The effects of sorghum and cowpea genotype and sorghum sowing density in an intercrop system.

Five diverse sorghum genotypes were sown at sole crop density and at intercrop density with-out cowpea and with two contrasting cowpea genotypes, in the post-rainy season at Hyderabad, India. The interaction of sorghum genotype with sowing density was significant for sorghum dry fodder and grain yield, but the interaction of sorghum genotype with cowpea was not, because of compensation between yield components. The likely response of sorghum genotypes to intercropping can therefore be assessed initially from the performance of low density sole crops, followed by assessment in the presence of a single standard cowpea variety. The cowpea genotypes were affected by the presence of sorghum but not by the sorghum genotype. This suggests that the effect on the cowpea can be ignored when selecting a sorghum genotype for intercropping, and that a cowpea genotype for intercropping can be selected in the presence of a single sorghum genotype. However, these conclusions are unlikery to apply to rain season sowings, when sorghum dominates the intercrop more completely

Logarithmic corrections to gap scaling in random-bond Ising strips

Numerical results for the first gap of the Lyapunov spectrum of the self-dual random-bond Ising model on strips are analysed. It is shown that finite-width corrections can be fitted very well by an inverse logarithmic form, predicted to hold when the Hamiltonian contains a marginal operator.Comment: LaTeX code with Institute of Physics macros for 7 pages, plus 2 Postscript figures; to appear in Journal of Physics A (Letter to the Editor

Connectivity-dependent properties of diluted sytems in a transfer-matrix description

We introduce a new approach to connectivity-dependent properties of diluted systems, which is based on the transfer-matrix formulation of the percolation problem. It simultaneously incorporates the connective properties reflected in non-zero matrix elements and allows one to use standard random-matrix multiplication techniques. Thus it is possible to investigate physical processes on the percolation structure with the high efficiency and precision characteristic of transfer-matrix methods, while avoiding disconnections. The method is illustrated for two-dimensional site percolation by calculating (i) the critical correlation length along the strip, and the finite-size longitudinal DC conductivity: (ii) at the percolation threshold, and (iii) very near the pure-system limit.Comment: 4 pages, no figures, RevTeX, Phys. Rev. E Rapid Communications (to be published

Surface crossover exponent for branched polymers in two dimensions

Transfer-matrix methods on finite-width strips with free boundary conditions are applied to lattice site animals, which provide a model for randomly branched polymers in a good solvent. By assigning a distinct fugacity to sites along the strip edges, critical properties at the special (adsorption) and ordinary transitions are assessed. The crossover exponent at the adsorption point is estimated as $\phi = 0.505 \pm 0.015$, consistent with recent predictions that $\phi = 1/2$ exactly for all space dimensionalities.Comment: 10 pages, LaTeX with Institute of Physics macros, to appear in Journal of Physics

On locations and properties of the multicritical point of Gaussian and +/-J Ising spin glasses

We use transfer-matrix and finite-size scaling methods to investigate the location and properties of the multicritical point of two-dimensional Ising spin glasses on square, triangular and honeycomb lattices, with both binary and Gaussian disorder distributions. For square and triangular lattices with binary disorder, the estimated position of the multicritical point is in numerical agreement with recent conjectures regarding its exact location. For the remaining four cases, our results indicate disagreement with the respective versions of the conjecture, though by very small amounts, never exceeding 0.2%. Our results for: (i) the correlation-length exponent $\nu$ governing the ferro-paramagnetic transition; (ii) the critical domain-wall energy amplitude $\eta$; (iii) the conformal anomaly $c$; (iv) the finite-size susceptibility exponent $\gamma/\nu$; and (v) the set of multifractal exponents $\{\eta_k \}$ associated to the moments of the probability distribution of spin-spin correlation functions at the multicritical point, are consistent with universality as regards lattice structure and disorder distribution, and in good agreement with existing estimates.Comment: RevTeX 4, 9 pages, 2 .eps figure

Efeito do cruzamento entre linhas diploides e tetraploides de melancia na producao de sementes hibridas.

Os hibridos triploides de melancia, apesar de crescentemente preferidos nos principais mercados consumidores dos EUA, Uniao Europeia e Japao, apresentam elevado preco da semente e problemas de germinacao. Correntemente, os mesmos sao produzidos pelo cruzamento de linhas diploides como fornecedoras de polen com linhas tetraploides. Em um experimento realizado em casa de vegetacao na Embrapa Semi- Arido, amostras de 20 sementes de uma linha parcialmente endogamica e da populacao Charleston Tetra Numero 3 (CT3) foram postas para germinar utilizando substrato comercial "Plantmax"para hortalicas e posteriormente transplantadas para sacos plasticos de 20 litros de solo, 15 apos o semeio. As plantas foram tutoradas e os ramos foram amarrados com fita plastica a medida que se desenvolveram. Quando as plantas iniciaram o florescimento foram feitos cruzamentos entre a linha diploide e a cultivar CT3 nos dois sentidos. Depois da colheita as sementes foram extraidas e postas para secar a sombra. De cada cruzamento foi retirada uma amostra de dez sementes para verificar a presenca de embrioes, que uma vez encontrados foram postos para germinar em condicoes de laboratorio. Observou-se que sementes triploides podem ser obtidas em cruzamentos envolvendo linhas diploides, resistente ao oidio, com plantas da populacao tetraploide CT3, nos dois sentidos. Foi observado que existe uma capacidade especifica de combinacao entre plantas diploides e tetraploides para formacao de sementes com embrioes, bem como, para a germinacao dos embrioes formados. Esta especificidade na combinacao entre plantas diploides e tetraploides, deve ser levada em conta no programa de melhoramento de melancia para o desenvolvimento de hibridos triploides.Suplemento. Edição do 41 Congresso Brasileiro de Olericultura; 1 Encontro sobre Plantas Medicinais, Aromáticas e Condimentares, Brasília, DF, jul. 2001

Genotypic variation in the response of sorghum to intercropping with cowpea, and in the effect on the associated legume.

Selection of sorghum genotypes for the sorghum-cowpea intercrop system would be simplified if it could be done in sole crop. In order to compare evaluation in sole crop and in the presence of the standard cowpea cultivar c 152, sorghum inbred lines, F2 hybrids and land races which differed in maturity date, height and canopy characters were grown in the two systems in two seasons at Hyderabad,India. Cowpea sole crop was included as an additional treatment. Sorghum canopy characters and yield components in intercrop were highly correlated with the same characters in sole crop. How-ever, multiple regression of sorghum grain yield in intercrop on characters measured in sole crop. Characters related to light interception were the most influential in determining sorghum yield, but some genetically determined variation in yield was unexplained by either multiple regression. Characters related to light interception had a negative influence on cowpea yield, though again some variation due to sorghum genotype was unexplained. Thus although the influence of sorghum plant characters on each component crop is predictable, compensation between the components makes the overall outcome more difficult to predict, and dependent upon which component isfavoured by the environment. The sorghum genotypes selected will therefore represent a compromise: they should not be dwarf types, but should be early maturing to escape drought, and have narrow canopies so as not to be too competitive on the cowpea. The final selection should be made in intercrop

Primeiro registro da família Tachinidae como parasitóide de psilídeo (Hemiptera: Psylloidea).

Resumo