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Bethlehem, South Africa

Oelofse R.M.,ARC Small Grain Institute | Labuschagne M.T.,University of the Free State | van Deventer C.S.,University of the Free State
Journal of Cereal Science | Year: 2010

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. © 2010 Elsevier Ltd. All rights reserved.

Preharvest sprouting (PHS) has been recognised as the primary cause of low falling numbers (FNs) in wheat. From recent research it is clear that there are a number of additional causes of low FNs, including late maturity α-amylase. FNs of certain cultivars have varied considerably from year to year and across environments in the wheat producing areas of the Free State Province. In this study we aimed to determine whether climatic conditions could contribute to unexpectedly low FNs. Eleven cultivars were planted over a 5 year period in five different locations in the Free State Province. Total rainfall, minimum and maximum temperatures and growing degree days were determined during six environmental periods. Results from this study indicated that rainfall during the later stages of grain filling and grain maturity had a negative effect on the FNs of 7 of the 11 cultivars, while maximum temperatures during these growing periods were positively correlated with FN in 8 of the 11 cultivars. Minimum temperatures just prior to harvest could also determine the FNs of certain cultivars. Principal component analysis identified three groupings of cultivars varying in the frequency of low FNs experienced over the 5 years of the study. It is clear from this study that rainfall just prior to harvest, and therefore PHS, was not the major factor responsible for the low FNs obtained during this study. © 2012 Springer Science+Business Media B.V.

Jankielsohn A.,ARC Small Grain Institute
Journal of Economic Entomology | Year: 2016

Russian wheat aphid Diuraphis noxia (Kurdjumov) has spread from its native area in central Asia to all the major wheat-producing countries in the world to become an international wheat pest. Because the Russian wheat aphid is a serious threat to the wheat industry in South Africa, it is important to investigate the key factors involved in the distribution of Russian wheat aphid biotypes and in the changes of the Russian wheat aphid biotype complex in South Africa. There are currently four known Russian wheat aphid biotypes occurring in South Africa. Russian wheat aphid samples were collected from 2011 to 2014 during the wheat-growing season in spring and summer and these samples were screened to determine the biotype status. RWASA1 occurred predominantly in the Western Cape, while RWASA2 and RWASA3 occurred predominantly in the Eastern Free State. Following the first record of RWASA4 in 2011, this biotype was restricted to the Eastern Free State. The surveys suggest that the Russian wheat aphid bioype complex was more diverse in the Eastern Free State than in the other wheat production areas. There was also a shift in Russian wheat aphid biotype composition over time. The Russian wheat aphid biotype complex is dynamic, influenced by environmental factors such as host plants, altitude, and climate, and it can change and diversify over time causing fluctuation in populations over sites and years. This dynamic nature of the Russian wheat aphid will continue to challenge the development of Russian wheat aphid-resistant wheat cultivars in South Africa, and the continued monitoring of the biotypic and genetic structure, to determine genetic relatedness and variation in different biotypes, of Russian wheat aphid populations is important for protecting wheat. © The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America.

Jankielsohn A.,ARC Small Grain Institute
Journal of Economic Entomology | Year: 2011

Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) was recorded for the first time in South Africa in 1978. In 2005, a second biotype, RWASA2, emerged, and here we report on the emergence of yet another biotype, found for the first time in 2009 The discovery of new Russian wheat aphid biotypes is a significant challenge to the wheat, Triticum aestivum L., industry in South Africa. Russian wheat aphid resistance in wheat, that offered wheat producers a long-term solution to Russian wheat aphid control, may no longer be effective in areas where the new biotypes occur. It is therefore critical to determine the diversity and extent of distribution of biotypes in South Africa to successfully deploy Russian wheat aphid resistance in wheat. Screening of 96 Russian wheat aphid clones resulted in identification of three Russian wheat aphid biotypes. Infestations of RWASA1 caused susceptible damage symptoms only in wheat entries containing the Dn3 gene. Infestations of RWASA2 caused susceptible damage symptoms in wheat entries containing Dn1, Dn2, Dn3, and Dn9 resistant genes. Based on the damage-rating scores for the seven resistance sources, a new biotype, which caused damage rating scores different from those for RWASA1 and RWASA2, was evident among the Russian wheat aphid populations tested. This new biotype is virulent to the same resistance sources as RWASA2 (Dn1, Dn2, Dn3, and Dn9), but it also has added virulence to Dn4, whereas RWASA2 is avirulent to this resistance source. © 2011 Entomological Society of America.

Kutu F.R.,University of Limpopo | Asiwe J.A.N.,ARC Small Grain Institute
African Journal of Agricultural Research | Year: 2010

The productivity of different maize-dry bean intercrop systems (single and double rows of dry bean planted between two maize rows at low and high bean population) was assessed in 2006/07-08 seasons at different fertilizer application regimes (unfertilized control, low, adjusted low and optimum). Sole maize and dry bean plots were included as checks and together with the intercrop systems, they constituted the main treatment while the fertilizer regimes constituted the sub treatment. Treatments were arranged as a split plot design with three replications. There was a significant season x fertilizer interaction effect on maize grain and total biomass yields, and a significant season x cropping system interaction on dry bean grain yield. Grain yield for both crops were significantly (P<0.001) higher in 2007/08 with the highest maize grain yield of 2644 kg ha-1 obtained at optimum fertilizer rate. Dry bean grain yield of 875 and 829 kg ha1 obtained in 2007/08 at optimum and adjusted low fertilizer rates, respectively were comparable. The highest mean grain yield of 2101 kg ha-1 for maize and 728 kg ha-1 for dry bean across the two seasons were obtained in single-bean row intercrop planted at low and high population, respectively. The single dry bean row intercrop system gave the highest productivity based on the total LER values and thus appears the most appropriate for small-scale farmers. © 2010 Academic Journals.

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