Rht1(B. dw), an alternative allelic variant for breeding semi-dwarf wheat varieties

The vast majority of the world's acreage of semi-dwarf wheat varieties is at present cultivated with varieties carrying one of two genetically similar dwarfing genes, Rht1 and Rht2, derived from the Japanese variety ‘Norin 10’. Near-isogenic lines have been developed and tested to determine the breeding potential of an allelic variant of Rht1, designated Rht1(B. dw). Following its introduction into four varietal backgrounds, Rht1 (B. dw) was seen to reduce height by around 25%, to increase the number of grains setting in spikelets and ears by around 20%, to reduce grain weight by 10%, and to increase yields of plants grown under spaced or drilled conditions by about 8%. When compared to the commercially utilized Rht1 allele, as near isogenic lines in a ‘Mercia’ varietal background, Rht1 (B. dw) gives a significantly greater reduction in plant height, a greater increase in spikelet and ear fertilities, slightly less reduction in 1000-grain weight, and significantly higher spikelet, ear and plot yields. If these results are repeatable in other varietal backgrounds, over seasons, and under differing environmental conditions, Rht1 (B. dw) should have considerable commercial potential as an alternative allele for producing shorter-than-average, high-yielding, semi-dwarf wheat varieties.     

Yield, biomass and yield components in dwarf, semi-dwarf and tall isogenic lines of spring wheat under recommended and late sowing dates

Grain yield and some of its physiological determinants were analysed in a field study conducted over two growing seasons with standard-height (SH), semi-dwarf (SD) and dwarf (DD) isogenic lines of a spring wheat sown at recommended and delayed dates. The objective was to test whether the action of Rht1 and Rht2 alleles in improving grain yield depended upon sowing date. As expected, the dwarfing genes significantly reduced plant height in both sowings and growing seasons. There was a tendency for the SD line to produce more biomass than the SH and DD lines, although the differences were mostly not significant. Harvest index was linearly and negatively related to plant height. Consequently, the SD and SH line showed the highest and lowest grain yields in all environments. The optimum height for grain yield was estimated to be c. 70 cm, and this value was not affected by sowing date. Lines carrying Rht1 and/or Rht2 alleles always showed more grains/m² (owing to an increased number of grains per spike and spikes/m²) than the SH line. Conversely, average grain weight was negatively associated with the number of grains/m². Because the slope of this negative relationship was smaller (less negative) than that representing complete compensation, the relationship between grain yield and number of grains/m² was hyperbolic. Although these relationships are frequently regarded as a reflection of increased competition among grains when the number of grains/m² is increased owing to the use of semi-dwarf genes, two alternative hypotheses are analysed and discussed.     

NORIN 10 semi-dwarfism in tetraploid wheat and associated effects on yield

Summary A genetic study of a range of NORIN 10 based semi-dwarf durum wheats showed that only Gai/Rht 1, located on chromosome 4A, was present. No varieties carrying a second Gai/Rht allele were identified and deliberate attempts to introduce Gai/Rht2 into tetraploid wheats have so far been unsuccessful.In a spaced plant trial of homozygous random F₃ lines from two tall x semi-dwarf crosses, the semi-dwarfs has lower ear yields, due mainly to reduced kernel weight, but had higher tiller numbers than the tall genotypes. Although there was no difference in overall plant yield between talls and semi-dwarfs, an analysis of character associations within the semi-dwarf F₃'s showed positive height-yield and height-kernel weight correlations indicating that selection for tall dwarfs may be a useful breeding strategy in tetraploid wheats.     

Genotypic association between grain yield and six agronomic traits in a cross between rice varieties of contrasting plant type

