Effect of planting density of maize on the progress and spread of northern leaf blight fromExserohilum turcicum infested residue source

Effect of plant density (37,037, 44,444 and 55,555 plants/ha) on the increase of northern leaf blight in time and space on two maize cultivars planted at spacings of 90, 75 and 60 between rows and 30 cm within rows was investigated.Exserohilum turcicum infested maize residue was used as an inoculum source. Maize density did not significantly affect the disease indices, but significantly influenced the grain yield of the two cultivars. In contrast, the two cultivars differed significantly (P0.01) in disease severity, but not grain yield. Higher disease severities and grain yields were associated with higher plant densities, whereas the apparent infection rate was lower in higher plant density. Distance from the maize residue (inoculum source) significantly influenced disease severity. The percentage leaf area blighted, area under disease progress curve and disease progress curve intercept decreased with distance from the maize residue area, but the apparent infection rate on EV8429-SR appeared to increase with distance. Disease gradients (b) were higher in closely planted maize and flattened with time in one location only.     

Pelargonium flower-break and pelargonium line pattern viruses in the Netherlands; purification,antiserum preparation,serological identification,and detection in pelargonium by ELISA

Two viruses, detected frequently in the Netherlands in pelargonium, were identified by serology and test plant reactions. Antisera were prepared and an ELISA procedure was developed to detect the viruses in pelargonium.One of the viruses, PFBV-N, proved to be pelargonium flower-break virus. With the antiserum to PFBV-N, it could be detected reliably throughout the year inPelargonium zonale Springtime Irene.The other virus, PLPV-N, was serologically closely related to pelargonium line pattern virus (PLPV) and to pelargonium ring pattern virus (PRPV), as were an old virus isolate from Saturnus, collected in the Netherlands in 1971 (L128), and PLPV isolates from Yugoslavia (PLPV-Y) and Denmark (PLPV-D). There were only minor differences in host-plant reactions between the virus isolates. Based on these tests, PLPV and PRPV are considered as isolates of the same virus, for which, for practical reasons, the name pelargonium line pattern virus is proposed.PLPV could be reliably detected by ELISA inP. zonale Springtime Irene and Amanda throughout the year with only a few exceptions. InPelargonium peltatum Tavira, however, reslts were erratic due to uneven distribution of virus in the plant. Best results were obtained when petioles of fully expanded leaves were tested.     

The fate of fluroxypyr in the soil in an oil palm agroecosystem

A study on the fate of fluroxypyr in Malaysian agricultural soils was carried out under natural conditions in an oil palm plantation. Three experimental plots in the oil palm estate were selected and three types of treatments were administered, namely fluroxypyr at the recommended dosage, double the recommended rate, and the untreated control. Residues of fluroxypyr in the soil, water, and oil palm leaf were monitored at regular intervals up to 90 days after treatment (DAT). The recovery of fluroxypyr in the water and soil samples ranged from 91–102% when fortified at 1–25 p.p.b. and 91–98% when fortified at 4–50 p.p.b. The recovery from the oil palm leaf ranged from 76–114% when the oil palm leaf sample was fortified at 0.05–1.0 p.p.m. The results showed that fluroxypyr leached down to 50 cm depth at 1 DAT when the plots were treated with either dosage. However, fluroxypyr was not detected in the soil residue at 14 and 21 DAT. Fluroxypyr was not detected in the oil palm leaf samples irrespective of the rates of herbicide application or sampling intervals. The residue of fluroxypyr was detected in water from a nearby stream up to 5 DAT at levels ranging from 0.06–0.21 µg L⁻¹. This result suggests that fluroxypyr persists for a short period in the soil and water ecosystems, but not in the oil palm leaf.     

猕猴桃实生苗组织培养体系建立的研究

以饱满成熟的猕猴桃种子为起始材料,用 2. 5g·L-1赤霉素处理 5小时,再用次氯酸钠灭菌消毒后,将萌芽的种子接种到MS+蔗糖 20g·L-1 +肌醇 100mg·L-1和 0. 75%琼脂的培养基上,根、茎、叶生长表现良好,初步建立了猕猴桃实生苗组织培养体系。猕猴桃实生苗组织培养同利用茎段、茎尖组织培养一样,培养基中无须附加任何激素。     

红千层的离体培养及快速繁殖

 研究了红千层离体快繁的若干影响因素。结果表明: 叶片在MS + 6-BA 115 mg·L ^{- 1}+NAA015 mg·L ^{- 1}中的愈伤组织诱导率43% , 并可直接从愈伤组织表面分化出不定芽, 分化率为69.2%; 腋芽启动培养基为MS + 6-BA 1～1.5 mg·L ^{- 1} + NAA 0.5 mg·L ^{- 1} , 萌动率为77%; 继代和增殖培养基为MS + 6-BA 1 mg·L ^{- 1} +NAA 0.25 mg·L ^{- 1} , 平均增殖系数为16.7; 生根壮苗培养基为1 /2MS +NAA 0.25 mg·L ^{- 1} , 生根率96.1%; 试管苗生根培养30～35 d移栽, 成活率最高可达90%以上。     

