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Abdel-Rahman E.M.,University of KwaZulu - Natal | Ahmed F.B.,University of KwaZulu - Natal | van den Berg M.,South African Sugarcane Research Institute
International Journal of Applied Earth Observation and Geoinformation | Year: 2010

The aim of this study was to explore the use of in situ spectroscopy for estimating sugarcane leaf nitrogen (N) concentration. Leaf spectral reflectance was measured using a field spectroradiometer in the 350-2500 nm range from sugarcane variety N19 crops of 6-7 months old under on-farm conditions. Lab-determined leaf N concentrations of the samples taken ranged from 1.00% to 1.55%. Vegetation indices based on simple ratio (SR); viz. SR (743, 1316), SR (743, 1317) and SR (741, 1323) generated from first-order derivatives of leaf reflectance showed the best correlation with leaf N concentration, with r2 values of 0.76 (P < 0.01), 0.75 (P < 0.01) and 0.74 (P < 0.01), respectively. The root mean square errors of prediction (RMSEP) using a leave-one-out cross validation method were 0.089% (P < 0.01) for SR (743, 1316), 0.092% (P < 0.01) for SR (743, 317) and 0.084% (P < 0.01) for SR (741, 1323). These results suggest that the in situ spectroscopy has potential use in predicting sugarcane leaf N. © 2009 Elsevier B.V. All rights reserved. Source

Ramburan S.,South African Sugarcane Research Institute
Field Crops Research | Year: 2014

Non-repeatable genotype. ×. ratoon (G. ×. R) and genotype. ×. site. ×. ratoon (G. ×. S. ×. R) interactions in sugarcane ( Saccharum sp.) restricts the evaluation of repeatable genotype. ×. site (G. ×. S) interactions, which is important for test site evaluation in breeding programs. Non-repeatable genotype. ×. environment (G. ×. E) interactions are rarely analysed and interpreted further in sugarcane. The aim of this study was to use environmental characterisation and multivariate methods when non-repeatable interactions dominate to (i) illustrate and interpret the confounding crop-year effects in sugarcane and its contribution to non-repeatable G. ×. E, (ii) investigate the nature and magnitude of G. ×. E interactions, and (iii) gain insights into test site similarities in the coastal region of South Africa to improve the efficiencies of the testing network. Variation in estimated recoverable crystal yield was larger for non-repeatable components compared to repeatable components in eight out of ten planting series. Additive main effects and multiplicative interaction (AMMI) biplots illustrated the differential genotype interactions with crop-years of the same trial. Principal components analysis (PCA) illustrated how crop-years clustered together on biplots in response to key environmental covariates derived from climatic data and crop growth models. Based on interpretations using integrated multivariate methods, it is hypothesised that non-repeatable G. ×. E interactions may be larger in autumn compared to spring harvests. AMMI biplots for individual crop-years showed that site T2 is redundant, and should be removed from the trial network without loss of information. Integrated environmental characterisation and multivariate visual appraisals are proposed as alternatives to understanding non-repeatable G. ×. E when crop and year effects cannot be separated experimentally. Hypotheses generated through visual appraisals should be subsequently tested quantitatively. © 2013 Elsevier B.V. Source

van Heerden P.D.R.,South African Sugarcane Research Institute
Sugar Tech | Year: 2014

Although information from Brazil and Australia indicate that trinexapac-ethyl (Moddus®) is an excellent new sugarcane ripener, there is no information on the response of South African varieties to this chemical. The objective of this investigation was to establish the ripening potential of this chemical in a local variety and to compare responses with current industry standards, 2-chloroethyl phosphonic acid (Ethephon®) and fluazifop-p-butyl (Fusilade Forte®). Evaluation was conducted in an irrigated plant and first ratoon crop of variety N32 at Pongola, South Africa. The field trial was laid out as a complete randomised design with five replicates per treatment. The nine treatments comprised: (a) untreated control, (b) Ethephon® (1.5 L/ha) applied 84 days before harvest (DBH), (c) Fusilade Forte® (0.2 L/ha) applied 43 DBH, (d) Moddus® at three rates (0.8, 1 and 2 L/ha) applied 70 DBH, (e) Ethephon® (1.5 L/ha) and Fusilade Forte® (0.2 L/ha) applied in combination 84 and 43 DBH, and (f) Moddus® (0.8 and 1 L/ha) and Fusilade Forte® (0.2 L/ha) applied in combination 70 and 43 DBH. The various ripener treatments improved estimated recoverable crystal (ERC) yields in the 12-month old crops by between 1.6 and 4.9 t/ha when compared with the control. Moddus® applied at 0.8 and 1 L/ha achieved similar improvements as Fusilade Forte® and Ethephon®, but at 2 L/ha outperformed the latter two ripeners by up to 1.9 t ERC/ha. Best ERC yield responses were achieved in the three combination treatments. However, the Moddus®-Fusilade Forte® combination treatments outperformed the standard Ethephon®-Fusilade Forte® combination treatment by up to 1 t ERC/ha. These results indicate that Moddus® is an effective sugarcane ripener under South African high-potential irrigated conditions and that improved in ERC yields exceeding those obtained with current industry standards might be possible. © 2013 Society for Sugar Research & Promotion. Source

Ramburan S.,South African Sugarcane Research Institute
Field Crops Research | Year: 2015

Recent changes in cultivar composition, the renewed drive to increase harvest age (HA), and the impacts of the Eldana borer (Eldana Saccharina Walker: Lepidoptera Pyralidae) in the rainfed regions of South Africa have created uncertainty about the optimal HA of sugarcane. This study aimed to (i) review the optimal HA of sugarcane in the coast and inland regions, (ii) determine the variability in optimal HA with cultivar, and (iii) investigate the interactions between cultivar eldana resistance levels and HA on productivity. A secondary objective was to summarise the results of dedicated cultivar. ×. HA experiments to evaluate the importance of this interaction. Cultivar evaluation trial data from 1980 to 2014 were categorized by region, HA, cultivar, and cultivar eldana resistance category. Mean estimated recoverable crystal yields (TERC) and percentage internodes bored (%IB) by eldana were plotted against HA using polynomial regression to investigate effects of region, cultivar, eldana resistance, and their interactions. Additionally, three separate cultivar. ×. HA factorial trials were analysed using linear mixed models. The HA and its associated interaction terms were highly significant (P<. 0.001) and generally accounted for more variation than the cultivar and crop main and interaction terms in the trial-based analyses. The combined data mining analysis showed that on average, the optimal HA in the coast and inland regions were 15 and 22 months, respectively. A cultivar. ×. HA. ×. region. ×. eldana infestation level interaction was demonstrated, suggesting that a generic optimal HA for specific cultivars cannot be recommended. There was a reduction in optimal HA for newer released cultivars, suggesting possible indirect selection for early maturity in the breeding programs for these regions. Eldana susceptible cultivars were more sensitive to damage as HA increased (4.1 compared with 3.1%IB per additional growth month for susceptible vs. resistant cultivars, respectively). Eldana resistance was essential for achieving the benefits of increased HA in the coastal region. The study highlights the importance of HA to sugarcane productivity and illustrates how an experimental database can be used to inform breeding strategies and gain insights into a key management factor of industrial importance. © 2015 Elsevier B.V. Source

Lopes M.S.,International Maize and Wheat Improvement CIMMYT | Araus J.L.,International Maize and Wheat Improvement CIMMYT | Araus J.L.,University of Barcelona | Van Heerden P.D.R.,South African Sugarcane Research Institute | Foyer C.H.,University of Leeds
Journal of Experimental Botany | Year: 2011

Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C 4 species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C 4 breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C 4 plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C 4 plants, shoot traits may also be important in maintaining high yields during drought. © 2011 The Author. Source

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