No description available.

No description available.

Thesis (MSC.Agriculture)) --University of Limpopo, 2009. / The aim of this experiment was to evaluate the effect of moisture stress on tomato, using non-destructive remote sensing techniques and agronomic traits under field and greenhouse conditions. Two tomato cultivars Roma VF and Flora Dade were used for the trial. The soil was fertilized optimally for all nutrients to avoid other stresses except water stress; a 2x2 factorial experiment was conducted using two levels of water regimes (stressed vs. control (non-stressed)) having four replicates and two cultivars using a Completely Randomized Design. Pots were put under greenhouse and field conditions. Canopy temperature was measured using an infrared thermometer, NDVI values were recorded using a green seeker hand-held optical sensor unit and stomatal opening were determined using a leaf porometer. Other agronomic traits including days taken for 50% flowering, plant height, number of fruits per plant and fruit yield per plant were recorded. Leaf temperature in stressed plants was high as compared to non-stressed plants, whereas NDVI and stomata conductance values were low. Number of fruits per plant was low; each plant had 4.00 fruits under field conditions and 5.00 fruits per plant under greenhouse conditions as compared to 9.00 fruits under field conditions and 13.00 under greenhouse conditions for non stressed plants. Stressed plants were shorter as compared to non-stressed plants and days taken for 50% flowering were delayed in both cultivars for stressed plants. Stressed plants showed a sign of stress at early stages of plant development. Most of these signs were found on the plants rather than on the fruits, the shape of the main stem of a growing plant was one of the good indicators as it became thin and stringy under stressed conditions. The experiment showed that it is possible to evaluate the effect of moisture stress on tomato by the use of canopy temperature, NDVI, stomatal conductance and agronomic traits.

Abstract Drought is the most common abiotic stress limiting chickpea production in the world. Ninety percent of the worlds chickpea is produced in areas relying upon conserved, receding soil moisture, therefore, crop productivity is largely dependent on efficient utilization of available soil moisture. Because of the variability in drought pattern from year to year, trait based selection could have an advantage over selection on the basis of grain yield alone. Trait based breeding, however, requires trait dissection into components. Successful marker identification would facilitate integration of MAS procedures in breeding programs enabling the pyramiding of favourable alleles.<p> The genetic map produced in this study was based on a population of recombinant inbred lines of a cross of ILC 588 x ILC 3279 containing 52 SSR markers spanned 335 cM of the chickpea genome at an average density of 6.4 cM. A total of 13 genomic regions were shown to be associated with drought tolerance traits. Some of these genomic regions showed pleiotropic effect on multiple traits. This was also supported by the analysis of phenotypic data where these traits were found to be correlated. For example, early flowering and maturity had a strong association with high grain yield. High grain yield was also associated with better portioning ability between biomass and grain yield, i.e. harvest index. Drought tolerance score (DTS) was associated with various important traits including biomass, early flowering, early maturity.<p> This study also concluded that chickpea genotypes differed in terms of root length, root length density, root weight density and root length to weight ratio at every 20 cm soil layer up to 100 cm depth in response to water deficits. Consideration of an efficient root system vs. a larger root system is also important, since in this research, large root systems were offset by low harvest index, presumably due to the lack of assimilate available for grain growth. A restricted root system is important in environments like Western Canada, where crop growth termination is usually required prior to fall frost. This study also reported significant associations of stomatal conductance (gs) with each of HI, grain yield under drought, drought susceptibility index and drought tolerance score (DTS). Stomatal conductance can also be used to assess plant stress due to drought. Values of gs less than 250 mmol m-2s-1 during flowering indicated drought stress under greenhouse conditions. A higher degree of plant stress due to drought was shown by increased stomatal closure at midday (gs <150 mmol m-2s-1). The study of 157 RILs under natural drought stress during 2005-07 revealed that the 17 RILs which had high grain yield under drought (Group A), also tended to have higher gs than the 42 RILs that had lower grain yield (Group B). Group A had mean gs values of 390 mmol m-2s-1 during the week before flowering, while Group B had mean gs value of 330 mmol m-2s-1. Stomatal conductance increased at flowering and then sharply decreased later in the reproductive period, particularly in Group B. These findings were also supported by canopy temperature differential measurements as Group A was also able to maintain lower canopy temperature than Group B, indicating the ability of these plants to maintain adequate transpiration and a cooler canopy under drought stress. This research indicated that gs and canopy temperature can be used to assess chickpea drought stress and to screen drought tolerant genotypes. This study identified a QTL on LG7 for gs, QTLs on LG1, LG3 and LG6 associated with canopy temperature differential, as well as QTLs associated with grain yield under drought, HI, DTS, days to flower, days to maturity, reproductive period and plant height. These QTLs identified for traits related to higher chickpea productivity under drought stress could have important implications for accelerating the process of pyramiding of favourable genes into adapted genotypes and on future marker-assisted breeding for drought prone areas.