Summary Phenotypic and genotypic correlation coefficients as well as path analysis were computed to evaluate the genetic association between six agronomic traits and rice grain yield and also among the traits in a representative sample of F₇ lines in the tall Peta × semi-dwarf I-geo-tze cross maintained as an unselected bulk from F₃ through F₅. Data were taken on grain yield, duration from seeding to heading, panicle number, ratio of panicles to tillers, angle of the flag leaf, angle of the leaf below the flag leaf, and plant height on the two parents and 139 F₇ lines. The F₇ lines were divided into three groups based on plant height: tall, intermediate, and short (semi-dwarf).Differences in grain yield were highly significant among lines in the tall and short groups, and significant among the intermediate lines. Significant to highly significant differences among lines were obtained in each of the height groups for all of the agronomic traits except for the ratio of panicles to tillers in the intermediate and tall groups.Path analysis showed that among the semi-dwarf progenies, erect flag leaf angle made the largest positive contribution to grain yield, followed by high panicle number and early maturity. Among the intermediates, the erectness of the leaf below the flag contributed most to high yield and was closely followed by earliness in maturity. For the tall lines, erect leaves below the flag leaf and high panicle number contributed positively to yield, whereas tallness and late maturity had a negative effect.Phenotypic and genotypic correlation coefficients indicated that low grain yield was closely associated with tall stature, drooping leaves, and low panicle number in the tall lines. In the intermediate lines, low grain yield was associated with late maturity and drooping leaves. Among the semi-dwarf lines, high grain yield was correlated with erect flag leaves and a high ratio of panicles to tillers. When the lines in different height groups were combined, highly significant phenotypic correlations were obtained between high yield levels and erect leaves, a short plant stature, early maturity, or a high panicle number. Erect flag leaves and high yield levels were associated at a significant level. The genotypic correlation coefficients of the above paired traits were identical in sign and generally greater in value than the corresponding phenotypic correlation coefficients.Mail address: P. O. Box 583, Manila, Philippines.     

Aneuploidy in semi dwarf wheat varieties

Summary Tall varietal impurities occurring in a number of new semi-dwarf winters wheats carrying the Norin 10 dwarfing genes Rht1 or Rht2 are causing problems at seed certification. Cytological analysis of such impurities from three varieties shows they are aneuploids and are mainly monosomic (2n=41) for chromosomes carrying semi-dwarfing genes. Because Rht1 and Rht2 act as suppressors of height, their reduced dosage as in monosomics, produces plants considerably taller than in the euploid condition.     

The reduced height genes do not affect the root penetration ability in wheat

Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b or Rht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of LD222 durum wheat and April Bearded bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b). One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thickness made from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b or Rht-D1b dwarfing genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant (r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.     

Chromosomal location of genes controlling grain size in a large grained selection of wheat (Triticum aestivum L.)

Summary Grain size in wheat is the most stable yield component and has a favorable effect on flour yield. To identify the chromosomes associated with the large grains of line G603-86, (grain weight over 60 mg and grain length of about 9 mm), F₃ lines, extracted from F₂ populations obtained from F₁ monosomics of crosses between G603-86 (P₁) and the monosomic set of Favorit (P₂) were tested in the field. ANOVA showed significant differences among parents for grain weight and grain length, but not for grain width or the factor expressing the difference in grain form and density. Homoeologous groups had significant effects on grain weight and on all components of grain weight, while genomes were not significantly different for any of these characters. Grain weight was significantly increased by chromosomes 6D and 4A of G603-86. Grain length was significantly increased by chromosomes 4A, 4B, 2B, 3A and 1B, grain width by chromosomes 1A and 1B, and the factor form-density by chromosomes 6D and 6A. The high grain size in G603-86 results from the effects of genes located on many chromosomes which affect grain dimensions, form and density.     

Ear:stem ratios in breeding populations of wheat: significance for yield improvement

Earlier studies showed that the ratio of the weight of the wheat ear to stem at anthesis (ear:stem ratio) may give a better indication of potential yield than harvest index because it is determined early in the life cycle and is not affected by post anthesis stress. These studies concluded that selection for high ear:stem ratio at anthesis may lead to further improvement in grain yield of wheat. The present work was undertaken in the field to identify lines varying in ear:stem ratio in breeding populations and to study its implications for yield improvement.At anthesis stem length, ear length, tiller number, dry weight of stem and ear and ear:stem ratio were measured in 14 crosses on F₂ single plants and F₂ derived lines grown in the F₃, F₄, and F₅ at three locations in Western Australia over four seasons. In addition, biomass, grain yield and yield components were measured on selected crosses at two locations on F₂ derived lines grown in the F₄ and F₅. There was a considerable range of ear:stem ratio between and within the crosses studied. Although ear:stem ratio was strongly correlated with stem length, there was substantial variation within stem length classes. Ear:stem ratio had a high mean broad sense heritability (82%), whereas HI, grain yield and above ground biomass had lower heritabilities, 68, 55 and 35% respectively. Ear:stem ratio was strongly correlated between generations and sites indicating stability of this character. Ear:stem ratio had a significant positive correlation with grain yield, HI, grains per ear and per m². The correlation of grain yield with HI was equal or slightly higher than that of grain yield with ear:stem ratio.Ear:stem ratio offers promise as a predictor of HI and yield potential where post-anthesis moisture stress can influence HI. Ear:stem ratio measurement is unlikely to be adopted for selection purposes in routine breeding programs, as it is laborious and time consuming. However, ear:stem ratio could be used to identify superior parental genotypes and early generation selections from special crosses in terms of its ability to partition assimilate.     

