A temporal limit to the association between flag leaf life extension by fungicides and wheat yields

Three field experiments, each repeated over two or three seasons, on winter wheat investigated a possible limit to the association between grain yield and flag leaf life, as extended by fungicide application. The experiments involved up to six cultivars and different application rates, timings and frequencies of the strobilurin azoxystrobin and the triazole epoxiconazole. In the 2000/01 and 2001/02 seasons, the relationships between the thermal time to 37 % green flag leaf area (m) and yield deviated from linearity. 'Broken stick' models were fitted to cultivar x experiment combinations within each season and the limit to the benefit to yield associated with extending flag leaf life was 700 degrees C days (S.E. = 20.7) and 725 degrees C days (S.E. = 9.33) after anthesis in 2000/01 and 2001/02, respectively. In 2002/03, the relationship between yield and in did not deviate significantly (P > 0.05) from linearity, but in this latter year the fungicide application failed to increase In past 700 degrees C days. (c) 2004 Elsevier B.V. All rights reserved.

Delaying senescence of wheat with fungicides has interacting effects with cultivar on grain sulphur concentration but not with sulphur yield or nitrogen: sulphur ratios

Winter wheat was grown in three field experiments, each repeated over two or three seasons, to investigate effects of extending flag leaf life by fungicide application on the concentration, kg ha(-1) and mg grain(-1) of nitrogen (N) and sulphur (S) as well as N:S ratio and sodium dodecyl sulphate (SDS) sedimentation volume. The experiments involved up to six cultivars and different application rates, timings and frequencies of azoxystrobin and epoxiconazole. For every day the duration to 37 % green flag leaf area (m) was extended, N yield was increased by 2.58 kg ha(-1), N per grain by 0.00957 mg, S yield by 0.186 kg ha(-1) and S per grain by 0.000718 mg. The N:S ratio decreased by 0.0135 per day. There was no evidence that these responses varied with cultivar. In contrast, the relationship between flag leaf life and N or S concentration interacted with cultivar. The N and S concentrations of Shamrock, the cultivar that suffered most from brown rust (Puccinia rccondita), increased with the extension of flag leaf life whereas the concentrations of N and S in Malacca, a cultivar more susceptible to Septoria tritici, decreased as flag leaf senescence was delayed. This was because the relationships between m and N and S yields were much better conserved over cultivars than those between m and thousand grain weight (TGW) and grain yield ha(-1). (c) 2004 Elsevier B.V. All rights reserved.

Cell and nuclear degradation in sweetpotato [Ipomoea batatas (L.) Lam.] root meristems following exposure to salinity

Sodium chloride-induced cell and nuclear degradation in the root meristems of sweetpotato [Ipomoea batatas (L.) Lam.] were determined using fluorescent microscopy and flow cytometry analysis. Two sweetpotato cultivars were grown in liquid Murashige and Skoog medium and subjected to 0 mM and 500 mM NaCl, with or without 15 mM CaCl2, for periods up to 24 h. Changes to the nuclei of root meristematic cells showed a similar pattern of damage to the nuclei using both fluorescent microscopy and flow cytometry analysis. Damage occurring after only a few hours was followed by nuclear degradation at 24 h. Flow cytometry histograms showed a reduction in G1 and G2 nuclei and an increase in degraded nuclei in NaCl-stressed roots. Salinity-induced nuclear degradation was alleviated by the addition of CaCl2.

The effects of adding picoxystrobin, azoxystrobin and nitrogen to a triazole programme on disease control, flag leaf senescence, yield and grain quality of winter wheat

The effect of adding strobilurins to a triazole (epoxiconazole) fungicide programme on the quality of a range of wheat cultivars was assessed in field experiments in three successive years. Strobilurin was applied at just flag leaf emergence (azoxystrobin) or at the start of stem extension (azoxystrobin or picoxystrobin) and again at flag leaf emergence or at flag leaf emergence and again at ear emergence (azoxystrobin). All strobilurin treatments reduced disease levels, delayed senescence of the flag leaf and consistently increased yields, thousand grain weight and specific weight. Reductions in Hagberg falling number were observed, even by fungicide applications at the start of stem extension, but effects were small compared to the variation among cultivars. Application of fungicide (triazole or strobilurin) before ear emergence increased the amount of blackpoint, but this was partly countered by applying azoxystrobin at ear emergence. The effect of fungicide on protein concentration differed over seasons and cultivar. Where they occurred. small reductions in protein concentration could be compensated for by extra application of nitrogen as foliar urea at anthesis. Foliar urea (40 kg N ha(-1)) applied at anthesis also improved Hagberg failing number and reduced blackpoint in one of the growing seasons. In one season, the effect of foliar urea at anthesis was compared with applications of granular fertiliser at flag leaf emergence. The granular treatment produced grain with more concentrated protein, while the later, foliar application produced higher specific weights. (C) 2003 Elsevier Science Ltd. All rights reserved.

