Short Anthesis-silking Interval Research Articles

Response of Maize-Hybrids Phenology Under high Plant Population Density in parts of Northern Guinea Savanna of Nigeria

Plant distribution in the field, as affected by plant density, has been one area that has received a great deal of attention over the last several decades. Population density, whether directly on the plant or indirectly on biotic factors associated with plant density is one of the most important factors in determining physiological attributes of a crop. Maize grain yield has a parabolic response to stand density that maximizes yield, which is widely known by the crop managers, physiologists and breeders; together with the concept that this optimum stand density varies with the environment. Development of breeding populations and hybrids with improved tolerance to high plant densities should be an important part of maize breeding programs. A field experiment was therefore conducted during 2015 and 2016 rainy season at Tudun Wada, Kano and Shika, Zaria in the Northern Guinea savanna of Nigeria in order to assess the phenological components of maize-hybrids at high plant population density. The experiment consisted of two plant populations of 53,333 plantha-1 and 88,888 plantsha-1 as main plot and eight recently developed drought–tolerant maize hybrids: M0826-7, M0926-8, M1026-10, M1026-13, M1124-4, M1124-10, M1227-12 and M1227-14 and two widely cultivated commercial hybrids as controls (Oba-98 and Oba super-1) as sub-plots laid out in a randomized split-plot design and replicated three times. Maize-hybrids responded to high plant population density in the two locations. Increasing plant population significantly decreased the phenology of maize-hybrids, which showed better adaptation of hybrids to high plant population density. Hybrids showed shorter days to maturity and shorter anthesis-silking interval. Maize-hybrids performed better at Zaria than at Tudun Wada because rainfall was higher and better distributed in this location. However recent hybrids were more tolerant to high plant population than the commercial hybrids, therefore the recently released maize-hybrids were more adapted to biotic stress.
 Keywords: Biotic stress, Growth, Phenology, Plant population density and Maize-hybrids

Fenotipeo y selección de líneas S1 segregantes de maíz tolerantes a estrés hídrico

La sequía reduce el rendimiento de grano del maíz; se requiere obtener líneas tolerantes a sequía para formar híbridos o variedades sintéticas. Los objetivos fueron: 1) fenotipear la población segregante en ambientes contrastantes de humedad, 2) seleccionar líneas de rendimiento alto y ASI corto con base a sequía y riego; y 3) determinar la heredabilidad y correlación de caracteres. El germoplasma fueron 193 líneas S1, progenitores y testigo; estos se evaluaron bajo riego y sequía inducida bajo el diseño látice alfa con dos repeticiones en dos localidades del Estado de Morelos, México. Las variables fueron floración masculina (FM) y femenina (FF), intervalo antesis-emergencia de estigmas (ASI), altura de planta (AP) y mazorca (AM); y rendimiento de grano (RG). Se observó reducción del 40 % en RG bajo sequía (0.75 t ha-1) con respecto a riego (1.26 ton ha-1), el ASI fue de 5 y 2 d en sequía y en riego, respectivamente. La heredabilidad para RG y ASI fue de 0.41. Existen líneas con herencia transgresiva para RG y ASI. La correlación del RG con FF y ASI fue de -0.23**y -0.37**, respectivamente. Existe germoplasma para generar una variedad sintética tolerante a estrés hídrico o iniciar un programa de hibridación.
 

Secondary Traits for Maize (Zea mays L.) Tolerance to Drought Combined with Reduced N Fertilization Rate

The secondary trait for a given abiotic stress tolerance, should be of strong correlation (r) with grain yield, high heritability (h2b) and high genetic advance (GA) under stressed conditions. The main objective of the present investigation was to identify secondary trait(s) for drought and/or low-N tolerance in maize genotypes. A two-year experiment was conducted, using a split-split-plot design. Main plots were allotted to two irrigation regimes, i.e. well watering (WW) and water stress at flowering (WS), sub-plots to three N fertilizer rates, i.e. low (LN), medium (MN) and high (HN) and sub-sub-plots to nineteen maize genotypes. Analysis of variance of randomized complete blocks design (RCBD) was also performed under each of the six environments (WW-HM, WW-MN, WW-LN, WS-HN, WS-MN and WS-LN). Tolerance to drought and/or low-N was strongly correlated with grain yield/plant (GYPP) under stressed environments. GYPP had high (h2b) and (GA); thus it is considered the best indicator of drought, low N or both stresses tolerance. The best secondary traits are high 100-kernel weight (100-KW), ears/plant (EPP), kernels/row (KPR), and short anthesis-silking interval (ASI) for low-N tolerance, high EPP, 100-KW, plant height (PH) and short ASI for drought tolerance, high 100-KW, EPP, KPR, PH and short ASI, for tolerance to drought combined with low N, and high 100-KW, rows/ear (RPE) and KPR under optimum conditions (WW-HN), since they show high (r), high (h2b) and high (GA) estimates under the respective environments. Under low-N and/or drought, future research should focus on the incorporation of secondary traits such as EPP, KPR, 100-KW, PH, ASI in the selection programs along with the grain yield trait.

