Genotypic variation for drought tolerance in Vicia faba

Instability of yield in faba bean is partly caused by drought susceptibility. Four sets with 10-19 faba bean genotypes each were evaluated in multilocal field trials between 1992 and 1996. Stress occurred as natural drought in one experiment and as artificial terminal drought in three experiments. Artificial drought was induced by rain shelters; the control treatment was irrigated. Tolerance was assessed as the ratio of yield under drought (Yd) to well-watered yield (Yw). Highly significant variances between genotypes occurred; heritability of tolerance was 0.51 < h² <0.88. Exotic (North African. Latin American) genotypes were more tolerant than adapted material. Correlations between Yw and Yd were 0.77** < r <0.97**, and variance of Yd was less than one-third of the variance of Yw. Drought tolerance was negatively correlated with Yd (-0.41 < r < -0.22). Relative reduction of plant height due to drought was a promising trait to improve drought tolerance indirectly in two sets. The prospects of improving Yd are good: heritability was 0.68 < h² < 0.86. Genetic improvement of drought tolerance also seems feasible. A specific cross was proposed to create improved material.     

Combining ability,heterosis and genetic diversity in tropical maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under stress and non-stress conditions

Drought and low soil fertility are considered the most important abiotic stresses limiting maize production in sub-Saharan Africa. Knowledge of the combining ability and diversity of inbred lines with tolerance to the two stresses and for those used as testers would be beneficial in setting breeding strategies for stress and nonstress environments. We used 15 tropical maize inbred lines to (i) evaluate the combining ability for grain yield (GY), (ii) assess the genetic diversity of this set of inbred lines using RFLP, SSR, and AFLP markers, (iii) estimate heterosis and assess the relationship between F₁ hybrid performance, genetic diversity and heterosis, and (iv) assess genotype × environment interaction of inbred lines and their hybrids. The F₁ diallel hybrids and parental inbreds were evaluated under drought stress, low N stress, and well-watered conditions at six locations in three countries. General combining ability (GCA) effects were highly significant (P < 0.01) for GY across stresses and well-watered environments. Inbred lines CML258, CML339, CML341, and CML343 had the best GCA effects for GY across environments. Additive genetic effects were more important for GY under drought stress and well-watered conditions but not under low N stress, suggesting different gene action in control of GY. Clustering based on genetic distance (GD) calculated using combined marker data grouped lines according to pedigree. Positive correlation was found between midparent heterosis (MPH) and specific combining ability (SCA), GD and GY. Hybrid breeding program targeting stress environments would benefit from the accumulation of favorable alleles for drought tolerance in both parental lines.     

Hybrid performance and AFLP- based genetic similarity in faba bean

Successful prediction of heterosis and performance of F₁-hybrids from the genetic similarity of their parents based on molecular markers has been reported in several crops and can be very helpful in hybrid breeding. The relationship between genetic similarities based on amplified fragment length polymorphism (AFLP) of 18 European faba bean lines and their hybrid performance and heterosis was investigated. Parental lines, 62 F₁-hybrids and their F₂-progenies were evaluated in field trials in four environments in Germany for seed yield, 1,000-seed weight and plant height. Results clearly demonstrated a stable superiority of the hybrids over their inbred parents and elite check cultivars, and showed a marked and varying amount of heterosis. Parental seed yield and F₂-hybrid yield were promising as predictors for F₁-hybrids. AFLP analysis of the 18 inbred lines using 26 EcoRI/MseI primer combinations resulted in 1202 polymorphic fragments. Cluster analysis based on genetic similarity estimates unambiguously identified pedigree-related inbred lines. No clear separation of the 18 inbred lines into subgroups was detected. Correlation coefficients between genetic similarity estimates and either heterosis or F₁-hybrid performance were small and not useful. Also correlations between specific genetic similarity and specific combining ability were too small for all traits to be of predictive value. Results showed that AFLP-based genetic similarities are not useful to predict the performance of hybrids or heterosis within the elite European faba bean gene pool.     

