Genotypic Variation In Grain Yield Research Articles

Ability of Different Growth Indicators to Detect Salt Tolerance of Advanced Spring Wheat Lines Grown in Real Field Conditions

Plant growth indicators (GIs) are important for evaluating how different genotypes respond to normal and stress conditions separately. They consider both the morphological and physiological components of plants between two successive growth stages. Despite their significance, GIs are not commonly used as screening criteria for detecting salt tolerance of genotypes. In this study, 36 recombinant inbred lines (RILs) along with four genotypes differing in their salt tolerance were grown under normal and 150 mM NaCl in a two-year field trial. The performance and salt tolerance of these germplasms were assessed through various GIs. The analysis of variance showed highly significant variation between salinity levels, genotypes, and their interaction for all GIs and other traits in each year and combined data for two years, with a few exceptions. All traits and GIs were significantly reduced by salinity stress, except for relative growth rate (RGR), net assimilation rate (NAR), and specific leaf weight (SLW), which increased under salinity conditions. Traits and GIs were more correlated with each other under salinity than under normal conditions. Principal component analysis organized traits and GIs into three main groups under both conditions, with RGR, NAR, and specific leaf area (SLA) closely associated with grain yield (GY) and harvest index, while leaf area duration (LAD) was closely associated with green leaf area (GLA), plant dry weight (PDW), and leaf area index (LAI). A hierarchical clustering heatmap based on GIs and traits organized germplasms into three and four groups under normal and salinity conditions, respectively. Based on the values of traits and GIs for each group, the germplasms varied from high- to low-performing groups under normal conditions and from salt-tolerant to salt-sensitive groups under salinity conditions. RGR, NAR, and LAD were important factors determining genotypic variation in GY of high- and low-performing groups, while all GIs, except leaf area duration (LAR), were major factors describing genotypic variation in GY of salt-tolerant and salt-sensitive groups. In conclusion, different GIs that reveal the relationship between the morphological and physiological components of genotypes could serve as valuable selection criteria for evaluating the performance of genotypes under normal conditions and their salt tolerance under salinity stress conditions.

Single- and multi-trait genomic prediction and genome-wide association analysis of grain yield and micronutrient-related traits in ICARDA wheat under drought environment.

Globally, over 2 billion people suffer from malnutrition due to inadequate intake of micronutrients. Genomic-assisted breeding is identified as a valuable method to facilitate developing new improved plant varieties targeting grain yield and micronutrient-related traits. In this study, a genome-wide association study (GWAS) and single- and multi-trait-based genomic prediction (GP) analysis was conducted using a set of 252 elite wheat genotypes from the International Center for Agricultural Research in Dry Areas (ICARDA). The objective was to identify linked SNP markers, putative candidate genes and to evaluate the genomic estimated breeding values (GEBVs) of grain yield and micronutrient-related traits.. For this purpose, a field trial was conducted at a drought-prone station, Merchouch, Morocco for 2 consecutive years (2018 and 2019) followed by GWAS and genomic prediction analysis with 10,173 quality SNP markers. The studied genotypes exhibited a significant genotypic variation in grain yield and micronutrient-related traits. The GWAS analysis identified highly significantly associated markers and linked putative genes on chromosomes 1B and 2B for zinc (Zn) and iron (Fe) contents, respectively. The genomic predictive ability of selenium (Se) and Fe traits with the multi-trait-based GP GBLUP model was 0.161 and 0.259 improving by 6.62 and 4.44%, respectively, compared to the corresponding single-trait-based models. The identified significantly linked SNP markers, associated putative genes, and developed GP models could potentially facilitate breeding programs targeting to improve the overall genetic gain of wheat breeding for grain yield and biofortification of micronutrients via marker-assisted (MAS) and genomic selection (GS) methods.

