Induced mutation in sweet potato aimed at improved quality and drought adaptation

Abstract

English: Induced mutation was incorporated into the South African sweet potato breeding programme to improve elite cultivars for yield, drought adaptation and nutritional quality. Three cream-fleshed cultivars namely Ndou, Monate and Mokone were selected, propagated in vitro and subjected to gamma ray mutagenesis from a 60Co source at SANBS. Radio-sensitivity tests were done on three node cuttings used as explants to determine optimum dosages for bulk irradiation. Data was subjected to regression analysis and calculated LD50 values were 64 Gy for Ndou, 38 Gy for Monate and 55 Gy for Mokone. Variation observed in lethal dosages highlighted the importance to test each genotype or plant material for sensitivity before mutagenic treatment. Bulk irradiation was done at respective optimum dosages and explants were propagated in vitro up to M1V4 and M2V5 stages to dissolve chimeras and obtain stable mutations. Three mutant populations comprised of 8 207 mutant plants were generated. These mutant plants were screened in the glasshouse for phenotypic/morphological changes visible to the naked eye. Mutant plants with changes in leaf shape, vine colour, fused veins, abaxial vein pigmentation, chlorophyll variegation on leaves and root flesh colour from cream to pale orange/yellow, were observed. After screening, 410 mutant plants (4.99%) with phenotypic changes were identified from the generated mutant populations. Mutant plants/lines derived from the cultivar Ndou were further subjected to vegetative drought and heat tolerance screening in the glasshouse. Two experiments were conducted and these mutant lines were evaluated for drought tolerance and drought and heat tolerance respectively. Thirteen mutant lines with improved drought and heat tolerance, when compared to Ndou, were identified from the first experiment. Further drought screening procedures will be conducted to confirm these results. Field evaluation trials were established to evaluate Ndou mutant lines. These were first evaluated in an initial evaluation trial at Lwamondo using single plants established from seedlings in a non-balanced completely randomised design. Mutant lines with three replicates each were harvested, data was collected on root yield and samples were taken and freeze dried for mineral and total starch content analyses. No mutant line had significantly improved root yields compared to Ndou. Thirteen mutant lines with significantly improved Mn and six mutant lines with significantly improved Mg contents compared to Ndou were identified. Total starch contents were significantly higher in four mutant lines than that of Ndou. Non-significant variations were observed in Zn and Fe contents between mutant lines and the control. Promising mutant lines were further identified and evaluated in a replicated preliminary yield evaluation trial at Towoomba. Top cuttings were used to establish the trial. Data was collected on marketable yield, unmarketable yield, total yield, root-flesh colour and dry mass content. Two mutant lines, M96 and M95, had improved total yields of 33.01 t ha-1 and 30.02 t ha-1 respectively compared to Ndou with 22.96 t ha-1. Dry mass contents were also improved in two mutant lines M47 (30.33%) and M28 (29.38%) compared to the control Ndou (27.00%). Root flesh colour changes were identified phenotypically in M224 and M6 with changes from cream to pale orange/yellow. All mutant lines will be subjected to advanced yield and nutrient evaluations including β- carotene quantification to identify mutant lines with improved yield, drought adaptation and enhanced nutritional contents to address food security and micronutrient deficiency in SA.