Heterosis for yield and other agronomic traits of winter triticale F1 and F2 hybrids

Triticale is generally treated as a self‐pollinating crop and line breeding is practised. Hybrid breeding has been discussed for some time, but there is little information for winter triticale. This study investigated heterosis for eight agronomic traits in F₁ and F₂ hybrids grown together with their parents as drilled plots in three environments. On average, grain yield heterosis was 12.5 dt/ha (a relative 10.5%) compared with the mid‐parent value for F₁ hybrids, and 6.2 dt/ha (5.0%) for F₂ hybrids and withawide range of 4.4–17.1 dt/ha for F₁ hybrids. A positive contribution to the heterosis of yield was made by kernels/spike and 1000‐kernel weight, whereas spikes/m² showed negative heterosis. Hybrid plants in F₁ and F₂ were taller than mid‐parents (8.3 cm and 5.3 cm, respectively), with a tendency to earlier heading. The negative heterosis for falling number in F₁ and F₂ hybrids could be a problem for commercial production of triticale hybrids. By selecting parents for combining ability and the identification of heterotic patterns, grain yield heterosis of 20% appears feasible.     

Identification of superior parents and hybrids for improving canola production under optimum and late sowing conditions

Major advancement in canola breeding depends on heterotic hybrids that require high general combining ability (GCA) and specific combining ability (SCA) inbred lines. In order to estimate heritability, gene action type, GCA, SCA and heterosis and to identify superior hybrids with wider adaptation to cold, one hundred canola hybrids were produced by crossing 10 lines and 10 testers in a Line?×?Tester mating design. The F₁ and F₂ generations were sown in α-lattice design in 2012 and 2013 growing seasons under optimum (early October) and late sowing (early November) conditions to be evaluated for days to flowering, days to physiological maturity, number of pods per plant, number of seeds per pod, thousand seed weight, seed yield and leaf electrical conductivity. The combined analysis indicated sufficient genetic diversity in the population and significant difference between two sowing date. The Line?×?Tester analysis presented significant GCA and SCA effects for all studied traits across optimum and late sowing conditions. The main gene action type was found to be non-additive, especially incomplete dominance and over-dominance in both conditions. Narrow-sense heritability ranged from low to moderate whereas broad-sense heritability was recorded more than 60% for all of the studied traits in both generations and conditions. The average heterosis in F₂ population for all studied traits was lower than that in F₁ representing this fact that heterosis is generally related to the heterozygosity at the population level and poorly correlated with heterozygosity at the individual level.     

Heterosis in yield, endotoxin expression and some physiological parameters in Bt transgenic cotton

Although heterosis in cotton has been studied for many decades, very little is known about the performance of hybrids derived from Bt transgenic cotton parents. In order to known better the heterosis performance, yield and endotoxin expression in 20 hybrids (F₁) and their Bt transgenic parents were examined from 2002 to 2003 (Experiment 1), and the dynamics of source, sink and their ratios in a well‐performing hybrid H01 were investigated in 2004 and 2005 (Experiment 2). Results in Experiment 1 showed an average mid‐parent heterosis of 21.3% and an over check heterosis of 7.6% in lint yield. Considerable heterosis was also detected in boll numbers, boll size and Bt protein content. Of the 20 hybrids, H01 (K0215 × K643) exhibited the greatest heterosis in yield and Bt protein content in 2002 and 2003, while lint yields of H01 were increased 12.6% and 9.1% in 2004, and 11.7% and 8.9% in 2005, compared with K0215 and K643 in Experiment 2, respectively. Significant heterosis for dry matter accumulation and dry matter allocation to reproductive organs and ratio of fruiting forms/total plant (w/w) were also detected in H01. Sources (leaf area, leaf area index, leaf dry weight per plant and diurnal performance of photosynthesis), sinks (number of fruiting nodes, fruiting forms and dry weight of fruiting forms per plant) and the flow from source to sink were significantly enhanced in H01 relative to its parents. Both total N and Bt protein in H01 were higher than those in its parents. Significant correlation was also found between total N and Bt protein in the main‐stem leaves (R² = 0.877**). It is concluded that there existed considerable heterosis in yield, yield components and endotoxin expression in some Bt transgenic hybrids. Yield advantage of hybrid cotton (F₁) over parents can be attributed to improved source, sink and flow, while the enforced expression of Bt genes in hybrid cotton appeared to be due to the enhanced nitrogen level in plants.     