Abstract Drought is the most common abiotic stress limiting chickpea production in the world. Ninety percent of the worlds chickpea is produced in areas relying upon conserved, receding soil moisture, therefore, crop productivity is largely dependent on efficient utilization of available soil moisture. Because of the variability in drought pattern from year to year, trait based selection could have an advantage over selection on the basis of grain yield alone. Trait based breeding, however, requires trait dissection into components. Successful marker identification would facilitate integration of MAS procedures in breeding programs enabling the pyramiding of favourable alleles.<p> The genetic map produced in this study was based on a population of recombinant inbred lines of a cross of ILC 588 x ILC 3279 containing 52 SSR markers spanned 335 cM of the chickpea genome at an average density of 6.4 cM. A total of 13 genomic regions were shown to be associated with drought tolerance traits. Some of these genomic regions showed pleiotropic effect on multiple traits. This was also supported by the analysis of phenotypic data where these traits were found to be correlated. For example, early flowering and maturity had a strong association with high grain yield. High grain yield was also associated with better portioning ability between biomass and grain yield, i.e. harvest index. Drought tolerance score (DTS) was associated with various important traits including biomass, early flowering, early maturity.<p> This study also concluded that chickpea genotypes differed in terms of root length, root length density, root weight density and root length to weight ratio at every 20 cm soil layer up to 100 cm depth in response to water deficits. Consideration of an efficient root system vs. a larger root system is also important, since in this research, large root systems were offset by low harvest index, presumably due to the lack of assimilate available for grain growth. A restricted root system is important in environments like Western Canada, where crop growth termination is usually required prior to fall frost. This study also reported significant associations of stomatal conductance (gs) with each of HI, grain yield under drought, drought susceptibility index and drought tolerance score (DTS). Stomatal conductance can also be used to assess plant stress due to drought. Values of gs less than 250 mmol m-2s-1 during flowering indicated drought stress under greenhouse conditions. A higher degree of plant stress due to drought was shown by increased stomatal closure at midday (gs <150 mmol m-2s-1). The study of 157 RILs under natural drought stress during 2005-07 revealed that the 17 RILs which had high grain yield under drought (Group A), also tended to have higher gs than the 42 RILs that had lower grain yield (Group B). Group A had mean gs values of 390 mmol m-2s-1 during the week before flowering, while Group B had mean gs value of 330 mmol m-2s-1. Stomatal conductance increased at flowering and then sharply decreased later in the reproductive period, particularly in Group B. These findings were also supported by canopy temperature differential measurements as Group A was also able to maintain lower canopy temperature than Group B, indicating the ability of these plants to maintain adequate transpiration and a cooler canopy under drought stress. This research indicated that gs and canopy temperature can be used to assess chickpea drought stress and to screen drought tolerant genotypes. This study identified a QTL on LG7 for gs, QTLs on LG1, LG3 and LG6 associated with canopy temperature differential, as well as QTLs associated with grain yield under drought, HI, DTS, days to flower, days to maturity, reproductive period and plant height. These QTLs identified for traits related to higher chickpea productivity under drought stress could have important implications for accelerating the process of pyramiding of favourable genes into adapted genotypes and on future marker-assisted breeding for drought prone areas.

Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Research was carried out to increase the current knowledge on sunburn development and its control in apples. In addition to its chief causes, viz. high irradiance and high temperatures, water stress has long been thought to contribute to sunburn susceptibility. Certain fruit chemical and textural characteristics have also been suspected to increase sunburn, while it is not clear how factors such as crop load affect sunburn in relation to other fruit quality parameters. In red and blushed cultivars, sunburn could be underestimated due to masking by the red colour overlay. Half and total irrigation water were withheld for two weeks in ‘Cripps’ Pink’ apples while in a concomitant trial, mulching with vermicompost (plus a thin layer of woodchips), woodchips, plant compost and black geotextile were used to regulate plant water by reducing soil evaporative loss. Sunburn increased with an increase in moisture stress. Mulching had no effect on plant water status, but it generally enhanced plant photochemistry, reducing fruit surface temperature (FST) and sunburn. Chemical and textural characteristics of exposed, but non-burned ‘Cripps’ Pink’ apples were compared with that of fruit with induced and naturally occurring sunburn. Flesh firmness, total soluble solids (TSS), and titratable acidity (TA) of induced and naturally occurring sunburnt fruit did not differ from each other, but were significantly different from the non-burnt fruit. Based on this, we concluded that sunburn induces textural and compositional changes in sunburnt fruit rather than some fruit being predisposed to develop sunburn due to their texture and chemical composition. Differences in heat stress tolerance, flesh texture and chemical composition of sun exposed and shaded fruit sides seem to relate to their light exposure history. The effect of crop load on sunburn and fruit quality were assessed on a fruit cluster level in 2008-09 and on a whole tree basis in 2009-10 in ‘Cripps’ Pink’. In 2008-09, sunburn, red colour and the proportion of first grade fruit decreased with an increase in number of fruit per cluster. Crop load did not have an effect on sunburn and fruit colour in 2009-10 although the lowest thinning severity seemed to increase sunburn severity while the proportion of first grade fruit was highest for the highest thinning severity. Fruit number per cluster had no effect on fruit size, while at the whole tree level, fruit size decreased with increasing crop load. Flesh firmness, starch breakdown, TA and TSS were neither affected by the number of fruit per cluster nor the crop load of the tree as a whole. Green ‘Granny Smith’ and ‘Golden Delicious’, blushed ‘Royal Gala’, ‘Fuji’, ‘Braeburn’ and ‘Cripps’ Pink’, and full red ‘Topred’ were used to assess how red colour (anthocyanins) masks superficial sunburn browning and bleaching. The greater reduction in superficial sunburn, but not in sunburn necrosis in red and blushed compared to green cultivars with increasing red colour a month towards harvest seemed to confirm the effect of masking. / AFRIKAANSE OPSOMMING: Hierdie navorsing is verrig ter uitbreiding van die huidige kennis oor die ontwikkeling en beheer van sonbrand in appels. Addisioneel tot die hoof oorsake van sonbrand, naamlik hoë irradiasie en hoë temperatuur, word waterstres gesien as bydraend tot sonbrandsensitiwiteit. Daar word ook vermoed dat sekere chemiese en teksturele eienskappe van die vrug sonbrand kan verhoog terwyl daar nie duidelikheid is oor hoe faktore soos oeslading sonbrand relatief tot ander vrugkwaliteitparameters kan affekteer nie. Die omvang van sonbrand in rooi en bloskultivars kan dalk onderskat word vanweë maskering deur die oorliggende rooi pigmentasie. Besproeiing is vir twee weke gehalveer of gestop in ‘Cripps’ Pink’ appels. Sonbrand het toegeneem met ‘n toename in vogstres. ‘n Deklaag van vermikompos (plus ‘n dun laag houtstukkies), houtstukkies, plantkompos en ‘n swart geotekstiel is toegedien om die plant waterstatus te reguleer deur evaporasie vanuit die grond te beperk. Die deklae het geen effek op die plant waterstatus gehad nie, maar het wel die blaar fotochemie bevorder en terselftertyd die vrugoppervlaktemperatuur verlaag en sonbrand verminder. Die chemiese en tekturele eienskappe van