Seedling blight of maize has significantly influenced field crop stands and seedling vigour over various localities and seasons. The extent of the problem is influenced by a number of factors which includes soil temperature (generally below 13 °C), waterlogged soils, inadequate fertilization, herbicide damage and fungal pathogens. The fungi generally causing seedling damping off are often involved in a complex and succession over time varying in importance depending on the field circumstances at a given time. These generally include the Pythium spp., Rhizoctonia spp. and various Fusarium spp. These have been recorded in a number of studies conducted by local researchers in the late 1980’s and early 1990’s on sorghum but to a lesser degree on maize. Uncertainty regarding the status of the etiology of maize seedling blights as maize production practices have changed dramatically in the last 10 years with increased plant populations, reduced tillage, increased crop rotation options and new short season maize hybrids. It is therefore essential to determine the present status of seedling blights in South Africa to confirm the necessity of fungicide seed treatments to ensure adequate plant densities and seedling vigour. Cob and tassel smut caused by Sphacelotheca reiliana is a disease of maize that was a problem in the 1970’s. Due to improved fertilisation, fungicide seed treatments and hybrid resistance this disease was reduced to such levels that the disease was only found to occur on research farms where seedlings were inoculated. Since 2007, the disease was reported to reach epidemic proportions on the heavy clay soils in the Standerton area. This disease has since spread over the last seven seasons to a range including northern KwaZulu/Natal, namely as far as Underberg/Swartberg, the Witbank, Ermelo, Middelburg and Delmas area in Mpumalanga and to Harrismith in the eastern Free State maize production area. This may be due to susceptible hybrids coming onto the local market or the inability of traditional fungicide seed treatments to contain infection. New and unregistered seed treatments available will be tested for their ability to control cob and tassel smut in two fields over two seasons. The aims of this dissertation were to determine the extent of the seedling blight problem in commercial fields throughout the maize industry. To determine the efficacy of fungicide seed treatments for the control of maize seedling blights using both field and greenhouse studies, and to determine the efficacy of fungicide seed treatments for the control of cob and tassel smut of maize in field trials. A total of 101 localities were sampled throughout the maize producing region of South Africa with root discolouration varying from 0 to 90 % root discolouration. Seventy different fungal species were isolated from the maize seedlings roots which include species such as Aspergillus, Clonostachus, Fusarium, Trichoderma and Penicillium. The most commonly isolated fungi which included Aspergillus niger, Fusarium solani, Fusarium verticillioides and Fusarium oxysporum were evaluated in glasshouse studies to determine their pathogenicity. Pathogenicity differed between isolates of the same fungal species, which were collected from different geographical regions, in the glasshouse studies. Field trials for seedling blight disease showed significant differences between the localities (P < 0.001) the trials were planted at, and between seed treatments. Significant season (P < 0.001) and locality (P < 0.05) differences were also found for cob and tassel smut trials planted at Potchefstroom, North-West province and Greytown, KwaZulu/Natal Province respectively. Fungicide seed treatments also showed significant differences for cob and tassel smut regarding plants infected (P < 0.001) and yield loss (P < 0.05). Overall seed treatments can be seen as an effective controlling agent for the control of seed- and soil-borne fungi on maize. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Seedling blight of maize has significantly influenced field crop stands and seedling vigour over various localities and seasons. The extent of the problem is influenced by a number of factors which includes soil temperature (generally below 13 °C), waterlogged soils, inadequate fertilization, herbicide damage and fungal pathogens. The fungi generally causing seedling damping off are often involved in a complex and succession over time varying in importance depending on the field circumstances at a given time. These generally include the Pythium spp., Rhizoctonia spp. and various Fusarium spp. These have been recorded in a number of studies conducted by local researchers in the late 1980’s and early 1990’s on sorghum but to a lesser degree on maize. Uncertainty regarding the status of the etiology of maize seedling blights as maize production practices have changed dramatically in the last 10 years with increased plant populations, reduced tillage, increased crop rotation options and new short season maize hybrids. It is therefore essential to determine the present status of seedling blights in South Africa to confirm the necessity of fungicide seed treatments to ensure adequate plant densities and seedling vigour. Cob and tassel smut caused by Sphacelotheca reiliana is a disease of maize that was a problem in the 1970’s. Due to improved fertilisation, fungicide seed treatments and hybrid resistance this disease was reduced to such levels that the disease was only found to occur on research farms where seedlings were inoculated. Since 2007, the disease was reported to reach epidemic proportions on the heavy clay soils in the Standerton area. This disease has since spread over the last seven seasons to a range including northern KwaZulu/Natal, namely as far as Underberg/Swartberg, the Witbank, Ermelo, Middelburg and Delmas area in Mpumalanga and to Harrismith in the eastern Free State maize production area. This may be due to susceptible hybrids coming onto the local market or the inability of traditional fungicide seed treatments to contain infection. New and unregistered seed treatments available will be tested for their ability to control cob and tassel smut in two fields over two seasons. The aims of this dissertation were to determine the extent of the seedling blight problem in commercial fields throughout the maize industry. To determine the efficacy of fungicide seed treatments for the control of maize seedling blights using both field and greenhouse studies, and to determine the efficacy of fungicide seed treatments for the control of cob and tassel smut of maize in field trials. A total of 101 localities were sampled throughout the maize producing region of South Africa with root discolouration varying from 0 to 90 % root discolouration. Seventy different fungal species were isolated from the maize seedlings roots which include species such as Aspergillus, Clonostachus, Fusarium, Trichoderma and Penicillium. The most commonly isolated fungi which included Aspergillus niger, Fusarium solani, Fusarium verticillioides and Fusarium oxysporum were evaluated in glasshouse studies to determine their pathogenicity. Pathogenicity differed between isolates of the same fungal species, which were collected from different geographical regions, in the glasshouse studies. Field trials for seedling blight disease showed significant differences between the localities (P < 0.001) the trials were planted at, and between seed treatments. Significant season (P < 0.001) and locality (P < 0.05) differences were also found for cob and tassel smut trials planted at Potchefstroom, North-West province and Greytown, KwaZulu/Natal Province respectively. Fungicide seed treatments also showed significant differences for cob and tassel smut regarding plants infected (P < 0.001) and yield loss (P < 0.05). Overall seed treatments can be seen as an effective controlling agent for the control of seed- and soil-borne fungi on maize. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Με στόχο την απομόνωση και χαρακτηρισμό εγγενών μυκοπαράσιτων του φυτοπαθογόνου μύκητα Sclerotinia sclerotiorum, απομονώθηκαν 199 υποψήφια μυκοπαράσιτα από χώματα καλλιεργουμένων εδαφών ή κήπων της δυτικής Ελλάδας. Από την προκαταρκτική αξιολόγηση των μυκοπαράσιτων αυτών επιλέχθηκαν τα πλέον αποτελεσματικά δεκαοκτώ, τα οποία αξιολογήθηκαν σε άγαρ ύδατος, σε αποστειρωμένο χώμα και σε μη-αποστειρωμένο (φυσικό χώμα). Σε γενικές γραμμές τα 18 μυκοπαράσιτα έδωσαν υψηλά επίπεδα παρασιτισμού του φυτοπαθογόνου απουσία ενδογενών ανταγωνιστών ενώ ένα από τα απομονωθέντα στελέχη του γένους Gliocladium παρουσίασε άριστα αποτελέσματα και παρουσία ενδογενών ανταγωνιστών. Ειδικότερα η απομόνωση Α-9 εκδήλωσε άριστη ανταγωνιστική δράση. Η μορφή του μολύσματος (υφές, σπόρια) αλλά και το περιβάλλον (άγαρ ύδατος, αποστειρωμένο και μη αποστειρωμένο χώμα) επηρεάζουν αποφασιστικά την συμπεριφορά και ικανότητα μυκοπαρασιτισμού των μυκοπαράσιτων με αποτέλεσμα στα πειράματα αξιολόγησης να παρατηρούνται σημαντικές διαφορές. Τα πλέον σταθερά στην συμπεριφορά τους ήταν τρία στελέχη που ανήκουν στο γένος Gliocladium. Ο ανταγωνισμός που υφίστανται τα προστιθέμενα μυκοπαράσιτα από τα ιθαγενή μικρόβια είναι σημαντικός και είναι ένας παράγοντας που θα πρέπει να λαμβάνεται σοβαρά υπόψη. Η ιστοπαθολογική μελέτη του παρασιτισμού των σκληρωτίων έδειξε ότι ένα από τα απομονωθέντα στελέχη του γένους Gliocladium ήταν το ταχύτερο και καταστρεπτικότερο μυκοπαράσιτο των σκληρωτίων του φυτοπαθογόνου μύκητα. Αρχικά διαπιστώθηκαν οι υφές του μυκοπαράσιτου κάτω από τον φλοιό του σκληρωτίου και λίγο αργότερα στην εντεριώνη. Παράλληλα σχηματίσθηκαν τα πρώτα χλαμυδοσπόρια κοντά στον φλοιό ακολουθούμενα από την εμφάνιση μεγάλα διάκενων. Τελικά οι υφές του μυκοπαράσιτου αποίκισαν ολόκληρο το σκληρώτιο και ακολούθησε αποδιοργάνωση του σκληρωτίου. Η μελέτη στο ηλεκτρονικό μικροσκόπιο σάρωσης έδειξε ότι η βλάστηση των σπορίων γενικεύεται στις 15 ώρες επώασης. Στις περισσότερες περιπτώσεις διαπιστώθηκε περιπλάνηση των βλαστικών σωλήνων πριν τη διείσδυσή τους εντός του σκληρωτίου, ενώ δεν διαπιστώθηκε σχηματισμός απρεσσορίων και διακλαδώσεων του βλαστικού σωλήνα. Τα πειράματα θερμοκηπίου έδειξαν ότι το πλέον καταστρεπτικό μυκοπαράσιτο του γένους Gliocladium συνέβαλε στη μέγιστη προστασία των σποριόφυτων λάχανου έναντι του φυτοπαθογόνου μύκητα S. sclerotiorum, γεγονός που υποδηλώνει ότι το μυκοπαράσιτο αυτό μπορεί να χρησιμοποιηθεί για την αποτελεσματική καταπολέμηση του φυτοπαθογόνου μύκητα στον αγρό. / In order to isolate and characterize endogenous mycoparasites against the phytopathogenic fungi, Sclerotinia sclerotiorum, we isolated 199 candidate mycoparasites from soils of western Greece. Preliminary evaluation resulted in the isolation of 18 isolates with significant mycoparasitic efficiency. Evaluation of these isolates in water agar, sterilized soil and natural soil gave good results upon the parasitism of sclerotia of S. sclerotiorum and revealed that one of them belonging to genus Gliocladium was the most efficient under all tried conditions. This isolate showed high efficiency at both presence and absence of endogenous antagonist. Particularly, isolation A-9 revealed excellent antagonistic action. Histopathology studies demonstrated that the isolated A-9 (Gliocladium spp) was the most fast in parasitizing and destroying the sclerotia of S. sclerotiorum. At the beginning of the infection, there were observed mycoparasite hyphae under the rind and little later into the medulla of the sclerotia. At the same time the first chlamydospores were formed near the rind followed by the appearance of gaps. Finally, the mycoparasite hyphae colonize the whole sclerotium leading to there disorganization. The added mycoparasites face out strong antagonism from the indigenous microorganism and this (antagonism) is an agent that must be seriously taken account. The scanning electron microscopy study showed spore germination initiation about 12 hours after the beginning of incubation and (the spore germination) is generalised after 15 hours of incubation. In most cases it was observed wandering of the germination tubes before sclerotic penetration. Formation of appressoria was difficult to be observed because of the shape of the surface and the crust that exists due to deflation of exudates. Evaluation of plant-protection capability in pot-trials showed that the isolated A-9 (Gliocladium spp) with the faster and highest parasitic exhibited presented the highest plant-protection capability a fact that indicates that this mycoparasite could be used for large-scale biocontrol applications against the phytopathogenic fungi, Sclerotinia sclerotiorum.

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