Modification of plant height via RNAi suppression of OsGA20ox2 gene in rice

GA 20-oxidase (GA20ox) is a regulatory enzyme for the syntheses of biologically active GAs in plants. The loss-of-function mutations in OsGA20ox2 of rice (Oryza sativa L.) generate the well-known Green Revolution gene sd-1, which cause the semi-dwarfism phenotype. In our present investigation, semi-dwarf plants were generated from a taller rice variety QX1 by RNAi suppression on the expression of OsGA20ox2. The 531bp-fragment of OsGA20ox2 was amplified by PCR from genomic DNA of QX1 and used to construct the hairpin RNAi vector pCQK2. The wild type QX1 was transformed with pCQK2 by Agrobacterium-mediated transformation and some independent transgenic RNAi lines exhibited semi-dwarfism. RT-PCR and Northern blot analyses showed that the expression of OsGA20ox2 was specifically suppressed in the RNAi semi-dwarf lines. Endogenous GA assays revealed that the contents of the GA20ox2-catalyzed products GA₁₉, GA₂₀ and the down-stream biologically active GA₁ were drastically reduced in the RNAi semi-dwarf lines. We further showed that the RNAi semi-dwarf lines could be restored to normal plant height by applying exogenous GA₃. The results indicated that the semi-dwarfism of the RNAi semi-dwarf lines was associated with the decreased expression of OsGA20ox2 gene and the reduced content of endogenous biologically active GA₁. Analyses of panicle length, seeds per panicle and 1000-grain weight suggested that the RNAi semi-dwarf lines showed stable grain yield compared with the wild type plants. It is demonstrated that the RNAi approach could be useful for plant breeding purposes in the future. Qing Yang, Chun-Lian Wang have contributed equally to this work.     

Genetics of grain yield and other agronomic characters in t'ef (Eragrostis tef Zucc. Trotter). I. Generation means and variances analysis

Quantitative genetics of grain yield and other agronomic characters of t'ef (Eragrostis tef) were studied using the F₁, F₂, BC₁, and BC₂ of the cross Fesho × Kay Murri. The study was carried out to estimate gene effects controlling the inheritance of grain yield and related agronomic characters. Significant additive [d] and dominance × dominance [l] interaction effects were detected for grain yield. The variations of yield per panicle and panicle weight were explained in terms of [d], dominance [h], and additive × additive [i] interactions. Non-allelic gene interactions were also detected for kernel weight, harvest index, tiller number, plant height, days to heading and days to maturity. The simple additive-dominance model explained the variation for panicle length, culm diameter and plant weight, allowing unbiased estimates of additive (D) and dominance (H) variance components. Large dominance variances (H) were estimated for grain yield, yield per panicle, and panicle weight. The additive variances for plant height, panicle length, days to heading and days to maturity were higher than the respective dominance variances. High narrow-sense heritability (h²) values (> 0.50) were estimated for plant height, panicle length, days to heading and days to maturity. The lowest h² (0.09) was obtained for kernel weight for which there was little variability. Since grain yield and several important agronomic characters of t'ef are influenced by non-allelic gene interaction, it is advisable to delay selection for yield to later generations with increased homozygosity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dwarfing effect associated with the threshability gene Q on wheat chromosome 5A

