Effects of isothiocyanates on purple (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.)

Purple and yellow nutsedge are two of the most troublesome weeds in the world. In the south-eastern USA, both weeds are common in vegetable crops and are the most difficult weeds to control in this region. A greenhouse experiment was conducted to evaluate the herbicidal activity of five liquid isothiocyanates (ITCs) (benzoyl, o -tolyl, m -tolyl, tert -octyl, and 3-fluorophenyl) on purple and yellow nutsedge. All ITCs were applied to soil in jars at 0, 100, 1000, 5000, and 10 000 nmol g⁻¹ of soil and sealed for 72 h to prevent gaseous losses, followed by nutsedge growth evaluations after an additional 18 days. All ITCs reduced purple and yellow nutsedge shoot density and shoot biomass over the concentrations evaluated, with differences in the effectiveness on each species apparent among the compounds. Based on the lethal concentration values for shoot density, all ITCs were more effective in suppressing purple nutsedge than yellow nutsedge. Benzoyl and 3-fluorophenyl were generally the most effective of the five ITCs evaluated.     

Movement of aphid-transmitted Sugarcane yellow leaf virus (ScYLV) within and between sugarcane plants

Sugarcane yellow leaf virus (ScYLV) is distributed worldwide and has been shown to be the cause of the disease sugarcane yellow leaf syndrome (YLS). This study was an investigation of the transmission and spread of ScYLV in Hawaii. Several aphids are known to transmit the virus, but investigation of infestation and transmission efficiency showed Melanaphis sacchari to be the only vector important for field spread of the disease. The initial multiplication of ScYLV in a virus-free plant occurred exclusively in very young sink tissues. When a single leaf was inoculated on a plant, that leaf and all older leaves remained virus-free, based on tissue-blot immunoassay, whereas meristems and all subsequently formed new leaves became infected. Therefore, only after those leaves which had already developed before inoculation had been shed, did the complete plant contain ScYLV. Spread of the viral infection to neighbouring plants in the plantation fields via aphids was relatively slow and in the range of a few metres per year. No indication of long-distance transfer could be seen. This indicates that it may be possible to produce and use virus-free seed cane for planting of high-yielding but YLS-susceptible cultivars.     

Competition between vegetative plants of wild oat (Avena fatua L.) and wheat (Triticum aestivum L.)

Competition between wild oat (Avena fatua L.) and wheat (Triticum aestivum L.) was studied in two experiments; a replacement series model and a technique for separation of root and shoot systems. Wild oat and wheat in association resulted in a relative yield total very close to unity showing that the two species were‘crowding for the same space’(or competing for the same resources) and were‘mutually exclusive'. Wild oat was more competitive than wheat, as shown by its aggressivity relative to wheat, relative yields, shoot dry weights and other plant attributes. The greater competitive ability of wild oat was predominantly due to its greater root competitive ability, while the two species had similar shoot competitive ability. Root competition had a much greater effect on the relative performance of the two species than did shoot competition. The effects of root and shoot competition were additive.     

黄粉虫实用人工饲料配方研究

采用均匀设计及其分析方法对黄粉虫人工饲料配方进行材料成本分析,在参试因子及水平因子较多的情况下,获得较为理想的结果。并得到材料成本最低的人工饲料各组分的最佳组合为:麦麸:113.03g;葡萄糖:26.72g;蔗糖:36.00g;胆固醇:0g;藻粉:14.93g。     

Transmission of a mycoplasma-like organism from cocos nucifera with root (wilt) disease to Catharanthus roseus by Cassytha filiformis

A mycoplasma-like organism (MLO) was successfully transmitted through dodder laurel (Cassytha filiformis) from root (wilt) diseased coconut to periwinkle (Catharanthus roseus) plants. Symptoms caused by the organism in periwinkle were chlorotic spots in the interveinal areas and at vein endings of fully opened leaves, later coalescing into yellow patches, and premature leaf abscission. Light and electron-microscopic examination revealed the presence of MLOs in diseased coconut palms, dodder laurels and periwinkles.Samenvatting Door de als warkruid groeiende lauraceeCassytha filiformis werd van kokosnootpalm (Cocos nucifera), aangetast door root(wilt), een mycoplasma-achtig organisme (MLO) overgebracht naar de toetsplantCatharanthus roseus. Hierop werden op de bladeren tussennervige, later ineenvloeiende vlekken en vroegtijdige bladval waargenomen. Uit onderzoek met de lichtmicroscoop en de elektronenmicroscoop kon de aanwezigheid van MLO's inCocos nucifera, Cassytha filiformis enCatharanthus roseus worden vastgesteld.CPCRI contribution No 622     

