Components Of Grain Yield Research Articles

High-throughput measurement of rice tillers using a conveyor equipped with x-ray computed tomography

Tillering is one of the most important agronomic traits because the number of shoots per plant determines panicle number, a key component of grain yield. The conventional method of counting tillers is still manual. Under the condition of mass measurement, the accuracy and efficiency could be gradually degraded along with fatigue of experienced staff. Thus, manual measurement, including counting and recording, is not only time consuming but also lack objectivity. To automate this process, we developed a high-throughput facility, dubbed high-throughput system for measuring automatically rice tillers (H-SMART), for measuring rice tillers based on a conventional x-ray computed tomography (CT) system and industrial conveyor. Each pot-grown rice plant was delivered into the CT system for scanning via the conveyor equipment. A filtered back-projection algorithm was used to reconstruct the transverse section image of the rice culms. The number of tillers was then automatically extracted by image segmentation. To evaluate the accuracy of this system, three batches of rice at different growth stages (tillering, heading, or filling) were tested, yielding absolute mean absolute errors of 0.22, 0.36, and 0.36, respectively. Subsequently, the complete machine was used under industry conditions to estimate its efficiency, which was 4320 pots per continuous 24 h workday. Thus, the H-SMART could determine the number of tillers of pot-grown rice plants, providing three advantages over the manual tillering method: absence of human disturbance, automation, and high throughput. This facility expands the application of agricultural photonics in plant phenomics.

Inheritance of kernel row number, a multicategorical threshold trait of maize ears

Information about the inheritance of threshold traits is scarce, especially in plants. We examined the genetic control of kernel row number in maize (Zea mays). Knowledge of this inheritance is especially important because it is a primary component of grain yield. This trait has a discontinuous distribution. Characters like these are conceptualized as threshold traits. Crosses were made between the inbred line Geneze 3 (G3) with many kernel rows and the inbreds Argentino IV (A4) and Dente de Cravo (DC), with fewer kernel rows. The F(1) and F(2) generations and the backcrosses BC(11) and BC(21) were obtained for the combinations G3 x A4 and G3 x DC. These populations were evaluated under field conditions, and the kernel row number was determined by direct counting of approximately 14, 140 and 75 ears for the F(1), F(2) and backcrosses, respectively. Genetic control was determined through estimates of generation means and variance analysis and was also performed by Wright's method for threshold traits. It was found that genetic control is predominantly due to additive alleles. The component a, was greater than zero, additive variance was positive and the variance of dominance did not differ from zero. In the F(2) generation, the range of the kernel row number was 10 to 28 in G3 x A4, while in G3 x DC it was 12 to 26. Inheritance of the number of kernel rows, estimated by the two methods, gave similar results. This correspondence is due to adjusting of the data to the normal distribution.

Characterization and precise mapping of a QTL increasing spike number with pleiotropic effects in wheat

Tiller number (TN) and spike number per plant (SN) are key components of grain yield and/or biomass in wheat. In this study, an introgression line 05210, developed by introgression of chromosomal segments from a synthetic exotic wheat Am3 into an elite cultivar Laizhou953, showed a significantly increased TN and SN, but shorter spike length (SL) and fewer grain number per spike (GNS) than Laizhou953. To investigate the quantitative trait locus (QTL) responsible for these variations, the introgressed segments in 05210 were screened by SSR markers and one follow-up segregation population was developed from the cross 05210/Laizhou953. The population showed 3:1 segregation ratios for SN, SL and GNS, indicating that QTLs for these traits have been dissected into single Mendelian factors. Bulked segregation analysis showed that the markers located on the 4B introgressed segment were polymorphic between the two bulks. Therefore, they were further analyzed in the F(2) population to construct a linkage map. Three new QTLs, QSn.sdau-4B, QSl.sdau-4B and QGns.sdau-4B, were detected for SN, SL and GNS, respectively, which explained a large portion of the phenotypic variation (30.1-67.6%) for these traits with overlapping peaks. Correlation analysis and multiple-trait, multiple-interval mapping (MMIM) suggested pleiotropic effects of the QTL on SN, SL and GNS. Therefore, the QTL was designated as QSn.sdau-4B. By a progeny test based on F(3) families using SN, the QTL was mapped as a Mendelian factor to the proximal region of 4BL. It is a key QTL responsible for variation in spike number and size, which had not been reported previously. Thus, it is an important QTL for wheat to achieve high and stable biomass and grain yield. Dissection and mapping of this QTL as a Mendelian factor laid a solid foundation for map-based cloning of grain yield-related QTLs in wheat.

