Genetic variability and inheritance of drought and plant density adaptive traits in maize

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Date
2005
Authors
Gebre, Gezahegn Bogale
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University of the Free State
Abstract
English: Drought and low N stresses are factors most frequently limiting maize production in the tropics, where the vast majority of farmers have limited access to improved techno logy. Previous studies confirmed good performance of the crop under these conditions by improving tolerance to drought occurring at flowering, which is essential for resource constrained farmers in countries like Ethiopia. In addition to screening at sites with rain free seasons, the available genotypic variability for drought adaptive traits within adapted maize populations is crucial for successful improvement of tolerance. At Melkasa in Ethiopia, 196 randomly derived S1 lines from Population A-511 were tested for high yield potential, and drought and plant density adaptive traits under two moisture regimes, using two plant densities. Both plant density and drought stress significantly affected the tested primary and secondary traits of the S1 lines. However, drought effects were more effective in reducing grain yield and its components, as well as in increasing anthesis-silking interval or in delaying days to 50% silking. Significant genotypic variability within Population A-511 was observed for grain yield and most stress (drought and high plant density) adaptive traits. The association of yield with stress adaptive traits that included ears plant -1 , anthesis-silking interval, kernels ear -1 , and kernels plant -1 increased with increased stress. In contrast, the genotypic variance and heritability of grain yield and its components increased with decreasing stress, except for ears plant -1 . Regarding the use of suitable environments for drought tolerance screening in areas with unpredictable rainfall patterns, indirect selection under drought stressed high plant density conditions and direct selection under drought stressed normal density conditions were found to be equally efficient. CIMMYT drought tolerant lines and their crosses were tested separately at two plant densities under both drought stressed and well watered conditions managed by irrigation, and also in rainfed environments. This was mainly to determine their potential in performance, combining ability and heterosis under both stress and reduced stress environmental conditions. Considerable differences in performance were observed among drought tolerant inbreds, and among their crosses under contrasting growing conditions. However, most crosses from drought tolerant lines provided higher yields than local hybrids, indicating their suitability for the environments in which they were tested. In rainfed environments, higher yields were recorded for most genotypes at high plant density (» 88 800 plants ha -1 ) than the recommended density (» 44 400 plants ha -1 ) for local hybrids. The opposite held true when unimproved S1 lines derived from population A-511 were tested in another experiment. This indicated the increased potential in performance and tolerance to high plant density stress, mainly due to improvement made in drought tolerance. CML442, Mex102, CML202 and Mex101 were superior lines in per se performance and GCA effects, especially for yield. Crosses in which these lines were involved were also superior in yield and most other traits as well as for the corresponding SCA effects. Both additive (GCA) and non-additive (SCA) effects were important for expression of the tested traits in rainfed environments. However, additive effects were relatively more important than non-additive effects for expression of these traits. Drought tolerant lines with high per se performance in yield across rainfed environments gave high yielding hybrids under similar conditions, reflecting an association between crosses and their parental lines. Similarly, for drought tolerant genotypes evaluated across drought stressed and irrigated environments, the highest grain yield was recorded under well- watered high plant density conditions. On the contrary, under drought stressed high plant density conditions, the yield of lines and their crosses was reduced by 73 and 56%, respectively. Furthermore, the estimated heterosis increased with increased stress. These results confirmed increased tolerance of the improved lines and their crosses to high plant density stress, and increased tolerance of the crosses to drought stress compared to their parental lines. Combining ability tested in contrasting environments showed a predominant role of additive (GCA) effects for secondary traits and non-additive (SCA) effects for yield. For drought adaptive traits and yield, lines CML202 and Ken were superior in GCA and per se performance across diverse environments, while Mex101 was superior under drought stress. Among crosses, CML440 x Ken, CML440 x CML442, and Mex103 x CML202 were relatively superior in each and across environments. Drought tolerant genotypes that perform well in a range of soil N and moisture regimes are expected to give better yields with reduced genotype by environment interaction (GEI) across diverse environments. The AMMI 2 analysis model efficiently estimated the drought tolerant GEI patterns over environments. Crosses developed from drought tolerant lines showed variability in mean yield and GEI across environments. High yielding hybrids such as Mex103 x CML442, Mex103 x CML202, CML440 x CML442, Mex101 x CML445, CM202 x CML445, CML202 x Ken, CML440 x Ken and BH140 showed minimum GEI, indicating their wide adaptation across stress and reduced stress environments. In contrast, the unstable, high yielding hybrids like Mex101 x Mex102, Mex101 x CML442 and Mex102 x CML442 were adapted to unfavourable environments that included drought stress, and eroded topsoil. When compared to conventional hybrids, 22 and 26 crosses produced from drought tolerant parents were better than BH540 in mean yield and stability, respectively. On the contrary, the other local hybrid, BH140 was superior in terms of both parameters, due to one of its parents being improved for reduced plant height by CIMMYT.