Evaluation of genotype by environment interaction and adaptability in lowland irrigated rice hybrids for grain yield under high temperature

Recent predictions on climate change indicate that high temperature episodes are expected to impact rice production and productivity worldwide. The present investigation was undertaken to assess the yield stability of 72 rice hybrids and their parental lines across three temperature regimes over two consecutive dry seasons using the additive main effect and multiplicative interaction (AMMI), genotype and genotype × environment interaction (GGE) stability model analysis. The combined ANOVA revealed that genotype × environment interaction (GEI) were significant due to the linear component for most of the traits studied. The AMMI and GGE biplot explained 57.2% and 69% of the observed genotypic variation for grain yield, respectively. Spikelet fertility was the most affected yield contributing trait and in contrast, plant height and tiller numbers were the least affected traits. In case of spikelet fertility, grain yield and other yield contributing traits, male parent contributed towards heat tolerance of the hybrids compared to the female parent. The parental lines G74 (IR58025B), G83 (IR40750R), G85 (C20R) and hybrids [G21 (IR58025A × KMR3); G3 (APMS6A × KMR3); G57 (IR68897A × KMR3) and G41 (IR79156A × RPHR1005)] were the most stable across the environments for grain yield. They can be considered as potential genotypes for cultivation under high temperature stress after evaluating under multi location trials.

LEVERAGING TRADITIONAL CROPS FOR FOOD AND FEED: A CASE OF HULLESS BARLEY (HORDEUM VULGARE) LANDRACES IN ETHIOPIA

This study explored food-feed traits in genotypes of 25 indigenous Ethiopian landraces, 13 landraces introduced into Ethiopia and 5 local checks of hulless barley (Hordeum vulgare). The genotypes were evaluated for straw fodder quality traits and the traits were related to grain yield and straw yield. The genotypes were grown in Ethiopia during the 2016 cropping season using augmented design consisting of 5 complete blocks. Results of the study showed high genotypic variability in grain yield (5.1 t/ha), straw yield (7.03 t/ha) and straw content of crude protein (CP: 29.1 g/kg), neutral detergent fiber (NDF: 77 g/kg), acid detergent fiber (ADF: 41 g/kg), acid detergent lignin (ADL: 22.7 g/kg) and invitro organic matter digestibility (IVOMD: 72 g/kg). Further, cluster analysis determined 6 genotypes i.e. 243231, 241790, 219177, 243235, 241787, 241789 among Ethiopian landraces that showed food-feed traits with an average of 3.44 t/ha of grain, 5.64 t/ha of straw and 55.9 g/kg of CP. The correlation between grain yield with straw yield and nutritive value parameters was insignificant. Principle component analysis determined that either CP, NDF or IVOMD can express the nutritive value of hulless barley straw. The study highlights the natural genotypic variation in grain yield and straw traits in hulless barley that can be exploited using appropriate breeding methods to develop varieties with a combination of food traits for human food and feed traits for livestock feed. These varieties would be particularly beneficial for mixed crop-livestock systems that are predominant in developing countries.

Performance of spring wheat lines near-isogenic for the reduced-tillering ‘tin’ trait across a wide range of water-stress environment-types

Agronomically-important traits were studied in 19 genetically-diverse sets of spring wheat (Triticum aestivum L.) lines near-isogenic (NILs) for the tiller inhibition gene (tin) in contrasting water-stress environment-types (ETs) in the Australian grainbelt between 2010 and 2014. The combination of NILs and ETs generated a wide range of spike numbers (103 to 885 spikes/m2), grain numbers per m2 (GNO; 1400 to 22800 grains/m2), and grain yields (0.3 to 8.2t/ha). On average, the presence of tin significantly reduced spike numbers (319 vs. 381 spikes/m2), increased the numbers of grains/spike (30 vs. 27 grains/spike), and thousand grain weight (TGW; 38.4 vs. 36.9g) at maturity. Variation in final biomass and GNO each explained over 70% of the genotypic variation in grain yield. Differences in anthesis biomass explained 38% of the variation in grain yield. The marginal yield response to increases in GNO was slightly greater in the tin-containing lines while the response to increases in final biomass was greater in the non-tin lines (p≤0.016). The harvest index varied with changes in ET (p<0.001) only. The interaction between presence/absence of tin and environment-type was significant for grain yield, total biomass, spike number, grains/spike, and GNO. Grain yields were similar between NIL groups in the lower-yielding ETs (mean yield <2t/ha) whereas non-tin lines were higher-yielding in more favourable ETs (mean yield >2t/ha). The rate of the response in grain yield, total biomass, spike number, and GNO to changes in environmental conditions from ‘unfavourable’ to ‘favourable’ was significantly greater in the non-tin lines, i.e. tin-containing genotypes were less responsive or plastic. Reduced-tillering plasticity was associated with increased plasticity in numbers of grains/spike and, to a lesser extent, TGW. The tin lines produced more grains/spike in ETs averaging 28 to 33 grains/spike while NIL groups had similar grains/spike in ETs with lower means. A slightly greater marginal yield response to increases in GNO in tin lines indicated that greater plasticity in the number of grains/spike and TGW can compensate for reduced spike numbers. It is concluded that large variability in adaptation exists within the group of tin-containing genotypes providing opportunities for further selection to improve wheat performance in environments yielding less than 2t/ha. Further work on the analysis of GNO and yield determination in tin wheat should also consider changes in resource utilisation and hence competition between plants as mediated by planting arrangement.