Performance of Drought-tolerant Varieties of Maize (Zea mays L.) under Water Deficit Stress Condition in the North Region of Cameroon

Aims: The present study aimed to assess the performance of three drought-tolerant maize genotypes (DTSTRSYNY-2 (V1), WHITE DTSTRSYN (V2) and TZL COMP.4DTF2 (V3)) developed by IITA under water deficit stress conditions.
 Place and Duration of Study: Experiment was carried out at Sanguere-Paul in the Soudano-Sahelian agro-ecological zone, North region, Cameroon from September to December 2019.
 Methodology: Experimental design employed was the Randomized Complete Block Design (RCBD) of 5 treatments corresponding to different maize varieties in 2 replicates. The drought-sensitive CMS 9015 (V4) and the drought-tolerant EVDT99 QPM W (V5) maize varieties performed by IRAD was used as negative and positive controls, respectively. For each maize variety, growth and production parameters were recorded alongside the experiment and grain yield was calculated.
 Results: Results showed that the three drought-tolerant maize genotypes and the positive control maize variety assessed significantly exhibited a good performance under water stress condition regarding the growth and production traits registered compared to the negative control. Concerning growth parameters, the drought-tolerant maize varieties V1, V2 and V3 presented short anthesis-silking interval (1-1.5 day), good plant aspect, low number of dried leaves above ear (8-15 leaves) and less dead plants (1.25 -1.50 plant)compared to the controls. For V1, V2 and V3 drought-tolerant maize varieties, high yields of 3.24, 3.58 and 3.73 ton/ha, respectively, were obtained compared to the controls(1.13 ton/ha for the negative control V4 and 2.27 ton/ha for the positive control V5).
 Conclusion: Thus, the three drought-tolerant maize varieties showed good performance in the Soudano-Sahelian agro-ecological zone of Cameroon and should be adopted by farmers to increase and improve the maize production in the country, even under water deficit conditions.

Analysis of combining ability over environments in diallel crosses of maize (Zea mays)

Utilization of stress tolerant maize is the key to sustainable production and food security, and hence studies were conducted at Dirab Research Station, Riyadh, Saudi Arabia, from 2009 to 2010 to estimate General Combining Ability (GCA), Specific Combining Ability (SCA) and their interactions with environment. Non-reciprocal diallel crossing was performed among six inbreds. The inbreds, 15 F1 hybrids and two checks were evaluated in split plot design. Regulated irrigation commenced before tasselling and stopped before grain filling stage, using Food and Agriculture Organization (FAO) evaporation pan as guide. Water was applied when pan reading was at 50, 70 and 90in. to create E1, E2 and E3 environments respectively. Data were analyzed using method 3 of Gardner and Eberhart. Analysis of variance showed highly significant variance (P⩽0.01) among almost all sources of variation. High significance GCA and SCA observed revealed the importance of both additive and non-additive genetic actions, while low GCA/SCA implied importance of dominant effects of gene. Anthesis-silking interval (ASI) was the most affected trait by water deficit indicating that selection for tolerance could be based on short ASI. Performance per se of the genotypes reveals the importance of hybrids with P1 and P6 but failed to indicate their suitability as combiners. The KSU 6–47 had highest significant GCA for grain yield under E1 and E2. KSU 3–69 had the lowest significant negative GCA for days to tasselling, while cross KSU 6–47×KSU 3–69 with high SCA for grain yield and 1000-kernel weight under all environments suggested their usefulness for improvement.