sonligblootgestelde ‘Cripps’ Pink’ appels sonder sonbrand is vergelyk met vrugte met geïnduseerde sonbrand en vrugte met sonbrand wat natuurlik ontwikkel het. Vrugvleisfermheid, totale oplosbare vastestowwe (TOV) en titreerbare suur (TS) van vrugte met natuurlik en geïnduseerde sonbrand het nie onderling verskil nie, maar het wel betekesnisvol verskil van vrugte sonder sonbrand. Ons het gevolglik afgelei dat sonbrand teksturele en komposisionele veranderinge teweeg bring eerder as dat sekere vrugte gepredisponeer word om sonbrand te ontwikkel vanweë hul tekstuur en chemiese samestelling. Dit kom voor dat verskille in hittestres toleransie, tekstuur en chemiese samestelling tussen die sonligblootgestelde en skadu kante van appels verband hou met hul verskil in sonligblootstelling. Die effek van oeslading op sonbrand en vrugkwaliteit in ‘Cripps’ Pink’ is ge-evalueer op trosvlak in 2008-09 en op ‘n per boom basis in 2009-10. Sonbrand, rooi kleur en die proporsie eersteklas vrugte het afgeneem met ‘n toename in die aantal vrugte per tros. Op ‘n per boom basis is rooi kleur en sonbrand egter nie deur oeslading geaffekteer nie. Die laagste vlak van vruguitdunning het wel oënskynlik die graad van sonbrand verhoog terwyl die hoogste vlak van vruguitdunning tot ‘n toename in die proporsie eersteklas vrugte gelei het. Die aantal vrugte per tros het geen effek op vruggrootte gehad nie terwyl vruggrootte afgeneem het met oeslading op ‘n heelboombasis. Vrugvleisfermheid, styselafbraak, TOV en TS is nie deur aantal vrugte per tros of die oeslading per boom geaffekteer nie. Groen ‘Granny Smith’ en ‘Golden Delicious’, rooiblos ‘Royal Gala’, ‘Fuji’, ‘Braeburn’ en ‘Cripps’ Pink’, en volrooi ‘Topred’ is gebruik om die maskering van oppervlakkige sonbrandverbruining en –verbleiking deur rooi antosianien te bestudeer. Oppervlakkige sonbrand het minder toegeneem in die maand voor oes in die rooi- en bloskultivars as in die groen kultivars terwyl vrugkleur skynbaar nie die aanwesigheid van die meer sigbare sonbrandnekrose geaffekteer het nie. Maskering speel dus ‘n rol in die aanwesigheid van sigbare sonbrand.

Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2015 / Cowpea (Vigna unguiculata L. Walp) is an important grain legume grown in many parts of the world mostly by smallholder (SH) farmers. Low soil phosphorus (P) and drought stress are major constraints to legume production and threaten food security. Root architecture is a spatial configuration of the root system which is influenced by moisture status and P uptake. A field experiment was conducted at Ukulima farm near Modimolle in Waterberg district during 2012/13 summer growing season. The treatments comprised of two levels each for soil P (low and high) and moisture status (water stress and well-watered); and eight cowpea genotypes (Tvu 4632, Tvu 6365, Tvu 9848, Tvu 15445, Tvu 16408, Tvu 15143, Oloyin and IT00K-1217). The low P level implied the available P in the soil measured in situ, which was less than 8 mg kg-1 while the high P level entailed fertilization at the rate of 40 kg P ha-1 application to achieve approximately 35 mg P kg-1 of soil . The root traits measured included angle of adventitious and basal roots, number of basal roots, tap root diameters at 5, 10, 15 and 20 cm soil depths; lateral branching densities at depth 5,10 and 15 cm, nodule score, deep score, shallowness score, 3rd order branching density, and 1.5 branching densities at 5 and 10 cm depth. Plant parameters measured were plant height, number of pods per plant, number of seeds per pod, length of the pods, unshelled weight, shelled weight and number of primary and secondary branches. Photosynthetic parameters measured were photosynthetic rate, intercellular CO2 concentration, water conductance, transpiration rate, vapour pressure deficits, sample cell CO2, sample cell H2O and relative humidity in the cell. All treatment factors were combined as split-split plot arrangement fitted into randomized complete block design; with four replicates. Results indicate that the lateral root branching density at 5 and 10 cm differed significantly (P≤0.05) across cowpea genotypes. Genotype showed significant effect on taproot diameter at 10 cm. Moisture status and P level exerted significant effect on cowpea genotypes 15 cm. There were significant differences (P≤0.05) for lateral root branching density observed at 5 and 10 cm depth in P rates x genotype interaction. Statistical analysis showed that P levels and cowpea genotypes had significant effects (P≤0.05) on mean plant height, biomass and highly significantly effects (P≤0.01) on number of branches, days to physiological maturity and mean pod length. The interaction between cowpea genotype and moisture stress condition significantly (P≤0.05) affected hundred (100) seed weight. Cowpea genotype Tvu16408 obtained highest grain yield of 3240 kg ha-1 and lowest was by IT00K1217 which obtained grain yield of 1256 kg ha-1. Results showed that photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O, relative humidity in the cell, intercellular CO2 and vapour pressure deficit differed significantly (P≤0.05) across cowpea genotypes. Soil moisture condition and cowpea genotype exerted significant (P≤0.01) effect on photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O and relative humidity in the cell. Variation in P levels had no significant effect on the measured photosynthetic parameters. Oloyin genotype had the highest photosynthetic rate followed by Tvu 4632 while cowpea genotype Tvu 9848 had the least photosynthetic rate. Interaction of moisture stress and cowpea genotype had a significant effect on intercellular CO2 concentration. Water stress reduced the intercellular CO2 concentration of Oloyin, Tvu 6365 and 4632 but resulted in a significant increase in intercellular CO2 concentration in Tvu 9848 genotype. Results showed that variation in soil P level exerted a significant (P≤0.05) effect on grain tissue P content and uptake, and a highly significant (P≤0.01) difference in P content across the various cowpea genotypes. Moisture stress exerted a significant (P≤0.05) difference on P uptake. The results showed that P levels and cowpea genotype variation exerted significant (P≤0.05) effects on P content, P uptake and nitrogen (N) uptake. Moisture status and cowpea genotype variation exerted significant (P≤0.05) effects on total N and N uptake. Cowpea genotype Tvu 9848 obtained more total N content (4.37%), while the lowest total N content was obtained by cowpea genotype Tvu 15445 with 3035 mg kg-1. The interaction between cowpea genotype and moisture status exerted a significant (P≤0.05) effect on N and P uptake of immature green pods harvested. There is a need to conduct more studies to identify cowpea genotypes, their root architecture and agronomic measures that can do well under xvii drought stress and low soil P conditions. Research needs to be conducted to enhance cowpea productivity under both low soil P and drought stress. Keywords: cowpea genotypes; moisture stress; phosphorus fertilisation; root traits

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22163号 / 農博第2377号 / 新制||農||1074(附属図書館) / 学位論文||R2||N5243(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 舟川 晋也, 教授 縄田 栄治, 准教授 真常 仁志 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Caracteres relacionados à tolerância ao estresse hídrico e correlacionados à produção de grãos têm sido considerados em programas de melhoramento de milho em função dos insucessos obtidos na seleção direta para produção de grãos sob estresse hídrico. O objetivo deste trabalho foi mapear QTLs de caracteres relacionados à tolerância ao estresse hídrico, estimar seus efeitos genéticos, e estudar a interação QTL por ambientes em duas populações de milho tropical. Duzentas e cinqüenta e seis progênies F2:3 de cada uma das duas populações, denominadas posteriormente U e D, foram avaliadas no delineamento em látice simples 16 x 16 em nove ou sete ambientes. As parcelas foram uma fileira de 4,0 m de comprimento, espaçadas entre si por 0,8 m, e 0,2 m entre plantas (62.500 plantas ha-1). Os caracteres avaliados foram produção de grãos com 15% de umidade dos grãos (PG), prolificidade (PROL), florescimento feminino (FF), florescimento masculino (FM), intervalo entre florescimentos (IF), número de ramificações do pendão (NRP) e stay-green (SG). Para o mapeamento de QTLs foi utilizado o mapeamento por intervalo composto expandido para múltiplos ambientes. Em ambas populações foi detectada variância genética para todos os caracteres. Produção de grãos apresentou correlação genética significativa nas populações D e U com PROL (0,88 e 0,79), e