Effect of Bt traits on transgenic rice's growth and weed competitiveness

Transgene escape could lead to genetically modified rice establishing wild populations in the natural environment and competing for survival space with weeds.However,whether the expression of the Bacillus thuringiensis(Bt)gene in rice will alter the relationship between transgene plants and weeds and induce undesirable environmental consequences are poorly understood.Thus,field experiments were conducted to investigate the weed competitiveness and assess the ecological risk of transgenic Bt rice under herbicide-free and lepidopterous pest-controlled environments.Results showed that weed–rice competition in the direct-sowing(DS)field was earlier and more severe than that in the transplanting(TP)field,which resulted in a significant decrease in biomass and yield in DS.However,conventional Bt and non-Bt rice yield was not significantly different.The weed number,weed coverage ratio,and weed diversity of conventional Bt rice were significantly higher than those of non-Bt rice at the early growth and mature stages,especially in DS plots,suggesting that Bt traits did not increase the weed competitiveness of transgenic rice and had no negative effect on weed diversity.Grain yield and weed number varied between different hybrid rice lines,but those differences were insignificant between Bt and non-Bt rice.The number of insects increased with the increase of weeds in hybrid rice plots,whereas the insect number and diversity did not display a significant difference between Bt and non-Bt rice.Therefore,the ecological risk of transgenic Bt rice is comparable to non-Bt rice.

Management of Grass and Broadleaf Weeds in Processing Potatoes (Solanum tuberosum L.) with Clomazone, in the Argentinian Pampas

Weed competition in the potato crop could cause up to a 95% yield reduction depending on the variety, the weed species and the competition period. In this work the effect of Clomazone (Command 36 CS®), when applied alone or in combination with Metribuzin (Sencorex® 48) upon grass and broad-leaved weeds was assessed. The work was carried out under the environmental conditions of the Argentinian Pampas, where close to 50% of the potatoes produced in the country are grown. The field trial was performed during the spring-summer crop, season 2008/09, with cv. Innovator, in a completely randomized design of the following treatments: (a) control, without weed control;(b) Clomazone 1.6 l·ha-1;(c) Clomazone 2.0 l·ha-1;(d) Clomazone 1 l·ha-1 + Metribuzin 0.75 l·ha-1;(e) Clomazone 1.6 l·ha-1 + Metribuzin 0.5 l·ha-1;and (f) Metribuzin 1.35 l·ha-1. Treatment effectiveness (TE), crop competition level (CCL) and weed suppression index (WSI) were assessed at 38, 53 and 72 days after planting (DAP), while yield and quality were also evaluated, following industry protocols. In those treatments were Clomazone was used alone, at 2 l·ha-1, or combined (Clomazone 1 l·ha-1 + Metribuzin 0.75 l·ha-1), a higher yield was observed. Besides, a high correlation between TE, WSI and tuber yield was also achieved. Clomazone improved TE, CCL and WSI, which was not only reflected in higher tuber yields, but also on better tuber quality.

Review on Causes of Forest Decline

Site degradation and yield decline of forest have attracted increasing attention from forest managers and scientists. Studies conducted by researchers from a variety of disciplines and perspectives have led to a variety of competing hypotheses concerning the causes of the problem. In this paper we review evidence of such a yield decline and examine the problem and its possible way to identify the individual contributions of the many determinants of yield decline, and their interactions.