Studies on Wilt Diseases of Cotton in Central Region, With Emphasis on Morbid Anatomy

Abstract

ABSTRACT In this research, the following investigations were under taken as follows: a) Random surveys of cotton plants for detection of both fusarium and physiological wilts. The surveys covered different localities through-out Central Sudan; b) laboratory investigations on isolations and identification of causal organisms in case of fusarium; c) Glass—house studies on pathogenicity tests ; and d) Anatomical studies within both resistant and susceptible cultivars. The results of the surveys showed that cotton wilt caused by Fusarium.oxysporummasinfizctum was widely distributed through-out the Gezira Scheme, including Managil extention; on Gossypium. barbadense cv. “Traditional Barakat” It was also present at some asite at the Gezira Research Station Farm (GRSF) on the same cultivar. As regards physiological wilt it was widely distributed through-out the Gezira Scheme , both on “Traditional Barakat” and “Shambat B" . As regards isolation studies, F.o.vasinfectum was consistently‘ associated with infected Traditional Barakat within all of the localities smveyed. 7 Pathogenicity tests proved that Gossypiumbarbadense cv. "Traditional Barakat” was highly susceptible to infection by F.o.vasinfectum isolate from GRSF. This cultivar also exhibited highest percentage of disease incidance. On the other hands, Gossypium. hirsutum cv “Shambat B” was found to be tolerant as it did not develop any of the known typical extemal symptoms. _ _ The results also proved that artificial inoculation by pure culture technique was most effective compared to the other technique known as Trash technique of Yassin (1986). '

lt was also worth noting that all of the incoulated plants of “Traditional Barakat” exhibited remarkable stunting as generalized symptoms; in addition to the known typical symptoms per se. Such stunting of plant was observed symptoms even in case of the highly “tolerant” cv Shambat B. Such observed on Shambat B is consideredthe first record known; as it was not mentioned by any of the previous investigators. - Anatomical investigations through the stems and roots in case of fusariurm wilt showed the occurrence of spores within the plant tissues in relation to time factor, e.g. at earlier stage of infection it was restricted to the epidermal and cortical layers. Subsequently such spore masses further extended to the phloem and xylem parenchyma. In older plants the pathogen spores and hyphae were present even within the xylem vessels as well as pith. In addition, plugging of the xylem vessels and tracheids was also form in case of “Traditional Barakat”. By comparison such plugging was only confined to the tracheids in case of Shambat B. , Plants of both cultivars namely Traditional Barakat and Sl1a1nbatB, affected by physiological wilt 6Xl1ll)lI6Cl excessive growth of ground tissue; exemplified by necrotic effects due to compaction of cells. Finally, best control methods, especially of pathogenic wilt, were suggested as follows: Use of resistant varieties, eg. “Barakat 90” and “Shambat B”. b)Appropriate rotation, c) Crop hygiene, eg. removal of plant debris from previous season, d) Biological control, e) Chemical control, using recommended fungicide, as last resort.