Using an Airborne Platform to Measure Canopy Temperature and NDVI under Heat Stress in Maize

In light of anticipated climate change, we assessed the possibility to use an airborne platform to measure canopy temperature (CT) and the normalized differential vegetation index (NDVI) as well as the suitability of both traits for their use in breeding for tolerance to heat stress. We evaluated 71 subtropical maize (Zea mays L.) hybrids under heat stress and combined heat and drought stress in an environment with average temperatures of 29.8°C during the growing season and 31.2°C during the flowering period. Grain yield (GY) ranged from 0.33 to 4.19 Mg ha−1 under heat stress and from 0 to 1.37 Mg ha−1 under combined heat and drought stress, going along with increases in CT from 42.5°C to 49.5°C and decreases in NDVI from 0.54 to 0.48. The NDVI explained differences between and within treatments, while CT explained differences in GY among treatments and genotypes within the heat and drought stress treatment, as indicated by genetic correlations with GY. A principal component analysis was used to identify combinations of physiological characteristics associated with genotypic variation in GY. Results showed that selection gains for GY could be improved by 0.486 Mg ha−1 and 0.015 Mg ha−1 under heat and combined heat and drought stress, respectively, if selection is simultaneously carried out for GY, NDVI, and lower CT and shorter anthesis silking interval. We postulate that the use of selection indices, including CT and NDVI in conjunction with GY, will improve selection gains and increase cost efficiency of breeding programs.

Delaying Weed Control Lengthens the Anthesis-Silking Interval in Maize

Stress caused by early weed competition is known to delay the rate of maize development which may result in a decrease in kernel number. Kernel number in maize is correlated negatively with the length of the anthesis-silking interval (ASI). A short ASI has been identified as an easily measured, visual trait which may identify enhanced drought tolerance in maize. Field studies were conducted to test whether: (1) delaying weed control would result in a lengthening of ASI in both a drought tolerant and non-drought tolerant maize hybrid and (2) the presence of drought tolerance genetics comes at a physiological cost, resulting in a greater yield reduction under weedy conditions. In this study, the response of a drought tolerant hybrid with its non-drought tolerant near-isoline was compared to seven different timings of weed control using wheat as a surrogate competitor. Results confirmed that there was no treatment by hybrid interaction at any site–yr for any of the parameters evaluated. Delaying weed control reduced plant height, leaf tip number, shifted and reduced biomass accumulation, kernel number and grain yield and lengthened ASI for both hybrids. Although yield losses occurred with the delay in weed control timing, no yield differences were observed between hybrids suggesting that there was no additional physiological cost associated with the drought tolerant traits. The drought tolerant hybrid, however, was found to have a shorter ASI, lower kernel number and higher kernel wt compared to the non-drought tolerant hybrid. This study confirmed that delaying weed control can influence the length of ASI, which is an important drought tolerant trait. The lengthening of ASI by early weed competition resulted in a rate of yield loss of 0.13 T ha−1growing degree days (GDD)−1when averaged across both hybrids and all treatments.

Genetic diversity assessment of extra-early maturing yellow maize inbreds and hybrid performance inStriga-infested andStriga-free environments

SUMMARYMaize (Zea maysL.), a major staple food crop in West and Central Africa (WCA), is adapted to all agro-ecologies in the sub-region. Its production in the sub-region is greatly constrained by infestation ofStriga hermonthica(Del.) Benth. The performance and stability of the extra-early maturing hybrids, which are particularly adapted to areas with short growing seasons, were assessed underStriga-infested andStriga-free conditions. A total of 120 extra-early hybrids and an open-pollinated variety (OPV) 2008 Syn EE-Y DT STR used as a control were evaluated at two locations each underStriga-infested (Mokwa and Abuja) andStriga-free (Ikenne and Mokwa) conditions in 2010/11. TheStriga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lowerStrigadamage rating, and lower number of emergedStrigaplants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. UnderStrigainfestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha underStriga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% underStrigainfestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under bothStriga-infested andStriga-free conditions. The genotype main effect plus genotype×environment interaction (GGE) biplot analysis identified TZEEI 88×TZEEI 79 and TZEEI 81×TZEEI 95 as the ideal hybrids across research environments. Twenty-three pairs of simple sequence repeat (SSR) markers were used to assess the genetic diversity among the inbred lines. The correlations between the SSR-based genetic distance (GD) estimates of parental lines and the means observed in F1hybrid underStrigainfestation and optimum growing conditions were not significant for grain yield and other traits except ASI under optimum conditions. Grain yield of inbreds was not significantly correlated with that of F1hybrids. However, a significant correlation existed between F1hybrid grain yield and heterosis underStrigainfestation (r=0·72,P<0·01). These hybrids have the potential for increasing maize production inStrigaendemic areas in WCA.