Genotypic variation of agronomic traits as well as concentrations of Fe, Zn, P and phytate in soybean cultivars

ABSTRACT The staple diet of most of the world population is provided by cereal, which present levels of iron (Fe) and zinc (Zn) below the nutritional demand of humans. Other factors that may substantially interfere for the low intake of Fe and Zn are the anti- nutritional factors present in the edible parts of plants, such as heavy metals and phytate. Hence, the objective of this study was to evaluate the genotypic variation in terms of yield (kg ha-1), plant height, insertion height of first pod, as well as concentrations of Fe, Zn, phosphorus (P) and the anti-nutrient phytate in grains of 24 soybean cultivars and to identify cultivars with potential for biofortification. The field experiment was conducted in Rio Verde, state of Goiás by the technological center of COMIGO. The experimental design used in the study was a randomized block design with 24 treatments and three replications. The results showed that there is genotypic variation for grain yield (kg ha-1), plant height, and insertion height of first pod, as well as for the concentrations of Zn, Fe, P and concentration of anti-nutient phytate in grains among the soybean cultivars. Non-significant or low correlations were found among the evaluated parameters except for the relationship between P and phytate (r=0.733). The diversity found among soybean cultivars offers genotypes such as 8197RR, M 7908RR and BRS 262 with potential to develop cultivars with better ability to accumulate nutrients in grains.

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.

Genotypic variation in grain yield and flowering pattern in terminal and intermittent drought screening methods in rainfed lowland rice

Rainfed lowland rice in the Mekong region is mostly grown in drought-prone areas, and drought resistant varieties could be selected using either terminal drought (severe water stress after flowering) or intermittent drought (frequent mild stress) screening. Delay in flowering is considered as a putative trait for selection of drought resistant genotypes, and its effectiveness as an indirect selection trait and its association with genotype's flowering duration, i.e. the time taken from the first to last flower in a plot, was evaluated under the two drought screening methods. These screening methods together with flood control were used at two locations, Chum Phae and Ubon in north-east Thailand using a total of 70 genotypes with different growing duration. Delay in flowering was estimated for the two drought screening methods and flowering of individual panicles within a plot was recorded to determine flowering duration of each genotype in the flood and terminal drought conditions.Mean reduction in grain yield was 52–55% under the terminal drought screening while it was 10–19% for the whole population and 23–33% for early flowering genotypes in the intermittent drought. Delay in flowering under intermittent drought condition at both locations was associated with yield reduction; genotypes that exhibited shorter delay in flowering had smaller yield reduction percentage and larger number of panicles. At Chum Phae, where grain yield reduction was associated with flowering time, genotypes with longer flowering duration under terminal drought had smaller yield reduction, and this was found even among genotypes that flowered about the same time under flood condition. However, there was no association between delay in flowering and flowering duration. It is concluded that delay in flowering appears promising as a selection criterion under intermittent drought conditions, provided a higher yield reduction can be achieved for example by using an increased irrigation interval.

Responses to phosphorus among wheat genotypes

Phosphorus (P) recovery and P-use efficiency (PUE) by wheat are low, and genetic improvement in PUE is a potential means of improving the effectiveness of P in farming systems. We examined variation in response to P in wheat to identify genotypes that showed consistent responsiveness to P fertiliser in the field and which may be the target of future studies, and examined differences in P uptake and partitioning. The response to P was studied among a diverse set of bread wheat germplasm at three sites in South Australia between 2009 and 2012. Up to 53 varieties and breeding lines were grown at two rates of P, 0 kg/ha and 30 kg/ha. Grain yield at 0 kg P/ha and response to P varied independently among genotypes. There were large effects of site and season on the response to P, but some genotypes showed consistently low and others high response to P. Analysis of a subset of lines revealed large responses in vegetative growth to P but the response diminished as crops matured, and variation in early vegetative growth was unrelated to the responses in biomass at maturity or grain yield. Genotypic variation in grain yield was more strongly related to variation in P utilisation efficiency than to variation in P uptake among wheat genotypes, which was associated with differences in P harvest index (PHI). Although breeding has improved yield, there has been no significant genetic gain in total P uptake; rather, improvements in PUE have been associated with an increase in P utilisation efficiency and PHI.