Heterosis performance of yield and fibre quality in F1 and F2 hybrids in upland cotton

Because of the difficulty of producing F₁ hybrid seeds by hand emasculation and pollination, wide use of heterosis in cotton production has been limited in China. The objective of this study was to evaluate the potential of F₂ hybrids for yield and fibre quality. A half diallel involving eight parents and their F₁ and F₂ hybrids was grown in replicated studies at Linqing and Nanjing in 1999 and Nanjing in 2000. Yield and fibre quality was determined for all 64 entries. Fibre quality was also determined for parents and F₁s, but only for Zhongmiansuo 28 (ZMS28), Xiangzamian 2 (XZM2) and Wanmian 13 (WM13) F₂s. These three F₂ hybrids are extensively planted in China and provide experimental controls with which to compare the performance of new hybrids. Average yield heterosis for F₁s and F₂s was 15.9 and 9.2%, respectively. Inbreeding depression for yield varied but some F₂s greatly out‐yielded the best variety. Average F₁ heterosis was 6.7, 6.2 and 2.9%, respectively for number of bolls per unit area, boll weight, and lint percentage. The average F₂ heterosis for the same traits was 4.4, 3.3 and 1.6%, respectively. F₁ heterosis for fibre traits was low. In general, parental average was a good indicator of the yield and fibre quality of F₁ hybrids. These encouraging results suggest there is sufficient heterosis for yield to use F₂s in China.     

Genetic distance and its association with heterosis in peas

Summary The relationship between the genetic distance of parents and both the heterosis of F₁ hybrids and the variance of F₅ lines was investigated in 72 crosses of pea (Pisum sativum L.). The genetic distance between each pair of parents was estimated, using isozyme (GDi), morphological (GDm) or quantitative (GDq) markers and finally a combination of isozyme and morphological markers (GDi+m). GDm was poorly correlated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F₁ generation, with the highest correlation obtained from GDi+m. GD was not significantly correlated with heterosis for yield over the better or best parent but it was significantly correlated with all three measures of heterosis for pods per plant and hundred seed weight. There was no correlation between genetic distance and the level of heterosis for yield and total dry matter in the F₂ generation, but GDi, GDi+m and GDq were predictive for the level of inbreeding depression in grain yield and total dry matter. When parents were high in genetic distance, crosses produced highly transgressive segregants for basal branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the variance of derived inbred lines. It was concluded that when choosing parents for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is considerable potential for optimising choice of parental combinations in the development of improved pea cultivars.     

Heterosis and hybrid performance in topless faba beans (Vicia faba L.)

Parental lines, F₁ and F₂ hybrids from a 7×7-diallel of topless faba beans and eight standard cultivars were grown in single-rows for two years at four sowing dates on a highly fertile loam soil near Göttingen. In grain yield, F₁ hybrids showed 21 to 54% advantage over the higher yielding parent. Compared with the midparental value an average heterosis of 50% was observed for grain yield. Corresponding heterosis mean values ranged from 3 to 37% for yield components and up to 11% for phenological traits. The grain yield of the highest yielding topless F₁ hybrid was equal to that of Alfred, the highest yielding indeterminate standard cultivar. High grain yield in the topless hybrids was closely correlated with high biomass yield, late ripening and tall plants generally having a high number of podded nodes and pods on the main stem. Due to their agronomic advantages, i.e., lower plant length, reduced lodging sensitivity and earlier ripening, efforts at breeding topless hybrids seemed to be worth-while in faba beans. However, their yielding ability must be improved further before they can compete with normal, semi-dwarf and stiff-strawed cultivars.     

