Abstract. In this paper, we report on the night-time equatorial F-layer height behaviour at Korhogo (9.2 • N, 5 • W; 2.4 • S dip lat), Ivory Coast, in the West African sector during the solar minimum period 1995-1997. The data were collected from quarter-hourly ionograms of an Ionospheric Prediction Service (IPS) 42-type vertical sounder. The main focus of this work was to study the seasonal changes in the F-layer height and to clarify the equinox transition process recently evidenced at Korhogo during 1995, the year of declining solar flux activity. The F-layer height was found to vary strongly with time, with up to three main phases. The night-to-night variability of these morphological phases was then analysed. The early post-sunset slow rise, commonly associated with rapid chemical recombination processes in the bottom part of the F layer, remained featureless and was observed regardless of the date. By contrast, the following event, either presented like the post-sunset height peak associated with the evening E × B drift, or was delayed to the midnight sector, thus involving another mechanism. The statistical analysis of the occurrence of these events throughout the solar minimum period 1995-1997 revealed two main F-layer height patterns, each characteristic of a specific season. The one with the post-sunset height peak was associated with the northern winter period, whereas the other, with the midnight height peak, characterized the northern summer period. The transition process from one pattern to the other took place during the equinox periods and was found to last only a few weeks. We discuss these results in the light of earlier works.

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Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (FOV) is a major damaging disease of cotton. Chemical control is currently ineffective and has led to resistance of the pathogen. In addition, pesticides are indexed for their negative impact on the environment and on human health. The objective of this study was to evaluate the impact of sugarcane stem residue filtrate (FCS) and cotton stem residue filtrate (FTC) residue filtrate on FOV causal agent of the disease. These two polysaccharide biocontrols allowed a good accumulation of gallic acid, caffeoyl D-glucose, catechin, gossypetin and 3-p-coumaroylquinic acid and the de novo synthesis of epicatechin, protocatechic acid, ferulic acid, trans-resveratrol, trans-piceide, pterosilbene, 5-caffeylquinic acid, rutin, astringin and isoquercetin. However, 5-caffeylquinic acid and rutin are specific to FCS while astringin and isoquercetin are specific only to FTC. This difference in polyphenol synthesis caused 1% mortality in FTC and 8% in FCS. This indicates that astringin and isoquercetin are phenolic markers of resistance to FOV followed by 5-caffeylquinic acid and rutin. FTC can be used as a preventive control of Fusarium wilt in cotton.

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