The extent of variation in salinity tolerance of the minicore collection of finger millet (Eleusine coracana L. Gaertn.) germplasm

Finger millet (Eleusine coracana L. Gaertn.) ranks third in production among the dry land cereals. It is widely cultivated in Africa and South Asia where soil salinization is a major production constraint. It is a potential crop for salt affected soils. To identify salt tolerant germplasm, the minicore finger millet germplasm (n=80) was screened for grain yield performance in a soil saturated with NaCl solution of 100 or 125mM. Genotype effect was significant for most traits, while salinity×genotype interaction was significant only in one year. Salinity delayed phenology, marginally reduced shoot biomass and grain yield. There was a large range of genotypic variation in grain yield under salinity and other traits. The yield loss was higher in accessions with prolific growth and yield potential was associated with saline yields. Based on saline yields, accessions were grouped in to four groups and the top tolerant group had 22 accessions with IE 4797 remaining at the top. Salinity had no adverse impact on grain yield of five accessions. Root anatomy in selected genotype of pearl and finger millet showed presence of porous cortex and well fortified endodermis in finger millet that can exclude Na+ and enhance N absorption.

Prediction of grain yield using reflectance spectra of canopy and leaves in maize plants grown under different water regimes

The ability to accurately estimate grain yield using spectral reflectance measurements prior harvest could be used to reduce phenotyping time and costs. In this study, grain yield of 300 maize testcrosses grown under different water and temperature regimes in the dry season 2010 was predicted using spectral reflectance (495–1853nm) of both leaves and canopy measured between tassel emergence until milk-grain stage. Partial least square regression (PLSR) was used for data analysis. Coefficients of determination (R2) between predicted and actual grain yield were highest for measurements conducted at anthesis and milk-grain stage, explaining at maximum 23% and 40% of the genotypic variation in grain yield after validation, respectively. PLSR models explained a higher proportion of the genetic variation in grain yield under drought stress compared to well-watered conditions. The association between predicted and actual grain yield was stronger in spectral reflectance measurements taken at the leaf level compared to canopy level. By combining the most predictive PLSR models across trials, at maximum of 40% of the variation in grain yield could be explained in each trial with a relative efficiency of selection of 0.88 and 0.68 using leaf and canopy reflectance, respectively. The most relevant wavelengths for predicting grain yield were associated with photosynthetic capacity (495–680nm), red inflection point (680–780nm) and plant water status (900, 970, and 1450nm, 1150–1260nm, and 1520–1540nm). Additional wavelengths based on leaf (800, 1000, and 1260–1830nm) and canopy (988–999nm and 1430–1640nm) reflectance of unknown physiological relevance were also identified for prediction of grain yield. Caution must be exercised before integrating our spectral reflectance approach into a breeding program because this is a pilot study based on a single location and season.

Plant characteristics associated with weed competitiveness of rice under upland and lowland conditions in West Africa

Weeds are a major constraint to rice ( Oryza spp.) production in West Africa. Superior weed competitive rice genotypes may reduce weed pressure and improve rice productivity. Two upland and two lowland experiments were conducted in southern Benin to examine genotypic variations in weed-suppressive ability and grain yield under weedy conditions, and to identify plant characteristics that could be used as selection criteria for improved weed competitiveness. A total of 19 genotypes, including Oryza sativa and Oryza glaberrima genotypes and interspecific hybrids developed from crossing O. sativa and O. glaberrima, were grown under weed-free and weedy conditions in an upland with supplemental irrigation and in a flooded lowland. In weedy plots, hand weeding was done once or not at all. Mean relative yield loss across all genotypes due to weed competition ranged from almost 0% to 61%. Large genotypic variations in weed biomass and grain yield under weedy conditions were found. Visual growth vigor at 42 and 63 days after sowing (DAS) under weed-free conditions significantly correlated with weed biomass at maturity in both upland and lowland experiments ( R 2 = 0.26–0.48). Where weed pressure was low to moderate, with mean relative yield loss less than 23%, the multiple regression models using grain yield and plant height at maturity or only grain yield measured under weed-free conditions as independent variables could explain 66–88% of the genotypic variation in grain yield under weedy conditions. At higher weed pressure (mean relative yield loss: 61%), as observed in one of the upland experiments, biomass accumulation of rice at 42 days after sowing was associated with higher grain yield under weedy conditions. Biomass accumulation also significantly correlated with visual growth vigor at the same sampling dates. Therefore, we conclude that grain yield, plant height at maturity and visual growth vigor at 42–63 DAS under weed-free conditions appear to be useful selection criteria for developing superior weed competitive rice genotypes.