A note on the biological control of Scurrula cordifolia (Wall.) G. Don by another mistletoe in Sivalik Hills (India)

Observations made on the hyperparasitism of Viscum loranthi Elmer on the parasitic weed Scurrula cordifolia (Wall.) G. Don in the Sivalik Hills suggest that the hyperparasite is providing effective biological control of the latter. Moreover, as the hyperparasite appears to attack only mistletoes, it can probably be introduced with safety into other localities where S. cordifolia is spreading.     

Elimination of Sugarcane yellow leaf virus from infected sugarcane plants by meristem tip culture visualized by tissue blot immunoassay

Sugarcane yellow leaf virus (SCYLV), a member of the Luteoviridae , is implicated in the sugarcane disease known as yellow leaf syndrome (YLS), which is characterized by yellowing of the leaf midrib followed by leaf necrosis and possible growth suppression. YLS is distributed worldwide and susceptible cultivars are commonly infected with SCYLV. However, not all cultivars infected with SCYLV show symptoms of YLS and some cultivars that show symptoms do so sporadically. Since it is difficult to obtain virus-free plants of susceptible cultivars, it has not been possible to study the factors involved in SCYLV infection nor the effects of infection on plant growth and yield. A tissue blot immunoassay was used to visualize in vivo presence of the virus so that virus-infected and virus-free plants could be distinguished. Meristem tip cultures were used to produce virus-free plantings of six SCYLV-susceptible sugarcane cultivars. Nearly all of the regenerated sugarcane lines remained virus-free over a period of up to 4 years, whether grown in isolated fields or in the glasshouse. Experimental re-infection of the virus-free plants by viruliferous aphids demonstrated that meristem tip culture did not affect susceptibility of sugarcane to SCYLV. Improved diagnosis and production of virus-free plants of SCYLV-susceptible cultivars will facilitate research to quantify the effect of the virus on yield and to analyse the processes involved in disease development.     

Diversity among agrobacteria isolated from diseased plants of blueberry (Vaccinium corymbosum) in Argentina

The aim of this study was to isolate, identify and analyze the diversity of the causative agents of crown galls and hairy roots from symptomatic plants of Vaccinium corymbossum by means of biological, biochemical and molecular tools. All the bacteria isolated from blueberries (n?=?78) were found to be Agrobacterium since they grew on three differential media, provoked cell and/or root proliferation on Kalanchoe, and contained a 730?bp partial sequence that codes for virulence genes within the virC operon found on Ti and/or Ri plasmids. Isolates were highly variable considering the ERIC-PCR patterns as well as biochemical reactions and were all represented by 7 different restriction patterns of the 16SrDNA. While most of the isolates belonged to Agrobacterium bv. 1 (n?=?33) or Agrobacterium bv. 2 (n?=?31) only fourteen were Agrobacterium rubi. A representative isolate of each of these three groups was further identified by sequencing the approximately 400?bp 16SrDNA. We concluded that Vaccinium plants are particularly susceptible to Agrobacterium bv. 1, Agrobacterium bv. 2, and also to Agrobacterium rubi. To our knowledge this is the first survey of Agrobacterium affecting blueberries in Argentina.     

Cirsium arvense (L.) Scop. competition with winter wheat (Triticum aestivum L.)

A series of field experiments was conducted to evaluate the competitive effect of Cirsium arvense (L.) Scop. on winter wheat (Triticum aestivum L. ‘Norstar’) yield. Grain yield at the centre of dense C. arvense patches ranged from 28–71% of the yield in adjacent weed-free plots, based on measurements made at 11 experimental sites over a 2-year period. The mean reduction in yield was 49%. Two models were used to describe grain yield reduction in terms of C. arvense shoot density: (a) linear regression of percentage yield reduction on the square root of shoot density, and (b) non-linear regression, based on a rectangular hyperbola. Both models give similar yield loss estimates at commonly occurring shoot densities of C. arvense, but the non-linear model accounted for more of the observed variation in grain yield. The major yield component affected by C. arvense competition was spikes per unit area, with kernel weight affected to a lesser extent.     