A dwarfing effect of the 44.1 cM chromosomal region between the threshability gene Q and Xfba068 on the long arm of hexaploid wheat chromosome 5A has been reported. To clarify whether Q or its adjacent region is responsible for regulating culm elongation, two precise genetic stocks of near‐isogenic lines (NIL), a single chromosome substitution line, ‘Chinese Spring’ (CS; ‘Cappelle‐Desprez’ 5A) (NIL‐Q) and a single chromosome recombinant substitution line (NIL‐q) were used. The target segment of NIL‐q included the q allele and QEet.ocs‐5A.1, an earlinessper se gene, from spelt wheat in the CS genetic background. They were grown under 16‐h day length with and/ or without vernalization treatment. Being independent of heading date, NIL‐Q showed shorter elongation in lower internodes and decreased internode differentiation in comparison with NIL‐q. The culm‐length reduction associated with Q was confirmed in the recombinant F5 population derived from the cross between NIL‐Q and NIL‐q. Vernalization promotion had a tendency to reduce this dwarfing effect.     

Quantitative trait loci for grain yield and yield components in a cross between a six-rowed and a two-rowed barley

Summary The positions of quantitative trait loci (QTL) for yield and yield components were estimated using a 85-point linkage map and phenotype data from a F₁-derived doubled haploid (DH) population of barley. Yield and its components were recorded in two growing seasons. Highly significant QTL effects were found for all traits at several sites in the genome. A major portion of the QTL was found on chromosome 2. The effect of the alleles in locus v on thousand grain weight and kernels per ear explained 70–80% of the genetic variation in the traits. QTL × year interaction was found for grain yield. Several different QTL were found within the two-rowed DH lines compared to those found in the six-rowed DH lines. Epistasis between locus v and several loci for yield and yield components indicates that genes are expressed differently in the two ear types. This may explain the difficulties of selecting high yielding lines from crosses between two-rowed and six-rowed barley.Abbreviations DH doubled haploid - QTL quantitative trait locus/loci - RAPD random amplified polymorphic DNA - RFLP restriction fragment length polymorphism - T. Prentice Tystofte Prentice - V. Gold Vogelsanger Gold     

Pleiotropic Effects of Genes for Reduced Height (Rht) and Day-Length Insensitivity (Ppd) on Yield and its Components for Wheat Grown in Middle Europe

Under field conditions in Germany over three growing seasons the pleiotropic effects on yield and its components of four sets of near isogenic lines carrying the GA insensitive dwarfing alleles Rht1, Rht2, Rht3, Rht1+2, Rht2+3 or rht (tall) in four different genetical backgrounds were examined together with 24 single chromosome recombinant lines segregating for the GA sensitive dwarfing gene Rht8 and the gene for day-length insensitivity Ppd1 in a ‘Cappelle-Desprez’ background. For the GA insensitive semi-dwarfs it was shown that in all three years a higher number of grains per ear was accompanied by a lower grain weight. Depending on the climatic conditions in a particular year, the increase in grain number was sufficient to compensate for the reduction in grain size and resulted in higher yields. For the Ppd1 allele yield advantages were found for wheats grown under environmental conditions of middle Europe.     

Genetic response to index selection for grain yield, kernel weight and per cent protein in four wheat crosses

Quantitative genetic theory was used to investigate selection differentials, expected and observed direct and correlated responses to simultaneous improvement of grain yield, kernel weight, and grain protein content in F₃ and F₄ populations of four spring wheat (Triticum aestivum L.) crosses. Selection in the F₃ generation based on the Smith-Hazel index (SH) and yield was found to be superior to the other methods studied in identifying high-yielding lines, but resulted in substantial decrease in grain protein level. Consequently, a 1.0% increase in protein from selection for protein depressed grain yield as much as 536 kg/ha below the population mean, reducing the expected yield gains per generation selection cycle by 250%. The weight-free indices (EW), particularly the index involving only yield and kernel weight (EW3) and its linear approximation (EW4), and the desired gains indices were effective in improving protein content but were less efficient in selecting top-yielding lines. Selection in the opposite direction using truncation of the lowest 10% of the population based on weight-free-index involving yield, kernel weight and protein (EW2) reduced all traits significantly compared with the mean of the unselected population indicating the effectiveness of the unweighted selection index. The observed genetic gains (Ra) from selection based on yield, the SH, EW3 and EW4 indices were slightly lower than the expected advances per cycle (R) in populations from crosses ‘Sinton’בGlenlea’ (C1), ‘Glenlea’בNB505’ (C2), and ‘A2P5’בNB320’ (C6) (Ra/R = 70 to 85%) but were higher in cross ‘NB505’בA2P5’ (C5) (Ra/R = 126 to 143%). It was concluded that weight-free and the desired gains indices can be used to improve wheat grain yield and grain protein simultaneously in F₃ generation selection, as revealed by response to selection measured in the F₄ generation.     

