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Partial Least Squares regression (PLS) was used to understand the relationship between 15 sensory attributes of potatoes boiled in their skins as dependent variables (Y), and six objective (chemical and physical) measurements as the independent variables (X). The ARC-Sensory Analysis Unit, at Irene, South Africa, conducted the study. A trained sensory panel (n=10) was used to determine the texture, aroma and flavour attributes of five potato cultivars; Mondial, BP1, Up-to-Date, Van der Plank and Caren. Four repetitions of each sample were used. The PLS regression formed three distinct groups of the cultivars: (1) Mondial, (2) BP1 and Van der Plank, which contrasted with (3) Caren and Up-to-Date. These groupings were confirmed by the culinary uses of the cultivars and their ability to retain shape after boiling. Mondial is favoured for making potato salad or boiling as it retains its shape during cooking. BP1 and Van der Plank are suitable for most uses of boiled potatoes as they retain their shape, whereas Caren and Up-to-Date do not retain their shape during cooking and are suitable for baking and frying.

Multi-environment trials are usually used to assess the grain yield stability of genotypes. Most of the common stability measures such as Finlay and Wilkinson (1963), Eberhart and Russell (1966) and Shukla (1972), can be accommodated by a linear mixed model where genotypes are a fixed effect and environments are a random effect. The objective of this paper was to examine the stability differences of tef genotypes using the mixed model approach. Yield stability of 13 tef genotypes was studied based on data collected over 12 environments where an environment constitutes a particular location and year combination. The combined analysis of variance from the 12 environments revealed significant differences among genotypes, environments and their interaction effects on the grain yield indicating the differential responses of genotypes to diverse environments. The likelihood ratio tests for Finlay-Wilkinson and Shukla models showed that the stability of tef genotypes was best assessed by an Eberhart-Russell mode...

Work carried out at the ARC-Institute for Soil, Climate and Water on soil phosphorus characteristics was reviewed. Regression functions were established in order to test the correlations between P parameters, single point indices and soil properties. The parameters investigated were selected indices of P sorption, including the Langmuir adsorption maximum (Lm), as well as indices of the P buffer power of the soil, including the slope of each of the Langmuir (Lbp), Freundlich (Fbp) and Temkin (Bt) P sorption isotherms. Other parameters included an index of the P requirement of the soil (P0.11), the phosphorus requirement factor in terms of the Ambic 2 extraction procedure (PRFAmbic2) and an index of the slow reaction of P sorption with soils (dx/dt)24. The results showed that to obtain a measurement of these parameters, cumbersome multiple point procedures could mostly be substituted by single point indices more suited for routine determination purposes. Lm, Lbp, Fbp and Bt could readily be estimated from ...

The phosphorus requirement (P0.11) of low to moderate P-fixing soils from the South African tobacco industry and KwaZulu-Natal was estimated from P sorption isotherms. The relationships between P0.11, Ambic 1 P, clay content and various indices of P sorption were investigated, using non-linear regression analysis. The results showed that a high degree of correlation existed between P0.11 and the Ambic 1 P content. Although this showed the Ambic 1 soil-P extractant to be a useful predictor of P0.11, the functions best describing the relationship between both these variables differed between the two regional groups of soils. The variance in P0.11 accounted for by the Ambic 1 P content was improved when supplementing it in a multiple regression equation with an index of the buffer power of the soils. This was especially true for the soils from KwaZulu-Natal or when the soils from the two different ecological regions were combined into a single group. A single point sorption test (SI) readily determined routi...

A short (24 h) laboratory incubation study was conducted and plots of P desorbed in Ambic 2 extraction solutions versus added P were constructed for a wide range of soils of varying P fixing capacity representative of the province of KwaZulu-Natal, South Africa. The plots were found to yield straight lines and, using linear regression analysis, equations of best fit describing these desorption functions were established for each soil. A two point test, the Ambic 2 Phosphorus Desorption Index (PDIAmbic2), was found to correlate closely with the slopes of the desorption functions (R2 = 0.943). This result showed the proposed quick two point PDIAmbic2 test to be a reliable index of the slope of the multiple point desorption functions. It established that, although simpler, it could be used advantageously as a time saver to estimate the slopes of the desorption functions routinely. PDIAmbic2 was further shown to correlate significantly to the Ambic 2 Phosphorus Requirement Factor (PRFAmbic2) obtained from a p...

Plots of the decline of the concentration of phosphorus in soil suspensions over time were constructed for 23 selected soils from South Africa and, using non-linear regression analysis, various models were fitted to the time curves, including mechanistic first and second order kinetic functions. The model best describing the data was found to be the empirical modified Freundlich kinetic function. The curvature of the Freundlich kinetic model, b, appeared to be independent of the initial concentration of P of the additional input solution. The parameter b is a useful soil-P kinetics index for the selection of P fertiliser strategies and making P fertiliser recommendations, especially in situations where the fertiliser cannot be incorporated into the plough layer annually as is the case with perennial crops or in no till cropping systems. The measurement of b, however, requires the construction of a multiple point time curve, a lengthy and cumbersome process that does not lend it easily to routine determina...

The phosphorus requirement (P0.11) of low to moderate P-fixing soils from the South African tobacco industry and KwaZulu-Natal was interpolated from multiple point P sorption isotherms. The relationship between P0.11 and a single point sorption measurement, consisting of the P concentration left in solution after equilibrating for 24 h additional rates of either 70 or 100 mg P kg−1 soil, over the soils of the tobacco industry was investigated using non-linear regression analysis. The results showed that a high degree of correlation existed between both variables, suggesting that P0.11 could simply and accurately be predicted from a single P sorption measurement instead of a multiple point sorption isotherm. Confirmation of the predictive value of the functions best fitting the data from the soils of the tobacco industry was validated using data of the soils from KwaZulu-Natal. The results showed that values of P0.11 predicted for the soils of KwaZulu-Natal, using the single point P sorption test in conjun...

Estimates of the phosphorus requirement (P0.11) of 20 selected soils of the South African tobacco industry were interpolated from phosphorus sorption isotherms. The relationships between P0.11 and various soil phosphorus characteristics, including Bray 2 P content and various indices of P-fixation, were investigated using regression analysis. The results showed that P0.11 varied widely and is influenced by both the level of Bray 2 P content and the P-fixation capacity of the soil. Measurements of the P-fixation capacity of the soil included the more formal buffer power indices derived from multiple point P sorption isotherms and both the phosphorus desorption index (PDI) and the sorption point index (SI), each a single point test easily determined routinely. SI was shown to relate closely to the buffer power indices and to be a quick and useful index of the soil P-fixation capacity. PDI, on the other hand, was found to be of limited value to predict the phosphorus fixation of the soils. An equation, allow...

Phosphorous isotherms for 21 selected soils from the Republic of South Africa were constructed and the Langmuir, Freundlich and Temkin sorption models were compared using regression analysis. Over a range of solution concentrations of 0.025 - 2.00 mg P I−1, all three sorption equations were found to fit the data well (R2 = 0.934 - 0.996). The values of the coefficients of the different equations were more accurately estimated by the Freundlich and Temkin models, whilst the Langmuir model was a slightly better indicator of adsorbed P. A multiple regression analysis between sorption coefficients and selected soil properties showed citrate bicarbonate dithionite-AI to be an important factor in P sorption. Other soil constituents important in P sorption included clay percentage, organic matter, citrate bicarbonate dithionite-Fe and Bray 2 P content. Although useful in identifying soil properties responsible for P sorption, the regression equations were too cumbersome and imprecise to be of any practical use i...

Russian wheat aphid, (Diuraphis noxia) causes severe damage to wheat in South Africa and producers have been forced to use insecticides for control. Plant resistance to Russian wheat aphid has been successfully transferred into bread wheat cultivars. A split plot field trial was undertaken firstly to compare the yield of susceptible wheat to that of a near-isogenic resistant wheat cultivar in combination with insecticide treatments and secondly to determine whether the inclusion of Russian wheat aphid resistance influences the bread- making quality of the cultivar. Resistant wheat yielded higher indicating that the resistance is effective under field conditions. Seed treatment with Imidacloprid increased yield of wheat in both years. Significant two and three-way interactions were found in both years. No negative effects on dough quality characteristics were associated with Russian wheat aphid resistance.

Preharvest sprouting significantly reduces the quality of the South African wheat crop. This study classified the preharvest sprouting resistance of 17 South African winter wheat cultivars sampled over a range of typical winter wheat growth environments. Sampling was performed under field conditions and sprouting responses were evaluated under controlled conditions. Variation in sprouting response between cultivars was predominantly genetically determined and varied from 1.7 to 7.4 on a scale from 1 (no visual sprouting) to 8 (fully sprouted). Canonical variate analysis and AMMI analysis, as well as the use of hierarchical clustering of cultivars over environments using the AMMI estimates, identified four distinct groups ranging from resistant to susceptible. The AMMI model was used as it combines the additive main effects of the analysis of variance with the interaction effects of principal components analysis. In general, Betta, and certain cultivars derived from Betta, showed good to moderate resistanc...

The variation in the processing quality of South African winter wheat cultivars over growth environments is detrimental to its market value. Variation in protein content has previously been identified as a primary contributor to this variation and should therefore be considered in the interpretation of quality data presented during the cultivar release procedure. The aim of the study was to analyse such effects on the interpretation of quality data of advanced wheat lines. Our results indicated a distinctive segregation between entries having higher (≥10%) and lower (

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.

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.

A suitable technique for the extraction of wheat flour protein fractions was pursued to assess the effect of quantitative protein composition on the bread-making quality of winter wheat cultivars on a large scale. Nine procedures involving the use of different sequential solvent extractions were quantitatively compared. The distribution of protein components in the different solubility classes was checked by means of sodium dodecyl sulphate Polyacrylamide gel electrophoresis. The most effective procedure to fractionate the four major protein groups sequentially was: albumin (water),' globulin (0.5 M NaCI + 0.05 mM Na-EDTA), gliadin [55% (v/v) propan-2-ol] and glutenin [0.0125 M Na2B4O7, 0.043 M NaOH, 0.5% (m/v) SDS, 1% (v/v) β-mercaptoethanol].To validate this procedure, linear correlations between quality parameters and protein extracted for all localities and cultivars were complemented by principal component and best subset regression analysis. Albumin and globulin were weakly correlated with quality a...

Potatoes, Solanum tuberosum (L), are cultivated in South Africa under a variety of different climates and seasons. The wide environmental variation encountered and the confirmed occurrence of genotype-environmental interaction necessitates the use of criteria, other than averages, in the evaluation and selection of new potato cultivars. Yield data from cultivar trials countrywide, were used to evaluate the use of the AMMI model against the existing Finlay-Wilkinson regression technique. The AMMI model was found to be suitable for determining the reaction of cultivars/lines in an environment. The usefulness of the technique improves with a graphical presentation of the results to display the stability of a genotype in different environments.

The AMMI model, which incorporates both additive and multiplicative components into an integrated, powerful, least squares analysis, is used for the analysis of cultivar trials at different localities. These trials are a major experimental component in crop production and plant breeding research. Multilocation trials have as objectives the assessment of the success of yield predictions, the grouping of sites for evaluation and the interpretation of genotype-environment interactions. The data used originated from the National Lucerne Evaluation Program and the lucerne cultivars were representative of dormancy groups 4–9, i.e. semi-, intermediate-, non- and highly non-dormant. Expected trends in results from the yield trials were not obvious using the additive main effects model (ANOVA), while the application of the AMMI model resulted in rankings of cultivars in different environments which could readily be explained by the breeding history and dormancy of the cultivars.

The use of multivariate techniques in the analysis of multivariate problems is illustrated by comparing the results of univariate and multivariate techniques applied to the problem of establishing the nutritional requirements of, and the acid tolerance differences between maize cultivars. Forty-eight maize cultivars were statistically separated into three groups, tolerant, intermediate and intolerant, using a univariate approach. A principal components analysis was then carried out to study the grouping at a multivariate level. The variates included were grain yield, plant height and ten leaf chemical analyses: Al, Mg, P, Ca, K, Mn, Zn, Fe, N and Cu. A non-hierarchical classification was applied to classify cultivars into the three tolerance classes. The univariate method resulted in different groupings for each variate under study, while the multivariate approach ensured one single classification of all cultivars into the three groups.

A field experiment was conducted on a Normandien clay loam (Plinthic Paleudult) to compare the acid tolerance of 48 commercially grown maize (Zea mays L.) cultivars. Cultivars were compared in terms of grain yield, plant height and leaf Al content at four levels of lime (0; 2,5; 10 and 15 t ha−1). Statistically significant cultivar × lime interactions were noted in the case of all three criteria. In the absence of lime relative yields ranged from over 90% to less than 10%, relative plant height varied from approximately 80% to 50%, and relative leaf Al content from less than 150% to over 300%. With a few notable exceptions, probably caused by environment × cultivar interaction, cultivar rankings obtained with the different performance criteria were generally very similar. After statistical separation of the cultivars into classes, either ‘tolerant’, ‘intermediate’ or ‘intolerant’ in their reaction to acidity, 23 of the cultivars were identically classed using either yield, height or Al content in the abse...