Study of Genetic Diversity by RAPD Markers and Identification of Informative Markers for Grain Yield and its Components in Hulless Barley Genotypes

Twenty hulless barley genotypes were assessed by 85 RAPD markers having 10 bps. Thirty five markers (41%) had suitable polymorphism using 227 amplified markers. The average number of amplified segments was 6.48. The size of amplified products varied from 400 to 2700 kb. Primer 540 had the highest and primers 498, 559, 577 and MT9 had the lowest amplified segments. Jacard similarity coefficient ranged from 0.3770 to 0.8. The highest similarity was observed between genotypes no. 15 and 16 (0.8) and also between no. 2 and 3 (0.759). The cluster analysis based on Jacard similarity and complete linkage method classified hulless barley genotypes into three groups. The results of the cluster analysis corresponded with the pedigree of the genotypes and the genotypes with the similar pedigree were grouped mostly in one cluster. This suggests the efficiency of RAPD markers in detecting genetic diversity of hulless barley germplasm. Principal coordinates analysis showed that five coordinates accounted for only 42.58% of variation which indicated the proper distribution of markers in the hulless barley genome because of relatively low percentage determined by the five first coordinates. Diversity of hulless barley genotypes was also evaluated by 25 agronomic characters using the range of every trait as a percent of mean. The results showed the existence of considerable variability among the genotypes for most of characters. Analysis of regression showed that 20, 19, 18, 14, 11 and 10 markers were informative for spike length, number of grains per plant, grain yield per plant, number of effective tillers, heading date and 1000 grain weight, respectively. From 18 informative markers for grain yield eight were similar with the markers informative for the number of grains per plant which suggests that from molecular view point this character could be regarded as the most important component of grain yield per plant in hulless barley

Mapping of quantitative trait loci and development of allele-specific markers for seed weight in Brassica napus

Seed weight is an important component of grain yield in oilseed rape (Brassica napus L.), but the genetic basis for the important quantitative trait is still not clear. In order to identify the genes for seed weight in oilseed rape, QTL mapping for thousand seed weight (TSW) was conducted with a doubled haploid (DH) population and an F(2) population. A complete linkage map of the DH population was constructed using 297 simple sequence repeat (SSR) markers. Among nine TSW QTLs detected, two major QTLs, TSWA7a and TSWA7b, were stably identified across years and collectively explained 27.6-37.9% of the trait variation in the DH population. No significant epistatic interactions for TSW detected in the DH population indicate that the seed weight variation may be primarily attributed to additive effects. The stability and significance of TSWA7a and TSWA7b were further validated in the F(2) population with different genetic backgrounds. By cloning BnMINI3a and BnTTG2a, two B. napus homologous genes to Arabidopsis thaliana, allele-specific markers were developed for TSWA5b and TSWA5c, two TSW QTLs on A5, respectively. The importance of the major and minor QTLs identified was further demonstrated by analysis of the allelic effects on TSW in the DH population.