Heterosis and heritability in crosses among Asian and Ethiopian parents of hot pepper genotypes

Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing’s fixed effect model analysis. An open field experiment was conducted in 2004/2005 to investigate heterosis for fourteen traits in 66 F₁ hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (H _b²) for fruit traits were more than 60% and with wide gap from narrow sense heritability (h _n²) for most of the important traits like number of fruit per plant (H _b² = 88.3% and h _n² = 46.0%), days to maturity (H _b² = 87.2% and h _n² = 23.1%) and dry fruit yield per plant (H _b² = 72.6% and h _n² = 14.6%). Maximum heterosis over mid-parent and better-parent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (−29.8, −31.5 and −23.6%). These observations suggested a possibility of utilizing dominance genetic potentiality available in diverse genotypes of the crop by heterosis breeding for improving hot pepper to the extent of better economic return compared to the current commercial cultivar under production in the country. Low narrow sense versus very high broad sense heritability for days to maturity and dry fruit yield per plant could be a sign for achievability of earliness and high fruit yield using heterosis in hot pepper. The maximum heterobeltiosis were recorded either from F₁s obtained from Ethiopian and Asian crosses or from within Asian crosses, suggesting the possibility of maximizing heterosis by considering genetically diverse parental genotypes. The manifestation of highest heterosis in hybrids from among Asian lines indicated existence of genetic diversity among Asian genotypes and the potentiality for improvement of hot pepper using genotypes from different regions of the world along with elite inbred lines from local cultivars.     

A diallel analysis of various traits in winter triticale

In triticale, preharvest sprouting tolerance is important for yield stability and quality of the grain. Therefore, an experiment was conducted to estimate quantitative genetic parameters of preharvest sprouting tolerance in triticale using a diallel of eight modern triticale cultivars and breeding lines. The 28 F₁‐hybrids and the parents were planted in the breeding nurseries in 2001 and 2002 at four locations. Heading, plant height, falling numbers of two harvest dates, thousand kernel weight (TKW) and preharvest sprouting (Spr) were measured. The heritabilities for plant height and TKW were the highest with 0.91 and 0.85, respectively. Falling number and sprouting showed heritabilities between 0.66 and 0.83. Mid‐parent heterosis (MPHET) was negative for heading, indicating a non‐significant earlier heading of the F₁‐hybrids. In plant height and TKW the heterosis was positive with 4.7% and 6.3% MPHET. Both falling numbers displayed a negative MPHET of nearly −15%. In contrast to falling numbers, the preharvest sprouting of hybrids was slightly reduced in comparison with the parents. In all traits analysed, general combining ability (GCA)‐variances were greater than specific combining ability (SCA)‐variances.     

Self-compatibility and heterosis in white clover (Trifolium repens L.)

Inbred lines of white clover (Trifolium repens L.) have been produced utilising the rare self-fertility (Sf) allele. Twenty-two lines of four distinct groups have been maintained through five generations of selfing by single seed descent. Fourteen lines were used in crosses to produce F¹s. Both parents and hybrids were analysed for a range of morphological characters. Positive heterosis for dry matter production was observed in half the hybrids. No other trait showed significant heterosis. The degree of heterosis appears to be related to the extent of variation in morphological characters between the parental lines, some combinations of lines yielding heterotic hybrids in all cases, others in none. The majority of the F¹ hybrids are superior in terms of dry matter production to eight control varieties. This revised version was published online in July 2006 with corrections to the Cover Date.     

