Características produtivas da melancia em diferentes espaçamentos de plantio Yield characteristics of watermelon in different planting spaces

Diferentes espaçamentos de plantio foram avaliados na produção de melancia em experimento da Embrapa Semi-Árido em Petrolina, de outubro a dezembro de 1998. Utilizou-se o delineamento experimental de blocos ao acaso em esquema fatorial 2 x 3, consistindo de dois espaçamentos entre linhas (2,50 e 3,00 m) e três espaçamentos entre plantas (0,40; 0,60 e 0,80 m) e 3 repetições, sendo utilizada a cultivar Crimson Sweet. O espaçamento entre linhas de 3,00 m apresentou maior produção (42,46 t/ha), sendo que entre plantas os espaçamentos de 0,60 e 0,80 m alcançaram as maiores produções com 42,50 e 45,29 t/ha, respectivamente, não mostrando diferenças entre si. Não foram verificadas diferenças significativas para produção de frutos refugo nos espaçamentos entre linhas. No entanto, o menor espaçamento entre plantas proporcionou maior produção com 20,21 t/ha, seguido pelos espaçamentos de 0,60 m (12,86 t/ha) e 0,80 m (8,62 t/ha). O incremento dos espaçamentos, tanto entre linhas como entre plantas, resultou em frutos de maior tamanho, tendo o espaçamento 3,00 x 0,80 m apresentado a maior massa fresca do fruto (8,83 kg/fruto). O maior número de frutos por planta (1,35 frutos) foi obtido com o espaçamento de 3,00 x 0,80 m.<br>The yield of watermelon as a result of different planting space was evaluated, from October to December 1998 in Petrolina, Pernambuco State, Brazil. The experimental design was a randomized blocks in a 5 x 3 factorial scheme, with three replications. The cultivar Crimson Sweet was planted in 2.5 and 3.0 m row spacing and in 0.4, 0.6 and 0.8 m inside the row. The 3.0 m row spacing resulted in the highest marketable yield with 42.46 t ha-1. Higher yields (42.50 and 45.29 t ha-1) were obtained with the 0.2 and 0.4 m plant spacing, with no difference between them. No significant differences were observed for unmarketable fruit yield in the row spacings. However, the smallest plant spacing (0.4 m) showed the highest yield with 20,21 t ha-1, followed by the 0.6 m (12.86 t ha-1) and 0,80 m (8.62 t ha-1). The increase of the row and plant spacing produced larger sized fruits, and the spacing 3.0 x 0.8 m showed the highest weight of fresh fruit mass (8.83 kg). The largest number of fruits per plant (1.35 fruits) was observed in the 3.00 x 0.8 m spacing

Aluminium tolerance in barley (Hordeum vulgare L.): physiological mechanisms, genetics and screening methods

Aluminium (Al) toxicity is one of the major limiting factors for barley production on acid soils. It inhibits root cell division and elongation, thus reducing water and nutrient uptake, consequently resulting in poor plant growth and yield. Plants tolerate Al either through external resistance mechanisms, by which Al is excluded from plant tissues or internal tolerance mechanisms, conferring the ability of plants to tolerate Al ion in the plant symplasm where Al that has permeated the plasmalemma is sequestered or converted into an innocuous form. Barley is considered to be most sensitive to Al toxicity among cereal species. Al tolerance in barley has been assessed by several methods, such as nutrient solution culture, soil bioassay and field screening. Genetic and molecular mapping research has shown that Al tolerance in barley is controlled by a single locus which is located on chromosome 4H. Molecular markers linked with Al tolerance loci have been identified and validated in a range of diverse populations. This paper reviews the (1) screening methods for evaluating Al tolerance, (2) genetics and (3) mechanisms underlying Al tolerance in barley