Genome mapping of kernel characteristics in hard red spring wheat breeding lines

Kernel characteristics, particularly kernel weight, kernel size, and grain protein content, are important components of grain yield and quality in wheat. Development of high performing wheat cultivars, with high grain yield and quality, is a major focus in wheat breeding programs worldwide. Here, we report chromosome regions harboring genes that influence kernel weight, kernel diameter, kernel size distribution, grain protein content, and grain yield in hard red spring wheat breeding lines adapted to the Upper Midwest region of the United States. A genetic linkage map composed of 531 SSR and DArT marker loci spanned a distance of 2,505 cM, covering all 21 chromosomes of wheat. Stable QTL clusters influencing kernel weight, kernel diameter, and kernel size distribution were identified on chromosomes 2A, 5B, and 7A. Phenotypic variation explained by individual QTL at these clusters varied from 5 to 20% depending on the trait. A QTL region on chromosome 2B confers an undesirable pleiotropic effect or a repulsion linkage between grain yield (LOD = 6.7; R (2) = 18%) and grain protein content (LOD = 6.2; R (2) = 13.3%). However, several grain protein and grain yield QTL independent of each other were also identified. Because some of the QTL identified in this study were consistent across environments, DNA markers will provide an opportunity for increasing the frequency of desirable alleles through marker-assisted selection.

Performance of different greenhouse cucumber cultivars (Cucumis sativus L.) in southern Iran

A 2 year trial was conducted with 15 cucumber ( Cucumis sativus L.) varieties from diverse origins in the greenhouse conditions (southern Iran) to study genetic variation and to identify genetically distant parents to be involved in a hybrid seed production as well as to identify the most effective components of grain yield. However, the potential of identifying genetically distant parents depends on genetic diversity of population. The varieties were cultivated in a randomized complete block design (RCBD) with 3 replications for 2 years (2004 - 2006 seasons). Characters such as, yield and number of fruits in surface unit (m 2 ), yield in cold season, diameter and length of stem, length and diameter of fruit were evaluated analyzed for 2 years. Compound variance analysis showed that there were significant differences ( Cucumis sativus L.) varieties from diverse origins in the greenhouse conditions (southern Iran) to study genetic variation and to identify genetically distant parents to be involved in a hybrid seed production as well as to identify the most effective components of grain yield. However, the potential of identifying genetically distant parents depends on genetic diversity of population. The varieties were cultivated in a randomized complete block design (RCBD) with 3 replications for 2 years (2004 - 2006 seasons). Characters such as, yield and number of fruits in surface unit (m 2 ), yield in cold season, diameter and length of stem, length and diameter of fruit were evaluated analyzed for 2 years. Compound variance analysis showed that there were significant differences ( Cucumis sativus L.) varieties from diverse origins in the greenhouse conditions (southern Iran) to study genetic variation and to identify genetically distant parents to be involved in a hybrid seed production as well as to identify the most effective components of grain yield. However, the potential of identifying genetically distant parents depends on genetic diversity of population. The varieties were cultivated in a randomized complete block design (RCBD) with 3 replications for 2 years (2004 - 2006 seasons). Characters such as, yield and number of fruits in surface unit (m 2 ), yield in cold season, diameter and length of stem, length and diameter of fruit were evaluated analyzed for 2 years. Compound variance analysis showed that there were significant differences (
= 0.01) in yield between varieties at 2 years and the highest yield (23.81 kg/m 2 ) was obtained for E3215516 variety. Correlation analysis of varietal means showed that the highest correlation (0.932) was observed between number of fruits (NOF) and yield, and the least (0.01) between diameter of stem (DOS) and length of fruit (LOF). Based on factor analysis, 3 components were identified, explaining 77.5% of observed variation. Factor 1 (yield factor) accounting for about 45% of the variation, was strongly associated with yield, yield in cold season and number of fruits. Factor 2 (source factor) accounting for about 18% of the variation, consisted of stem related components including diameter of stem (DOS) and length of stem (LOS). Factor 3 (sink factor) accounting for about 15% of the total variation, associated with length and diameter of fruit (LOF and DOF). Using cluster analysis, the lines were classified into 2 distinct classes A and B. Class B contained lines from different origins.

