Potato (Solanum tuberosum L.) production in a changing climate: analysis of responses to elevated temperature and moisture conditions

Summaries in English, Zulu and Tsonga

This study was undertaken to investigate the effects of increasing atmospheric temperature, combined with either drought or flooding, on the growth, development and productivity of the Markies and Fianna potato cultivars. Furthermore, the effects of abiotic stress on the metabolomic profile of these two potato cultivars were studied and a comparison of their quality, growth and yield was drawn. These two potato cultivars (i.e. Markies and Fianna) were planted over three growing seasons. The first experiment (2016) was a preliminary study, undertaken to evaluate the methodology to be used for research on the effects of environmental stresses brought by climatic changes (that is, drought, flooding and increasing temperature) on potato growth and development. During this experimentation year (2016) growth chambers were used to control temperature on three levels: Growth chamber 1 (24°C), Growth chamber 2 (25°C) and Growth chamber 3 (27°C). Due to the size constraint of growth chambers, only 32 plants could be planted. The other two growing seasons (2017 and 2018), each experiment consisted of 108 potatoes planted (total 216 plants) and were exposed to three different water treatments, i.e. normal (control), flooding and drought; administered using portable water in a completely randomised block design in the greenhouse. In total, 98 metabolites were detected through LC-MS from the potato leaves. In addition, representative tubers of the treated plants were collected 91 days after planting. The tuber samples were freeze-dried, and ground to a fine powder in liquid nitrogen. The fine powder of the tuber samples was analysed by nuclear magnetic resonance spectroscopy (NMR) to identify their metabolomic profiles. The NMR data was analysed using principal component analysis and orthogonal partial least square discriminant analysis to identify any variations between the treatments. In both models, plants exposed to drought clearly separated from the plants that received either excess or moderate water. The potato tubers that experienced drought and flood treatments had the highest quantities of aspartic acid, asparagine, and isoleucine. The treatments resulted in varied quantities of metabolite production in both cultivars. Plants defense metabolites, such as phenylalanine, 2-aminobutyric, amino acids, valine, isoleucine and leucine were increased in the drought and flood experiments, supporting the notion that abiotic stress can result in strong expression of compounds such as these, as a tolerance mechanism. Therefore, influence of increasing temperature and the availability of water was observed on the plant growth and development response of these potatoes. Although the study was carried out in greenhouses during 2017 and 2018, the experimentation years, atmospheric temperature data were obtained from the South African Weather Services (SAWS). The temperature data from SAWS revealed that a 0.75°C temperature increase was recorded in the 2018 experimentation year. As a result, drought treatment in this experiment, combined with increasing temperature, proved to be more detrimental to plant growth and development, whereas flooding treatment began to impact negatively on plant growth and development when the temperature kept rising. The cultivar differences were observed, as the Fianna and Markies performed differently even though the treatments administered were the same. The varied responses of these potato cultivars because of the treatment application were also evident in the quantities of each metabolite produced. For example, asparagine metabolite was not produced under drought irrigation treatment, yet it was produced in large quantities under both normal and flooding irrigation treatments. Similarly, the correlation of metabolites to different plant growth parameters, also between treatment groups and metabolites, signifies how whole plants respond metabolically to water stress (that is, drought, flooding, or a normal water regime). However, despite biochemical changes, the essential nutrients were still produced by these potato cultivars. This research further showed that the content of crude protein in potato tubers is not only strongly dependent on cultivated potato cultivars but also on the interaction of different abiotic conditions. The findings from this study should assist in identifying drought-or flood-resistant potato cultivars that could provide high quality yields despite changing climatic conditions.

