Doubled-haploid versus single-seed descent and S1-family variation for testcross performance in a maize population

Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance. DH and single-seed descent (SSD) lines were produced from random S₁ progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the genetic variance of S₁ families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance of S₁ families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all traits, heritability of SSD or DH lines was higher than heritability of S₁ families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S₁ testcross progenies and DH or SSD testcross progenies, meaning that the S₁ testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation in DH lines appeared to be more in accordance with the observed variation among S₁ families than with the observed variation among SSD lines.     

Breeding maize lines for complete and partial resistance to maize streak virus (MSV)

Summary S₁ to S₅ inbred lines, derived from a maize population bred for its overall resistance to three tropical viruses, were screened for resistance to maize streak virus (MSV) by artificial plant infection using viruliferous leafhoppers. Symptoms were rated and intra-line frequency distributions studied for all pedigree inbred lines. Mortality due to MSV was very low among these inbreds. Symptoms appeared later, developed slower and were less severe than in the susceptible control hybrid. Results of a study of 500 S₁ and 93 S₂ lines suggested that resistance is under genetic control via a system involving loci with major genes (with dominance for resistance) controlling high to complete resistance, associated with a genetic system involving loci with minor genes controlling partial resistance. Lines expressing complete resistance to MSV were developed from 5 cycles of inbreeding and selection. The relevance of such complete and partial resistance is discussed.Abbreviations MRPS Mean Rating for Plants exhibiting Symptoms     

Magnitude of inbreeding depression and genetic variation analysis of agro‐morphological traits in orchardgrass

Inbreeding depression is the reduction in the fitness of inbred offspring relative to progeny from unrelated parents. In orchardgrass (Dactylis glomerata L.), limited efforts have been made to evaluate the effects of deliberate selfing on agro‐morphological traits and to estimate the genetic variation of traits. Twenty‐five genotypes of orchardgrass, along with 25 S₁ (full‐sibs) and 25 families of half‐sibs, were created in 2012 and used to assess the consequences of the first generation of inbreeding and outcrossing for offspring fitness and to estimate heritabilities, genetic parameters and correlations of agro‐morphological traits during the period of 2013–2014 in the field. Different levels of inbreeding depression were observed for the traits, with higher values for plant height, days to inflorescence emergence and dry matter yield. The degree of inbreeding or outbreeding effects varied among the studied genotypes. This facilitates the development of inbred lines for further studies. The results showed that some of the studied genotypes were self‐fertile, thereby indicating the possibility of developing inbred lines from these genotypes. Heritabilities ranged from 0.10 for the number of stems per plant to 0.64 for spread among the studied populations. Spread had high heritability as well as high correlation with forage yield, thereby indicating that this trait could be used to improve forage yield indirectly.     

