬季赤道东太平洋海区呈La Nina型分布、同期夏季北半球极涡减弱时,副高加强北抬,极端最高气温偏高。     

绵刺(Potaninia mongolica)繁殖对策与种群更新的生境选择行为研究

以绵刺地表枯落物水浸液和蒸馏水为对比,对绵刺的种子发芽时间、种子发芽率和幼苗生长速度进行实验。实验结果表明:绵刺地表枯落物水浸液对绵刺种子萌发时间、萌发率和幼苗生长速度相对于蒸馏水有明显地抑制作用。10%枯落物水浸液和2%土壤表层水浸液对绵刺种子萌发时间、种子萌发率和幼苗生长速度抑制作用最为显著;说明绵刺枯落物具有化学他感作用,但这种他感作用与目前研究的异株克生作用不同,它在绵刺母株株丛内,排斥自身种子定居,以无性繁殖扩大对株丛内均质性生境的利用,实现种群的更新;在株丛外,以种子占据异质性生境进行种群的更新。因此,绵刺繁殖对策和生境的选择具有行为性,即绵刺植株以无性繁殖方式进行亲本基因的识别,有效地保存基因,而通过他感排斥作用,使种子携带的基因通过种子扩散器的作用,进行长距离的传播,在新的生境中定居,避免了亲代与子代有限资源的争夺,传播基因,这种繁殖策略的采用和生境的选择行为既保存了基因,又提高了种群的适合度。     

低能N+离子注入对紫花苜蓿幼苗生长和营养成分的影响

以紫花苜蓿为材料,研究了其幼苗生长,氨基酸和粗蛋白等营养成分对不同剂量N注入的响应。结果表明,不同剂量的N 离子注入影响着紫花苜蓿的发芽率、根长、百株干重、叶绿素含量和营养成分,剂量在0～2.08×1016/cm2范围内,其发芽率、根长、氨基酸和各种营养成分随剂量的增大而具有正效应;剂量在0～1.04×1016/cm2范围内,其百株干重、粗蛋白含量随剂量的增大而增加;叶绿素含量随剂量的增加而降低,当剂量为6.76×1016/cm2时,有一突变株。     

洋桔梗茎尖组织培养研究

以洋桔梗茎尖为外植体,采用MS作为基本培养基,组配不同种类和浓度的生长素和细胞分裂素,探讨不同激素组合对不定芽、愈伤组织诱导分化和生根的影响。结果表明:适宜的不定芽诱导培养基为MS+GA 0.4 mg/L+BA 0.2 mg/L,每个茎尖产生的不定芽数为3.3个;适宜的继代培养基为MS+BA 0.2 mg/L+NAA 0.05 mg/L,芽的增殖率为5.5;适宜的生根培养基为1/2 MS+IBA 1.0 mg/L,根的诱导率为92%,平均根条数为7.3条;对植株进行驯化移栽,15 d后植株的存活率为92%。     

内蒙古大青山主要植被类型综合生态效益的评价

【目的】对内蒙古大青山主要植被类型综合生态效益进行评价。【方法】应用层次分析法(AHP)建立内蒙古大青山主要植被类型综合生态效益的评价指标体系和评价模型,对3种森林类型(油松林、白桦林、落叶松林)的20个指标进行测定,对各指标进行无纲量化处理后计算各自的权重,然后计算大青山油松林、落叶松林、白桦林3种森林类型的综合生态效益指数。【结果】3种森林类型6种评价指标的生态效益排序中,就生态系统结构与功能而言,白桦林>落叶松林>油松林;就涵养水源而言,落叶松林>白桦林>油松林;就改良小气候、水土保持和改良土壤而言,白桦林>落叶松林>油松林;就固碳放氧而言,落叶松林>油松林>白桦林。【结论】内蒙古大青山3种森林类型综合生态效益大小依次为:白桦林(1.067)>落叶松林(1.036)>油松林(0.742)。