Effect of Nitrogen Fertilization on Photosynthetic Characters and Dry Matter Production in F₁ Hybrids of Rice (Oryza sativa L.)

Abstract

This study was carried out to determine heterosis in different photosynthetic and morphological characters, and to observe photosynthetic ability and dry matter production potentiality of two F₁ hybrids of rice grown in pots supplied with N fertilizer in the normal or double dose. Photosynthetic rate in terms of CO₂ exchange rate (CER), leaf N concentration, SPAD value, soluble protein content and ribulose-1, 5-bisphosphate carboxylase (Rubisco) activity was increased significantly by doubling the dose of fertilizer in most parental cultivars and F1 hybrids, but the rate of increase was higher in F₁ hybrids than in their parents. Several morphological parameters were also increased significantly by doubling the dose of fertilizer, but not the percentage of dead leaf blades. The rates of increase of plant height, leaf area and dry matter production were higher in F₁ hybrids. In particular, the rates of increase of total dry matter and root weight were very high in one of the F₁ hybrids. The percentage of dead leaf blades decreased significantly in plants grown with a high dose of fertilizer as a result of higher leaf N concentration. At a normal fertilizer dose, both F₁ hybrids failed to show positive heterosis in most photosynthetic characters. However, positive heterosis was found at a high fertilizer dose. Both F₁ hybrids showed positive heterosis over mid-parent in dry matter production per plant at both fertilizer doses. One of the F₁ hybrids also showed positive heterosis over the better parent. Heterosis in most photosynthetic and morphological characters was increased by increasing the dose of fertilizer. The sufficient supply by doubling the dose of fertilizer increased the leaf N concentration, chlorophyll content, soluble protein content and Rubisco activity in F₁ hybrids, which led to higher positive heterosis in CER. A larger leaf area plus higher CER, especially at a high fertilizer dose, contributed to higher dry matter production in F₁ hybrids of rice.