The influence of winter oilseed rape (Brassica napus ssp oleifera var. biennis) cultivar and grass genotype on the competitive balance between crop and grass weeds

Three experiments conducted over two years (2002-04) at the Crops Research Unit, University of Reading, investigated competition between autumn sown oilseed rape cultivars (Brassica napus L. ssp. oleifera var. biennis (DC.) Metzg.) and Lolium multiflorum Lam., L. x boucheanum Kunth and Alopecurus myosuroides Huds., sown as indicative grass weeds. Rape cultivar (cv.) had a substantial effect on grass weed seed return. Over the six cultivars tested, L. multiflorum spikelet production ranged from just under 400 spikelets/m(2) in the presence of cv. Winner to nearly 5800 in competition with cv. Lutin. Cultivar competitiveness was associated with high biomass, large dense floral layers and early stem extension. There was some evidence of differential competitive tolerance between rape cultivars. The results suggested that rape cultivars could be screened for competitiveness by measuring floral layer interception of photosynthetic active radiation. L. x boucheanum cultivars varied in ability to compete with rape. In the absence of inter-specific competition, spikelet density was similar for Aberecho and Polly (circa 31000 spikelets/m(2)) but when grown with rape Polly outyielded Aberecho (i.e. 12 090 and 7990 spikelets/m(2) respectively).

Comparing rice production systems: A challenge for agronomic research and for the dissemination of knowledge-intensive farming practices

This article is a commentary on several research studies conducted on the prospects for aerobic rice production systems that aim at reducing the demand for irrigation water which in certain major rice producing areas of the world is becoming increasingly scarce. The research studies considered, as reported in published articles mainly under the aegis of the International Rice Research Institute (IRRI), have a narrow scope in that they test only 3 or 4 rice varieties under different soil moisture treatments obtained with controlled irrigation, but with other agronomic factors of production held as constant. Consequently, these studies do not permit an assessment of the interactions among agronomic factors that will be of critical significance to the performance of any production system. Varying the production factor of "water" will seriously affect also the levels of the other factors required to optimise the performance of a production system. The major weakness in the studies analysed in this article originates from not taking account of the interactions between experimental and non-experimental factors involved in the comparisons between different production systems. This applies to the experimental field design used for the research studies as well as to the subsequent statistical analyses of the results. The existence of such interactions is a serious complicating element that makes meaningful comparisons between different crop production systems difficult. Consequently, the data and conclusions drawn from such research readily become biased towards proposing standardised solutions for possible introduction to farmers through a linear technology transfer process. Yet, the variability and diversity encountered in the real-world farming environment demand more flexible solutions and approaches in the dissemination of knowledge-intensive production practices through "experiential learning" types of processes, such as those employed by farmer field schools. This article illustrates, based on expertise of the 'system of rice intensification' (SRI), that several cost-effective and environment-friendly agronomic solutions to reduce the demand for irrigation water, other than the asserted need for the introduction of new cultivars, are feasible. Further, these agronomic Solutions can offer immediate benefits of reduced water requirements and increased net returns that Would be readily accessible to a wide range of rice producers, particularly the resource poor smallholders. (C) 2009 Elsevier B.V. All rights reserved.

The effect of environment on endosperm cell-wall development in Triticum aestivum during grain filling: an infrared spectroscopic imaging study

One of the major factors contributing to the failure of new wheat varieties is seasonal variability in end-use quality. Consequently, it is important to produce varieties which are robust and stable over a range of environmental conditions. Recently developed sample preparation methods have allowed the application of FT-IR spectroscopic imaging methods to the analysis of wheat endosperm cell wall composition, allowing the spatial distribution of structural components to be determined without the limitations of conventional chemical analysis. The advantages of the methods, described in this paper, are that they determine the composition of endosperm cell walls in situ and with minimal modification during preparation. Two bread-making wheat cultivars, Spark and Rialto, were selected to determine the impact of environmental conditions on the cell-wall composition of the starchy endosperm of the developing and mature grain, focusing on the period of grain filling (starting at about 14 days after anthesis). Studies carried out over two successive seasons show that the structure of the arabinoxylans in the endosperm cell walls changes from a highly branched form to a less branched form. Furthermore, during development the rate of restructuring was faster when the plants were grown at higher temperature with restricted water availability from 14 days after anthesis with differences in the rate of restructuring occurring between the two cultivars.