陆地棉主要农艺与纤维品质性状的双列杂交分 析简

 本文利用加性-显性与环境互作的遗传模型（ADE模型）,分析8个陆地棉亲本及其F1在不同环境下的农艺和纤维品质性状,在估算遗传方差分量、遗传效应的基础上,分析各类性状间的遗传相关性,并预测F1和F2的杂种优势,为棉花杂种优势利用和新品种选育提供了较有价值的信息。研究表明,农艺与纤维品质性状的遗传主要受加性、显性和加性与环境互作效应控制。遗传相关分析表明,皮棉产量与纤维品质性状的显性相关系数值较大,利用杂种优势在早期世代可以得到协同改良,纤维品质性状间易实现协同改良。杂种优势分析表明,F₁和F₂的皮棉产量均具有显著的超亲优势,纤维品质性状的杂种优势不明显。     

Relationship between molecular marker heterozygosity and hybrid performance in intra- and interspecific hybrids of cotton

The present study was conducted to investigate the relationship between parental molecular marker diversity and hybrid performance in both intra‐ and interspecific hybrids of cotton to evaluate the feasibility of predicting hybrid performance using molecular markers. Three cytoplasmic male sterile (CMS) lines were crossed with 10 restorer lines to produce 22 F₁ hybrids during 2003. Of 22 F₁s, 14 hybrids were intraspecific (Gossypium hirsutum × G. hirsutum) and eight interspecific (G. hirsutum × G. barbadense). These 22 F₁ hybrids and their parents were evaluated for yield and fibre quality traits at Zhejiang University, Hangzhou, China during 2004 and 2005. Genetic distances (GD) among the parents were calculated from 56 random‐amplified polymorphic DNAs (RAPD) and 66 simple sequence repeat (SSR) marker data, and their correlation with hybrid performance and heterosis were analysed. The parents could be discriminated into G. hirsutum and G. barbadense clusters by cluster analysis based on both RAPD and SSR markers data. The correlation (r = 0.503, P ≤ 0.05) was calculated between GD_rapd (GD based on RAPD markers) and GD_ssr (GD based on SSR markers). Correlation of GD with hybrid performance and heterosis differed considerably between intra‐ and interspecific hybrids. The correlation between GD and hybrid performance was non‐significant for most of traits within the hybrids of G. hirsutum species. However, it was significantly and positively correlated for fibre length, fibre strength and elongation in interspecific hybrids. The relationship between GD and heterosis was observed to be positively significant for boll weight within hybrids of G. hirsutum with significant and negative correlations for fibre length and elongation. In conclusion, the power of predicting hybrid performance using molecular markers in cotton is low. But, the relationship between SSR marker heterozygosity and hybrid performance can be used to predict fibre length during interspecific hybrid cotton breeding.     

Indica-Japonica differentiation of paddy rice and its relationship with heterosis

The Indica‐Japonica differentiation of three photoperiod‐sensitive and/or thermosensitive genetic male‐sterile rice (PGMS or TGMS, respectively) lines and 47 male parental lines from seven ecotypes were studied for their restriction fragment length polymorphism marker data to determine which ecotype crosses with the three PGMS and/or TGMS lines could lead to higher yield potential, and to estimate the relationship between the Indica‐Japonica differentiation of parents and heterosis in grain yield and its components. The results indicated that hybrids derived from ‘N422s’ and the early‐middle ripening Indica varieties from southern China, and hybrids between ‘Pei'ai64s’ and three Japonica ecotypes, including North‐eastern Japonica varieties, restoring lines of Japonica hybrid rice and north China Japonica varieties, showed the highest grain yields. There was less variation of yield among the F1s between ‘108s’ and the seven ecotypes than among the other F₁s. Highly significant positive correlations between heterosis of the F₁ yield and genetic distance of the parents were detected, although the correlation between F₁ yield performance and genetic distance did not reach a significant level. Considerable variation of correlation between heterosis and genetic distance was also detected in the Indica × Indica crosses and Indica × Japonica crosses. There was much higher correlation (r = 0.63) between the F₁ yield performance and the genetic distance of parents in the Indica × Indica crosses than in the others. It is proposed that a genetic distance of 0.4‐0.8 between the two parents of hybrid rice might be appropriate not only for F₁ performance, but also for heterosis.     