Afrikaans: Droogte en lae N is stremmingsfaktore wat gereeld mielieproduksie in die trope benadeel, waar die verre meerderheid van produsente beperkte toegang tot gevorderde tegnologie het. Vorige studies het aangetoon dat verbeterde verdraagsaamheid teen droogte tydens die blomstadium tot goeie produksie onder wisselvallige toestande kan lei, wat noodsaaklik is vir hulpbronbehoewende boere in lande soos Ethiopië. Bykomend tot sifting van teelmateriaal in reënvrye omgewings, is genotipiese variasie vir droogteaangepaste eienskappe in omgewingsaangepaste mieliepopulasies noodsaaklik vir suksesvolle teelverbetering. By Melkasa in Ethiopië is 196 ewekansig verkreë S1 lyne uit Populasie A-511 by twee vogregimes en twee plantdigthede getoets vir opbrengspotensiaal sowel as droogte- en standaangepastheid. Plantdigtheid sowel as droogtestremming het beide die primêre en sekondêre droogteverwante eienskappe beduidend ge-affekteer. Droogte was egter meer effektief as hoë stand om opbrengs en opbrengskomponente te beïnvloed, sowel as om die interval tussen antese en baardverskyning of tyd tot 50% baardverskyning te verleng. Beduidende genotipiese variasie is binne Populasie A-511 vir opbrengs en stremmingsaangepastheidseienskappe gevind. Die verwantskap tussen opbrengs en stremmingsaangepastheidseienskappe wat koppe plant-1, pitte per kop-1, pitte plant-1 en antese-baard interval ingesluit het, het toegeneem met toenemende stremming. Hierteenoor het die genotipiese variasie en erflikheid van opbrengs en opbrengskomponente met die uitsondering van meerkoppigheid, toegeneem met toenemende stremming. Wat die keuse van geskikte omgewings vir seleksie vir droogtegehardheid betref, was indirekte seleksie by hoë plantdigthede onder droogtestremming en direkte seleksie onder stremming by normale digthede ewe effektief. Droogteverdraagsame lyne vanaf CIMMYT en hulle kruisings is afsonderlik by twee plantdigthede onder beide besproeiing en droogtestremming getoets, sowel as onder droëlandtoestande. Die doel was om hulle potensiaal, kombineervermoë en heterose onder nie-stremming en stremming te bepaal. Aansienlike verskille in prestasie is waargeneem. Meeste van die kruisings afkomstig vanaf droogtegeharde lyne het beter as plaaslike basters presteer, wat hulle geskiktheid vir die teikengebiede bevestig. Onder droëlandtoestande het die meeste genotipes hoër opbrengste by hoë stand (88 800 plante ha-1) as by die aanbevole stand vir lokale basters (44 400 plante ha-1) gelewer. In ‘n bykomende eksperiment met onverbeterde S1 lyne uit Populasie A-511 het die omgekeerde gebeur. Die resultaat bevestig die verhoogde potensiaal wat droogteweerstand onder hoëstandstremming tot gevolg gehad het. Lyne CML442, Mex102, CML202 en Mex101 was superieur wat algemene prestasie en algemene kombineervermoë betref, veral ten opsigte van opbrengspotensiaal. Kruisings waarin hierdie lyne gebruik was, was ook superieur wat opbrengs en meeste ander eienskappe betref, ook ten opsigte van spesifieke kombineervermoë. Beide additiewe (algemene kombineervermoë) en nie-additiewe (spesifieke kombineervermoë) effekte was belangrik vir die uitdrukking van stremmingsaangepastheidseienskappe onder droëlandtoestande. Droogtegeharde lyne met hoë algemene prestasie onder droëland toestande het as kruisings ook hoë opbrengste onder soortgelyke omstandighede gelewer, wat op ‘n prestasieverwantskap tussen kruisings en hulle ouerlyne dui. Soortgelyk het droogtegeharde genotipes wat onder beide stremming en besproeiing geevalueer was, die hoogste opbrengs onder besproeing en hoë stand gelewer. Hierteenoor is die lyne en kruisings se opbrengs onder droogtetoestande en hoë stand met 73 en 56% respektiewelik verlaag. Verder het die beraamde heterose onder stremming toegeneem. Die resultate bevestig dat die verbeterde lyne en hulle kruisings verdraagsaam teenoor hoëstand stremming was en dat kruisings hoër verdraagsaamheid as hulle ouerlyne het. Toetsing van kombineervermoë in kontrasterende omgewings het ‘n oorwegende rol van additiewe effekte vir sekondêre eienskappe en nie-additiewe effekte vir opbrengspotensiaal aangetoon. Ten opsigte van droogteaangepastheidseienskappe en opbrengs was die genotypes CML202 en Ken superieur in algemene kombineervermoë en algemene prestasie oor uiteenlopende omgewings, terwyl Mex101 superieur onder droogtestremming was. Van die kruisings was CML440 x Ken, CML440 x CML442 en Mex103 x CML202 relatief superieur in individuele sowel as oor omgewings. Droogtegeharde genotipes wat onder ‘n verskeidenheid van grond N en vogregimes goed presteer, word verwag om in verskillende omgewings beter opbrengste te lewer as gevolg van verminderde genotipe by omgewingsinteraksie (GOI). Die AMMI 2 model is suksesvol gebruik om droogtegeharde GOI patrone oor omgewings te beraam. Kruisings tussen droogtegeharde lyne het variabiliteit in gemiddelde opbrengs en GOI oor omgewings getoon. Hoog produserende basters soos Mex103 x CML442, Mex103 x CML202, CML440 x CML442, Mex101 x CML445, CML202 x CML445, CML202 x Ken, CML440 x Ken en BH140 het die minimum GOI getoon, wat dui op wye aanpassing oor stremmings- en nie-stremmingsomgewings. Hierteenoor was onstabiele hoog produserende basters soos Mex101 x Mex102, Mex101 x CML442 en Mex102 x CML442 beter aangepas by ongunstige omgewings, wat droogtestremming en verweerde bogrond insluit. In vergelyking met konvensionele basters het 22 en 26 kruisings tussen droogtegeharde lyne beter as BH540 gepresteer ten opsigte van opbrengs en stabiliteit respektiewelik. ‘n Ander plaaslike baster, BH140 was in albei opsigte beter aangesien dit ‘n topkruis is waarvan een ouer vir verminderde planthoogte verbeter was.
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Corn -- Drought tolerance, Corn -- Effect of stress on, Corn -- Spacing, Thesis (Ph.D. (Plant Scienes: Plant Breeding))--University of the Free State, 2005
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