Prediction of cottonseed longevity

The objective of this work was to determine the viability equation constants for cottonseed and to detect the occurrence and depletion of hardseededness. Three seedlots of Brazilian cultivars IAC-19 and IAC-20 were tested, using 12 moisture content levels, ranging from 2.2 to 21.7% and three storage temperatures, 40, 50 and 65 degrees C. Seed moisture content level was reached from the initial value (around 8.8%) either by rehydration, in a closed container, or by drying in desiccators containing silica gel, both at 20 degrees C. Twelve seed subsamples for each moisture content/temperature treatment were sealed in laminated aluminium-foil packets and stored in incubators at those temperatures, until complete survival curves were obtained. Seed equilibrium relative humidity was recorded. Hardseededness was detected at moisture content levels below 6% and its releasing was achieved either naturally, during storage period, or artificially through seed coat removal. The viability equation quantified the response of seed longevity to storage environment well with K-E = 9.240, C-W = 5.190, C-H = 0.03965 and C-Q = 0.000426. The lower limit estimated for application of this equation at 65 degrees C was 3.6% moisture content.

The effects of dwarfing genes on seedling root growth of wheat

Most modern wheat cultivars contain major dwarfing genes, but their effects on root growth are unclear. Near-isogenic lines (NILs) containing Rht-B1b, Rht-D1b, Rht-B1c, Rht8c, Rht-D1c, and Rht12 were used to characterize the effects of semi-dwarfing and dwarfing alleles on root growth of 'Mercia' and 'Maris Widgeon' wheat cultivars. Wheat seedlings were grown in gel chambers, soil-filled columns, and in the field. Roots were extracted and length and dry mass measured. No significant differences in root length were found between semi-dwarfing lines and the control lines in any experiment, nor was there a significant difference between the root lengths of the two cultivars grown in the field. Total root length of the dwarf lines (Rht-B1c, Rht-D1c, and Rht12) was significantly different from that of the control although the effect was dependent on the experimental methodology; in gel chambers root length of dwarfing lines was increased by; 40% while in both soil media it was decreased (by 24-33%). Root dry mass was 22-30% of the total dry mass in the soil-filled column and field experiments. Root length increased proportionally with grain mass, which varied between NILs, so grain mass was a covariate for the analysis of variance. Although total root length was altered by dwarf lines, root architecture (average root diameter, lateral root: total root ratio) was not affected by reduced height alleles. A direct effect of dwarfing alleles on root growth during seedling establishment, rather than a secondary partitioning effect, was suggested by the present experiments.

Evaluation of a predictive model for Mycosphaerella graminicola for economic and environmental benefits

A method was developed to evaluate crop disease predictive models for their economic and environmental benefits. Benefits were quantified as the value of a prediction measured by costs saved and fungicide dose saved. The value of prediction was defined as the net gain made by using predictions, measured as the difference between a scenario where predictions are available and used and a scenario without prediction. Comparable 'with' and 'without' scenarios were created with the use of risk levels. These risk levels were derived from a probability distribution fitted to observed disease severities. These distributions were used to calculate the probability that a certain disease induced economic loss was incurred. The method was exemplified by using it to evaluate a model developed for Mycosphaerella graminicola risk prediction. Based on the value of prediction, the tested model may have economic and environmental benefits to growers if used to guide treatment decisions on resistant cultivars. It is shown that the value of prediction measured by fungicide dose saved and costs saved is constant with the risk level. The model could also be used to evaluate similar crop disease predictive models.

A predictive model for early-warning of Septoria leaf blotch on winter wheat

Disease-weather relationships influencing Septoria leaf blotch (SLB) preceding growth stage (GS) 31 were identified using data from 12 sites in the UK covering 8 years. Based on these relationships, an early-warning predictive model for SLB on winter wheat was formulated to predict the occurrence of a damaging epidemic (defined as disease severity of 5% or > 5% on the top three leaf layers). The final model was based on accumulated rain > 3 mm in the 80-day period preceding GS 31 (roughly from early-February to the end of April) and accumulated minimum temperature with a 0A degrees C base in the 50-day period starting from 120 days preceding GS 31 (approximately January and February). The model was validated on an independent data set on which the prediction accuracy was influenced by cultivar resistance. Over all observations, the model had a true positive proportion of 0.61, a true negative proportion of 0.73, a sensitivity of 0.83, and a specificity of 0.18. True negative proportion increased to 0.85 for resistant cultivars and decreased to 0.50 for susceptible cultivars. Potential fungicide savings are most likely to be made with resistant cultivars, but such benefits would need to be identified with an in-depth evaluation.