Breeding wheat and rye for resistance to Fusarium diseases

Fusarium culmorum and F. graminearum Groups 1 and 2 cause seedling blight, crown rot, foot rot and head blight in wheat and rye that may affect grain yield and quality for baking and feeding. This review starts with an analysis of Fusarium populations with regard to their genetic variation for aggressiveness, mycotoxin production, and isolate-by-host genotype interaction. To assess resistance in the different host growth stages, quantitative inoculation and disease assessment techniques are necessary. Based on estimated population parameters, breeding strategies are reviewed to improve Fusarium resistance in wheat and rye. Epidemiological and toxicological aspects of Fusarium resistance that are important for resistance breeding are discussed. F. culmorum and F. graminearum display large genetic variation for aggressiveness in isolate collections and in naturally occurring populations. The production of mycotoxins, especially deoxynivalenol and its derivatives, is a common trait in these populations. Significant isolate-by-host genotype interactions were not found across environments in wheat and rye. Artificial infections in the field are indispensable for improving Fusarium crown rot, foot rot and head blight resistance in wheat and rye. For a reliable disease assessment of large populations, disease severity ratings were found to be the most convenient. The differentiation of host resistance is greatly influenced by an array of nongenetic factors (macro-environment, microclimate, host growth stage, host organ) that show significant interactions with host genotype. Selection for environmentally stable resistance has to be performed in several environments under a maximum array of different infection levels. Selection in early growth stages or on one plant organ does not in most cases allow prediction of resistance in adult-plant stages or another plant organ. Significant genetic variation for resistance exists for all Fusarium-incited diseases in breeding populations of wheat and rye. The patho-systems studied displayed a prevalence of additive gene action with no consistent specific combining ability effects and thus rapid progress can be expected from recurrent selection. In wheat, intensive testing of parental genotypes allows good prediction of the mean head blight resistance after crossing. Subsequent selection during selfing generations enables the use of transgression towards resistance. In hybrid breeding of winter rye, the close correlation between foot rot resistance of inbred lines and their GCA effects implies that selection based on the lines per se should be highly effective. This is not valid for F. culmorum head blight of winter rye caused by a greater susceptibility of the inbred lines compared to their crosses. For both foot rot and head blight resistance, a high correlation between the resistance to F. graminearum and F. culmorum was found in wheat and rye. Mycotoxin accumulation occurs to a great extent in naturally and artificially infected plant stands. The correlation between resistance traits and mycotoxin contents are medium and highly dependent on the environment. Further experiments are needed to clarify whether greater resistance will lead to a correlated reduction of the mycotoxin content of the grains under natural infection.     

Effect of inbreeding on horticultural performance of lines developed from an open-pollinated pickling cucumber population

Summary The effect of self-pollination of cucumber (Cucumis sativus L.) for 6 generations in lines developed from the North Carolina Medium Base Pickle population was determined by regression of trait expression for each generation on Wright's coefficient of inbreeding. Two yield traits (total and marketable), earliness and 3 fruit quality traits (shape, color and seedcell size) were evaluated in 2 environments (spring and summer, 1983). The regression did not result in significant negative slopes, indicating that inbreeding depression was not important in the population for the traits studied. Midparent heterosis was found for most traits in many hybrids obtained from crossing S₆ lines with the gynoecious inbred line, Gy 14A.     

Effects of inbreeding on nodal root system morphology and architecture of white clover (<Emphasis Type="Italic">Trifolium repens</Emphasis> L.)

Plants of white clover (Trifolium repens L.) cultivar Crau, a self-fertile Crau genotype, and nine generations of inbred progeny were raised in sand culture in a glasshouse experiment. Digital images of the root systems were made and root morphological characteristics were determined on all the plants. Root architectural parameters were measured on the Crau parent and the S₁, S₄, S₆, and S₉ inbred lines. The clover roots became shorter and thicker with inbreeding but the number of root tips per plant was unchanged. Root architecture (branching pattern) was largely unaffected by inbreeding. It is concluded that inbreeding white clover will lead to shorter, thicker roots, and reduced nutrient uptake efficiency compared with the parent clover. The degree to which these deleterious traits are overcome during the development of F₁ hybrids needs to be determined.     

Testcross performance and diversity analysis of white maize lines derived from backcrosses containing exotic germplasm

Introgression from exotic maize (Zea mays L.) into adapted breeding pools can broaden and diversify the genetic base of adapted germplasm. The first objective of this study was to determine the agronomic performance of white maize lines derived from adapted × exotic backcrosses in tropical environments. Six exotic white maize inbred lines were crossed to an adapted white line (1368) and the F₁s were backcrossed to 1368. Forty-one BC₁F₄ lines derived from these backcrosses and the recurrent parent were crossed with a common inbred tester (9071) and the progeny were evaluated at eight environments in Nigeria. The testcrosses × environment interaction mean square was not significant for all agronomic traits. The BC-derived lines containing exotic germplasm contributed significantly to the variation in testcross mean grain yields and other agronomic traits. Among the 41 testcrosses, only 5 yielded significantly less than 1368 × 9071, with the 7 best testcrosses producing between 304 and 867 kg ha⁻¹ more grain than 1368 × 9071. The second objective of this study was to assess the genetic divergence of the BC-derived white lines from their adapted recurrent parent. Thirty-nine BC-derived white lines along with 1368 and 9071 were genotyped with ten AFLP primer pairs that generated 506 polymorphic fragments. The average allelic diversity of the lines was 31 ± 0.07. The genetic distance (GD) estimates of each BC-derived line from 1368 varied from 0.76 to 0.84, with a mean of 0.80 ± 0.003. The average GD for all pairs of the BC-derived lines was 0.63 ± 0.005, varying from 0.31 to 0.89. The observed significant amount of variation among the BC-derived white lines suggests that they can contribute new alleles for expanding the genetic base of tropical maize and for developing high-yielding hybrids.     