FF (-0,44 e -0,76); PG também foi geneticamente correlacionado com FM (-0,74) na população U, e com SG (-0,50) na população D. Vinte e quatro, 19, 16, 14, 15, 12 e 20 QTLs foram mapeados na população D, e 17, 22, 34, 28, 17, 26 e 33 QTLs foram mapeados na população U para PG, PROL, IF, FF, FM, NRP e SG, respectivamente. Os QTLs foram distribuídos por todos os 10 cromossomos, mas um menor número de QTLs foi mapeado nos cromossomos 6, 7, 9 e 10 em ambas populações. QTLs para diferentes caracteres foram mapeados em posições coincidentes para várias regiões genômicas em ambas populações. Cerca de 90% dos QTLs mapeados apresentaram pequenos efeitos genéticos, cada um explicando menos de 5% da variância fenotípica dos caracteres. A variância fenotípica total explicada pelos QTLs variou de 32,17% (FF) a 64,55% (FM) na população D, e de 41,70% (PG) a 69,30% (IF) na população U. O grau médio de dominância variou de dominância parcial a sobredominância na população D, enquanto na população U a sobredominância foi o grau médio de dominância para a maioria dos caracteres. Para todos os caracteres a maioria dos QTLs interagiu significativamente com os ambientes em ambas populações. Os QTLs com efeitos mais pronunciados foram, em geral, mais estáveis entre ambientes. Esses QTLs estáveis foram previamente relatados em outras populações sugerindo que eles também poderiam ser mais estáveis entre germoplasmas. QTLs estáveis poderiam ser úteis em estratégias de seleção assistida por marcadores para desenvolver híbridos de milho com alta produtividade e com baixa redução na produção de grãos sob estresse hídrico. / Traits related to moisture stress tolerance and correlated to grain yield have been considered in maize breeding programs because direct selection for grain yield under moisture stress has been unsuccessful. The objectives of this paper were to map QTLs of traits related to moisture stress tolerance, to estimate their genetic effects, and to study the QTL by environment interaction in two tropical maize populations. Two hundred and fifty-six F2:3 progenies from each of the two populations, thereafter named U and D, were evaluated in 16 x 16 simple lattice designs at nine or seven environments. Plots were one row 4.0 m long, 0.8 m spaced apart, and 0.20 m between plants (62,500 plants ha-1). The traits were recorded on grain yield at 15% grain moisture (GY), prolificacy (PRO), days to silk extrusion (SD), days to anthesis (AD), anthesis-silking interval (ASI), number of tassel branches (TB), and stay-green (SG). The composite interval mapping extended to multiple environments was used to map QTLs. Significant genetic variances were detected for all traits in both populations. Grain yield showed significant genetic correlations in populations D and U with PRO (0.88 and 0.79), and SD (-0.44 and -0.76); GY was also genetically correlated with SD (-0.74) in population U, and with SG (-0.50) in population D. Twenty-four, 19, 16, 14, 15, 12, and 20 QTLs were mapped in population D, and 17, 22, 34, 28, 17, 26, and 33 QTLs were mapped in population U for GY, PRO, ASI, SD, AD, TB, and SG, respectively. The QTLs were distributed along the 10 chromosomes, but a lower number of QTLs was mapped in both populations in chromosomes 6, 7, 9, and 10. QTLs for different traits were mapped in the same positions for several genomic regions in both populations. About 90% of the QTLs mapped presented lower genetic effects, each explaining less than 5% of the phenotypic variance of the traits. The total phenotypic variance explained by the QTLs ranged from 32.17% (SD) to 64.55% (AD) in population D, and from 41.70% (GY) to 69.30% (ASI) in population U. The average level of dominance ranged from partial dominance to overdominance in population D, but in population U overdominance was the average level of dominance for most of the traits. For all traits most of the QTLs interacted significantly with environments in both populations. The QTLs with larger effects were, in general, more stable across environments. These stable QTLs were previously reported in other populations suggesting that they could also be more stable across germplasms. Stable QTLs could be useful in marker-assisted selection strategies to develop high yielding maize hybrids with low grain yield decrease under moisture stress.