How yield relates to ash content, Delta 13C and Delta 18O in maize grown under different water regimes.

Stable isotopes have proved a valuable phenotyping tool when breeding for yield potential and drought adaptation; however, the cost and technical skills involved in isotope analysis limit its large-scale application in breeding programmes. This is particularly so for Delta(18)O despite the potential relevance of this trait in C(4) crops. The accumulation of minerals (measured as ash content) has been proposed as an inexpensive way to evaluate drought adaptation and yield in C(3) cereals, but little is known of the usefulness of this measure in C(4) cereals such as maize (Zea mays). The present study investigates how yield relates to ash content, Delta(13)C and Delta(18)O, and evaluates the use of ash content as an alternative or complementary criterion to stable isotopes in assessing yield potential and drought resistance in maize. A set of tropical maize hybrids developed by CIMMYT were subjected to different water availabilities, in order to induce water stress during the reproductive stages under field conditions. Ash content and Delta(13)C were determined in leaves and kernels. In addition, Delta(18)O was measured in kernels. Water regime significantly affected yield, ash content and stable isotopes. The results revealed a close relationship between ash content in leaves and the traits informing about plant water status. Ash content in kernels appeared to reflect differences in sink-source balance. Genotypic variation in grain yield was mainly explained by the combination of ash content and Delta(18)O, whilst Delta(13)C did not explain a significant percentage of such variation. Ash content in leaves and kernels proved a useful alternative or complementary criterion to Delta(18)O in kernels for assessing yield performance in maize grown under drought conditions.

Consistency of genotypic performance of lowland rice in wet and dry season in Lao PDR

Lowland rice in Laos as in some other SE Asian countries is grown mostly under rainfed conditions in wet season (WS), but some crops are grown under irrigated conditions in dry season (DS). In Laos, the rice breeding program is concentrating on development of photoperiod insensitive varieties which can be grown in both WS and DS, nevertheless most selection is conducted in WS. In order to determine consistency of genotypic performance between WS and DS, 23 advanced breeding lines and varieties were grown in both seasons for 2–3 years at four locations in the country. All experiments in DS showed significant genotypic variation for grain yield, while genotypic variation was smaller and often not significant in each experiment in WS. The heritability was also higher in DS than in WS. Significant genotype-by-environment interaction was found, and some of this interaction was due to long duration genotypes being affected by extreme temperature conditions in DS particularly at a high altitude location in Northern Laos. Cluster analyses indicate that the genotypic discrimination was large in experiments with intermediate yield levels (mean yield of 2.9–3.8 t/ha). It is concluded that the use of DS trials should be increased to improve the efficiency of selection for widely adapted varieties in the lowland rice breeding program in Laos and other countries of similar growing conditions.

Improving the production and utilization of sorghum and pearl millet as livestock feed: progress towards dual-purpose genotypes

The overall objective of this work was to investigate variation in grain yield (GY), stover yield (SY), fodder quality of stover and their association in sorghum and pearl millet. These relationships were investigated in India in 12 genotypes of sorghum and six genotypes of pearl millet grown under high fertilizer (HF) and low fertilizer (LF) application. Fodder quality of stover was assessed by digestibility and intake measurements in bulls. In sorghum, highly significant genotype-dependent variation was found for GY, SY and fodder value of stover regardless of level of fertilizer application. GY and fodder quality of stover were not inversely related and the genotype with the highest GY, for example, had also the best fodder quality in the stover. High GY and high fodder quality in sorghum stover seem to be compatible traits. In pearl millet, genotypic variation in GY and SY and quality was expressed under HF but not under LF application. No consistent significant genotypic differences were found for fodder quality measurements in pearl millet except for cell wall digestibility. Digestible organic matter intake (DOMI) when bulls were fed to appetite was considered the crucial determinant of stover quality in sorghum and pearl millet. Live weight changes in bulls estimated by DOMI varied genotype-dependently from −140 to +100 g per day in 300 kg bulls. However, this paper argues that genotypes promoting high DOMI are only suitable for farmers with sufficient amounts of stover to allow the feeding of animals to appetite. Farmers with restricted amounts of stover are better served by genotypes that promote high digestibility under restricted feed intake.

