Weed Control of Four Higher Plant Species in Paddy Rice Fields in Southeast Asia

Four higher plants, namely glory bowers (Clerodendrum trichotomum L.), jimsonweed (Datura stramonium L.), beggarweed (Desmodium triflorum L.) and Chinaberry (Melia azedarach L.), with the strong allelopathic potential among 19 allelopathic species from Southeast Asia, were tested for their effects on weed emergence in paddy soil and field. In a greenhouse experiment, D. stramonium, D. triflorumand M. azedarach exhibited similar inhibitory magnitude at 1 t ha^?1 achieving more than 90 % weed control. C. trichotomum achieved about 70 % weed reduction at 2 t ha^?1. In paddy fields, D. triflorum was the most promising material for weed control and attained the highest rice yield among treatments, at the concentration of 2 t ha^?1, whereas the inhibition of D. stramonium and M. azedarach was weakened in the greenhouse. No injury of rice plants was observed. These plants might be used as natural herbicides to reduce the dependence on synthetic herbicides.     

Tree phenology and water availability in semi-arid agroforestry systems

Four common agroforestry trees, including both exotic and native species, were used to provide a range of leafing phenologies to test the hypothesis that temporal complementarity between trees and crops reduces competition for water in agroforestry systems during the cropping period and improves utilisation of annual rainfall. Species examined included Melia volkensii, which sheds its leaves twice a year, Senna spectabilis and Gliricidia sepium, which shed their leaves once during the long dry season, and the evergreen Croton megalocarpus. Phenological patterns were examined in relation to climatic conditions in the bimodal rainfall regions of Kenya to identify factors which dictate the intensity of competition between trees and crops.

The main differences in leaf cover patterns were between indigenous and exotic tree species. The Central American species, S. spectabilis and G. sepium, shed their foliage during the dry season before the short rains, whereas the native species, M. volkensii and C. megalocarpus, exhibited reduced leaf cover during both dry seasons. C. megalocarpus was the only species to maintain leaf cover throughout the 2-year experimental period. M. volkensii and S. spectabilis exhibited similar leafing phenology, losing almost all leaf cover during the long dry season (July–October) and flushing before the onset of the ensuing rains. S. spectabilis lost few leaves during the short dry season, whereas M. volkensii shed a greater proportion of its foliage before flushing prior to the long rains (March–July). M. volkensii lost much of its leaf cover during the 1997/1998 short rains (October–February), when soil water content was unusually high. Although essentially evergreen, leaf cover in C. megalocarpus decreased during the dry season and increased rapidly during periods of high rainfall. G. sepium exhibited a period of low leaf cover during the long dry season and did not regain full leaf cover until mid-way through the short rains. The mechanisms responsible for these phenological changes and the implications of tree phenology for resource utilisation and competition with crops are discussed.     

为害楝树的一叶蝉新种

本文记述为害楝树的一叶蝉新种—揀白小叶蝉(Elbelus melianusKuoh),此种属叶蝉总科小叶蝉科,发生于中国中南部,为害相当严重。     

植物性杀虫剂川楝素的开发研究

在研究、开发和使用新型植物性杀虫剂的过程中,以菜青虫为主,对苦楝、川楝树皮中的呋喃三萜类物质——川楝素,从药效、致毒机理、使用技术以及剂型加工工艺等方面做了10多年的研究。这种植物性杀虫物质可破坏菜青虫的中肠组织,并引起一系列生理病变。用楝树皮提取物为主要成份加工配制成0.5％楝素杀虫乳油,取名“蔬果净”,已正式投入生产。该剂安全、高效,使用后无毒害残留,尤适于经济作物上防治有害昆虫,是配合“无污染”蔬菜、果品、茶叶、烟草、中草药等作物生产的良好药剂。     

楝树嫁接育苗试验及影响因素分析

对楝树进行的不同嫁接方法、不同嫁接时间和对接穗采集时间及其处理不同的多水平试验结果表明,采用冬前采集经沙藏的接穗,在芽萌动膨大期运用芽接法嫁接育苗方法可行,培育出的苗木成活率高,可以在楝树无性苗木繁殖中推广应用。统计分析表明：接穗采集时间及处理因素在0．05检验水平上差异显著。     

阔叶材热板干燥技术初探

本文论述苦楝中板(25mm)热板干燥的试验研究。结果表明,采用热板干燥法可大大缩短阔叶材的干燥时间;若采用合理的锯剖法,蜂窝裂缺陷显著减少;热压板的压力和温度对板材的厚度收缩有显著的影响。从整体考虑,热板干燥较佳工艺为干燥温度160℃,压力700kPa。热板干燥法适合于一些小型工艺木制品厂。     