木那格葡萄的组培快繁试验

以木那格葡萄的茎尖、单芽茎段为外植体，进行组培快繁试验。蛄果看出，适宜茎尖分化的培养基为B5 BA1．0mg／L IBA 0．1mg／L。适宜单芽茎段一次成苗生长的培养基为B3 BA0．05mg/L IBA0．2mg／L。适宜的生根培齐基为1／2MS IBA 0．2mg／L 蔗糖40g／L。健壮生根的试管苗要待4片叶以上移栽，移栽基质以蛭石较好。时间宜在4—5月份。     

Detection of airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae in oilseed rape crops by polymerase chain reaction (PCR) assays

The potential use of DNA-based methods for detecting airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae , both damaging pathogens of oilseed rape, was investigated. A method for purifying DNA from spores collected using Hirst-type spore samplers and detecting it using polymerase chain reaction (PCR) assays is described. For both pathogens, the sensitivities of the DNA assays were similar for spore-trap samples and pure spore suspensions. As few as 10 spores of L. maculans or P. brassicae could be detected by PCR and spores of both species could be detected against a background of spores of six other species. The method successfully detected spores of P. brassicae collected using spore traps in oilseed rape crops that were infected with P. brassicae. Leptosphaeria maculans spores were detected using spore traps on open ground close to L. maculans -infected oilseed rape stems. The potential use of PCR detection of airborne inoculum in forecasting the diseases caused by these pathogens is discussed.     

Movement of Xanthomonas campestris pv. vitians in the stems of lettuce and seed contamination

Xanthomonas campestris pv. vitians , the causal agent of bacterial leaf spot of lettuce (BLS), can be seedborne, but the mechanism by which the bacteria contaminates and/or infects lettuce seed is not known. In this study, the capacity of X. campestris pv. vitians to enter and translocate within the vascular system of lettuce plants was examined. The stems of 8- to 11-week-old lettuce plants were stab-inoculated, and movement of X. campestris pv. vitians was monitored at various intervals. At 4, 8, 12 and 16 h post-inoculation (hpi), X. campestris pv. vitians was recovered from 2 to 10 cm above (depending on stem length) and 2 cm below the inoculation site. Xanthomonas campestris pv. vitians was also recovered from surface-disinfested stem sections of spray-inoculated plants. Together, these results are consistent with X. campestris pv. vitians invading and moving systemically within the vascular system of lettuce plants. To investigate the mechanism of seed contamination, lettuce plants at the vegetative stage of growth were spray-inoculated with X. campestris pv. vitians and allowed to develop BLS. Seed collected from these plants had a 2% incidence of X. campestris pv. vitians external colonization, but no bacteria were recovered from within the seed.     

Genetic variability within Phaeoisariopsis griseola from Central America and its implications for resistance breeding of common bean

The genetic and virulence variability of 112 isolates of Phaeoisariopsis griseola , collected from various locations in Central America, were studied using seven random amplified polymorphic DNA (RAPD) primers and 12 common-bean differential genotypes. Broad molecular diversity ( H  = 0·92) among isolates was found using RAPD markers. Fifty pathotypes were identified on 12 differential bean genotypes, 29 of which were represented by only one isolate. Only 18 pathotypes were found in two or more countries. Pathotype 63-63 was the most virulent and caused leaf spots on all 12 common-bean differential genotypes. Comparison of virulence phenotypes and RAPD profiles to known Andean P. griseola isolates confirmed that all isolates belonged to the Mesoamerican group. Pairwise comparison between individual RAPD loci showed that the majority were in gametic phase linkage disequilibrium, revealing that P. griseola maintains a genetic structure that is consistent with asexual reproduction. The molecular and virulence diversities of P. griseola isolates from Central America imply that using single resistance genes to manage angular leaf spot is inadequate and stacking resistance genes may be necessary to manage the disease effectively.     

Effects of aqueous extracts and decomposition of Mikania micrantha H.B.K. debris on selected agronomic crops

Laboratory and greenhouse experiments were conducted to determine the effects of aqueous extract and the debris of Mile-a-Minute ( Mikania micrantha H.B.K.) on the germination and growth of four test species, viz. tomato ( Lycopersicon esculentum Mill.), Chinese cabbage ( Brassica chinensis L.), corn ( Zea mays L.) and long bean ( Vigna sesquipedalis L.). Germination percentage, radicle length and fresh weight of two crops, Chinese cabbage and tomato, decreased progressively when plants were exposed to increasing concentrations (12.5, 25, 37.5 and 50 g L⁻¹) of aqueous extract of Mikania , but did not affect those of corn and long bean seedlings. The emergence of tomato and Chinese cabbage was greatly reduced when Mikania debris was incorporated into the soil, irrespective of the amount of debris and the decomposition period. In contrast, the emergence of corn and long bean seedlings was not affected. The application of fertilizer (NPK 15 : 15 : 15) enhanced the fresh weight of all seedlings tested as compared with those not supplied with the fertilizer. Four compounds were identified in the leaf extract of Mikania , viz. caffeic acid, p -hydroxybenzaldehyde, resorcinol and vanillic acid.