Lolu cwaningo lwenzelwe ukuphenya imiphumela yokwanda kwezinga lokushisa komoya, kuhlangene nesomiso sezulu esiguquguqukayo esihlanganisa izikhukhula noma isomiso, ngenxa yokuthuthukiswa kwenqala sizinda okanye ukuncola kwomkhathi ngenxa yezimboni. Ucwaningo lwenziwe iminyaka emithathu. Unyaka wokuqala (2016) wawubheka ukuthi lungenziwa kanjani lolugcwaningo, ngokutshala amazambane angu 32. Iminyaka emibili eyalandela (2017 no 2018 amazambane angu 108 unyaka ngamunye) yabe seyenza lona uqobo lolucwaningo. Imiphumela yalolu cwaning yenziwe ngokusebenzisa i LC-MS yona uyaveza 98 metabolites ngokuhlaziya amacembe amazambane. Amazambane uqobo wona ahlaziywa kusetshenziswa i NMR. Ukuhlaziya lemiphumela ekukhiqizweni kwezambane, izinhlobo ezimbili zezimbewu zamazambane eMarkies kanye neFianna zisetshenzisiwe kulolucwaningo. Ngaphezu kwalokho, imiphumela yengcindezi emvelweni nase zilwanyaneni ngenxa yokuguquka kwesimo sezulu ihlaziyiwe kulamazambane amabili, ukuze kubonakale ukuthi izinga lemisoco kanye nezakhamuzimba alithikamazekanga. Lemiphumela yacwanisiswa futhi kwaqhathaniswa nezinga lokukhula kwezitshalo zalamazambane, neqophelo lomkhiqizo, kanye nobungako besivuno sawo. Umthelela wokwanda kwezinga lokushisa nokutholakala kwamanzi noma imvula wabonakala ekukhuleni kwesitshalo kanye nokusabela kwentuthuko yala mazambane. Nakuba ucwaningo lwenziwa ezindlini zokugcina izitshalo ngonyaka ka 2017 kanyenoka 2018, amazinga okushisa komkhathi yatholwa kwaSouth African Weather Services (SAWS). Imininigwane ngokushisa evela kwa-SAWS iveza ukuthi ukunyuka kwezinga lokushisa okulingana no 0.75 ° C kuqoshwe ngonyaka wokuhlola ka 2018. Ngenxa yalokho kunyuka kwezinga lokushisa komkhathi, kucatshangwa ukuthi isimo sezulu sinomthelela endleleni lamazambane akhule ngayo kanye nomkhiqizo ogcine utholakele ongabanga muhle ngonyaka ka 2018 uma uqhathaniswa nolona owatholakala ngonyaka ka 2017. Umehluko walezitshalo zalamazambane ubulokhu uqashelwe futhi uqoshwa njalo ngosuku luka 14 (amaviki amabili). Ngaphezu kwalokho kunobufakazi bokuthi izinhlobo ezahlukene zamazambane azithikanyezwa yisimo sezulu ngendlela efanayo njengoba iFianna neMarkies yenza ngokuhlukile nakuba izimo ezazibhekene zamo, njengamazinga okushisa kanye nenani lamanzi ezaziwathola lalifana. Izimpendulo ezihlukene zalezi zitshalo zamazambane ngenxa yokuniselwa ngezindlela ezahlukahlukene ziphinde zabonakala enanini esivuno kanye nezinga leqophelo lalesosivuno. Isibonelo, izakha muzimba ezithile, njenge asparajini, ayizange ikhiqizwe ngaphansi kokwehliswa kwenani lamanzi uma kuniselwa ukuze kubesezingeni lesomiso, kwalandele okwezikhukhula; kodwa yakhiqizwa ngobuningi futhi eqophelweni eliphezulu ngaphansi kokunisela ngezinga lamanzi adingwa ngamazambane ukuze akhule. Ngokufanayo, ukuqhathaniswa kwezakhamzimba ezitholakale kulamazambane nenani lawo yabe yehlukahluekene, ihambisana yokukhula kwezitshalo, kanye nokuniselwa okwakweneka. Lokho kubonisa ngokusobala ukuthi izitshalo zonke zisabela kanjani ekushintshashintsheni kwezimo zokushisha namanzi okube yingcindezi kuzo (lezozimo zihlanganisa, amazinga okushisa komkhathi, izikhukhula, noma isomiso). Kodwa-ke, okuhle ukuthi naphezu kwezinguquko zezimo zezule ezazihlasele lamazambane uma ekhula, izakhamuzimba nemisoco ebalulekile yakhiqizwa yilamazamazambane omabili. Lolu cwaningo luphinde lwathola ukuthi amzinga esakhamuzimba iprotheyini engahluziwe kulamazambane ayincikile nje kuphela ezitshalweni kodwa futhi nasekusebenzelaneni kwezimo ezihlukahlukene zesimo senncindezi esenziwa yizinambuzane nokunukubezeka kwemvelo. Okutholwe kulolu cwaningo kufanele kusize ekuhlonzeni izithombo zamazambane ezingakwazi ukumelana nesomiso sezulu esiguquguqukayo, esihlanganisa izikhukhula noma isomiso, noma ukunyuka kwamazinga okushisa okungenzeka nganoma yisiphi isikwathi futhi kudonse izinsuku ezingaziwa.