Genetic variation in testcrosses of European maize inbreds for resistance to the European corn borer and relations to line per se performance

The European com borer (ECB) Ostrinia nubilalis H. is a major pest in World maize Zea mays L. production. Objectives of this study were to (1) investigate the genotypic variance and covariance in testcrosses of European flint and dent inbreds for ECB resistance and agronomic traits, and (2) estimate the correlation between line per se and testcross performance for ECB resistance traits. A total of 16 flint and 24 dent inbreds and their testcrosses with two testers from the opposite germplasm pool were evaluated in four and three German environments, respectively. Using artificial infestation with ECB larvae, resistance was assessed by damage rating of stalks, tunnel length in dissected stalks, and relative yield of infested plots compared with protected plots. Yield losses due to ECB damage in testcross hybrids amounted to 40%. Significant genotypic variances between flint and dent lines and high heritabilities were found for damage rating of stalks for both line per se and testcross performance. Heritabilities were low or intermediate for tunnel length and relative grain yield. Correlations between line per se and testcross performance were tight for the damage rating of stalks and moderate for tunnel length and relative yield in both flint and dent germplasm. For damage rating of stalks, per se performance of lines tested in a few environments can be used to predict their testcross performance. In contrast, assessment of testcross performance for tunnel length and relative yield requires evaluating testcrosses with several testers in multi-environment trials.     

Relationships between line per se and testcross performance for agronomic traits in two broad-based populations of maize

Degree of the association between line per se performance (LP) and testcross performance (TP) is important in breeding programs and simultaneous improvement of commercial hybrids and their parental lines. This experiment was designed to study genetic variability and genetic correlation for several agronomic traits in two maize (Zea mays L.) broad-based populations (NS12-SG and NS14-SG). Independent trials with 80 entries of S₁ progenies as well as their testcrosses were arranged according to an incomplete block design with replicates in sets. Grain yield, stay green, anthesis-silking interval, stalk water content and grain moisture were evaluated in four environments. The anthesis-silking interval had the highest genetic variation, followed by stay green. High heritability estimates (>0.50) for all traits, pointed out that further selection would be possible. Genetic correlations between line per se and testcross performance were lowest for grain yield (0.396** and 0.592**, for NS12-SG and NS14-SG, respectively), and highest for grain moisture (0.937** and 0.821**, respectively). High correlations between line per se and their testcrosses for stay green, anthesis-silking interval, stalk water content and grain moisture indicated that additive gene action might be more important than dominance in controlling the expression of these traits.     

Advanced cycle pedigree breeding in sunflower. II: combining ability for oil yield and its components

Combining ability is one of the most important information breeders use to identify superior inbred lines on the basis of their performance in hybrid combinations. The objectives of our study were (i) to quantify the importance of general combining ability (GCA) and specific combining ability (SCA) variances for seed yield, oil content and oil yield; and (ii) estimate GCA and SCA effects of seed yield, oil content and oil yield of inbred lines developed from advanced cycle pedigree breeding populations in sunflower. A total of 109 female S₃ cytoplasmic male sterile (CMS) lines from four bi-parental populations in advanced cycle pedigree breeding were crossed with two testers to form 218 testcross hybrids (TCHs). The TCHs were then evaluated in three environments. Variance component analysis results showed predominance of σ²gca over σ²sca for seed yield and oil yield indicating that superior TCHs can be identified based on positive and significant GCA effects of the female lines. For oil content σ²sca was predominant over σ²gca indicating that selecting for TCHs with high oil content would be best among line × tester combinations and not among female S₃CMS lines per se. The proportion of GCA and SCA effects in the best five TCHs in each breeding population also confirmed the predominance of GCA effects over SCA effects for seed yield and oil yield while for oil content both GCA and SCA effects appear to be important, with SCA effects having more influence than GCA. The best selection strategy would therefore be to capture the GCA in the early stages of inbreeding and then SCA for the few unique combinations when lines are almost fixed.     