Genotype–environment interaction of no-till winter wheat in Western Canada

Differences among cultivars in their response to changes in crop water availability are reflected in genotype–environment (GE) interactions for grain yield. With the recent expansion of the winter wheat production area in western Canada, it is important that plant breeders and agronomists have an understanding of the significance of GE interactions as they relate to regional adaptation of genotypes. Consequently, the objective of this study was to determine the phenotypic stability of recent high-yielding winter wheat genotypes grown under drought and low stress conditions on the Canadian prairies and to assess the effect that crop water status has on GE interactions. Eighteen field trials were conducted throughout Saskatchewan over a 3-yr period. Five hard red winter wheat genotypes were selected for evaluation in these trials on the basis of unique characteristics identified in earlier studies. Natural variation in weather among locations and years and irrigation produced a wide range in the timing and intensity of drought stress. The high yield potential of recent winter wheat selections was confirmed. A nonsignificant genotype-location effect meant that geographic subregions requiring specific adaptive traits could not be identified. In contrast, significant effects of years and genotype-year and location-year interactions indicated that annual differences in weather had a greater influence on relative genotype performance than weather differences among locations. Significant within-site genotypic variation for grain yield was observed only at high rainfall and irrigated sites, and the GE interaction was larger than the genotypic variance component when there were wide differences in environmental conditions. The GE interaction effect was not significant when only dryland sites were considered. A poor association between yield rank at the highly productive and drought-stressed sites was attributed to genotypic differences in yield potential and the effect of drought on the expression of yield potential. Joint regression, pairwise correlated response, stability, and convergence analyses were conducted in an effort to better interpret the practical importance of the GE interactions. A tendency for the genotype regression lines to converge below the range of grain yields expected in the region indicated that genotypes with the highest mean yield were widely adapted and that winter wheat breeders should select for high yield potential in low stress environments. However, the expression of grain yield potential was reduced enough to suggest that winter wheat yields in western Canada are likely to benefit from this “high” yield potential only under moderate and low stress conditions. Therefore, because there is a wide diversity of crop water conditions in this region, trial locations should also include targeted high stress environments to identify genotypes with high performance over a wide range of environments. Key words: Triticum aestivum L., drought stress, stability, regression analyses, grain yield

Genotype differences in nutrient uptake and utilisation for grain yield production of rainfed lowland rice under fertilised and non-fertilised conditions

A large number of rainfed lowland rice genotypes were grown under two fertiliser conditions to identify whether a genotype’s ability to extract more nutrients or to use absorbed nutrients more efficiently to produce grain yield was more important in determining genotypic variation in grain yield. From the yield responses of lines to fertiliser application, 16 contrasting lines were selected, and dry matter and nutrient (N, P and K) contents were determined for grain and straw separately for crops grown under non-fertilised and fertilised (60–13–16 N–P–K kg ha −1) conditions at three locations in Laos. There were significant effects of both genotype and genotype-by-fertiliser interaction for grain yield, which were closely associated with total N and P content at maturity. There was, however, also significant genotypic variation in nutrient-use efficiency (grain yield per unit nutrient absorbed), and this also contributed to the genotypic variation for grain yield. There was a large effect of genotype and a smaller effect of genotype-by-location interaction for nitrogen-use efficiency for grain yield. Nitrogen-use efficiency was negatively correlated with grain N concentration at two of the three locations. Both N- and P-use efficiency were consistent across fertiliser levels, and hence are likely to be used as selection criteria. The work also indicates that genotypes with high harvest index (HI) are likely to perform well in different fertility conditions.

