Mycotoxin contamination of maize and groundnut produced by subsistence farmers in northern KwaZulu-Natal

Thesis (MScAgric)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Subsistence farmers in South Africa face many production challenges including infection of their grain crops with mycotoxigenic fungi and concomitant mycotoxin contamination. Fusarium spp. and Aspergillus spp. are the most common fungal species infecting maize and groundnuts while plant-parasitic nematodes are also associated with groundnuts in South Africa. Maize and groundnut questionnaires regarding production practices were presented to subsistence farmers in Pongola, Vryheid, Jozini, Manguzi and Mbazwana districts of northern KwaZulu-Natal (KZN), South Africa. Maize and groundnut grain samples were also collected at harvest and after three months of storage during the 2012/13 and 2013/14 seasons. Groundnuts, roots and soil samples were collected before harvest during the 2013/14 season, only. Fusarium graminearum, F. verticillioides and A. flavus target DNA levels were quantified in maize using quantitative polymerase chain reaction and the presence of multi-mycotoxins were determined using the liquid chromatography tandem mass spectrometry. Nematodes were extracted using sieving method and identified microscopically. Questionnaires revealed that over 90% of farmers were not aware of mycotoxins or their implications on human and livestock health. Visually diseased grain was often fed to livestock sensitive to mycotoxicosis such as chickens. Production practices amongst some farmers including crop rotation and the well-ventilated storage of grain may contribute to reduced mycotoxin contamination. In maize grain the Fusarium graminearum levels were significantly higher than F. verticillioides and A. flavus levels in both seasons. Contrary to expectations, zearalenone, produced by F. graminearum, was very low (<0.02 μg/g) at harvest and storage during both seasons while deoxynivalenol and nivalenol was not detected. There were significant differences between districts (localities) and collection periods (harvest and storage) and localities per seasons (P < 0.05) for all mycotoxigenic fungi and mycotoxins evaluated. Maize sampled in Jozini district was the most contaminated with mycotoxigenic fungi and mycotoxins while Mbazwana and Manguzi districts were the least contaminated. Four plant-parasitic nematodes, namely D. africanus, Pratylenchus spp., Meloidogyne spp. and Helicotylenchus spp., were identified from groundnut samples obtained in Jozini, Manguzi and Mbazwana during the 2012/13 and 2013/14 seasons. Furthermore, Tylenchus spp. was identified for the first time in groundnuts, pegs and soil collected before harvest during the 2013/14 season. Results from this study showed that there is a need for mycotoxin awareness campaigns and additional surveillance to continuously monitor mycotoxin contamination and potential exposure. More in-depth analyses of all the potential factors contributing to mycotoxin contamination and exposure, particularly in the subsistence production are of northern KZN, is warranted.AFRIKAANSE OPSOMMING: Bestaansboere in Suid-Afrika het talle produksie uitdagings, insluitende die infeksie van hul graangewasse met mikotoksigeniese swamme en gepaardgaande mikotoksien besmetting. Fusarium spp. en Aspergillus spp. is die algemeenste swam spesies wat mielies en grondbone besmet, terwyl plant-parasitiese aalwurms ook met grondbone in Suid-Afrika geassosieer word. Vraelyste aangaande mielie- en grondboon verbouingspraktyke is vir bestaansboere in die Pongola, Vryheid, Jozini, Manguzi en Mbazwana areas van noord KwaZulu-Natal (KZN), Suid-Afrika, weergegee. Mielies- en grondboon- graanmonsters is teen oestyd en na `n drie maande opbergingsperiode, gedurende die 2012/13 en 2013/14 seisoene, ingesamel. Grondbone, wortels en grondmonsters is net voor oestyd gedurende die 2013/14-seisoen versamel. Fusarium graminearum, F. verticillioides en A. flavus geteikende DNA vlakke is in mielies deur die gebruik van kwantitatiewe polimerase ketting reaksie (kPKR) gekwantifiseer en die teenwoordigheid van multi-mikotoksiene is met behulp van die vloeistof kromatografie massaspektrometrie bepaal. Aalwurms is deur middel van `nsiftings metode vanuit die grond geïsoleer en mikroskopies geïdentifiseer. Vraelyste het aan die lig gebring dat meer as 90% van die boere nie bewus is van mikotoksiene asook die gesondheidsrisiko’s wat dit vir mens- en dier inhou nie. Grane wat visueel siek vertoon, word dikwels aan diere wat sensitief is vir mikotoksikose, soos hoenders, gevoer. Sommige verbouingspraktyke wat deur sommige boere toegepas word, insluitend wisselbou en die gebruik van goed geventileerde opberging kondisies vir graan, kan tot verminderde mikotoksien besmetting bydra. F. graminearum vlakke in mielies was aansienlik hoër as die van F. verticillioides en A. flavus vir beide seisoene. In teenstelling was zearalenone, wat deur F. graminearum geproduseer word, baie laag (<0,02 μg/g) gedurende oes en opberging vir albei seisoene, terwyl dexoynivalenol en nivalenol nie opgetel is nie. Daar was betekenisvolle verskille tussen areas (lokaliteite) en versamelingsperiodes (oes en opberging) en lokaliteite per seisoen (P < 0.05) vir alle mikotoksigeniese swamme en mikotoksiene geëvalueer. Mielies vanaf Jozini distrik was die meeste besmet met swamme en mikotoksiene terwyl mieliegraan vanaf Mbazwana and Manguzi distrikte die minste besmet was. Vier plant-parasitiese aalwurms, naamlik D. africanus, Pratylenchus spp., Meloidogyne spp. en Helicotylenchus spp., is uit grondboonmonsters wat gedurende die 2012/13 en 2013/14 seisoene in Jozini, Manguzi en Mbazwana verkry is, geïdentifiseer. Alhoewel, Tylenchus spp. is gedurende die 2013/14 seisoen vir die eerste keer in grondbone, penne en grond wat voor oes versamel is, geïdentifiseer. Resultate van hierdie studie toon dat daar 'n behoefte aan bewusmakingsveldtogte vir mikotoksien besmetting ontstaan en dat bykomende hulp nodig is om mikotoksien kontaminasie asook potensiële blootstellings te monitor. Meer in-diepte ontledings van al die moontlike faktore wat bydra tot die besoedeling en blootstelling van mikotoksien, veral in die bestaansproduksie area van noord KZN, is geregverdig.Master