A Dominant Inhibitor Gene Inhibits the Expression of Ht2 against Exserohilum turcicum Race 2 in Corn Inbred Lines Related to B14

The purpose of this study was to elucidate the genetic cause for the lack of express ion of the gene Ht2 against Exserohilum turcicum race 2 on certain genetic backgrounds related to the inbred line B14. Two such inbreds (A635Rp and B59), susceptible to this pathogen were crossed onto the inbred Oh43—-Ht2Ht2. The following generations: F₁, F₂, F₃, F₄, backcrosses to both parents, selfings of the backcrosses, in addition to the parent lines, were evaluated for Ht2 expression in this study. Plants of each generation were inoculated with E. turcicum race 2 and evaluated for the expression of the chlorotic-lesion resistance determined by the gene Ht2. In spite of the reported dominance of Ht2 on some genetic backgrounds, the F₁ generations studied here did not show Ht2 resistant lesions. The data presented herein suggest that B₁₄ and related inbred lines carry a dominant gene(I) that inhibits the expression of the Ht2 gene. Chi-square analyses of the reactions of 108 progeny families studied supported this hypothesis.     

Genetic control of resistance to the aphid Brevicoryne brassicae in the wild species Brassica fruticulosa

Initial studies have shown variable resistance in Brassica fruticulosa to the aphid Brevicoryne brassicae The aim of this work was to fix high levels of resistance to B. brassicae in true breeding lines of B. fruticulosa and obtain data on the genetic control of resistance. Plants from initially variable B. fruticulosa accessions were selfed to produce inbred resistant and susceptible lines that were studied in three separate experiments to determine the extent to which resistance to B. brassicae had been fixed. Results from three experiments using successive generations of resistant and susceptible inbred lines showed that continued selection resulted in resistant inbred lines that supported an average of three aphids per plant compared with an average of 96 aphids per plant for susceptible inbred lines. Data collected from an experiment determining the resistant phenotype of lines including the selfed progenies and the F₁ and F₂ progeny of a cross between resistant and susceptible individual plants indicated that the resistance was not controlled by a single gene.     

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.     

Estimates of combining ability for resistance of winter rye to Fusarium culmorum head blight

Summary Head blight caused by Fusarium culmorum and F. graminearum is damaging in all winter rye (Secale cereale L.) growing areas. For hybrid breeding, the relative magnitude of general (GCA) and specific combining ability (SCA) is a crucial parameter for developing appropriate selection procedures. Forty single-cross hybrids were produced by crossing six and seven inbred lines of the Petkus and Carsten gene pool, respectively, in a factorial design. Hybrids were evaluated in two years with artificial F. culmorum inoculation. Resistance traits were head blight rating and grain weight relative to the non-inoculated control. Both resistance traits were closely correlated across both years (r-0.8, P=0.01). Significant genotypic variation was found for both traits with medium to high estimates of heritability (h²=0.6-0.8). Components of variance for GCA were, across years, 10 and 6 times larger than those for SCA for head blight rating and relative grain weight, respectively. Significant SCA effects were found for 15 to 20% of all cross combinations across both traits in each year. SCA effects were, however, inconsistent over years leading to a high SCA-year interaction. In conclusion, resistance to Fusarium head blight among the interpool hybrids tested was conditioned mainly by additive gene action that could be utilized by recurrent selection in multi-environment trials.Abbreviations GCA general combining ability - SCA specific combining ability     

Breeding the common bean (Phaseolus vulgaris L.) for resistance to bean common mosaic virus: alternatives to backcrossing