Challenges of in situ conservation of crop wild relatives

Crop wild relatives (CWRs) will gain in importance as changing climates put both traditional and advanced cultivars under increasing stress, leading to a need for plant breeding to produce new varieties able to grow under the new climate regimes. Traditionally, the approach to the conservation of CWRs has been ex situ - the collection and maintenance of seed accessions in national, regional, and international germplasm banks, supplemented by field genebanks for species with recalcitrant seeds. More recently the need to maintain CWRs in their natural habitats (in situ) has been advocated. This is very different from on-farm conservation of traditional land races and is a complex multidisciplinary process. Particular problems that have to be addressed include the adoption of a workable definition of what is a CWR, application of priority-determining mechanisms because of the large number of candidate species of CWRs, assessment of the effectiveness of conservation approaches, the relative costs of in situ and ex situ approaches, integration of CWR in situ conservation into national programmes, and the challenges posed by global change. CWRs may be conserved in both protected and non-protected areas. Presence in the former is no guarantee of their survival and in most cases some degree of management intervention is required. Experience derived from recent EU- and GEF-funded CWR conservation initiatives will be drawn upon.

Application of real-time and multiplex PCR assays to study leaf blotch epidemics in barley

Leaf blotch, caused by Rhynchosporium secalis, was studied in a range of winter barley cultivars using a combination of traditional plant pathological techniques and newly developed multiplex and real-time polymerase chain reaction (PCR) assays. Using PCR, symptomless leaf blotch colonization was shown to occur throughout the growing season in the resistant winter barley cv. Leonie. The dynamics of colonization throughout the growing season were similar in both Leonie and Vertige, a susceptible cultivar. However, pathogen DNA levels were approximately 10-fold higher in the susceptible cultivar, which expressed symptoms throughout the growing season. Visual assessments and PCR also were used to determine levels of R. secalis colonization and infection in samples from a field experiment used to test a range of winter barley cultivars with different levels of leaf blotch resistance. The correlation between the PCR and visual assessment data was better at higher infection levels (R(2) = 0.81 for leaf samples with >0.3% disease). Although resistance ratings did not correlate well with levels of disease for all cultivars tested, low levels of infection were observed in the cultivar with the highest resistance rating and high levels of infection in the cultivar with the lowest resistance rating.

The influence of winter oilseed rape (Brassica napus ssp oleifera var. biennis) cultivar and grass genotype on the competitive balance between crop and grass weeds

Three experiments conducted over two years (2002-04) at the Crops Research Unit, University of Reading, investigated competition between autumn sown oilseed rape cultivars (Brassica napus L. ssp. oleifera var. biennis (DC.) Metzg.) and Lolium multiflorum Lam., L. x boucheanum Kunth and Alopecurus myosuroides Huds., sown as indicative grass weeds. Rape cultivar (cv.) had a substantial effect on grass weed seed return. Over the six cultivars tested, L. multiflorum spikelet production ranged from just under 400 spikelets/m(2) in the presence of cv. Winner to nearly 5800 in competition with cv. Lutin. Cultivar competitiveness was associated with high biomass, large dense floral layers and early stem extension. There was some evidence of differential competitive tolerance between rape cultivars. The results suggested that rape cultivars could be screened for competitiveness by measuring floral layer interception of photosynthetic active radiation. L. x boucheanum cultivars varied in ability to compete with rape. In the absence of inter-specific competition, spikelet density was similar for Aberecho and Polly (circa 31000 spikelets/m(2)) but when grown with rape Polly outyielded Aberecho (i.e. 12 090 and 7990 spikelets/m(2) respectively).

An enhanced microsatellite map of diploid Fragaria

A total of 45 microsatellites (SSRs) were developed for mapping in Fragaria. They included 31 newly isolated codominant genomic SSRs from F. nubicola and a further 14 SSRs, derived from an expressed sequence tagged library (EST-SSRs) of the cultivated strawberry, F. × ananassa. These, and an additional 64 previously characterised but unmapped SSRs and EST-SSRs, were scored in the diploid Fragaria interspecific F2 mapping population (FV×FN) derived from a cross between F. vesca 815 and F. nubicola 601. The cosegregation data of these 109 SSRs, and of 73 previously mapped molecular markers, were used to elaborate an enhanced linkage map. The map is composed of 182 molecular markers (175 microsatellites, six gene specific markers and one sequence-characterised amplified region) and spans 424 cM over seven linkage groups. The average marker spacing is 2.3 cM/marker and the map now contains just eight gaps longer than 10 cM. The transferability of the new SSR markers to the cultivated strawberry was demonstrated using eight cultivars. Because of the transferable nature of these markers, the map produced will provide a useful reference framework for the development of linkage maps of the cultivated strawberry and for the development of other key resources for Fragaria such as a physical map. In addition, the map now provides a framework upon which to place transferable markers, such as genes of known function, for comparative mapping purposes within Rosaceae.