Effect of planting date and nitrogen fertilization on photosynthesis and soluble carbohydrate contents of cotton in relation to silverleaf whitefly (Bemisia tabaci biotype 'B') populations

摘要

The impacts of planting date and nitrogen fertilization on cotton (Gossypium hirsutum L.) photosynthesis and soluble carbohydrate contents in relation to silverleaf whitefly, Bemisia tabaci (Gennadius) biotype "B", populations were examined in field experiments. Cotton planted in late April and early June was treated with 0,112,168 and 224 kg/N hectare in soil using urea fertilizer. The mean photosynthetic rate of April-planted cotton was 4%—20% higher than that of June-planted cotton early in the season, but 10%-18% lower than that of June-planted cotton late in the season. The photosynthetic rates for both planting dates were positively correlated with levels of added nitrogen. While levels of glucose for both planting dates were positively correlated with nitrogen levels, fructose and sucrose levels were not. The mean levels of fructose were up to 40% lower, while that of sucrose were up to 59% higher, in April-planted cotton than in June-planted cotton. Levels of photosynthetic rate or stomatal conductance were not correlated with adult whitefly densities for either planting date. Levels of glucose and fructose were positively correlated with whitefly densities only for June-planted cotton late in the season.