Chlorsulfuron [2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino] carbonyl] benzenesulfonamide], applied at 9 to 560 g ai/ha to the soil surface, stopped shoot elongation of well established Canada thistle [Cirsium arvense (L.) Scop. #4 CIRAR] plants in the greenhouse. Root fresh weight decreased progressively as chlorsulfuron rate was increased when measured 1 month after treatment. In contrast, the number of visible root buds plus secondary shoots increased 1.9- to 2.3-fold between 9 and 67 g/ha chlorsulfuron 1 month after soil surface treatment. Despite more numerous root buds, the number of secondary shoots arising from adventitious root buds progressively decreased as chlorsulfuron rate was raised. Increases in the number of visible root buds were observed first between 3 and 4 weeks following soil application with 67 g/ha of chlorsulfuron, 2 weeks after shoot growth stopped.

Introduction. Natural flowering is an obstacle for the management of pineapple production. This phenomenon is at the origin of considerable and increasing fruit losses on an international scale. The objective of this work was to determine, at various times of the year, the role of substances inhibiting the vegetative growth of the plant to prevent, reduce or delay the natural pineapple flowering of the variety `Perola', most planted in Brazil. Materials and methods. Two trials were conducted in the experimental field in Cruz das Almas, Bahia, Brasil, during the years 1996 to 1999. Various growth substances were tested at various con- centrations: propionic acid 2-(3-chlorophenoxy) (ACP) at (45, 90 and 120) mg·L-1, paclobutra- zole (PBZ) at (77.4, 155.8 and 320) mg·L-1, mepiquat chlorure (MC) at (60 and 120) mg·L-1, gibberelic acid (GA3) at (30 and 60) mg·L-1, tebuconazole (TBZ) at (60 and 120) mg·L-1 and propaconazole (PPZ) at 120 mg·L-1. The treatments were applied onto two, three or four split applications, every 15 days, from 7:00 to 9:00 a.m. and from April to July (the critical period for natural flowering in the region). Results and discussion. The results obtained show that ACP and PBZ are capable of inhibiting, reducing and delaying the natural flowering of pine- apple with the concentrations of (90 to 240) mg·L-1. The best results were obtained when the growth regulators were applied during April and May. The other products did not have an effect on the natural flowering of pineapple. Conclusion. The variation observed in the effects and efficiencies of the growth regulators used indicates the necessity of validating the best treatments under different environmental and cultural conditions. The selected growth regulators can be a valuable tool for physiological studies on the mechanisms of flowering initiation in pineapple.

The already known benzoquinone, embelin (mixed with rapanone), and two new benzoquinones, myrsinone and myrsinaquinone, were isolated from the Myrsinaceae plant, Rapanea melanphloes (L), Mez. All the three compounds showed antifeedant activity when bioassayed on nymphs of the desert locust, Schistocerca gregaria (Forsk). They also inhibited growth of second-instar larvae of mosquito Aedes aegypti at low doses, and had acute lethal effects at higher doses.