Black shank, caused by Phytophthora parasitica var. nicotianae, is a widespread and destructive disease of tobacco. Crop rotation is essential in controlling black shank. Here, we confirmed that rotating black shank-infested fields with rapeseed (Brassica napus) suppressed the incidence this disease. Further study demonstrated that rapeseed roots have a strong ability to attract zoospores and subsequently stop the swimming of zoospores into cystospores. Then, rapeseed roots secrete a series of antimicrobial compounds, including 2-butenoic acid, benzothiazole, 2-(methylthio)benzothiazole, 1-(4-ethylphenyl)-ethanone, and 4-methoxyindole, to inhibit the cystospore germination and mycelial growth of P. parasitica var. nicotianae. Thus, rapeseed rotated with tobacco suppresses tobacco black shank disease through the chemical weapons secreted by rapeseed roots.

The aims of this study were to ascertain the difference of nitrogen uptake and verify the absorption law of the nitrogen from soil and fertilizer for tobacco grown in southwest China with red soil, yellow soil, and paddy soil by 15 N tracer. The results showed a significant positive correlation between N accumulation amount and yield in flue-cured tobacco, and a suitable nitrogen demand of 60-100 kg ha -1 for tobacco in southwest zone. Absorption dynamics of nitrogen were different for flue-cured tobacco planted in various types of soil. For rate of nitrogen absorption before topping, the highest was for the tobacco planted in red soil, followed by that in paddy soil and the lowest was for that in yellow soil. N uptake peaks of tobacco planted in red soil, paddy soil and yellow soil were peaked in 7 weeks, 9 weeks, and 11 weeks after transplanting respectively. The absorption changes of soil nitrogen and fertilizer nitrogen in tobacco all showed a single peak curve, and the peak of the absorption curves of fertilizer nitrogen was earlier than soil nitrogen. Uptake rate of soil nitrogen in flue-cured tobacco was gradually higher than fertilizer nitrogen after starting prosperous growth and transferred to the stage of soil nitrogen-dominated absorption. The accumulation ratios of soil nitrogen and fertilizer nitrogen in tobacco before topping accounted 59.8% and 72.1% respectively. The proportions of N accumulation before topping were 87.8%, 47.3%, and 49.2% for tobacco grown in red soil, yellow soil and paddy soil respectively. In conclusion, the fertilizer N demand for tobacco should be estimated with N requirement and soil N supply before topping under proper N demand according to nitrogen absorption law.

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Advances in Internet technologies and multimedia technologies provide a way of redefining the approaches of teaching and learning. In this paper we design and implement a web-based personalized learning and assessment system to evaluate student learning outcomes and teacher instructional practices in real time. Index Terms-educational assessment, web-based environment, web-based testing (WBT), B/S