The pyramid of transgenes TsVP and BetA effectively enhances the drought tolerance of maize plants

Stress resistance has repeatedly been enhanced in plants by the transfer of a single gene using genetic engineering. However, further enhancement of resistance to abiotic stress is still necessary. In our research, maize plants that were transgenic for both betA (encoding choline dehydrogenase from Escherichia coli) and TsVP (encoding V-H+ -PPase from Thellungiella halophila) were produced by cross-pollination. The existence of the transgenes in the pyramided plants was demonstrated by PCR and Southern blotting. The stable expression of transgenes was confirmed by real-time RT-PCR (reverse transcription polymerase chain reaction) analysis. An examination of the drought resistance characteristics demonstrated that the pyramided transgenic plants had higher glycinebetaine contents and H+ -PPase activity compared with the parental lines, which had either betA or TsVP, and contained higher relative water content (RWC), greater solute accumulation and lower cell damage under drought stress treatment. The pyramided plants grew more vigorously with less growth retardation, shorter anthesis-silking interval and higher yields than their parental lines and the wild-type. We concluded that co-expression of the two genes involved in different metabolism pathways in pyramided transgenic maize helped to improve the drought resistance over their parental lines that contained either single transgene. Our study suggests that the co-expression of multiple, effective genes in transgenic plants could effectively enhance the resistance to abiotic stress and provide a feasible approach for obtaining maize plants with improved drought resistance.

Genetic location and evaluation of chromosomal segments for drought tolerance at flowering stage in maize using selected backcross populations

Development and evaluation of introgression lines have become one of the promising approaches to understanding genetic mechanisms of important traits in crops. In this study, three sets of drought tolerance (DT) selected backcross populations in maize, including two BC2S1 populations and one BC3S1 population, from a cross of Qi319 and Huangzaosi (recurrent parent) were developed by selecting for short anthesis-silking interval (ASI) under the condition of serious water stress at flowering stage. The introgression of chromosome segments was identified using microsatellite markers. The results showed that the marker allele introgression frequencies in the three DT populations significantly increased compared with the expected value under no selection. There was a notable increase of introgression frequency for the most of these markers which were located on all chromosomes except chromosome 8, but most concentrated on some chromosomes, especially on chromosomes 4 and 5. For example, chromosome 4 harboured the largest number of introgression regions, on which five segments were detected. The ASI in the DT populations significantly shortened compared with the initial BC2 population.

Heterologous expression of the TsVP gene improves the drought resistance of maize

In this study, it was shown that the TsVP gene [vacuolar H+-pyrophosphatase (V-H+-PPase) gene from a dicotyledonous halophyte Thellungiella halophila] could be transferred into the monocotyledonous crop maize (Zea mays L.), and that the heterologous expression of the transgene improved the drought resistance of transgenic plants. Polymerase chain reaction amplification and Southern blotting confirmed the existence of the foreign gene in transformed plants and their progeny. Expression differences of the TsVP gene in different transgenic lines were monitored by reverse transcriptase-polymerase chain reaction. The measurement of isolated vacuolar membrane vesicles from the TsVP transgenic and wild-type (WT) plants demonstrated that the transgenic plants had higher V-H+-PPase activity, and the performance of maize-expressed TsVP in response to osmotic/drought stress was better in lines with higher V-H+-PPase activity. Transgenic plants showed a higher percentage of seed germination, better developed root systems and greater biomass, greater solute accumulation and less cell membrane damage relative to WT plants under osmotic stress. After drought stress treatment, transgenic plants showed less growth retardation and shorter anthesis-silking interval, and produced much larger grain yields, than WT plants. It was concluded that the high V-H+-PPase activity of transgenic maize improved the drought resistance of plants. This report provides a feasible approach to increase monocotyledonous crop yields under conditions of soil water deficit by the heterologous expression of TsVP.