Over‐expression of the rice LRK1 gene improves quantitative yield components

In rice (Oryza sativa L.), the number of panicles, spikelets per panicle and grain weight are important components of grain yield. These characteristics are controlled by quantitative trait loci (QTLs) and are derived from variation inherent in crops. As a result of the complex genetic basis of these traits, only a few genes involved in their control have been cloned and characterized. We have previously map-cloned a gene cluster including eight leucine-rich repeat receptor-like kinase (LRK) genes in Dongxiang wild rice (Oryza rufipogon Griff.), which increased the grain yield by 16%. In the present study, we characterized the LRK1 gene, which was contained in the donor parent (Dongxiang wild rice) genome and absent from the recurrent parent genome (Guichao2, Oryza sativa L. ssp. indica). Our data showed that rice LRK1 is a plasma membrane protein expressed constitutively in leaves, young panicles, roots and culms. The over-expression of rice LRK1 results in increased panicles, spikelets per panicle, weight per grain and enhanced cellular proliferation, leading to a 27.09% increase in total grain yield per plant. The increased number of panicles and spikelets per panicle are associated with increased branch number. Our data suggest that rice LRK1 regulates rice branch number by enhancing cellular proliferation. The functional characterization of rice LRK1 facilitates an understanding of the mechanisms involved in cereal crop yield, and may have utility in improving grain yield in cereal crops.

Genetic and phenotypic relationship between grain yield and components of grain yield of maize (Zea mays L.)

For efficient selection of grain yield, like the most importance economic trait, in regard to its on the great influence the environmental factors, has complex mode of inheritance and low heritability, is necessary to know genotypic and phenotypic coefficient of correlations between grain yield and morphological traits of the plant and ear which are influencing on the grain yield. The objective of this paper was to determine relationship between grain yield and morphological traits, in 8 inbred lines and their hybrids. Strong genetic and phenotypic correlations were found between grain yield and other studied traits, except between grain yield, on one side, and kernel row number where we found medium correlations. Between other studied traits, the highest values of genotypic and phenotypic coefficient of correlations were found between ear length and cob weight.

Determination of grain number in sorghum

Grain number is an important component of grain yield in sorghum. Research in wheat and maize has indicated a dependency of grain number on the crop or panicle growth rate around anthesis (CGR a and PGR a respectively), but little quantitative information is available for sorghum. The aim of this paper was firstly to quantify the effect of CGR a and PGR a on grain number and secondly, to identify other parameters that could be used as substitutes for PGR a. Analyses included data from a number of experiments, covering a range in nitrogen and drought treatments and including both tall (single dwarf) and short (triple dwarf) hybrids. CGR a and SGR a (stem growth rate) were calculated from the derivative of a curvilinear function fitted to experimental data, and PGR a was obtained by subtraction of SGR a from CGR a. Results indicated a linear relationship between grain number and CGR a, but the slope differed for tall and short hybrids. This was due to a difference in the proportion of dry matter allocated to the reproductive organs around anthesis ( P r), as PGR a was closely related to grain number, irrespective of crop height. Since panicle dry mass at maturity (excluding grain) was closely correlated with reproductive biomass shortly after anthesis, this indicator represents an integration of panicle growth during the critical period for yield determination in sorghum (i.e. flag leaf until start of grain filling). Panicle biomass at maturity (excluding grain) was thus also linearly related to grain number, and the relationship was independent of crop height and of the timing, severity, or type of stress. Our results indicate that panicle mass at maturity could provide an alternative to PGR a for the estimation of grain number.