Ndzavisiso lowu wu endliwe ku lavisisa hi vuyelo bya ku ngeteleleka ka mahiselo ya xibakabaka, swi pfangana na dyandza kumbe ndhambi eka ku kula, ku hluvuka na prodakthivhithi ya ti-cultivar ta mazambana ya Markies na Fianna. Kasi hi tlhelo rinwana vuyelo bya ntshikilelo wa abiotic eka profayili ya metabolomic ya ti-cultivar ta mazambana mambirhi ku endliwe ndzavisiso hi wona na ku pimanisa nkoka ya wona, ku kula na ntshovelo lowu nga kumeka hi wona Nkucetelo wa ku ngeteleleka ka mahiselo na ku kumeka ka mati na swona swi langutiwile hi ku kula ka swimila na ndlela ya angulo wa mazambana lawa. Hambileswi ndzavisiso wu endliwe eka ti-greenhouse exikarhi ka 2017 na 2018, malembe ya xikamibisiso, vutivi bya mahiselo ya xibakabaka swi kumekile eka va nhlangano wa South African Weather Services (SAWS). Vutivi bya mahiselo byo huma eka va SAWS byi kombise leswo ku ngeteleleka ka mahiselo hi 0.75% swi kandziyisiwile eka lembe ra ku endliwa ka xikambisiso hi 2018. Hikokwalaho ku langutiwa ka xikambisiso xa dyandza, swi hlangana na ku ya ehenhla ka mahiselo, swi kombise ku vaviseka ka ku kula ka swimila na nhluvuko wa swona, kasi ku langutana na ndhambi swi ve na vuyelo byo biha eka ku kula na nhluvuko wa swimila loko mahiselo ya karhi ya ya ehenhla. Ku hambana ka cultivar swi langutiwile tanihiloko Fianna na Markies swi tirhe hi ku hambana hambi loko swilo leswi swi langutiwe hi ndlela yo fanana. Ku angula ko hambana ka ti-cultivar ta mazambana lawa tanihi vuyelo bya ku tirhisiwa ka ku langutiwa ka leswi na swona swi vonake swi ri vumbhoni eka vunyingi bya metabolite leyi yi nga humesiwa. Xikombiso, asparagine metabolite a yi humesiwangi ehansi ka ku endliwa ka ncheleto hi nkarhi wa dyandza, kambe ku humesiwa hi vunyingi lebyikulu ehansi ka ku endliwa hi nkarhi wa ntolovelo na ncheleto wa ndhambi. Hikufanana na swona, ku fambelana ka ti-metabolite eka ku kula ko hambana ka swimila, na le xikarhi ka ku ongoriwa ka mitlawa na ti-metabolite swi kombise nkoka wa vuanguri bya swimila hinkwawo hi metabolikali eka ntshikilelo hi swa mati (hileswo, dyandza, ndhambi kumbe nkarhi wa ntolovelo hi ku kumeka ka mati). Kambe, hambi ku va na ku cinca ka biochemical, tinutriyente leti faneleke a ta ha humesiwangi hi ti-cultivar ta mazambana lawa. Ndzavisiso lowu wu tlhele wu komba leswo vundzeni bya protheyini ya rihlaza eka tichubara ta mazambane a ti titshegangi ngopfu eka ti-cultivar ta mazambana lama byariwaka kambe ti tlhela ti titshega na swiyimo swa ti-abiotic to hambana. Mimbuyelo ya ndzavisiso lowu yi fanele ku pfuneta ti-cultivar ta mazambana lama ya khodelelaku eka dyandza kumbe ndhambi, leswi swi nga pfunetaku ku va na ntshovelo wa nkoka hambi loko swiyimo swa tshamelo-maxelo swi karhi swi cinca.

Agriculture and  Animal Health

Ph D. (Agriculture)