NaCl胁迫对苦楝细胞膜透性和有机渗透调节物质含量的影响

以一年生苦楝实生苗为试验材料,测定了其在不同浓度和时间盐分胁迫下的反应。结果表明,苦楝对2‰的低盐胁迫具有一定的抗性。但是在6‰高盐胁迫下,其膜透性增加,增加幅度与胁迫时间呈正相关。对有机渗调物质含量的分析表明,盐胁迫下苦楝叶片中脯氨酸含量显著上升,可溶性蛋白、可溶性糖变化趋势不明显,说明脯氨酸是苦楝在盐分胁迫下的重要有机渗透调节物质。相关性分析表明,脯氨酸与MDA呈负相关,说明脯氨酸的累积对减弱盐分胁迫下的膜质过氧化作用具有重要意义。     

中国不同地区楝属植物中川楝素含量测定

应用高速液相色谱(HPLC)对我国楝属(Melia)植物主要分布区的川楝、苦楝的树皮、果实及叶片中川楝素含量进行了测定。结果表明,采自不同地区川棘、苦楝样本中川楝素的含量差别较大。树皮中的含量以贵州(沿河),陕西(西乡)采的苦楝及河南(扶沟)采的川楝较高,分别为5.160、4.697和4.223mg/g。果实中川楝素的含量都较低,苦楝果中仅含微量或测不出。杭州采的川楝果中川楝素含量却显著高于其它楝果样本,而且比其树皮的含量还高(分别为0.800和0.574mg/g)。所采的楝叶中在该测定条件下测不到川楝素存在。楝科中其它9种非楝属植物树皮中不含有川楝素。从整个测定结果可以看出,川楝素只存在于楝属植物树皮中,果中也有少量分布,川楝中川楝素的含量不一定高于苦楝。各样本中川楝素含量的差异是否与其分布区的地理环境、气候及土壤等因素有关,有必要作进一步研究。     

苦楝内生真菌及其代谢产物的杀虫活性

在对290株苦楝内生真菌分离纯化鉴定的基础上,研究了30株具有代表性的内生真菌及其代谢产物的杀虫活性。结果表明其中5个菌株对马尾松毛虫5d校正死亡率大于60%,杀虫活性最强的KL042菌株经鉴定为球孢白僵菌。球孢白僵菌作为内生真菌,在国内尚未见报道。进一步选取杀虫活性较强的9株内生真菌,研究其代谢产物的胃毒和触杀活性,结果表明拟青霉KL017菌株发酵液10倍浓缩液对柳蓝叶甲胃毒活性最强,48h校正死亡率达90.09%。球孢白僵菌KL042、拟青霉KL017和交链孢KL062发酵液10倍浓缩液点滴马尾松毛虫前胸背板后,48h校正死亡率分别为76.67%、56.67%和53.33%。     

Evaluation of the effectiveness of soil-applied plant derivatives of Meliaceae species on nitrogen availability to peach trees

We assessed the effect of soil-applied derivatives of melia (Melia azedarach L.) and neem (Azadirachta indica A. Juss) on nitrogen (N) soil availability, root uptake and peach (Prunus persica L.) growth. First we evaluated the effectiveness of experimentally prepared amendments made with fresh ground melia leaves or commercial neem cake incorporated into the soil as nitrification inhibitors, then we evaluated the effect of fresh ground melia fruits and neem cake on growth and N root uptake of potted peach trees, and on soil microbial respiration. Soil-applied fresh ground melia leaves at 10 and 20 g kg⁻¹ of soil as well as commercial neem cake (10 g kg⁻¹) were ineffective in decreasing the level of mineral N after soil application of urea-N as a source of mineral N, rather they increased soil concentration of nitric N and ammonium N. The incorporation into the soil of fresh ground melia fruits (at 20 and 40 g kg⁻¹) and neem cake (at 10 and 20 g kg⁻¹) increased N concentration in leaves of GF677 peach × almond (Prunus amygdalus) hybrid rootstock alone or grafted with one-year-old variety Rome Star peach trees. An increase in microbial respiration, leaf green color and plant biomass compared to the control trees were also observed. The Meliaceae derivatives did not affect, in the short term (7 days), N root uptake efficiency, as demonstrated by the use of stable isotope ¹⁵N, rather they promoted in the long term an increase of soil N availability, N leaf concentration and plant growth.