Ovule dichotomy per locule of the trilocular pistil in cassava,Manihot esculenta: a useful abnormality for increased seed production?

Histologically, the cassava pistil is trilocular with a single ovule in each locule producing a maximum of three seeds in nature. Heat stress (35°/45°C, night/day temperatures), as a physical treatment was attempted to induce useful reproductive and vegetative traits in 10 F₁ hybrids derived from ‘OMR 36‐41’and ‘OMR 36‐42’crosses, and two Asian cassava cultivars,‘Rayong 60’and ‘Rayong 1′, under greenhouse and field conditions. Cytoembryological examination of the repro‐ ductive organs revealed morpho‐structural features of normal pistil in all clones except ‘Rayong 1’which exhibited reproductive variations under greenhouse culture. Genetically, an important variation was ovule dichotomy per locule of the trilocular pistil so that each pistil contained six instead of the usual three ovules and lacked any outer integument. These ovules possessed functional embryo sacs with varying nuclear number. A pair of the dichotomous ovules possessed two embryo sacs of apparent different megaspore mother cells. Vegetatively, F₁ hybrids were dwarf (0.50m) in their phenotype and flowered 1 month earlier than the 1.5‐2.0m tall cultivars under greenhouse conditions.     

Variation for bioactive compounds in ají (Capsicum baccatum L.) and rocoto (C. pubescens R. & P.) and implications for breeding

Ají (Capsicum baccatum L.) and rocoto (C. pubescens R. & P.) are two Capsicum pepper species native to the Andean region that have not been subjected to intensive breeding. However, the increase in its demand in European markets has sparked the development of breeding programmes for adaptation to Mediterranean climates, which include breeding for higher levels of bioactive compounds. We have studied the composition of red and yellow carotenoids (C _R and C _Y, respectively), ascorbic acid (AA), and total phenolics (TP) in 34 accessions of Capsicum, including 23 of C. baccatum, eight of C. pubescens, and 3 controls of C. annuum, which were grown in Spain both under greenhouse (GH) and open field (OF) conditions. The results show that in both growing conditions C. baccatum presents a considerable variation for most of the traits studied, with several accessions having similar or higher levels than C. annuum for the compounds studied. This indicates that C. baccatum is an important source of antioxidant compounds with nutritional value. On the contrary, C. pubescens had a poor performance, with low levels for all the compounds studied, and a poor adaptation to the conditions of Mediterranean climates. When considering the GH or OF growing cycles separately, heritability values were high (>0.75) for C _R, C _Y and AA, and moderate (0.42 for GH and 0.62 for OF) for TP. The existence of an important genotype × environment interaction resulted in lower levels for heritability when considering both growing cycles together, although the values were still high for C _R and AA (>0.6). Positive significant genotypic correlations among all the traits studied were found, except for TP with C _R and AA in the OF cycle. This information indicates that there are good prospects for developing C. baccatum varieties with higher levels of bioactive compounds.     

SR 15 — A new gene for use in the classification of puccinia graminis var. tritici

Sr15, a new gene giving resistance to certain strains of the wheat stem rust organism has been found in several varieties including Norka and Thew. It is located on chromosome 7A (XI), and is closely linked with the genes controlling resistance to certain strains of the organisms causing wheat leaf rust and powdery mildew. By the use of Sr15 in conjunction with genes present in stocks previously described, it has been possible to subdivide standard race 21 of stem rust into 24 components. The significance of this in relation to sources of resistance used in breeding is discussed.     

Will breeding for nitrogen use efficient crops lead to nitrogen use efficient cropping systems?: a simulation study of G×E×M interactions

The benefits of improving nitrogen use efficiency (NUE) in crops are typically studied through the performance of the individual crop. However, in order to increase yields in a sustainable way, improving NUE of the cropping systems must be the aim. We did a model simulation study to investigate how improvement of NUE traits of individual crops affects the succeeding crops and the NUE of the crop rotation. Based on experimental results parameterization was altered for different types of improved NUE in the EU-Rotate_N model, e.g. through higher N harvest index, reduced litter loss or improved root depth penetration rate. The different ways of improving NUE have different effects on the cropping system, affecting either N uptake, the ability of the crop to hold on to N already taken up, or the fraction of crop N being harvested. Due to the different modes of action, the model simulations show that these changes in NUE traits will also have different effects on N leaching loss and on N availability and N loss in the following years. Simulations also show that the effect of genotypes with improved NUE depend on environment and crop management. This is true for the improved crop itself and when its effect is analyzed for the whole cropping system. The environmental conditions, crop choices and management will all affect the fate of the N left in the soil, and whether this will contribute mainly to leaching loss or be used for production in later crops. As an example, increasing pre-crop fertilization was shown to affect the leaching after the following oilseed rape crop with up to 50 kg N ha^?1 taken up before it was lost to the environment when pre-crop fertilization as well as root depth penetration rate was high. All in all, the simulations illustrate the concept of NUE as the result of interactions between genotype, environment and crop management (G×E×M).     

