Incomplete resistance to coffee leaf rust (Hemileia vastatrix)

Incomplete resistance to coffee leaf rust ( Hemileia vastatrix ) may be of value in obtaining durable resistance, which is of great importance for the perennial coffee crop. Methods were developed to assess incomplete resistance to coffee leaf rust by using illustrated scales ranging from 0 to 9 (Chapter 1). A laboratory screening method, which uses leaf disks, has been standardized. The method is satisfactory for the assessment of complete and incomplete resistance (Chapter 2). Resistance to coffee leaf rust appeared to be affected by light intensity and leaf age (Chapters 3 and 4). In general, coffee leaves were more resistant under low than under high light intensities. The effect of leaf age varied with the coffee genotype. In general, however, old leaves were more susceptible than adult or young leaves.From 1976 to 1980, seven new races of H. vastatrix were found in breeding plots in Campinas (Chapter 5). Four races overcome combinations of known resistance genes in Coffea arabica and three races overcome yet unidentified resistances from C. canephora . Three other rust genotypes were found with intermediate virulence to certain resistance genes. Possibilities for obtaining durable resistance based on major genes are discussed.In Chapters 6, 7 and 8 a characterization is given of incomplete resistance in C. arabica , C. canephora cv. 'Kouillou' and in the 'Icatu' population. Icatu derives from a cross between C. canephora and C. arabica . In C. arabica , the period between the onset of sporulation till leaf abscission (leaf retention period) appeared to be an important determinant of the disease level in the field. Significant variation for latency period and lesion density was observed, but results were fairly inconsistent. Disease level in the field was positively correlated with productivity. In 'Kouillou' large variation for incomplete resistance was found. Genotypes were detected with high resistance expressed by a low lesion density and a quite high reaction type. These genotypes may have value for obtaining durable resistance to coffee leaf rust. Incomplete resistance in Icatu was mainly expressed by heterogeneous reaction types. Components of resistance were related to reaction type. Incomplete resistance of varying degrees was race-specific.In the general discussion the relevance of the findings for coffee breeding and the links to resistance theories are pointed out

Hubbard model versus t-J model: The one-particle spectrum

The origin of the apparent discrepancies between the one-particle spectra of the Hubbard and t-J models is revealed: Wavefunction corrections, in addition to the three-site terms, should supplement the bare t-J. In this way a quantitative agreement between the two models is obtained, even for the intermediate-$U$ values appropriate for the high-Tc cuprate superconductors. Numerical results for clusters of up to 20 sites are presented. The momentum dependence of the observed intensities in the photoemission spectra of Sr2CuO2Cl2 are well described by this complete strong-coupling approach.Comment: 4 two-column RevTeX pages, including 4 Postscript figures. Uses epsf. Accepted for publication in Physical Review B, Rapid Communicatio

Global approaches to cocoa germplasm utilization and conservation: Final report of the CFC/ICCO/IPGRI project on ”Cocoa Germplasm Utilization and Conservation: a Global Approach” (1998-2004)

Cocoa is a commodity produced in the developing countries of the tropics and consumed mostly in the middle- and high-income countries of the world's temperate zones. Currently, over 50 countries engage in cocoa production, of which some heavily rely on cocoa exports for their economic development as they contribute significantly to their foreign exchange earnings. From a level of 1.5 million tonnes in 1983-84, world production of cocoa beans is steadily rising and has reached a peak of 3.5 million tonnes in 2003-04. This significant increase is almost entirely due to an expansion of production area. Over 90% of world cocoa is produced by smallholder farmers who rely almost entirely on the supply of improved planting material from national and international research institutes. Nearly all producing countries grow cocoa on an extensive basis resulting in low average yields, which - on global average - have only increased little over the past three decades. This contrasts with the often dramatic advances in yields of other tropical or temperate crops and in particular for other raw materials, often used to manufacture snack foods which are competitive with cocoa. Gains in global yield and productivity of cocoa are now essential. As pressure on available land increases, the need for higher yielding, pest- and disease-resistant cocoa varieties becomes ever more urgent. This Technical Paper is the result of work undertaken in the CFC/ICCO/IPGRI project: ”Cocoa Germplasm Utilization and Conservation: a Global Approach”, which aimed at a more sustainable production of cocoa at lower costs, by making optimal use of cocoa germplasm. Special attention was paid to the evaluation and selection of resistance to some of the major diseases and pests, such as black pod, witches' broom, vascular streak dieback, moniliasis, cocoa swollen shoot virus and mirids, which together cause losses of an estimated 40% percent of annual world cocoa production. The Common Fund for Commodities acknowledges the significant inputs of both the International Cocoa Organization (ICCO) as Project Supervisory Body, and the International Plant Genetic Resources Institute (IPGRI) as Project Executing Agency for the successful implementation of the project in 12 countries. In line with the policy to disseminate the information produced by activities financed by the Fund, it is my expectation that this publication will be instrumental to make the results and experiences of this project available to a wider audience. It is hoped that extension workers, researchers and policy-makers would find this publication useful and relevant for improving access of higher yielding, good bean quality and disease-resistant cocoa varieties to farmers

Superconductivity in the two dimensional Hubbard Model.

Quasiparticle bands of the two-dimensional Hubbard model are calculated using the Roth two-pole approximation to the one particle Green's function. Excellent agreement is obtained with recent Monte Carlo calculations, including an anomalous volume of the Fermi surface near half-filling, which can possibly be explained in terms of a breakdown of Fermi liquid theory. The calculated bands are very flat around the (pi,0) points of the Brillouin zone in agreement with photoemission measurements of cuprate superconductors. With doping there is a shift in spectral weight from the upper band to the lower band. The Roth method is extended to deal with superconductivity within a four-pole approximation allowing electron-hole mixing. It is shown that triplet p-wave pairing never occurs. Singlet d_{x^2-y^2}-wave pairing is strongly favoured and optimal doping occurs when the van Hove singularity, corresponding to the flat band part, lies at the Fermi level. Nearest neighbour antiferromagnetic correlations play an important role in flattening the bands near the Fermi level and in favouring superconductivity. However the mechanism for superconductivity is a local one, in contrast to spin fluctuation exchange models. For reasonable values of the hopping parameter the transition temperature T_c is in the range 10-100K. The optimum doping delta_c lies between 0.14 and 0.25, depending on the ratio U/t. The gap equation has a BCS-like form and (2*Delta_{max})/(kT_c) ~ 4.Comment: REVTeX, 35 pages, including 19 PostScript figures numbered 1a to 11. Uses epsf.sty (included). Everything in uuencoded gz-compressed .tar file, (self-unpacking, see header). Submitted to Phys. Rev. B (24-2-95

Comparison of two cacao (Theobroma cacao L.) clones for the effect of pollination intensity on fruit set and seed content

We compared the influence of pollination intensity (PI) on fruit set and seed number per pod in two cacao (Theobroma cacao L.) clones, IFC5 (Forastero Lower-Amazon Amelonado), which is self-compatible and known to produce a high number of seeds per pod under open pollination, and SCA6 (Forastero Upper-Amazon), which is self-incompatible and known to produce a low number of seeds per pod under open pollination. With both clones, PI had a positive effect on fruit set, with the maximum rate requiring more than 150 pollen grains per pod. One-half of the maximum rate of fruit set was reached with 39 pollen grains per pod for SCA6, and 78 for IFC5. With SCA6, a significant positive effect of PI on seed number per pod was also observed, with maximum seed number requiring more than 200 pollen grains per pod. In contrast, seed numbers with IFC5 were approximately equal over the PI range 100-800 pollen grains per pod. Patterns of seed number per pod were compared after: (1) open insect pollination, (2) low-intensity hand pollination and (3) high-intensity hand pollination. The patterns obtained with IFC5 under open pollination showed a peak of 40-50 seeds per pod, whereas the distribution patterns were more even with SCA6. The pattern of seed number under open pollination was similar to that obtained with high-intensity hand pollination for IFC5, and with low-intensity hand pollination for SCA6. We concluded that the high number of seeds per pod observed with IFC5 under natural insect pollination may be explained by a high number of compatible self-pollen grains on the stigma and by a severe drop of low-pollinated flowers eliminating potential low-filled fruits. With SCA6, however, the number of compatible pollen grains deposited on the stigma was probably low under open pollination, and the flowers required lower pollen quantities to set fruit, which resulted in a high frequency of low seed numbers per fruit. This difference in the capacity to set low-seeded fruits might be considered as an adaptive trait related to the mode of reproduction [KEYWORDS: Theobroma cacao, pollination intensity, fruit set, seed set, self-compatibility]

Phenotypic diversity of cacao (Theobroma cacao L.) on farms and in the gene bank in Cameroon.

open access International audienceA survey was undertaken in the 2 major cocoa producing areas (Southern and Western) of Cameroon to study the morphological diversity existing in cacao farms in relation to genetic diversity in gene bank accessions. A total of 300 farm accessions (FA) were selected in the field which were compared to 77 gene bank accessions distributed into 4 groups (AGs) according to their origin. The 17 quantitative and qualitative descriptors used in this study were related to leaf (flush colour), flower (ligule colour), pod (weight, length, width, apex form, shape, rugosity, colour, husk hardness, basal constriction and pod index) and seed (number, length, width, dry weight and colour) characters. For the qualitative characters evaluated, considerable morphological variation was observed using the Shannon Weaver diversity index (SWDI) within FA and gene bank accessions. Among the FA, a differentiation between southern and western regions was only possible when using quantitative pod traits. Mean quantitative traits values of FA were not too different than those of most gene bank AGs, except for a few traits of agronomical interest (seed weight and pod index). No significant variation was observed for seed traits in all FA groups (southern/western). The morphological structure (quantitative traits) showed spatial differentiation between western and southern FA and a closer relationship between gene bank and some farm accessions. Furthermore, a molecular study done earlier using microsatellite profiles of the same FA did not show any genetic difference between FA of both regions, suggesting that the agro-morphological performance of FA is rather due to non-genetic factors. In contrast, microsatellites have shown that most of the gene bank accessions were genetically distant from the FA, suggesting the low intake of some breeders’ genotypes to farmers’ fields. The level of diversity found in farmers’ germplasm could enhance the gene bank and current breeding programs

Collaborative and participatory approaches to cocoa variety improvement: Final report of the CFC/ICCO/Bioversity project on “Cocoa Productivity and quality improvement: a Participatory Approach” (2004-2010)

This Final Report summarizes the outcomes of the Closing Workshop of the CFC/ICCO/Bioversity project on “Cocoa Productivity and Quality Improvement: a Participatory Approach”, convened at the end of May 2010 in Accra, Ghana. The workshop formally marked the conclusion of the project that was launched in June 2004, but which was building on the achievements of the CFC/ICCO/IPGRI project on “Cocoa Germplasm Utilization and Conservation: a Global Approach” implemented between 1998 and 2004. Thus many of the results presented here reflect the work done over a long period of tim

Antixenosis as a mechanism of cocoa resistance to the cocoa mirid, Sahlbergella singularis (Hemiptera: Miridae)

Poster presented at 16th International Cocoa Research Conference Towards Rational Cocoa Production and Efficient Use for a Sustainable World Cocoa Economy. Summaries. Denpasar, Bali (Indonesia), 16-21 Nov 200