Alteration of drought tolerance of winter wheat caused by translocation of rye chromosome segment 1RS

In Hungary 53% of wheat ( Triticum aestivum L.) cultivars registered during the last twenty years carry the 1RS translocation, the short arm of rye ( Secale cereale L.) chromosome 1. Wheat production in Hungary is limited primarily by drought. Despite the widespread use of this translocation there is no information about its effect on stress tolerance. The objective of this study was to investigate the effect of 1BL. 1RS on drought tolerance. ‘Mv5791-1B.1R’ and the sister line ‘Mv5791-1B.1B’ were examined among other cultivars in greenhouse under well-watered and drought conditions. Data were obtained for anthesis-and maturity date, plant height, root/shoot ratio, components of grain yield, Harvest Index (HI) and Water Use Efficiency (WUE). The translocation line had higher root-and shoot dry weight in both treatments and an increased root/shoot ratio, which was more than the sister line in dry treatment (69 and 38%, respectively). The larger root biomass of the 1RS translocation line could contribute to ...

Genomic targeting and mapping of tiller inhibition gene (tin3) of wheat using ESTs and synteny with rice

Changes in plant architecture have been central to the domestication of wild species. Tillering or the degree of branching determines shoot architecture and is a key component of grain yield and/or biomass. Previously, a tiller inhibition mutant with monoculm phenotype was isolated and the mutant gene (tin3) was mapped in the distal region of chromosome arm 3AmL of Triticum monococcum. As a first step towards isolating a candidate gene for tin3, the gene was mapped in relation to physically mapped expressed sequence tags (ESTs) and sequence tag site (STS) markers developed based on synteny with rice. In addition, we investigated the relationship of the wheat region containing tin3 with the corresponding region in rice by comparative genomic analysis. Wheat ESTs that had been previously mapped to deletion bins provided a useful framework to identify closely related rice sequences and to establish the most likely syntenous region in rice for the wheat tin3 region. The tin3 gene was mapped to a 324-kb region spanned by two overlapping bacterial artificial chromosomes (BACs) of rice chromosome arm 1L. Wheat-rice synteny was exceptionally high at the tin3 region despite being located in the high-recombination, gene-rich region of wheat. Identification of tightly linked flanking EST and STS markers to the tin3 gene and its localization to highly syntenic rice BACs will assist in the future development of a high-resolution map and map-based cloning of the tin3 gene.

A QTL for rice grain width and weight encodes a previously unknown RING-type E3 ubiquitin ligase

Grain weight is one of the most important components of grain yield and is controlled by quantitative trait loci (QTLs) derived from natural variations in crops. However, the molecular roles of QTLs in the regulation of grain weight have not been fully elucidated. Here, we report the cloning and characterization of GW2, a new QTL that controls rice grain width and weight. Our data show that GW2 encodes a previously unknown RING-type protein with E3 ubiquitin ligase activity, which is known to function in the degradation by the ubiquitin-proteasome pathway. Loss of GW2 function increased cell numbers, resulting in a larger (wider) spikelet hull, and it accelerated the grain milk filling rate, resulting in enhanced grain width, weight and yield. Our results suggest that GW2 negatively regulates cell division by targeting its substrate(s) to proteasomes for regulated proteolysis. The functional characterization of GW2 provides insight into the mechanism of seed development and is a potential tool for improving grain yield in crops.

Correlation and pthat coefficient analysis of grain yield related chatacters in maize (<i> Zea mays L. </i>) under umudike condtitions of south eastern Nigeria

The relationships between grain yield and its components of 19 open pollinated (op) maize were studied using linear correlation and path co-efficient analyses. Plants were grown for two years. Grain yield showed positive significant correlations with fresh ear weight, ear diameter, shelling percentage, cob length, 100-seed weight, number of leaves at harvest and plant height at harvest. Days to 50% tasselling and silking were negatively correlated with yield in both years. Path co-efficient analysis revealed that fresh ear weight and shelling percentage were moderately consistent in their direct and indirect contributions to yield in both years. Fresh ear weight had 55% direct effect and 45% indirect effect through ear diameter and shelling percentage in 1998. In 1999, it had 73% direct effect on yield and 27% indirect effect through 100-seed weight and shelling percentage. In 1998, shelling percentage had 66% direct effect on grain yield and 34% indirect effect through ear diameter and fresh ear weight. It had 40% direct effect on yield and 60% of the indirect effect was accounted for mainly through fresh ear weight and 100 seed weight in 1999. These two traits are therefore, very important components of grain yield and should be given high weightage in any selection process aimed at improving grain yield in maize. Keywords : Linear correlation co-efficient, Path co-efficient, Maize genotypes, Agronomic characters Agro-Science Vol. 4 (1) 2005: pp. 24-28 1-5