Agricultural practices and their potential role in mycotoxin contamination of maize and groundnut subsistence farming

Mycotoxigenic fungi are common pathogens of maize and groundnuts; they produce mycotoxins which reduce the yield and quality of these grain crops. Numerous agricultural practices including crop rotation and storage methods have been shown to impact mycotoxin accumulation. Therefore, the farming and storage practices in maize and groundnut subsistence farming systems in Pongola, Vryheid, Jozini, Manguzi and Mbazwana Districts of northern KwaZulu-Natal (South Africa) were surveyed to determine their potential role in promoting or mitigating mycotoxin contamination. A questionnaire about agricultural farming practices and storage facilities was presented to 65 subsistence maize and/or groundnut farmers. At least 90% of the farmers surveyed were not aware of mycotoxins and their consequences to animal and human health. The majority of the farmers did not practise crop rotation. However, they practised intercropping and sorted damaged and mouldy grain (maize and groundnuts) before storage. The damaged or mouldy grain was largely used as animal feed, thereby exposing animals to an increased risk of mycotoxicoses. Metal tanks and inqolobane (a type of wooden structure) were identified as the most common storage structures. Harvested homegrown maize was mostly used for the farmers’ own consumption but also sometimes sold to the local community. The implementation of mycotoxin awareness campaigns is necessary, particularly in these districts. The storage facilities used by the subsistence farmers allowed increased moisture and insect invasion. The need for the surveillance of mycotoxins in subsistence-farmed food crops is vital. Significance: The main finding of this study is the extent of post-harvest losses and mycotoxin contamination of maize produced by smallholder farmers in South Africa. We further identify methods to manage the risk of mycotoxin exposure to smallholder farmers and their communities as well as reduce post-harvest losses