摘要:

Flavour component differences between six tomato varieties and their F1, progenies were investigated. A diallel crossing system, excluding the reciprocal crosses was used. The F-1and parent varieties were compared by carrying out a sensory evaluation and a chemical component analysis. Statistical analysis of these two data sets revealed significant differences among the F1and parents for the chemical analysis variables, whereas the sensory variables showed considerably fewer significant differences. The number of correlations found between the chemical analysis and the sensory evaluation were relatively few. In the combining ability analysis, all the chemical analysis variables showed significant differences for general combining ability and specific combining ability. None of the sensory variables showed significant differences for specific combining ability and only one sensory variable, juiciness, showed highly significant differences for general combining ability. Both types of analyses, chemical analysis and sensory evaluations, are important for studies investigating flavour in tomatoes. Sensory evaluations cannot entirely be replaced by chemical analyses.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634994

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

MON 37532 (sulfosulfuron) is a new herbicide for the selective control of grasses and annual broadleaf weeds in wheat (Triticum aestivumL.). In this glasshouse study done in 2-litre pots filled with coarse sand, the product was evaluated for the selective control ofBromus diandrusRoth, in spring wheat. Dosage rates of MON 37532 varying between 0 and 45 g a.i ha-1plus 0.25% of the surfactant, Agral 90, were applied at the 1-, 2-, 3- and 4-leaf stage of the weed plants. Although efficient control (> 85%) was only achieved when weeds were sprayed at the 1 -leaf stage, leaf growth of allB. diandrusplants ceased within 5 days after spraying, irrespective of time of spraying. Leaf area and dry mass determinations done at 6 weeks after spraying in this study confirmed that even if sprayed at the 4-leaf stage, MON 37532 stopsB. diandrusfrom further growth and competition with the wheat plants. Higher dosage rates may be needed when sprayed at later growth stages. Growth of the spring wheat cultivar, SST 55, used in this study was not affected by the herbicide.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634995

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Bromus diandrusRoth, is one of the most troublesome weeds in spring wheat crops of the western Cape wheat producing area of the Republic of South Africa and Australia. The selective control of this weed in wheat crops may, in future, be possible with MON 37532 (sulfosulfuron) a new herbicide developed by Monsanto SA. The effect of the relative density ofB. diandrusin a wheat crop on the efficacy of this herbicide sprayed at either the 2- or6-leaf stage of the weed was studied in a pot experiment in a temperature-controlled glasshouse. A density of 3 plants pot-1(170 plants rrr-2) was used for the wheat crop, while that ofB. diandrusvaried between 0 and 10 plants pot-1(565 plants-2). At early applications (2-leaf stage), efficacy of MON 37532 improved with higher densities ofB. diandrus.This was possibly due to stress conditions created by higher weed densities. This tendency was less evident when MON 37532 was applied at the 6-leaf stage. Reduced susceptibility in the older plants and less efficient wetting of weeds in pots with high weed densities were probably the reason for reduced percentage control when plants were sprayed at this stage.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634996

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Russian wheat aphid,Diuraphis noxia, is a serious pest of wheat grown in the summer rainfall regions of South Africa. The use of D.noxiaresistant cultivars may reduce the impact of this pest on cereal production, at the same time reducing environmental risks and minimizing control costs. The objective of the study was to determine the inheritance of D.noxiaresistance present in the lines OSU ID 2808 (Triticum aestivum)and Aus 22498 (Triticum aestivumvar.vavilovi)in order to ensure their judicious use in a backcross breeding programme. Resistant lines OSU ID 2808 and Aus 22498 were crossed with the susceptible cultivar Tugela after being screened withD. noxia.Resistance reactions of the F1, BC1and F2plants, and individual F2plant derived F3families indicated that the resistance in both genotypes is controlled by single dominant genes. It is unknown whether these genes are identical to any known, designated resistance genes or each other.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634997

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Opencast coal mining on the Highveld of Mpumalanga involves the disturbance of highly productive soils, which must then be rehabilitated on top of the mined spoil. Various problems in this process may occur, however, which may lead to water-logging, compaction and/or decreased soil volume. Ground penetrating radar (GPR) is a useful technique in the characterisation of the rehabilitated soil and in determining the depth contours of the spoil layer. Studies with GPR were conducted at three rehabilitated opencast coal mines. In most cases GPR was able to clearly detect the top of the spoil layer and thus identify the variations in soil depth covering the spoil. Three-dimensional imaging can be achieved by means of a grid system, thereby identifying basins which could cause waterlogging. Advantages in the use of GPR include its capacity for obtaining continuous imagery and penetration to greater depths than is possible by soil augering. Time, manpower and financial savings can be achieved, increasing the potential to improve post-mining agricultural conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634998

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Due to a lack of electrical ovens, it is often found that in the households of the lower-income communities, a home-made steamed bread is prepared in a saucepan on a gas cooker or an open fire. The requirements of flour used to produce high-quality steamed bread are poorly defined. The suitability of Western and Southern Cape wheat for steamed bread production was, therefore, investigated. A marked increase in the nutritive value of steamed bread was reported compared to that of conventionally baked bread, mainly due to the loss of available lysine during conventional baking. Samples of three spring wheat cultivars that were produced during the 1995 and 1996 seasons in the Western and Southern Cape were selected. Flour protein content of these samples varied between 8 and 16%. Flour protein content, Falling Number determinations, gluten content, Mixograph, Alveograph and Rheofermentometer measurements and the 10 g baking test were performed on each of the flours. Steamed and conventionally baked breads were prepared for each cultivar at the four selected flour protein levels, respectively. Total bread volume, weight, height and texture, crust and crumb colour and lysine availability were measured for each loaf of bread. None of the Rheofermentometer measurements correlated significantly with flour protein content or any of the analytical and rheological measurements performed on the flour. All the crust colour parameters of conventionally baked bread correlated significantly with flour protein content. Even though significant correlation was observed for three crust colour parameters of steamed bread, the correlation was lower compared to that of conventionally baked bread. At the four different protein levels, more variation was observed in the elasticity of conventionally baked bread compared to the steamed bread, the texture of the steamed bread was finer and firmer and the crumb was more sticky. The browning reaction occurring in conventionally baked bread results in less available lysine than would be the case for steamed bread. In this study, higher availability of lysine was only the case when steamed bread was produced from high protein flour. Western and Southern Cape spring wheat, irrespective of protein content are, therefore, suitable for the production of good quality steamed bread.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634999

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Lolium multiflorumcv. Barmultra was used to evaluate the P and K status of plants grown on a smectitic soil commonly used for the construction of cricket pitches in the coastal regions of South Africa. Bulli was treated with P and K and, following treatment, soil test levels for P ranged between 2 and 28.5 mg L-1and for K between 109.5 and 480.5 mg L-1. The amount of P required per unit increase in soil P test value declined sharply as the P application rate increased but the relationship between K applied and soil K test was linear. Plant yield increased asymptotically with increasing soil P level, whereas the response to K was significantly quadratic although relatively small. There was a significant yield interaction between soil P and soil K, with response to K being more marked at high than at low P levels. Potassium addition had a much greater effect on nutrient levels in plant tissue than did P addition but both significantly affected not only the P and K levels in the herbage material, but also the levels of other plant nutrients. In particular, there was a strong negative relationship between soil K and plant Na and a weaker negative relationship between soil P and plant Mg.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10635000

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two experiments were carried out to study groundnut (Arachis hypogaeaL.) response to thinning time and intensity after anthesis at Redland Bay Farm, Southeast Queensland, Australia, during 1987/88 (Experiment 1) and 1989/90 (Experiment 2). Six cultivars were included in Experiment 1: Improved Virginia Bunch (IVB), NC7, Q18801 (Virginia type), TMV-2, McCubbin and Red Spanish (Spanish type); and two cultivars in Experiment 2: IVB and Red Spanish. These were thinned to 0 (control) or 50% at 42 or 91 days after planting (DAP) in Experiment 1; and 0 (control), 33, 50, 66 or 75% at 42 DAP in Experiment 2. Treatments were laid out in a randomized complete block design (RCBD) with three replications in both seasons. A 50% thinning at 42 DAP reduced intercepted photosynthetically active radiation but fadiation use efficiency, crop growth rate and total dry mass increased in all cultivars by maturity. A 50% thinning at 91 DAP significantly reduced groundnut production. Also, a thinning intensity of >66% reduced groundnut production. Thus, 50% plant removal during early reproductive growth may not significantly reduce groundnut production. This implies that an early control of insect pests (e.g. termites) could result in yield compensation amongst the remaining plants such that yield losses would be minimal by maturity of the crop.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10635001

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A sample of 48 sorghum varieties and inbred lines were planted in randomized block designs in two trials, one of which was irrigated. The effect of moisture stress on grain yield, tillering, seeds per ear, ear mass, seeds per plot, thousand seed mass, stover mass, biomass and harvest index was quantified for each genotype. Moisture stress resulted in increased tillering while the means of all other characteristics were reduced. Increased tillering caused an increase in grain yield under dryland conditions in those genotypes that indicated least reductions in seed number per ear and seed mass. The value of this screening method which includes both yield and drought resistance is discusséd with respect to developing improved cultivars for the target environment.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10635002

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Empirical soil loss models are relatively simple and have been applied in many parts of the world. The application of the Soil Loss Estimation Model for Southern Africa (SLEMSA), the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE) in southern Africa is investigated. Strictly speaking, these empirical models are modelling techniques or frameworks, rather than mechanistic descriptions of the system and should, therefore, make no claim of universality. The current set of sub-models for calculating SLEMSA factors were developed specifically for the Zimbabwean highveld, but the sub-models are being used to give best estimates of sheet erosion throughout Zimbabwe and elsewhere in southern Africa. As an index of the spatial distribution of soil loss, SLEMSA can be regarded as a useful model to differentiate areas of high and low erosion potential. USLE is the most widely known and used soil loss equation in the world. In southern Africa efforts were made to determine local values for USLE factors, but the model was never widely implemented. RUSLE can be described as a software version of a greatly improved USLE. A few studies, executed under different conditions in southern Africa, showed its potential for use outside its country of origin. The model proved to be a promising tool for conservation planning, as it provides a dynamic approach to predicting soil loss. The need is recognised,however, forimproved verification of the results. A theoretical evaluation and sensitivity analysis performed on the above three models, clearly showed the advantage of themoreflexible and dynamic structure of RUSLE against the strict empirical structures of USLE and SLEMSA. Although empirical models could be expected to be used mainly as screening tools in integrated studies, land resource assessments would demand increased accuracy in quantification of erosion rates in a spatial and temporal context. If data requirements can be met, process-based models (e.g. the Water Erosion Prediction Project, WEPP) can be expected to find increased application in producing quantitative estimates of soil loss and sediment yield in southern Africa.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10635003

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor