摘要:

The inheritance of resistance to grey leaf spot of maize (Zea maysL.), caused byCercospora zeae-maydis, was studied using a 12×12 diallel cross. Information on the heterotic performance of the inbred lines enabled identification of patterns of transmission of resistance to susceptible genotypes. The study confirmed that an accurate evaluation of heterotic patterns for grey leaf spot requires an assessment of both the inbred lines and all the single crosses among them. Resistance of the tested maize genotypes to grey leaf spot can be expressed in terms of an additive-dominance model, with dominance almost complete. As the incidence of this fungus reached epidemic proportions only after physiological maturity, yield was not adversely affected by grey leaf spot. Genotypic correlations between grey leaf spot ratings, yield and kernel quality traits suggested that certain of the tested genotypes displayed sink-induced susceptibility to the disease. Hayman's (1954) variance-covariance graphical technique confirmed several findings of the heterotic pattern analysis and it provided additional information that will be used in the development of resistant genotypes.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634352

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The relationship between the sodium dodecyl sulphate sedimentation volume (SDSS test) and the protein content and bread volume of wheat cultivars was determined to ascertain whether the SDSS test could be used to predict these parameters of baking quality. This test proved to be a good indication of baking quality as the SDS sedimentation volumes were positively correlated with both protein content and bread volume of the cultivars. Nitrogen fertilization affected the SDS sedimentation volume as well as the protein content and bread volume, thereby affecting the relationship between these parameters. Higher correlation coefficients between the different parameters were found at higher nitrogen applications. Some of the correlation coefficients were affected by the locality where the wheat was grown.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634353

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Die invloed van waterstremming in aartappelplante op netto fotosintesetempo en stomatadiffusieweerstand is tydens 'n herfsaanplanting ondersoek. Watertoediening is op 14, 28 en 42 dae na opkom gestaak om sodoende verskillende waterstremmingsperiodes tydens die groeiseisoen toe te pas. Hierdie Studie is onder 'n outomaties-beweegbare reënskerm uitgevoer. Die plante waarvan water vir die kortste periode weerhou is, het deurgaans die hoogste gemiddelde fotosintesetempo gehandhaaf. Direk na die weerhouding van water het die fotosintesetempo van al die behandelings begin daal, terwyl stomatadiffusieweerstand begin toeneem het. Tydens hierdie ondersoek is gevind dat die gemiddelde fotosintesetempo gedurende die groeiseisoen goed gekorreleer het (r= 0.95) met totale opbrengs. Die gemiddelde fotosintesetempo het 'n negatiewe lineêre verband (r=−0.88) met gemiddelde grondwateronttrekking getoon. Uit hierdie Studie het dit geblyk dat beide fotosintesa en stomatadiffusieweerstand as goeie indikators van waterstremming kan dien.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634354

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Dit is bekend dat 'n goeie wortellengte en/of worteldigtheid in die eerste paar weke belangrik is om goeie saailingvestiging te verkry. Die doel van hierdie studie was om die uitwerking van minimumbewerking (wisselgangskotteleg en vlerkskaar), beitelploeg- en konvensionele bewerking op die groei van koring ten opsigte van vroeëwortelontwikkeling en biomassa te evalueer. Hierdie bewerkingsbehandelings is oor 'n periode van drie jaar op 'n Avalon sandkleileemgrond in die Sentraal-Vrystaat uitgevoer. Grondwaterinhoud was tydens plant dieselfde vir elke bewerking, behalwe vir geringe verskille in die boonste grondlae. Carina het die hoogste graanopbrengs (1 571 kg ha−1) gelewer by wisselgangskottelegbewerking in 1992, terwyl Molen in 1993 die hoogste graanopbrengs (2 462 kg ha−1) gelewer het by vlerkskaarbewerking. Die wortelontwikkeling en biomassa gedurende 1992 en 1993 toon dieselfde tendens waar Carina die grootste wortellengte en -massa in 1992 gehad het, maar in 1993 het Scheepers 69 en Carina geen verskille ten opsigte van wortelontwikkeling en biomassa getoon nie. Geen afleiding ten opsigte van watter bewerkingsbehandeling die wortelontwikkeling bevoordeel kan gemaak word nie. Die resultate dui wel daarop dat kultivars ten opsigte van vroeëwortelont-wikkeling verskil.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634355

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effect of citrate interference on the direct colorimetric determination of P in 1% citric acid soil extracts of a wide range of soils was investigated and compared to that of removing the citric acid by dry ashing. It was found that dilution of the soil extracts to ratios greater than 1:20 caused minimal interference with colour development using the molybdenum blue method. Dilutions of 1:10 and 1:5 caused a 10% and 55% reduction in absorbance values respectively. Despite this interference, the measurement of P in the presence of 1% citric acid is possible if the same concentration of this acid, present in the soil extract, is present in the calibration standards. Generally a 1:10 dilution of soil extracts provides sufficient sensitivity for the determination of P in soils with a P status<5 mg kg−1and can accommodate soils with a P status up to 100 mg kg−1. The effect of dry ashing the soil extracts and measuring the P colorimetrically resulted in slightly higher P values, in the order of 2 mg kg−1. Similar results were obtained when the soil extracts were aspirated into a direct-current plasma and the P was measured by emission spectrometry. It was concluded that quantities of P could be present in the soil extracts, either organically or inorganically bound, and were responsible for this difference. These forms of P were not determined by colorimetric procedures but were released by a high-temperature plasma or by dry ashing. For most practical purposes these low values can be ignored.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634356

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The attributes of yield and bread-making quality of winter wheats produced in the Free State are subject to environmental effects. The result is a supply to the baking industry of flour of inconsistent quality, which in turn is detrimental to the market value of wheat. Various genetic and environmental factors may affect bread-making quality. In the first part of this study we demonstrated the magnitude of environmental and genetic factors, and used principal-components analysis to examine the underlying source of variability in the bread-making quality of winter wheat cultivars. Yield and protein concentration responded to environmental influences, whereas the dough-mixing requirement was primarily inherently determined. Variation in protein concentration accounted for variation in the mixing requirement of one cultivar and the SDS sedimentation volume of most cultivars.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634357

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The inconsistent production of winter wheat with acceptable bread-making quality in the Free State reduces the commercial value of the wheat crop. In the second part of this study, canonical correlation analysis was used to determine to what extent variation of biochemical components in wheat flours was responsible for differences in bread-making quality. In addition, the effects of environmental variables such as climate, crop history and edaphic attributes on yield, rheological and biochemical traits were examined by means of canonical variate analysis. It appeared that climatic factors contributed most to variation in yield and quality characteristics. Favourable conditions during the grain-filling period improved yield and modified storage and monomeric protein ratios. Modifications under stress-related conditions, however, were not sufficient to influence mixing requirement or baking quality.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634358

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The role of forestry plantation residues (leaf and branch) in the suppression of establishment of four weed species (Conyza sumatrensis, Trifoliumspp.,Echinochloa utilisandLactica sativa) was investigated. Of the three residue types used,Pinus patularesidues were found to have the greatest suppressive effects, followed byEucalyptus grandisand thenAcacia mearnsii.Medium-grade residue was found to be more effective than either the coarse or fine grades, and positioning the weed seeds below the mulch resulted in greater suppression than when placed above it. Water extracts from the three residues also resulted in significant suppression of weed establishment, suggesting an allelopathic effect. Finally, suppression of the dicotyledon species was generally greater than suppression of the grass used in this study.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634359

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

FourStenocarpella maydis(Berk.) Sutton inoculation techniques were compared over two seasons at Potchefstroom and Bethlehem on six maize cultivars differing in ear rot susceptibility. The techniques showed differentiation between cultivar susceptibility. Application of a conidial suspension behind the ear resulted in significant correlation with the disease potentials over two seasons. Similarly, the technique of placing ground-infected kernels in the leaf whorl at three growth stages is recommended for evaluation of maize genotypes for resistance to maize ear rot.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634360

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Yellow berry is a physiological condition in wheat which is associated with nitrogen stress. Results from an experiment where some treatments resulted in unusually large percentages of yellow berry kernels indicated a negative relationship between the incidence of yellow berry and both grain protein content and yield. The occurence of yellow berry, however, was more related to variation in grain protein content (r2= 65.68%) than variation in yield (r2= 18.0%). Chemical analysis of the kernels showed that the proportion of storage proteins (gliadin and glutenin) responsible for good baking quality was remarkably low in yellowish grains, when compared to normal kernels. In contrast to this, the proportion of cytoplasmic proteins (albumin and globulin) was reduced to a far lesser extent.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634361

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor