CAPACIDADE DE COMBINAÇÃO ENTRE LINHAGENS DE PIMENTÃO DIFERINDO NA TOLERÂNCIA AO BAIXO TEOR DE FÓSFORO NO SOLO COMBINING ABILITY AMONG LINES OF SWEET PEPPER DIFFERING IN TOLERANCE TO LOW PHOSPHORUS CONTENT IN SOIL

Seis linhagens de pimentão (Capsicum annuum L.) diferindo na tolerância ao baixo teor de fósforo (P) no solo, os híbridos F1 e seus recíprocos, obtidos de um cruzamento dialélico completo, foram avaliados em casa de vegetação, para estimar as capacidades combinatórias em relação à acumulação de matéria seca total, matéria seca da parte aérea, matéria seca das raízes, razão raiz:parte aérea, área foliar, altura da planta, conteúdo de P total na planta e coeficiente de translocação de P. Ambas as capacidades, geral (CGC) e específica de combinação (CEC), foram estatisticamente significativas, com o componente quadrático associado à CEC superior ao relativo à CGC em todas as características avaliadas, evidenciando predominância de efeitos gênicos não aditivos nos cruzamentos. Linhagens tolerantes à baixa disponibilidade de P exibiram elevadas estimativas positivas da CGC, foram as mais divergentes e seus híbridos revelaram médias elevadas para a maioria das características avaliadas, enquanto comportamento inverso foi apresentado pelas linhagens intolerantes. Levando-se em consideração o desempenho das linhagens, as heteroses e o efeito da CEC, destacaram-se as combinações P-141-190-F16 x P-142-403-F11, P-142-215-F15 x P-142-270-F12, P-141-152-F14 x P-142-215-F15, P-141-152-F14 x P-142-403-F11 e P-141-150-F10 x P-141-152-F14. Não houve ocorrência de diferenças entre cruzamentos recíprocos, em relação às características avaliadas<br>Six lines of sweet pepper (Capsicum annuum L.) differing in tolerance to low phosphorus (P) content in the soil, their F1 hybrids and reciprocals, obtained from a complete diallel cross, were assessed under greenhouse conditions in order to estimate their combining abilities for total dry matter accumulation (shoot) dry matter, root dry matter, root (shoot) ratio, leaf area, plant height, total P content in the plant and P translocation coefficient. Both general (GCA) and specific (SCA) combining abilities were statistically significant with quadratic component associed to SCA which was always greater in magnitude than GCA for all traits, showing a predominance of non-additive genic effects in crosses. In addition to high positive GCA estimates, the tolerant lines to low P availability were the most divergent and their hybrids showed high average values for most of the assessed traits, while an opposite behaviour was observed in the tolerant lines. Considering the performance of the lines, the heterosis and the SCA effect, the following are promissing combinations: P-141-190--F16 x P-142-403-F11, P-142-215-F15 x P-142-270-F12, P-141-152-F14 x P-142-215-F15, P-141-152-F14 x P-142-403-F11 and P-141-150-F10 x P-141-152-F14. No difference was found among reciprocal crosses in relation to the assessed traits

The involvement of the transpirational bypass flow in sodium uptake by high- and low-sodium-transporting lines of rice developed through intravarietal selection

We report the characterization of high- and low-sodium-transporting lines developed by intravarietal selection within a cultivar, IR36, of rice (Oryza sativa L.). The purpose was to investigate the mechanistic basis of sodium uptake in material in which differences in salt uptake could be isolated from the many other morphological and physiological characteristics that affect the phenotypic expression of salt tolerance. The lines differed in mean sodium transport by a factor of 2. They differed in vigour and water use efficiency, which are characters that modify the effects of salt transport, by only 12% or 13%. The lines did not differ significantly in other physiological traits that are components of salt resistance: compartmentalization at the leaf and cellular levels. There was a strong correlation between the transport of sodium and a tracer for apoplastic pathways (trisodium, 3-hydroxy-5,8,10-pyrene trisulphonic acid, PTS) in both lines. The regression coefficient for sodium transport on PTS transport was the same in both lines. The individual variation in PTS transport was similar to that in sodium transport, and the variation in the transport of both was very much greater than the variation in any other character studied. The high-sodium-transporting line took up proportionately more PTS than the low-sodium-transporting line. It is concluded that the transpirational bypass flow is of major importance in sodium uptake by rice and that selection for differences in sodium transport has been brought about by selection for heritable differences in the bypass flow