摘要:

Aqueous extracts from leaves, stems, roots of the aromatic shrubArtemisia afraand soil on whichArtemisiawas grown, were used to investigate their inhibitory effects on germination and seedling development of maize (Zea mays), bean (Phaseolus vulgaris) and ryegrass (Lolium perenne). Dilutions of 1:1,1:2.5 and 1:5 v/v of the original extracts were prepared by adding deionised water to the original (undiluted) extracts. Deionised water and extracts from soil on whichA. afrahad never grown were used as controls. Extracts fromA. afrasoil and plant parts significantly (p < 0.05) reduced seed germination, height and dry matter of all the seedlings compared with the controls. However, as the dilution of the original extracts increased, there was a significant increase in seed germination and dry matter yields. This observation was consistent in all the plant species indicating that there was reduction in the concentration of the compounds inhibiting germination and seedling growth. The inhibitory effects on both seed germination and seedling development by the extracts was in the order leaves > stems = roots > soil. It was observed that germination was the process relatively more adversely affected by the inhibitory compounds in the extracts than growth of the seedlings. The results confirm that there are water-soluble compounds in the tissue of theA. afrashrub which can inhibit seed germination and growth of plant seedlings.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635106

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The performance of the plant canopy analyzer (PCA), model LAI-2000 (LI-COR, Lincoln, NE, USA), has been tested in two separate field trials for 18 annual crop and pasture species. The objective was to recommend appropriate techniques for reliable estimates of fractional interception of radiation (Fl), leaf area index (LAI) and canopy extinction coefficients. At least six below-canopy measurements and the use of 180° view restriction masks are recommended for row crops. Measurements should preferably be carried out before 8:00. Alternatively, shading of the sensor and sampling area is recommended during sunshine hours. The PCA's fisheye sensor proved to be more suitable than the sunfleck ceptometer (Decagon Devices, Pullman, WA, USA) for a daily estimation of canopy cover. The ceptometer would be preferable for the estimation of hourly Fl which is affected by solar orientation. The PCA's indirect, non-destructive and time saving measurement can accurately estimate LAI of soybean, sorghum, pearl millet and small canopies of wheat and milkvetch (LAI < 1.5). LAI of maize, cow- peas, rye, oats, triticele, ryegrass and perennial grasses obtained with the PCA should be corrected using the derived empirical functions. Potential users should investigate specific measurement techniques for other crops to determine whether the PCA provides reliable data. Fl and LAI measurements with the PCA were used to generate a database of extinction coefficients for photosynthetically active and global solar radiation.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635107

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The herbaceous aromatic shrub African wormwood (Artemisia afra) is thought to be indigenous to the Eastern Cape region of South Africa. In the natural environment, wherever the plant grows, patches of hard, bare ground develop around the plant. To investigate whether the growth of the plant directly affects the physical and chemical properties of the soil, we compared selected properties of soil from the bare patches beneath the canopy of the shrub with those from contiguous land with the same soil but whereArtemisiahad never been grown (control). The results showed that soil from underA. afrahad significantly (p < 0.01) higher stability of aggregates (2.0–5.6 mm) than the control, in spite of the fact that the organic C and bulk density did not differ significantly between the two soils. There was no significant difference in the pH, Bray 1-P, electrical conductivity and exchangeable cations (Ca, Mg, K & Na) content of the two soils. Analysis of the organic compounds present in theA. afraextracts indicated that it contained a mixture of unsaturated hydrocarbons, carboxyls and benzene, which were either absent or present only in very small amounts in the control soils. It is considered that these compounds contributed to the increased stability of aggregates inA. afrasoil. The findings of this study are significant because the observed increase in aggregate stability would lead to reduction in soil erodibility, so that the introduction ofA. afraon cultivated agricultural lands could be beneficial from both the economic and soil management stand points.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635108

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The daily maximum temperature in the upper 20 mm of sandy soils is often higher than 45°C on cloudless days during November, December and January in the summer rainfall region of South Africa. At these supra-optimal temperatures, sunflower seedling vigour declines, resulting in a low plant population and lack of uniformity of plant density. The aim of this experiment was to quantify the effect of peak daily temperatures on the emergence of sunflower in a controlled environment. A3×4×5×3 factorial design with three cultivars, four growth chamber temperature treatments of 40, 45, 50 and 55°C, applied daily for periods of 3, 4, 5, 6 and 7 hours and three replicates of 20 seeds, were used. Seeds were planted to a depth of 25 mm in sand moistened to field capacity and incubated at 30°C. Treatments commenced after 24 hours. Emerged seedlings were counted daily. An emergence index, which takes both the rate and homogeneity of emergence into account, was calculated. Cultivars differed in their heat tolerance. This may be due to genotype or seed quality differences. The index declined rapidly above a threshold temperature of ca. 44°C. Some seedlings survived and emerged at temperatures above 50°C.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635109

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Die toenemende vraag na goeie kwaliteit oonddroogtabak het aanleiding gegee tot navorsing om te bepaal watter rol stikstofbemesting, tophoogte en kultivars speel. Vyf oonddroogtabakkultivars (TL 33, OD86, A4, OD224 en OD212) is in 'n veldproef onderwerp aan drie stikstofbemestingspeile (70, 100 en 130 kg N ha−1) en twee tophoogtes (14 en 18 blare). Hoër stikstofbemesting en laer top het bladkwaliteit ietwat verbeter, maar 'n toe- name in onbemarkbare blare veroorsaak, wet gelei het tot laer bemerkbare opbrengs en inkomste. Klein verskille in opbrengs en kwaliteit het tussen cultivars voorgekom, terwyl aanduidings ook gevind is dat kultivars verskil in hul reaksie op stikstofbemesting.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635110

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Die toenemende vraag na beter kwaliteit oonddroogtabak, het aanleiding gegee tot navorsing om te bepaal watter rol stikstofbemesting, tophoogte en kultivar speel. Vyf oonddroogtabakkultivars (TL33, OD86, A4, OD224 en OD212) is in 'n veldproef onderwerp aan drie stikstofbemestingspeile (70, 100 en 130 kg N ha−1) en twee tophoogtes (14 en 18 blare). Hoér stikstofbemesting en laer top het die konsentrasies van N, K, Cl en nikotien in die blad verhoog, terwyl die suikerinhoud terselfdertyd afgeneem het. Die K-inhoud het verminder van die onderste na die boonste blare, terwyl die CI- en nikotien-konsentrasies toegeneem het. Meer van die gesogte donker tabak is geproduseer waar die blad 'n hoér nikotien met gepaardgaande laer suikerinhoud gelewer het. 'n Swak verwantskap tussen fisiese en chemiese eienskappe het voorgekom.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635111

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Nineteen maize genotypes resistant to various stalk borer species were evaluated for resistance to the maize stalk borer,Busseola fusca(Fuller), using artificially infested plants grown in a greenhouse. The inbred line GT-FAWCC (C5) resistant to the fall armywormSpodoptera frugiperda(Smith) was identified as a new source of high level leaf feeding resistance toB. fusca, whereas the inbred GT115 resistant to the corn earwormHelicoverpa zea(Boddie) presented a source of resistance to ear feeding byB. fusca.The latter is the first record of resistance toB. fuscanot derived from an Antigua Group 2 background.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635112

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The mechanistic basis of Al rhizotoxicity was investigated through a time-based analysis of the growth reactions seen in hydroponically-grown roots of wheat isolines (IS and IT) differing in Al tolerance, when exposed to 75 μM Al (pH 4.1) for times ranging between 2 minutes and 48 h. Notwithstanding genotypic differences in the timing and the magnitude of the reactions, it was clear that the root growth adjustments made in response to Al involved three phases, 1) the primary response (IS and IT ≤ 60 min) which produced a net increase in root extension growth, 2) an intermediate period of growth inhibition (IS, 6 h; IT, 24 h.) and 3) recovery (IT 48 h) which included growth stimulation. Close relationships also emerged between the time-dependent, Al-induced increases and decreases in root extension growth and the volume (length) of the root cap and the length of root epidermal cells which suggested that cap volume and root epidermal cell extensibility may also be components of the Al response network. These findings are discussed with a view to developing a coherent theory of Al rhizo- toxicity/root growth control. Genotypic similarities and differences in the root growth responses shown to Al are used to distinguish between Al escape strategies (stress avoidance, IT and IS) and the longer term activation of genetically controlled mechanisms of Al tolerance (IT) involved in the recovery from Al.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635113

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The objectives of this preliminary study were to identifyFusariumspecies associated with wheat seed obtained from head blight infected fields and to determine whether the causal organism(s) of head blight could colonise plants systemically from infected seed. SixFusariumspp. were isolated from grain samples of the cultivar Palmiet.Fusarium graminearumcomprised 48.4% of the isolates,F. moniliforme36.3%,F. equiseti9.7%,F. chlamydosporum3.2%,F. subglutinans1.6%,and F. oxysporum0.8%. No systemic colonisation of roots, culms, leaves or heads of plants grown from infected seed was observed for any of these species.Fusarium equiseti, F. graminearum, andF. oxysporumwere, however, isolated from surface-sterilised crowns.Fusarium graminearumwas also isolated from 0.9% of seeds from which the embryos failed to emerge, and from 3.9% of blighted seedlings.

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635114

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0257-1862    

DOI:10.1080/02571862.1998.10635115

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor