General combining ability of six genotypes of spring wheat (Triticum aestivum) for biscuit-making quality characteristics

The first South African soft wheat breeding programme was initiated in 19 90 , consequently almost no information is available on soft wheat quality characteristics. The aim of this study was to determine general combining ability (GCA) of several spring wheats for biscuit-making quality characteristics. A full dialled cross was made with five spring wheats with good biscuit-making quality and a sixth hard wheat with poor biscuit-making quality. Seventeen quality characteristics were measured. When the GCA to specific combining ability (SCA) ratios were calculated, strong additive gene action was shown for all characteristics, excluding flour colour and biscuit diameter, which suggested high heritabilities for most characteristics. None of the characteristics showed more non-additive than additive gene action. Three of the soft wheat cultivars combined well for the characteristics important for biscuit-making quality.     

Desktop classification of inland wetlands for systematic conservation planning in data‐scarce countries: mapping wetland ecosystem types,disturbance indices and threatened species associations at country‐wide scale

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The effect ofGlu-B1 high molecular weight glutenin subunits on biscuit-making quality of wheat

Summary The aim of this study was to assess the effect of specificGlu-B1 HMW-GS on biscuit-making quality. Three soft spring wheat cultivars with the sameGlu-A1 andGlu-D1 HMW-GS, but differentGlu-B1 HMW-GS were used in crosses. F₂₄ derived lines were developed from these crosses.Glu-B1 HMW-GS 6+8 and 17+18; and 7+9 and 17+18 were compared. Lines with HMW-GS 6+8 versus those with HMW-GS 17+18 had a higher flour protein- and alveograph P/L ratio, shorter mixograph mixing time, more vitreous kernels, and a lower alveograph distensibility and strength (all values significant at p=0.05). Lines with HMW-GS 7+9 compared to those with 17+18 showed significant differences for flour extraction and biscuit diameter. The presence of HMW-GS 17+18 was significantly correlated with several biscuit-making quality characteristics in the Dirkwin/Zaragosa F₂₄ lines but not in the Waverley/Zaragosa F₂₄ lines, therefore the effect of HMW-GS 17+18 was modified by the genetic background in which they were expressed.     

Biscuit-making quality of backcross derivatives of wheat differing in kernel hardness

Kernel texture in wheat has been found to be directly controlled by one or two major genes. Generally, good biscuit-making wheats are those with soft endosperm texture, lower protein content, more breakflour and a smaller particle size. The aim of this study was to determine the effect of the dominant soft endosperm genes on biscuit-making quality. Backcross derivatives were developed with a backcrossing procedure. The backcross derivatives and parents were planted in a randomised block design with six replications. Fourteen quality characteristics were measured. Except for hectolitremass and mixing time, the presence of the soft endosperm genes had a major effect on all characteristics used to predict biscuit-making quality. In the soft backcross derivatives there was a significant decrease in alkaline water retention capacity (AWRC), alveograph stability, alveograph strength, alveograph P/L ratio, flour extraction, and protein content. There was a significant increase in alveograph extensibility, biscuit diameter and breakflour yield. In this study, the presence of the soft endosperm genes was associated with good biscuit-making quality characteristics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quality of Ethiopian Durum Wheat Lines in Two Diverse Environments

In Ethiopia, durum wheat is largely used for production of local fermented and flat bread. Two diverse environments (Motta and Adet) were used to evaluate 15 durum wheat genotypes for grain yield and quality traits. The mean flour protein content of genotypes ranged from 10.1 % to 12.5 % and 6.7 % to 8.1 % at Motta and Adet respectively. The mean mixograph development time was 4 min at Motta and 2.8 min at Adet and SDS (Sodium dodecyl sulphate) sedimentation ranged between 10.7 and 32.3 ml across locations. Flour protein content was correlated negatively with mixograph development time and positively with vitreous kernels and single‐kernel hardness at both environments. Mixograph development time was selected to predict the gluten strength. Flour protein content, SDS sedimentation and seed weight were included in a stepwise regression. A prediction model was compiled that explained 69 % of the variation for mixograph development time.     

Assessing the effects of subtropical forest fragmentation on leaf nitrogen distribution using remote sensing data

Subtropical forest loss resulting from conversion of forest to other land-cover types such as grassland, secondary forest, subsistence crop farms and small forest patches affects leaf nitrogen (N) stocks in the landscape. This study explores the utility of new remote sensing tools to model the spatial distribution of leaf N concentration in a forested landscape undergoing deforestation in KwaZulu-Natal, South Africa. Leaf N was mapped using models developed from RapidEye imagery; a relatively new space-borne multispectral sensor. RapidEye consists of five spectral bands in the visible to near infra-red (NIR) and has a spatial resolution of 5 m. MERIS terrestrial chlorophyll index derived from the RapidEye explained 50 % of the variance in leaf N across different land-cover types with a model standard error of prediction of 29 % (i.e. of the observed mean leaf N) when assessed on an independent test data. The results showed that indigenous forest fragmentation leads to significant losses in leaf N as most of the land-cover types (e.g. grasslands and subsistence farmlands) resulting from forest degradation showed lower leaf N when compared to the original indigenous forest. Further analysis of the spatial variation of leaf N revealed an autocorrelation distance of about 50 m for leaf N in the fragmented landscape, a scale corresponding to the average dimension of subsistence fields (2,781 m²) in the region. The availability of new multispectral sensors such as RapidEye thus, moves remote sensing closer to widespread monitoring of the effect of tropical forest degradation on leaf N distribution.     

Influencing factors of sodium dodecyl sulfate sedimentation in bread wheat

Bread wheat elite lines and F4 populations were evaluated to determine the influence of genotype and environment on variation in sodium dodecyl sulphate (SDS) sedimentation, and the relation between SDS sedimentation and other quality characteristics. Nine intermediate hard red wheat elite lines and two checks were evaluated for three years over eight locations, and six F4 populations and two hard red wheat checks were evaluated at three locations. In both sets of material, the genotype and location main effect, and genotype × location interaction were highly significant. The genotype component contributed 85.96% of the total variation in SDS sedimentation in the F4 material, and the genotype × location component only 12.87%. In the elite material the contribution of genotype was high enough to make effective selection for SDS sedimentation possible. The genotype × year effect was large, indicating that testing genotypes across years may be more important than across locations. SDS sedimentation was significantly positively correlated with protein content and mixograph development time, and negatively with yield. Selection of higher SDS sedimentation may lead to overly strong dough and lower yields. Therefore a careful approach should be taken in the selection process, balancing the different objectives in a breeding program.     

A six week screening method for mechanisms of host plant resistance to Diuraphis noxia in wheat accessions

The Russian wheat aphid Diuraphis noxia (Kurdjumov) is a serious pest of wheat in South Africa. The use of D. noxia-resistant cultivars may reduce the impact of this pest on wheat production and at the same time reduce environmental risks and control costs. The mechanisms of resistance in two new sources of resistance were compared by using various methods, in order to establish a rapid and relatively accurate screening protocol. The resistant lines OSU ID 2808 and Aus 22498 were compared to the susceptible cultivars Betta and Tugela. The predominant mechanism of resistance in OSU ID 2808 was antibiosis, although a low level of antixenosis may also be present. The line Aus 22498 was primarily a tolerant type, with a moderate level of antibiosis and a low level of antixenosis. A six week screening procedure is described using the colony count technique for antibiosis, a completely random free choice experiment for antixenosis and a three week test measuring initial and final plant height, initial and final D. noxia infestation, damage rating, leaf area and dry plant mass for tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessment of cropping‐system impact on soil organic matter levels in short‐term field experiments

It has been suggested that short‐term field experiments are not suitable for the quantitative assessment of cropping‐systems impact on soil organic matter (SOM) levels in arable soils, as expectable temporal changes are very small compared to a large spatial variation of SOM background levels. However, applying an optimized sampling design based on repeated sampling in small plots, we were able to detect soil total carbon (STC) and nitrogen (STN) changes in the magnitude of ≈ 1% (STC) and ≈ 2% (STN) of background levels with only four replications, respectively. Gradually enlarging the sample size up to n = 24 did not considerably improve change detectability with STC, but with STN (n = 15 allowing for the dection of ≈ 1% change of background levels). The common calculation of minimum detectable differences (MDD) based on a state analysis of SOM levels instead of repeated measurements considerably underestimated change detectability.