Effect of Drought and Weed Management on Maize Genotypes and the Tensiometric Soil Water Content of an Eutric Nitisol in South Western Nigeria

In the dry savannas of West and Central Africa, where low soil fertility, unpredictable rainfall, weed competition and recurrent drought are major constraints to maize production, the development of tropical maize genotypes with high and stable yields under drought and low-nitrogen condition is very important since access to these improved genotypes may be the only affordable alternative to many small scale farmers. Field trials were conducted in 2002 and 2003 at Ikenne southwestern Nigeria to investigate the effect of weed pressures and drought stress on 2 maize (Zea mays L.) hybrids (9134-14, 9803-9) and 2 open-pollinated varieties (STREVIWD, IYFDCO1). Irrigation was withdrawn 4 weeks after planting (about four weeks to mid-flowering) in the drought stress while the adjacent watered treatment had irrigation throughout the growing period. The weed pressures were the completely weeded plots (hand weeding every week) and weedy plots (weeded once, 2 weeks after planting). The experiment was a split plot in a randomized complete block design with four replicates. Drought stress reduced the stover weight and grain yield of the maize cultivars by 6% and 34% respectively. Weed-free plots had maize with higher agronomic traits than unweeded treatments. Hybrid 9803-9 was more susceptible to drought and weed stress as indicated in the stover weight and grain yield. STREVIWD an open-pollinated variety (OPV) and Hybrid 9134-14 had superior performances in terms of grain yield and shorter anthesis silking interval. Soil moisture content was higher in the unweeded plots while the uptake of moisture was highest in drought susceptible hybrid 9803-9. Irrespective of the genotypes, maize (hybrid and OPV) was more tolerant to drought in a weed-free environment than in unweeded conditions. There existed a negative but significant correlation between weed biomass and chlorophyll content (−0.29, P < 0.01), grain yield (−0.45, P < 0.05), ear plant−1 (−0.27, P < 0.05) and kernel-number (−0.366 P < 0.01).

Patterns of population structure in maize landraces from the Central Valleys of Oaxaca in Mexico.

Assessing the impact of farmer management of maize landraces in the Central Valleys of Oaxaca, Mexico is crucial to an understanding of maize evolution, as it was first domesticated there. In this paper, we report on the impact of traditional farmer management of maize populations in this region in structuring molecular diversity and on the population dynamics of maize landraces. These populations, from a sample of local landraces cultivated by farmers in six villages, show little among-population differentiation (Fst=0.011). Most surprisingly, there is no isolation by distance and small among-village differentiation (Fst=0.003). For an outbreeding plant such as maize, one would expect populations to fit Hardy-Weinberg equilibrium, but significant homozygote excess (Fis=0.13) was found. This homozygote excess shows remarkable interpopulation and interlocus differences. We show that this pattern is related to variation in the mean anthesis-silking interval as well as to the flowering range or heterogeneity in flowering of a given population. A short anthesis-silking interval and high level of heterogeneity in flowering precocity will favor assortative mating. This leads to a locus-dependent population substructure giving an unusual case of Wahlund effect and inbreeding while high levels of seed exchange among farmers prevent population differentiation at both village and regional levels.

Secondary traits in parental inbreds and hybrids under stress and non-stress environments in tropical maize

Secondary traits other than grain yield (GY) have been successfully used to enhance the rate of genetic improvement for maize ( Zea mays L.) populations under abiotic stresses. With increasing trend towards the development of hybrids in the tropics there is a need to understand the genetics of these traits in inbred–hybrid breeding systems. The objectives of this study were to estimate the general combining abilities for secondary traits and their relationship with GY in a group of tropical white inbred lines and their hybrids under stress and non-stress environments. Traits were measured in inbred lines and their hybrid combinations across stress and non-stress subtropical and tropical environments in México. Hybrids showed earlier flowering, taller plants, more ears per plant (EPP), higher shelling percentage, slower leaf senescence, and higher leaf chlorophyll content than inbreds under all environments. La Posta Sequı́a (LP)-derived inbreds in general had desirable GCA for traits such as anthesis–silking interval (ASI), EPP, and leaf senescence but were more susceptible to foliar diseases. Conventionally bred maize lines had better standability, stay green, and resistance to diseases. Higher GY in lines and hybrids was associated with shorter ASI, earlier flowering, increased plant and ear height, increased EPP, increased shelling percentage, delayed senescence, and greater leaf chlorophyll concentrations. Under stress vs. non-stress conditions, we observed a higher variability for ASI and EPP, a higher inbred–hybrid correlation, and significant correlations between these traits and GY. Inbreds from LP appear to have high frequency of favorable dominant alleles for ASI and EPP.