Evaluating interspecific wheat hybrids based on heat and drought stress tolerance

Three durum and three bread wheat genotypes were crossed to produce three tetraploid, three hexaploid and nine interspecific (pentaploid) F₁ hybrids. All genotypes were evaluated for heat tolerance in the field and for drought using polyethylene glycol in vitro. Chromosome numbers and meiotic behavior in pentaploid F₁ hybrids (2n=5x=35, genomes AABBD) were confirmed. Heat stress significantly reduced grain yield/plant and 1000-kernel weight (1000-KW), while grain protein content (GPC) was increased. Drought caused a significant reduction in root length, shoot length and seedling fresh weight, whereas root/shoot ratio was increased. P₃ (durum), P₄ (bread) and their pentaploid F₁ hybrid could be considered as the most heat-tolerant genotypes. However, P₂ (durum), P₆ (bread) and their F1 were most tolerant to drought. The addition of a D genome single dose into pentaploid F1 hybrids obviously reduced grain yield/plant, 1000-KW and seedling traits, however GPC was increased. Moderate to high broad-sense heritability and genetic advance were obtained for the most investigated traits. Grain yield/plant was strongly positively correlated with stress tolerance index (STI), yield index (YI), mean productivity (MP), geometric mean productivity (GMP) and harmonic mean (HM) under heat stress and with root length under drought condition, suggesting that STI, YI, MP, GMP and HM are powerful indices for heat tolerance, while root length is most effective for drought. Successful interspecific hybridization obtained in the study is only an initial step for desired genes introgression. Successive progenies are going to be evaluated for further genetic studies aiming at improving abiotic stress tolerance in wheat.     

Breeding for wide adaptation in faba bean

Summary Broadening agronomic adaptation will improve yield stability in the grain legume Vicia faba L. We gathered information on the adaptation of European and Mediterranean material to European and Mediterranean environments. The material comprised 20 inbred lines (12 European and 8 Mediterranean lines) and 99 intra- and interpool-crosses in generation F₁. These were evaluated in 9 environments: two spring-sown Southern German environments (SGermE), and seven autumn-sown Mediterranean environments (MedE) in Sicily, Puglia, Andalucia and South Africa. Standard ANOVA, stability analyses and AMMI analysis were performed. Mean yield in F₁ was 257 g/row, the overall parental mean was 144 g/row. The range of environmental means was from 94 g/row to 411 g/row. The average regression coefficient in F₁ was b _i =1.07, being significantly greater than for the parents (b _i =0.68). The opposite was true for the relative magnitude of the deviations from the regressions, which were highly correlated to the AMMI-PC1-results. The AMMI analysis clearly separated the SGermE from the MedE, as well as the germplasm pools. Though the superiority of the F₁-hybrids over their parents was striking, their pattern of interactions with the environments strictly reflected that of their parents. A number of promising crosses was identified as a nucleus of a widely adapted faba bean genepool.     

Drought tolerance variability in S<Subscript>1</Subscript> pollinator lines developed from a sugar beet open population

Drought tolerance is one of the most important objectives of sugar beet breeding programs in semi-arid regions, particularly during the last decade. Due to global climate changes and limitations of agricultural irrigation water, varieties with drought tolerance are taken into consideration in order to avoid yield losses due to drought. In this study, drought tolerance of 76 S₁ lines (full-sib families) that had been extracted from a genetically broad base multigerm sugar beet open pollinated population, were examined. Test crosses were made between the lines as pollinators and a cytoplasmic male sterile (CMS) single cross. The consequent hybrids along with checks were evaluated during 2007 and 23 more tolerant hybrids during 2008, in two adjacent experiments under drought stress and non-stress conditions. Drought tolerance indices calculated based on sugar yield, such as mean productivity (MP), geometric mean productivity (GMP) and stress tolerance index (STI) were used to assess hybrids responses to drought. The results showed significant genetic differences for root yield and sugar yield under both conditions. Drought tolerance indices displayed significant genetic variability for sugar yield among the hybrids. Many hybrids were drought tolerant as compared with the original base population as indicated by their high STI. The estimates of heritability for sugar yield in stress and non-stress conditions were much close to each other (0.31 and 0.34, respectively). Whereas, for root yield the heritability estimate in stress condition (0.46) was relatively higher than that in non-stress condition (0.34). Significant differences were observed among the selected hybrids for root yield and sugar yield, indicating genotypic variability for pollinator lines derived from the population. There were no significant differences for sugar content. For increasing the drought tolerance potential in a breeding population and developing drought-tolerant varieties by male parent, the drought-tolerant lines could be used.     