Mapping Genes for Cotton Fiber Quality: A. thaliana as a Source of Candidate Genes

Cellulose synthesis could play an important rolein determining certain aspects of cotton fiberquality,and despite it's abundance in nature,little is known about the biosynthesis of thispolymer.Recent advances in understanding thesynthesis of cellulose come from the analysis ofArabidopsis thaliana cellulose-deficient mutants,and the isolation of a number of genes involved     

Development of bio-assays and screening for resistance to beet armyworm (Spodoptera Exigua Hübner) in Allium cepa L. and its wild relatives

The beet armyworm (Spodoptera exigua Hübner)is the most important pest in tropical Alliumcultivations. All shallot (Allium cepa L. group Aggregatum) cultivars are susceptible to this pest. Therefore accessions from three wild Alliumspecies, namely A. galanthum Kar. et Kir., A. fistulosum L. and A. royleiStearn, next to A. cepa L. were used to screen for resistance. First of all, a reliable bio-assay had to be developed. To this end transparent plastic cages with in total 5 plants of one accession per cage were placed on per lite in a heated greenhouse. Five 3-day old larvae were inoculated on each plant. Eight days after inoculation the number of surviving larvae per cage and the mean fresh weightper larva was determined. The lowest larval survival (36%) was found on A. roylei. This was not, however, significantly different from other Allium accessions. Significant differences were found in the fresh weight per larva fed on different Allium accessions. The larvae survived on A. roylei had a very low fresh weight (10.3 mg per larva), while those on an accession of A. fistulosum had the highest fresh weight (45.1 mg per larva). The larval fresh weight on A. roylei was lower than all the other accessions except from the tropical shallot cultivar Bawang Bali. To check whether or not a toxic compound was involved in the resistance present in A. roylei, tenaccessions from four Allium species were screened. Five 3-day old larvae were inoculated on regularly replaced leaf material of each accession ofAllium species. No significant differences were found in mean fresh weight per larva and mean survival of larvae among different accessions. There were also no significant differences in pupal weight and developmental time. All larvae became pupae 10 days after inoculation. The data indicate that there is no toxic compound present in A. roylei. These results are underlined by the observation in the greenhouse bio-assay that A. roylei plants were equally damaged by the beet armyworm compared to otherAllium species. The results obtained so far therefore suggest that introduction of resistance to S. exigua via the exploitation of variation for resistance to the beet armyworm in A. roylei is unclear and that genetic engineering using Cry sequences could provide a way forward. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identifying the impact of multi-hazards on crop yield—A case for heat stress and dry stress on winter wheat yield in northern China

Winter wheat production in northern China severely suffered from high temperatures and low relative humidity. However, the spatio-temporal pattern of heat stress and dry stress and the impacts of these multi-hazards on winter wheat yield have rarely been investigated. Using historical climate data, phenology data and yield records from 1980 to 2008, an analysis was performed to characterize the spatio-temporal variability of heat stress and dry stress in the post-heading stages of wheat growth in northern China. Additionally, these stresses’ impacts on winter wheat yield fluctuations were evaluated. Spatially, the central and northern parts of northern China have seen more serious heat stress, while greater dry stress has been observed in the northwest and north of the research area. Temporally, the heat stress has increased in the western part but decreased in the central and eastern parts of research area. Dry stress has aggravated in the entire northern China during the past decades, indicating the complexity of the exposure to adverse climate conditions. These two hazards (heat stress and dry stress) have contributed significant yield loss (up to 1.28% yield yr⁻¹) in most parts of the research region. The yield in the west was more sensitive to heat stress, and dry stress was the main hazard in the south. Additionally, the opposite spatial pattern between the sensitivity and exposure revealed that the climate is not the only factor controlling the yield fluctuation, the local adaptation measures used to mitigate negative influences of extreme events should not be ignored. In general, this study highlighted a focus on the impacts of multi-hazards on agricultural production, and an equal importance of considering local adaptation ability during the evaluation of agricultural risk in the future. Additionally, paying more attention to higher sensitive areas and to more reasonable and practical adaptive strategies is critical and significant for food supply security.     

Resistance to rice sheath blight (<Emphasis Type="Italic">Rhizoctonia solani</Emphasis> Kühn) [(teleomorph: <Emphasis Type="Italic">Thanatephorus cucumeris</Emphasis> (A.B. Frank) Donk.] disease: current status and perspectives

Sheath blight (ShB) disease, caused by Rhizoctonia solani, is an economically important rice disease worldwide, especially in intensive production systems. Several studies have been conducted to identify sources for ShB resistance in different species of rice, including local accessions and landraces. To date, none of the genotypes screened are immune to ShB, although variation in levels of resistance have been reported. Several quantitative trait loci (QTL) for ShB resistance have been identified using mapping populations derived from indica or japonica rice. A total of 33 QTL associated with ShB resistance located on all 12 rice chromosomes have been reported, with ten of these co-localizing with QTL for morphological attributes, especially plant height, or for heading date. Sixteen QTL, from the same or differing genetic backgrounds, have been mapped at least twice. Of these, nine QTL were independent of morphological traits and heading date. We hypothesize that two main, distinct, mechanisms contribute to ShB resistance: physiological resistance and disease escape. Strategies to improve our understanding of the genetics of resistance to ShB are discussed.