A series of field experiments was undertaken in order to determine whether resistance to bean common mosaic virus (BCMV) could be incorporated into genotypes of the common bean (Phaseolus vulgaris L.) suitable for cultivation in Zimbabwe without recourse to backcrossing. Six inbred genotypes carrying the resistance-conferring alleles at the loci I and Bc-3 were crossed with five locally-adapted inbred genotypes. The first experiment comprised F₃ progeny rows, each derived from a single unselected F₂ plant, the second, F₃ bulks selected for resistance, and the third, a comparison of selected and unselected F₂-derived F₄ lines. The number of days to flowering and to maturity, the incidence of mosaic and necrosis symptoms, seed yield and seed size were recorded. There was evidence that late flowering and maturity were associated with BCMV resistance in some crosses, though not strongly enough to present an obstacle to plant breeding. The incidence of virus symptoms and seed yield were influenced by genetic factors additional to the major resistance genes, and variation in seed yield was present not only between bulk populations of crosses, but also between single-row plots of lines within crosses. This indicates that early-generation selection for yield in the presence of BCMV, even among progeny selected for BCMV-resistace, is likely to be effective. However, the variation in yield among F₄ lines was least in the highest-yielding crosses, which may represent a limit to successful selection for yield. Seed size was partly under additive genetic control, but there was also evidence of non-allelic interactions. There was no association between large seed size, preferred by consumers, and susceptibility to BCMV in the progeny, indicating that the association between these characters in the parent lines is fortuitous and will not present an obstacle to plant breeding. It is noted that a considerable amount of useful genetic information can be obtained without recourse to elaborate crossing schemes, provided that unselected progeny are included in experiments as controls. The evidence presented indicates that resistance to BCMV can be combined with appropriate values of maturity date, yield and seed size without the need for backcrossing.     

Genome-wide association mapping and genomic prediction of Fusarium head blight resistance,heading stage and plant height in winter rye (Secale cereale)

Rye is a multi-purpose cereal crop grown in Central and Eastern Europe as well as in Western Canada. Fusarium head blight (FHB) is one of the diseases that have a severe negative impact on rye, but knowledge about FHB resistance at the genomic level is totally missing in rye. The objective of this study was to elucidate the genetic architecture of FHB resistance in winter rye using genome-wide association (GWA) mapping complemented by genomic prediction (GP) in comparison with marker-assisted selection (MAS). Additionally, plant height and heading stage were analysed. A panel of 465 S₁-inbred lines of winter rye was phenotyped in three environments (location–year combinations) for FHB resistance by inoculation with Fusarium culmorum and genotyped with a 15k SNP array. Significant genotypic variation and high heritabilities were found for FHB resistance, heading stage and plant height. FHB did not correlate with heading stage, but was moderately correlated with plant height (r = −.52, p < .001) caused by some susceptible short inbred lines. The GWA scan identified 15 QTL for FHB resistance that jointly explained 74% of the genotypic variance. In addition, we detected 11 QTL for heading stage and 8 QTL for plant height, explaining 26% and 14% of the genotypic variance, respectively. A genome-wide prediction approach resulted in 44% higher prediction abilities than marker-assisted selection for FHB resistance. In conclusion, genomic approaches appear promising to improve and accelerate breeding for complex traits in winter rye.     

Inbreeding Depression and Other Genetic Effects in Populations of Maize Containing Highland Tropical Germplasm