Effect of d2 dwarfing gene on grain yield and yield components in pearl millet near-isogenic lines

Summary A d₂ dwarfing gene in pearl millet [Pennisetum glaucum (L.) R. Br.] is currently being extensively used for the development of hybrid parents. Its effect on grain yield and yield components is poorly understood. Twelve pairs of tall and dwarf near-isogenic lines developed in the diverse genetic background of three composites were evaluated for grain yield and yield components for 2 years at two locations in southern India. The d₂ gene or the genes linked to it, on an average, reduced plant height by 42%, grain yield by 14%, and head girth by 8% but increased head length and number of tillers per plant by about 5–6%. Large variations were observed among pairs (genetic background) for the difference between tall and dwarf near-isogenic lines for all of the above yield components resulting in no significant difference in five pairs and 17–35% less yield in dwarfs as compared to their tall counterparts in six pairs. Days to 50% flowering and seed weight were least affected by the d₂ gene with the average difference between tall and dwarf groups of near-isogenic lines being of the order of 1–2%. These results indicate that the advantageous effects of d₂ dwarfing gene can be effectively exploited by manipulating the genetic background. The difference between the average grain yields of tall and dwarf groups of near-isogenic lines showed considerable variation across environments with the dwarfs yielding as much as tall group in one environment and up to 30% less than the tall group in the other, thus, indicating that the d₂ gene effect may be substantially modified by the environments.Submitted as JA No. 979 by the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT).     

Relationship between phenotypic and genetic diversity of parental genotypes and the frequency of transgression effects in barley (Hordeum vulgare L.)

The aim of the study was to evaluate the relationship between genetic and phenotypic distances of parents and the genetic potential of crosses as measured by the frequency of transgressive segregants in homozygous populations. Material for the study involved 17 barley cross‐combinations. In each cross, the parental genotypes, F₂ hybrids and doubled haploid (DH) lines were analysed. Yield and yield‐related traits were observed in the experiments. Phenotypic (univariate and multivariate) and genetic distances (GD) were investigated between pairs of parental genotypes. Genetic distance was evaluated by using random amplified polymorphic DNA markers. In F₂ generations, the genetic coefficient of variability (GCV) was evaluated. Within all the cross‐combinations studied, each DH line was compared with both parents to distinguish the positive and negative transgressive lines. In addition, the coefficient of gene distribution (r) along parental genomes was evaluated. Relationships between frequency of transgression and both phenotypic and GDs, GCV and r, were assessed by regression analysis. It was found that for all the traits studied the frequency of transgressive lines depended mainly on gene distribution (r). Genetic distance between parents appeared to be significant for the occurrence of transgression effects in plant height, ear length, grain weight per ear and grain yield per plot. Regression analysis has shown that phenotypic differences between parental genotypes were also important for the frequency of transgressive lines. A weak relationship was found between the variation of F₂ hybrids and the occurrence of transgressive lines. The results indicate that occurrence of transgressive segregants in a homozygous population should be considered as a phenomenon dependent simultaneously on several factors characterizing parental genotypes. Among them, the most important are: gene distribution, phenotypic diversity and GD.     

Transgressive segregation in inter and intraspecific crosses of barley

Summary Six populations of F₂-derived lines of barley and their parents were evaluated for heading date, plant height, grain yield, bundle weight, and harvest index in a replicated experiment in the field. These data were used to estimate the minimum number of effective factor pairs segregating for each trait, the number of favorable factors contributed by each parent in a cross, and the frequencies and magnitudes of transgressive segregates.Heading date, plant height, and harvest index were controlled by three to four effective factor pairs, whereas grain yield and bundle weight were controlled by five or more.All three H. spontaneum strains used in our study contributed one or more useful genes for each of the traits, grain yield, heading date, plant height, bundle weight, and harvest index. Therefore, it seems that H. spontaneum can be a useful source of favorable genes for quantitative traits, especially for grain yield, which could be incorporated into barley varieties readily by backcrossing. Transgressive segregates for grain yield in the interspecific crosses may provide the basic materials for improving the productivity of cultivated barley varieties.Journal Paper No. J-9760 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2227. Supported in part by a grant from the Science and Education Administration-Cooperative Research, United States Department of Agriculture.     