Caracteres relacionados à tolerância ao estresse hídrico e correlacionados à produção de grãos têm sido considerados em programas de melhoramento de milho em função dos insucessos obtidos na seleção direta para produção de grãos sob estresse hídrico. O objetivo deste trabalho foi mapear QTLs de caracteres relacionados à tolerância ao estresse hídrico, estimar seus efeitos genéticos, e estudar a interação QTL por ambientes em duas populações de milho tropical. Duzentas e cinqüenta e seis progênies F2:3 de cada uma das duas populações, denominadas posteriormente U e D, foram avaliadas no delineamento em látice simples 16 x 16 em nove ou sete ambientes. As parcelas foram uma fileira de 4,0 m de comprimento, espaçadas entre si por 0,8 m, e 0,2 m entre plantas (62.500 plantas ha-1). Os caracteres avaliados foram produção de grãos com 15% de umidade dos grãos (PG), prolificidade (PROL), florescimento feminino (FF), florescimento masculino (FM), intervalo entre florescimentos (IF), número de ramificações do pendão (NRP) e stay-green (SG). Para o mapeamento de QTLs foi utilizado o mapeamento por intervalo composto expandido para múltiplos ambientes. Em ambas populações foi detectada variância genética para todos os caracteres. Produção de grãos apresentou correlação genética significativa nas populações D e U com PROL (0,88 e 0,79), e FF (-0,44 e -0,76); PG também foi geneticamente correlacionado com FM (-0,74) na população U, e com SG (-0,50) na população D. Vinte e quatro, 19, 16, 14, 15, 12 e 20 QTLs foram mapeados na população D, e 17, 22, 34, 28, 17, 26 e 33 QTLs foram mapeados na população U para PG, PROL, IF, FF, FM, NRP e SG, respectivamente. Os QTLs foram distribuídos por todos os 10 cromossomos, mas um menor número de QTLs foi mapeado nos cromossomos 6, 7, 9 e 10 em ambas populações. QTLs para diferentes caracteres foram mapeados em posições coincidentes para várias regiões genômicas em ambas populações. Cerca de 90% dos QTLs mapeados apresentaram pequenos efeitos genéticos, cada um explicando menos de 5% da variância fenotípica dos caracteres. A variância fenotípica total explicada pelos QTLs variou de 32,17% (FF) a 64,55% (FM) na população D, e de 41,70% (PG) a 69,30% (IF) na população U. O grau médio de dominância variou de dominância parcial a sobredominância na população D, enquanto na população U a sobredominância foi o grau médio de dominância para a maioria dos caracteres. Para todos os caracteres a maioria dos QTLs interagiu significativamente com os ambientes em ambas populações. Os QTLs com efeitos mais pronunciados foram, em geral, mais estáveis entre ambientes. Esses QTLs estáveis foram previamente relatados em outras populações sugerindo que eles também poderiam ser mais estáveis entre germoplasmas. QTLs estáveis poderiam ser úteis em estratégias de seleção assistida por marcadores para desenvolver híbridos de milho com alta produtividade e com baixa redução na produção de grãos sob estresse hídrico. / Traits related to moisture stress tolerance and correlated to grain yield have been considered in maize breeding programs because direct selection for grain yield under moisture stress has been unsuccessful. The objectives of this paper were to map QTLs of traits related to moisture stress tolerance, to estimate their genetic effects, and to study the QTL by environment interaction in two tropical maize populations. Two hundred and fifty-six F2:3 progenies from each of the two populations, thereafter named U and D, were evaluated in 16 x 16 simple lattice designs at nine or seven environments. Plots were one row 4.0 m long, 0.8 m spaced apart, and 0.20 m between plants (62,500 plants ha-1). The traits were recorded on grain yield at 15% grain moisture (GY), prolificacy (PRO), days to silk extrusion (SD), days to anthesis (AD), anthesis-silking interval (ASI), number of tassel branches (TB), and stay-green (SG). The composite interval mapping extended to multiple environments was used to map QTLs. Significant genetic variances were detected for all traits in both populations. Grain yield showed significant genetic correlations in populations D and U with PRO (0.88 and 0.79), and SD (-0.44 and -0.76); GY was also genetically correlated with SD (-0.74) in population U, and with SG (-0.50) in population D. Twenty-four, 19, 16, 14, 15, 12, and 20 QTLs were mapped in population D, and 17, 22, 34, 28, 17, 26, and 33 QTLs were mapped in population U for GY, PRO, ASI, SD, AD, TB, and SG, respectively. The QTLs were distributed along the 10 chromosomes, but a lower number of QTLs was mapped in both populations in chromosomes 6, 7, 9, and 10. QTLs for different traits were mapped in the same positions for several genomic regions in both populations. About 90% of the QTLs mapped presented lower genetic effects, each explaining less than 5% of the phenotypic variance of the traits. The total phenotypic variance explained by the QTLs ranged from 32.17% (SD) to 64.55% (AD) in population D, and from 41.70% (GY) to 69.30% (ASI) in population U. The average level of dominance ranged from partial dominance to overdominance in population D, but in population U overdominance was the average level of dominance for most of the traits. For all traits most of the QTLs interacted significantly with environments in both populations. The QTLs with larger effects were, in general, more stable across environments. These stable QTLs were previously reported in other populations suggesting that they could also be more stable across germplasms. Stable QTLs could be useful in marker-assisted selection strategies to develop high yielding maize hybrids with low grain yield decrease under moisture stress.