绿薄荷茎和叶的乙醇提取物对小菜蛾拒食和产卵忌避活性的影响

为有效控制小菜蛾的危害,明确绿薄荷对小菜蛾的防治效果,采用95%乙醇对绿薄荷茎和叶进行索式抽提,并测定了茎和叶提取物12.5、25.0和50.0 mg/mL浓度下小菜蛾幼虫的拒食率和成虫产卵忌避活性。结果显示,绿薄荷茎和叶的乙醇提取物对小菜蛾幼虫的拒食和成虫的产卵忌避均有显著作用,提取物浓度越高,拒食率和产卵忌避率越大。当茎和叶提取物浓度为12.5 mg/mL时,小菜蛾的拒食率最低,分别为36.16%和59.81%,产卵忌避率最低,分别为46.18%和57.78%;茎和叶提取物浓度为50.0 mg/mL时,拒食率最高,分别为82.67%和87.15%,产卵忌避率最高,分别为88.29%和98.27%。茎和叶对应的拒食中浓度(AFC_(50))最高分别为18.93 mg/mL和15.97 mg/mL,产卵忌避中浓度(AOC_(50))最高分别为16.38 mg/mL和15.03 mg/mL。     

Influence of leaf hairiness on the resistance of bhendi or lady's finger,Abelmoschus esculentus (L.) Moench,to the leaf hopper,Amrasca devastans (Dist.)

Abstract

The resistance of Abelmoschus esculentus (L.) Moench to the leafhopper, Amrasca devastans (Dist.), was studied with reference to the hairiness of leaves. Resistant varieties had more and longer hairs on the midrib and lamina than the susceptible varieties. The number and length of hairs rather than the density influences plant resistance.     

Characterization of a strain of clover yellow vein potyvirus infecting borage (Borago officinalis L.) in Spain

A disease of borage ( Borago officinalis ) in Spain, characterized by severe mosaic and deformation of the leaves, was shown to be caused by a potyvirus. The borage-infecting potyvirus was characterized biologically by the symptoms induced in 23 indicator species and was shown to be transmitted experimentally by the aphid Myzus persicae in a non-persistent manner. In order to classify the borage-infecting potyvirus we have cloned and sequenced the entire coat protein gene and 3' non-coding region of the viral RNA. By comparing this nucleotide sequence with those of other members of the Potyviridae , we can identify the Spanish borage-infecting potyvirus as an isolate of clover yellow vein virus (CYVV), a virus so far only known to cause important diseases in forage legumes. This is the first record of CYVV in Spain and of CYVV infecting a natural host of the Boraginaceae.     

Impact of sugarcane yellow leaf virus (ScYLV) on the carbohydrate status of sugarcane: Comparison of virus-free plants with symptomatic and asymptomatic virus-infected plants

The carbohydrate concentration of old and young sugarcane plants, either virus-free or infected by sugarcane yellow leaf virus, was compared. Internode lengths and fresh weights of symptomatic plants were reduced, but not the sucrose concentrations. Starch and sucrose concentration in green leaf tops of mature (18 months old) was the highest in asymptomatic plants followed by symptomatic, and then by virus-free plants. Carbohydrates increased during daytime by 5–20%. The carbohydrate concentration in leaves of young, 6 months old plants was much lower than in mature plants and it increased to 500% during daytime. Asymptomatic leaves had a higher level of carbohydrates, especially starch, from late afternoon until the end of the night, suggesting a reduction of assimilate export.     

Management of Cercospora leaf spot of groundnut (Arachis hypogaea L.) with a single fungicidal spray

Field trials were conducted during the rainy seasons of 1993/94 for chemical control of groundnut leaf spot using a single spray. A fungicide mixture ofcarbendazim 0.05%+mancozeb 0.2% was applied once in different treatments. Spray timings varied from 30 d.a.s. to 80 d.a.s. at 10-day intervals. Spray application reduced the percent disease index in all treatments. A statistically significant increase in pod yield was obtained in treatments sprayed up to 50 d.a.s. in 1993. The yield data were not significantly different in 1994. Sprays at 40 d.a.s. in 1993 and 50 d.a.s. in 1994 gave maximum returns. The cost of treatmentdid notvary significantly. The benefitto cost ratio oftreatments ranged from 1.1 to 8.1 in 1993 and 4.1 to 5.5 in 1994.