A variety cross diallel of five populations of maize (Zea mays L.) was evaluated in a cool, temperate environment. Two of the parental populations were Corn Belt Dent synthetics (AS3 and BS22), one was developed from selected lines from a CIMMYT population developed for highland regions of the tropics and four Corn Belt Dent inbred lines (NZS3), and the other two had the pedigrees ‘Criollo de Toluca’× AS3² (NZS1) and ‘San Gerónimo’× BS222 (NZS2). ‘Criollo de Toluca’ is from the highlands of Mexico and ‘San Gerönimo’ is from the highlands of Peru. The objective was to study the influence of introgressing highland tropical germplasm into elite Corn Belt Dent synthetics on genetic effects, especially inbreeding depression, and to develop recommendations for the utilization of the introgressed populations. Inbreeding depression explained the greatest proportion of the variation among entries for grain yield, days to silking and plant height, but not for grain moisture at harvest and root lodging. For grain yield, NZS1, NZS2, and NZS3 had high levels of inbreeding depression and the difference between NZS1 and AS3 was statistically significant. High levels of root lodging were associated with NZS1 and high grain moisture at harvest with NZS2. These results indicate that a recurrent selection method, such as S₁ selection, which effectively reduces inbreeding depression, should be used in early cycles of selection with introgressed populations containing highland tropical germplasm.     

Effect of inbreeding on pseudo-self-compatibility in red clover (Trifolium pratense L.)

Summary The effect of inbreeding on pseudo-self-compatibility (PSC) was investigated in I₀, I₁, and I₂ clones of red clover, Trifolium pratense L., at 40°C. PSC was found to decrease with inbreeding. Significant differences were found among I₀ clones, among I₁ clones, and among I₂ clones for PSC. Significant differences in PSC within generations were found in two of eight I₁ clones and one of five I₂ clones.A new method of inbred line maintenance is proposed which combines the desirable features of vegetative and seed maintenance of inbred lines. Superior I₁ clones with different but homozygous S genotypes and PSC values of 8 to 10% would be vegetatively increased. Clones would be isolated under high temperature field conditions and selfed seed (PSC) would produce the I₂. Selfed seed from two different I₁ clonal lines would then be mixed and sown to produce single-cross seed. Singlecross seed obtained from different clonal sources would be mixed and sown for the production of double-cross hybrid red clover.Contribution from the Kentucky Agricultural Experiment Station. This paper (72-3-125) is published with approval of the Director, Kentucky Agricultural Experiment Station, Lexington.     

Genetic Variation for Agronomic Characters in a Burley Tobacco Synthetic Following Recurrent Selection for Increased Black Shank Resistance

Black shank, a fuagal disease caused by Phytophthora parasitica var. nicotianae, is a major hazard in the production of burley tobacco (Nicotiutta tubacum L.). Moderate levels of resistance have been bred into cultivars, but little success has been achieved in utilizing high levels of resistance found in the cigar line. Beinhart 1000-1. Beinhirt 1000-1 and seven burley cultivars were combined into a synthetic population and three cycles of selection for increased black slunk resistance were conducted. The objectives of this study were (i) t0 estimate genetic variability for agronomic traits in the original base population (C_o) and die three selection cycles and (ii) to characterize the effects of selection for black shank resistance on the agronomic traits. Fifty selfed lines From the base population and each of three selection cycles were evaluated in replicated field trials at Lexington and Princeton, KY. Differences among cycle means for six agronomic traits were not statistically significant. Genetic variation for the six traits among lines within cycles was highly significant and did not change during selection. The results indicated that previously assumed associations between black shank resistance in Beinhart 1000-1 and undesirable agronomic traits were due to chromosomal linkages which were apparently broken by intercrossing. The C₃ population would be a useful base population for selection to improve agronomic performance in black shank resistant genotypes.     

Inbreeding depression and single cross hybrids in leeks (Allium ampeloprasum ssp. porrum)

Summary All current commercial cultivars of leeks are open-pollinated and one of the major problems with the crop is poor uniformity with much of the variation being genetic in origin. Inbred lines and single cross hybrids were produced to try to reduce the genetic variation. Inbreds were generated by single seed descent from 5400 plants taken from six commercial cultivars and performance data for uniformity, yield and quality are presented for the S₁-S₃ generations. A few relatively vigorous inbred lines were obtained but overall, inbreeding depression was very severe with no compensating increase in uniformity as measured by coefficients of variation. In contrast, the experimental hybrids gave significant uniformity, yield and quality benefits compared to open-pollinated commercial cultivars and can be used as the basis for developing a range of commercial hybrid cultivars.Abbreviations SSD Single Seed Descent - HRI Horticulture Research International