Identification and mapping of a tiller inhibition gene (tin3) in wheat

Tillering is one of the most important agronomic traits in cereal crops because tiller number per plant determines the number of spikes or panicles per plant, a key component of grain yield and/or biomass. In order to characterize the underlying genetic variation for tillering, we have isolated mutants that are compromised in tillering ability using ethyl methanesulphonate (EMS)-based mutagenesis in diploid wheat (Triticum monococcum subsp. monococcum). The tillering mutant, tiller inhibition (tin3) produces only one main culm compared to the wild type with many tillers. The monoculm phenotype of tin3 is due to a single recessive mutation. Genetic and molecular mapping in an F(2) population of diploid wheat located the tin3 gene on the long arm of chromosome 3A(m). One codominant RFLP marker Xpsr1205 cosegregated with tin3 in the F(2) population. Physical mapping of PSR1205 in a set of Chinese Spring deletion lines of group-3 chromosomes placed the tin3 gene in the distal 10% of the long arm of chromosome 3A, which is a recombination-rich region in wheat. The implications of the mapping of tin3 on chromosome arm 3A(m)L are discussed with respect to putative orthologs of tin3 in the 3L colinear regions across various cereal genomes and other tillering traits in grasses.

Path coefficient analysis of the components of grain yield in intercropped cowpea, growth in Borno, Nigeria

Yield and yield components data obtained from the response of inter cropped cowpea to some agronomic practices were correlated and path coefficients computed. The result revealed that cowpea yield was strongly correlated with 100-seed weight, number of pods per plant and number of seeds per pod. Within the yield components, there was a highly significant correlation (P = 0.01) between 100 seed weight and number of seeds per pod as well as between number of pods per plant and number of seeds per pod. Yield analyses indicated that the direct contribution of number of pods per plant and 100-seed weight were the main yield contributing factors in both years. The combined contribution of 100-seed weight and number of seeds per pod was however highest in both years. The total contributions (direct and combined) were found to be 96.30% and 53.80% in 2001 and 2002 seasons, respectively. International Journal of Natural and Applied Sciences Vol. 2 (4) 2006: pp. 310-316

Effect of Broad bean mottle bromovirus and its DI-RNAs on productivity and yield components in broad bean

Defective interfering RNA molecules (DI-RNAs) are being studied to get a better understanding about how they are formed and how they can regulate their helper virus replication. However, the effect of defective interfering molecules on yield has not been well established. Preliminary observations in broad beans and peas suggest that Broad bean mottle bromovirus (BBMV) DI-RNAs could affect productivity, exacerbating the yield reduction produced by the virus alone. To quantify the effect of BBMV and its DI-RNAs on components of grain yield and productivity, broad bean plants growing under field conditions in a screenhouse, were inoculated, 3 weeks after sowing, with the transcribed genomic RNA of the virus, plus, depending on the treatment, the small DI-RNA (1900 nt) or the large DI-RNA (2400 nt). Some plants were inoculated only with a DI-RNA-free virion RNA preparation of the helper virus at different phenological stages (19, 38, 52, 66 and 80 d after sowing (DAS)). The plants were harvested 130 d later. The results obtained indicated that the virus had an important effect on productivity, reducing yield between 75% (inoculation 38 DAS) and 36% (inoculation 52 DAS). All the plants inoculated with BBMV produced less grain, statistically different from the treatment without inoculation. Presence of the large and small DI-RNAs reduced grain yield even more than the loss in productivity caused by the virus without DI-RNAs.