Fine mapping of grain weight QTLs using near isogenic lines from a Cross between <Emphasis Type="Italic">Oryza sativa</Emphasis> and <Emphasis Type="Italic">O. grandiglumis</Emphasis>

In a previous study, we reported the grain weight QTL, tgw2 in the 150 F2:3 lines derived from a cross between Oryza sativa subssp. Japonica cv. Hwaseongbyeo and HG101. This QTL was confirmed in F4 lines (CR1242) segregating for the target region. For fine mapping of tgw2, one F₅ plant homozygous for the O. grandiglumis DNA in the target region was selected from CR1242 and crossed with Hwaseongbyeo to produce the F₂ and F₃ populations. QTL analysis using 490 F₂ plants confirmed the existence of tgw2 with an R ² value of 28.0%. This QTL explained 61.3% of the phenotypic variance for 1,000-grain weight in 64 F₃ lines. Substitution mapping with 47 F₃ lines and 74 F₄ plants with informative recombination breakpoints in the target region was carried out to narrow down the position of the tgw2. The result indicated that tgw2 was located in the 384-kb interval between two SSR markers, RM12813 and RM12836. Annotation data of BACs in this 384-kb region revealed that forty-five putative genes exist in this interval including the GW2 gene responsible for grain weight and width. Considering the position of the QTL tgw2, it appears that tgw2 is functionally related to the gene GW2. However, the possibility that another unknown mechanism might be responsible for regulation of grain weight at tgw2 cannot be ruled out. Four QTLs for grain length, grain width, and grain thickness were also located in the same interval suggesting that a single gene is involved in controlling these four traits. Substitution mapping also indicated that two QTLs for grain weight and culm length, tgw2 and cl2, were tightly linked.     

Direct and indirect selection for yield in chickpea

Summary The efficiency of indirect selection for seed yield was compared with direct selection for yield per se in chickpea. A total of 2500 single F₂ plants, derived from 50 crosses with 50 plants from each cross, were divided into five sub-populations (SP1 to SP5) of 500 plants each by including 10 plants from each of the 50 crosses. The five sub-populations were advanced upto F₆ by exercising 10% selection intensity for four successive generations for number of pods per plant in SP1, number of seeds per pod in SP2, seed weight in SP3, seed yield in SP4 and random selection in SP5. The efficiency of direct and indirect selection for yield was evaluated by comparing groups of 50 F₆ lines from each sub-population. SP1 and SP3 F₆ lines showed higher mean grain yield than the other three methods. SP1 and SP3 were found to be almost equally efficient in developing F₆ lines which were significantly superior to the check. This suggests that indirect selection for yield via pod number and seed weight is more efficient than direct selection for yield.     

Single and Multiple Traits Selection in a Segregating Population of Wheat, Triticum aestivum L.

The breeding materials used in this study were the F₃, F₄ and F₅-generations of the cross between Giza 158 × Sonora 64 (Triticum aestivum L.). The objective of this study was to compare the relative merits of Smith-Hazel, desired gain selection indices, independent culling levels and single trait selection in improving grain yield, heading date and several agronomic traits. Highly significant differences among F₃ families and a satisfactory genotypic coefficient of variability were obtained for all the traits studied. The genotypic correlations were high between yield and each of spike weight, kernels/spike and spikes; plant, intermediate with 1000 kernel weight and very low with heading date, plant height and spike1 length-After two cycles of selection, the results of the gains realized indicated that the most effective method for improving yield was the Smith-Hazel index (SH₇) of seven traits followed by the desired gain index of seven traits (DG₇), SH₅, independent culling levels, DG₅ and direct selection (or grain yield/plant. Direct selection for heading date, plant height and spike length was the best method for improving these traits, but undesirable correlated responses in the other traits were obtained.