Heterosis,combining ability and genetic effect,and relationship with genetic distance based on a diallel of hybrids from five diverse <Emphasis Type="Italic">Gossypium barbadense</Emphasis> cotton genotypes

The cultivated tetraploid Gossypium barbadense L. cotton produces superior natural fibers for the textile industry in the world. However, the possibility in utilization of heterosis to further increase its lint yield has not been extensively explored. In this study, two commercial US Pima cotton cultivars and three exotic G. barbadense lines, together with all of their possible hybrids in F₁ and F₂ progeny without reciprocals, were tested for lint yield, yield components, and fiber quality traits in four environments in 2005–2007. With a few exceptions, genotype (G), environment (E), and G × E were all significant or highly significant for all the traits studied. General combining ability (GCA) variances for all the traits in both F₁ and F₂ were also significant, while specific combining ability (SCA) variances were detected only for lint yield, fiber length, and micronaire in both generations and boll weight in F₁. GCA × E was also detected for lint percent, seed index, and fiber length in both F₁ and F₂, and boll weight in F₁, but none of the traits had significant SCA × E. As a group, F₁ and F₂ out-yielded the parent group by 20–40% and 6–10%, respectively. Mid-parent heterosis (MPH) for lint yield in F₁ was generally positive, ranging from ?4.7 to 116.4% with an average of 21.2–48.7%, while lint yield MPH in F₂ ranged from ?23.3 to 69.4% with an average of 6.4–12.4%. However, useful heterosis in lint yield was only detected in the hybrid between the two US commercial cultivars Pima S-7 and DP 340. MPH for other traits was low or not detected. MPH in F₂ was lower than that in F₁ but they were generally positively correlated. The genetic distances (GD) of the parents (based on 467 polymorphic RAPD and AFLP markers) between the five parents was not consistently correlated with MPH and SCA of their hybrids and dominant effects for lint yield and other traits. However, significant and positive correlations between GD of parents and the performance of their hybrids were detected for lint yield, lint percentage, and lint index in both F₁ and F₂ in most of the tests. GD of parents was also correlated with their GCA and additive effects in lint yield, lint percent, lint index, micronaire, plant height, and elongation. The results suggest that the close correlation between GD and hybrid performance per se was mainly due to the existence of GCA and additive effects from parents.     

Hybrid performance and heterosis in strawberry (Fragaria × ananassa Duchesne), regarding acidity,soluble solids and dry matter content in fruits

A top‐cross‐mating design among 29 S₄ inbred lines and tester (cultivar ‘Dukat’) was carried out to study their breeding value in terms of general combining ability (GCA). The objectives of this study were to evaluate the acidity, soluble solids and dry matter contents in fruits of progeny F₁ in comparison with S₄ inbred lines as well as the cultivars (S₀); identify strawberry genotypes with high value of GCA for use in cultivar development; and determine mid‐parent heterosis regarding S₄ inbred lines and cultivated strawberry. The 2‐year observations showed statistically significant differences between tested genotypes in terms of the studied traits. The highest breeding value based on GCA was estimated for Chandler 123‐5 for soluble solids and dry matter content, and Kent 7‐6 for acidity. Estimated mid‐parent heterosis had positive and negative values. The highest heterosis in terms of extract and dry matter content (26.71% and 17.50%, respectively) occurred in the offspring Chandler 123‐5 × ‘Dukat’, but as regards acidity in hybrid Chandler 123‐22 with cv. ‘Dukat’. The study of genetic divergence by dendrograms may help to identify parents suitable for obtaining hybrids with higher heterosis effects.