Genetic and molecular basis of grain size and grain number and its relevance to grain productivity in higher plants

Grain size and grain number constitute 2 important components of grain yield. In particular, the grain size also influences the end-use quality (e.g., flour yield and protein content) and attracts consumer preference. These 2 traits are also the components of the domestication syndrome of crop plants. A number of important studies have recently been conducted to understand the genetic and molecular basis of these 2 important yield-contributing traits. Information generated from these studies was collected and synthesized for the benefit of plant biologists, particularly plant breeders. In the present article, this information is briefly reviewed and the prospects of using this information for improvement of grain productivity in crop plants are discussed.

Aplicability of phenotypic and canonic correlations and path coefficients in the selection of oat genotypes

Indirect selection through traits of higher heritability and of case measurements can result in larger genetic progress compared to using direct selection. This work was performed with the following objectives: (1) to estimative the phenotypic correlations between individual plant grain yield and agronomic traits of importance in the selection of white oat (Avena sativa L.) genotypes; (2) to identify traits that have the higher direct and indirect effects on grain yield; (3) to determine the intensity of association between primary and secondary components of grain yield; and, (4) to evaluate the consistency of these estimates using five oat genotypes crossed in a diallel format. The number of panicles per plant (NPP) showed to be the trait highest correlated with individual plant grain yield (GY) both through single correlations and through direct effects on grain yields. For weight of a thousand grains (WTG) <FONT FACE=Symbol>´</FONT> GY, in most crosses there was no detected association, leading to possible troubles for breeders, since larger grains were not associated to higher yield, except for the crosses UPF16 <FONT FACE=Symbol>´</FONT> UFRGS17 and UFRGS17 <FONT FACE=Symbol>´</FONT> URPel95/015. The trait number of grains per plant (NGP) was directly correlated with GY in all crosses, although the direct effects estimates on GY were negative for the crosses UPF16 <FONT FACE=Symbol>´</FONT> UPF18, UPF16 <FONT FACE=Symbol>´</FONT> URPel95/015, UPF18 <FONT FACE=Symbol>´</FONT> UFRGS17 and UFRGS7 <FONT FACE=Symbol>´</FONT> URPel95/015, indicating that correlations are not the main causes altering GY, which could be explained, in the present work, by indirect effects via NPP and mainly via panicle weight (PW).

Yield Formation in Mediterranean durum wheats under two contrasting water regimes based on path-coefficient analysis

The components of grain yield are altered by adverse growing conditions as the effects of certain environmental factors on crop growth and yield differ depending upon the developmental stages when these conditions occur. Path-coefficient analysis was used to investigate the main processes influencing grain yield and its formation under Mediterranean conditions. Twenty-five durum wheat genotypes, consisting of four Spanish commercial varieties and 21 inbred lines from the ICARDA durum wheat breeding program, were grown during 1997 and 1998 under both rainfed and irrigated conditions in southern Spain. {P}ath-coefficient analysis revealed that under favourable conditions grain yield depended in equal proportion on the three primary yield components (i.e. spikes m−2, grains spike−1, and mean grain weight), whereas in the rainfed experiments, variations in grain yield were due mainly to spikes m−2 and to a lesser extent to grains spike−1. Compensatory effects were almost absent under irrigated treatments; however, under water shortage, spikes m−2 exerted a negative influence on grain spike−1 due mainly to a negative interrelationship between tiller production and apical development. These compensatory effects could partially explain the restricted success in durum wheat breeding observed in water-limited environments of the Mediterranean region. Under rainfed conditions the number of spikes m−2 depended mainly on the ability for tiller production, whereas in the irrigated experiments the final number of spikes was determined mostly by tiller survival.