Rainfed lowland rice breeding strategies for Northeast Thailand.: I. Genotypic variation and genotype × environment interactions for grain yield

The magnitude and nature of genotype-by-environment (G × E) interactions for grain yield, days-to-flower and plant height of rainfed lowland rice in Northeast Thailand were examined using random F 7 lines from seven crosses developed by the Thai breeding program. A total of 1116 lines and checks were evaluated in a multi-environment trial conducted across three years (1995–1997) and eight sites. The G × E interaction was partitioned into components attributed to genotype-by-site (G × S), genotype-by-year (G × Y) and genotype-by-site-by-year (G × S × Y) interactions. The G × S × Y interaction was the largest G × E interaction component of variance for all three traits. There was little G × S interaction for grain yield and days-to-flower. The G × S interaction was significant for plant height, but was the smallest component of variance for that trait. The G × Y interaction component of variance was significant for all three traits, but was small relative to the genotypic component for days-to-flower and plant height. For grain yield the G × Y interaction component was comparable in size to the genotypic component. Partitioning the genotypic and G × E interaction components of variance into among-cross and within-cross components indicated that there was significant variation both among and within the crosses for each trait. The relationships between the three traits differed among the crosses and the environments. A major factor contributing to the large G × S × Y interactions for grain yield was the genotypic variation for days-to-flower in combination with environmental variation for the timing and intensity of drought. Some of the interactions associated with timing of drought were repeatable across the environments sampled in the multi-environment trial, and to some extent the environments were characterised on the basis of whether there was pre-flowering, intermittent, or terminal drought. There was genotypic variation for grain yield after taking into consideration the influences of timing of drought in relation to plant development. Three of the seven crosses involved the Thai cultivars KDML105 and RD6 as parents. These crosses produced an array of progeny with lower yield than the Thai cultivars, suggesting it would be difficult to improve on the yield of these cultivars. In contrast three of the remaining four crosses, which did not have a Thai cultivar as a parent, produced progeny that had higher yield than KDML105 and RD6 indicating that yield of rainfed lowland rice could be improved above that of the these popular cultivars.

Genotypic variation for grain yield and grain nitrogen concentration among sorghum hybrids under different levels of nitrogen fertiliser and water supply

Sorghum [Sorghum bicolor (L.) Moench] is often grown under nitrogen- or water-limited conditions, but there is little information on genotypic variation for grain yield and grain nitrogen (N) concentration under these conditions. This study examined the expression of specific adaptation of hybrids to these stress conditions and, secondly, the effect of N fertiliser application on yield and grain N concentration of the hybrids. Two experiments, one irrigated and the other under rainfed conditions, were conducted in 2 seasons to examine 14 hybrids grown under 3 levels of fertiliser N supply (0, 60, and 240 kg/ha). Genotypic variation for yield and grain N concentration was generally larger than the in˚uence of genotype environment (predominantly N and water) interactions. Genotypic variation for phenology was important in determining variation for yield and grain N concentration in high-input and rainfed conditions when N was not the limiting factor, but not under N-limiting conditions. Under high-input conditions (240 kg/ha of N fertiliser and irrigated), maturity date accounted for about 50% of the genotypic variation for grain yield (798-1049 g/m2), with later maturing hybrids having a higher yield. Maturity date had little effect on plant N content at maturity or N harvest index, and hence grain N concentration (1·67-2·01%) was negatively correlated with grain yield. Under N-limiting conditions, N fertiliser application had large effects on yield and/or grain N concentration in both well-watered and pre-anthesis water stress conditions. In the irrigated experiment, when N was limiting (0 and 60 kg/ha of N fertiliser), genotypic variation for grain yield (225-729 g/m2) was not related to that for maturity date. It was, however, related to the variation in N uptake and dry matter growth by anthesis in the non-fertilised treatment. There was significant genotypic variation for grain N concentration (0·94-1·26%), which was not explained by variation for grain yield. Under rainfed conditions, where severe pre-anthesis water stress occurred, phenology was important in determining about 40% of the genotypic variation for yield (69-286 g/m2). The late-flowering hybrids escaped the major impact of the pre-anthesis water stress, had reduced damage to panicle development, and had higher N utilisation, consequently producing higher grain yield. Grain N concentration (1·09-2·85%) was again negatively related with grain yield. Genetic improvement of N uptake is identified as a possible breeding strategy for raising productivity and quality of grain sorghum under N-limiting conditions.