Afrikaans: Geïnduseerde mutante is in die Suid-Afrikaanse soetpatat-teelprogram geïnkorporeer om elite-kultivars te verbeter ten opsigte van opbrengs, droogte aanpasbaarheid en voedingskwaliteit. Drie roomvleiskleurige kultivars naamlik Ndou, Monate en Mokone is geselekteer, in vitro voortgeplant en aan gamma radiasie, vanaf ‘n 60Co bron van die SANBS, blootgestel. Stralings-sensitiewe toetse is op drie-stingelknoop-steggies gedoen om vas te stel wat die optimum dosering vir massa bestraling moet wees. Data is onderwerp aan regressie ontledings en die LD50 waarde is bepaal; dit was 64 Gy vir Ndou, 38 Gy vir Monate en 55 Gy vir Mokone. Variasie in die dodelike dosis wat waargeneem is beklemtoon die belangrikheid om genotipiese- en plant materiaal sensitiwiteit te toets vòòr die mutasie-behandeling. Massa bestraling is by die onderskeie optimum doserings gedoen en plantjies is deur weefselkultuur ontwikkel tot op M1V4 en M2V5 stadium om moontlike chimeras te verwyder en ‘n stabiele mutant te kry. Drie mutante populasies bestaande uit 8 207 gemuteerde plante is gegenereer. Die gemuteerde plante is met die blote oog, in die glashuis, vir fenotipiese/morfologiese veranderinge ondersoek. Mutante met veranderde blaarvorm, aarkleur, versmelte are, abaksiaal-aar pigmentasie, veelkleurige cholorfil vlekke op die blare en wortelvleiskleur vanaf room tot lig oranje/geel is waargeneem. Daar is 410 gemuteerdelyne (4.99%) met fenotipiese veranderinge geïdentifiseer vanuit die mutante populasie. Gemuteerde plante/lyne afkomstig vanaf die kultivar Ndou is verder blootgestel aan vegetatiewe droogte en hitte verdraagsaamheids-evaluasies in die glashuis. Twee eksperimente is gedoen en die gemuteerde lyne is geëvalueer vir droogte verdraagsaamheid as ook vir droogte en hitte verdraagsaamheid onderskeidelik. Dertien gemuteerde lyne met verbeterde droogte en hitte verdraagsaamheid in vergelyking met Ndou is geïdentifiseer uit die eerste eksperiment. Verdere droogte-evaluasieprosedures sal nog uitgevoer moet word om die resultate te bevestig. Veld-evaluasie proewe is gevestig om die Ndou gemuteerde lyne te evalueer. Hierdie lyne is aanvanklike in ‘n proef in Lwamondo geëvalueer, enkel plante is van saailinge af gevestig en in ‘n ongebalenseerde volledig ewekansige-ontwerp uitgelê. Gemuteerde lyne met drie herhalings elk is geoes, data op wortelopbrengs is versamel en monsters is geneem en gevriesdroog vir minerale en totale stysel bepalings. Geen gemuteerde lyne het ‘n betekenisvolle verbetering vir wortel-opbrengs in vergelyking met Ndou getoon nie. Dertien gemuteerde lyne met betekenisvolle verbeterde Mn en ses gemuteerde lyne met betekenisvol verbeterde Mg in vergelyking met Ndou is geïdentifiseer. Totale stysel inhoud was betekenisvol hoër in vier gemuteerde lyne in vergelyking met Ndou. Geen betekenisvolle variasie is waargeneem in Zn en Fe inhoud tussen die gemuteerde lyne en die kontrole nie. Belowende gemuteerde lyne is verder geïdentifiseer en geëvalueer in ‘n gerepliseerde voorlopige opbrengsevaluasie proef by Towoomba. Top steggies is gebruik om die proef te vestig. Data is ingesamel vir bemarkbare opbrengs, onbemarkbare opbrengs, totale opbrengs, wortelvleiskleur en droëmassa inhoud. Twee gemuteerde lyne, M96 en M95, het verbeterde totale opbrengste van 33.01 t ha-1 en 30.02 t ha-1 onderskeidelik gelewer in vergelyking met Ndou se 22.96 t ha-1. Droëmassa-inhoud het ook verbeter in twee gemuteerde lyne M47 (30.33%) en M28 (29.38%), in vergelyking met die kontrole Ndou (27.00%). Wortelvleis-kleur veranderings is fenotipies geïdentifiseer vir M224 en M6 met verandering van room to lig oranje/geel. Alle gemuteerde lyne sal getoets word in ‘n gevorderde opbrengs- en voedingsevaluasieproef wat β-karoteen kwantifisering insluit om gemuteerde lyne te identifiseer met verbeterde opbrengs, droogte aanpasbaarheid en verhoogde voedingswaarde om voedsel veiligheid en mikrovoedingstekorte in SA aan te spreek.