Physiological mechanisms contributing to the increased N stress tolerance of tropical maize selected for drought tolerance

An improved response of crop varieties to various stress factors may be associated to constitutive stress tolerance mechanisms that increase yield and yield stability. Increased leaf longevity, increased water and nutrient uptake, greater assimilate supply during grain filling, and increased grain and ear set have been associated with constitutive stress tolerance mechanisms in maize ( Zea mays L.). We examined tropical maize for adaptive changes associated with drought tolerance that are sustained under N stress and therefore may indicate constitutive stress tolerance mechanisms. Original and drought-tolerant selection cycles of four populations were evaluated in five experiments differing in N supply at Poza Rica, Mexico between 1992 and 1994. Selection for tolerance to mid-season drought stress consistently increased grain yield across N levels due to an increase in both the number of ears per plant and kernel weight. The number of ears per plant was associated with a shorter anthesis–silking interval (ASI) of drought-tolerant cycles. Reduction in ASI due to selection was greater under N stress as compared to well-fertilized conditions, however, it was not associated with either biomass or N accumulation of plants and ears around flowering. The N content of individual kernels did not change with selection and grain N concentration decreased. Greater kernel weights were likely the result of delayed leaf senescence and increased assimilate supply during grain filling. We conclude that decreased ear abortion and increased assimilate supply during grain filling of maize selected for tolerance to mid-season drought also provide tolerance to N stress and therefore may contribute to increased yield and yield stability.

Identification of quantitative trait loci under drought conditions in tropical maize. 2. Yield components and marker-assisted selection strategies

In most maize-growing areas yield reductions due to drought have been observed. Drought at flowering time is, in some cases, the most damaging. In the experiment reported here, trials with F3 families, derived from a segregating F2 population, were conducted in the field under well-watered conditions (WW) and two other water-stress regimes affecting flowering (intermediate stress, IS, and severe stress, SS). Several yield components were measured on equal numbers of plants per family: grain yield (GY), ear number (ENO), kernel number (KNO), and 100-kernel weight (HKWT). Correlation analysis of these traits showed that they were not independent of each other. Drought resulted in a 60% decrease of GY under SS conditions. By comparing yield under WW and SS conditions, the families that performed best under WW conditions were found to be proportionately more affected by stress, and the yield reductions due to SS conditions were inversely proportional to the performance under drought. Moreover, no positive correlation was observed between a drought-tolerance index (DTI) and yield under WW conditions. The correlation between GY under WW and SS conditions was 0.31. Therefore, in this experiment, selection for yield improvement under WW conditions only, would not be very effective for yield improvement under drought. Quantitative trait loci (QTLs) were identified for GY, ENO and KNO using composite interval mapping (CIM). No major QTLs, expressing more then 13% of the phenotypic variance, were detected for any of these traits, and there were inconsistencies in their genomic positions across water regimes. The use of CIM allowed the evaluation of QTL-by-environment interactions (Q×E) and could thus identify “stable” QTLs CIMMYT, Apartado Postal 6-641, 06600 Mexico D.F., Mexico across drought environments. Two such QTLs for GY, on chromosomes 1 and 10, coincided with two stable QTLs for KNO. Moreover, four genomic regions were identified for the expression of both GY and the anthesis-silking interval (ASI). In three of these, the allelic contributions were for short ASI and GY increase, while for that on chromosome 10 the allelic contribution for short ASI corresponded to a yield reduction. From these results, we hypothesize that to improve yield under drought, marker-assisted selection (MAS) using only the QTLs involved in the expression of yield components appears not to be the best strategy, and neither does MAS using only QTLs involved in the expression of ASI. We would therefore favour a MAS strategy that takes into account a combination of the “best QTLs” for different traits. These QTLs should be stable across target environments, represent the largest percentage possible of the phenotypic variance, and, though not involved directly in the expression of yield, should be involved in the expression of traits significantly correlated with yield, such as ASI.