Tuber yield and quality of 4x-2x (FDR) potato progenies derived from the wild diploid species Solanum berthaultii and Solanum tarijense

Field experiments were carried out in order to evaluate 4x‐2x families derived from crosses between elite 4x potato cultivars and 2x Tuberosum‐Solanum tarijense and 2x Tuberosum‐Solanum berthaultii clones. Three traits were assessed: total tuber yield (TTY), haulm maturity (HM) and general tuber appearance (GTA). The degree of heterosis of these hybrid families was evaluated by comparison with the respective 2x and 4x parents as well as with seven 4x cultivars. The parental haploid species hybrids derived from S. berthaultii and S. tarijense combined two or more positive horticultural characteristics. Expressed as yield percentage of the 4x parents, the TTY of the families ranged from 53% to 246%. For TTY, the best 4x‐2x hybrid family ranked better than seven out of nine elite 4x cultivars. Some families had GTA scores in the range of the highly selected 4x cultivars. The families, however, were generally later maturing than the 4x parent group. Specific combining ability for TTY and GTA were the only two significant sources of variation observed in this genetic material. Parent‐offspring correlation coefficients were low for all traits, and indicated that parental performance would not be informative at either ploidy level. These results parallel previous investigations with distinct haploid species hybrids where a 4x‐2x breeding scheme was found to be an effective strategy for increasing progeny TTY over the 4x parents. However, the high degree of heterosis for TTY along with good GTA scores observed in certain cross combinations derived from these unadapted 2x species was a somewhat surprising result. Thus far, the importance of these two South American wild potato species, from the potato‐breeding standpoint, has been limited to the fact that they are natural reservoirs of major genes controlling resistance against important diseases and insects. However, the level of performance of some 4x‐2x families in comparative assays with elite cultivars suggests the unanticipated possibility of introgressing genetic factors from S. berthaultii and S. tarijense with positive effects on quantitative traits of horticultural importance along with these major resistance genes.     

Combining ability and correlations for yield components in early generations of potato breeding

A partial diallel set of crosses was made between 14 potato cultivars chosen for their fertility, from those included in a potato breeding programme at the NEIKER – Basque Institute for Agricultural Research. The progeny were grown in completely randomized trials from 1997 to 1999. Performance for yield, tuber number and average tuber weight was analysed in seedling and two clonal generations. Variance estimates due to both general combining ability (GCA) and specific combining ability (SCA) were significant in all generations for all traits under study. However, SCA was more important than GCA in almost all cases. Correlation coefficients among characters, generations, GCA and SCA effects were examined. For tuber yield no relation was obtained between generations; however, average tuber weight and yield were positively associated in all generations. The results indicate that appropriate selection criteria depend strongly on the particular cross. The implication for a breeding strategy are discussed.     

Assessment under short-day conditions of genetic materials derived from three potato breeding strategies: 4x-4x (intra-Tuberosum), 4x-2x (FDR 2n-pollen), and 4x-4x (diplandrous tetraploid)

Families and cultivars derived from three breeding strategies [the conventional 4x-4x (intra-Tuberosum), the interploid 4x (Tub)-2x (Phureja-haploid Tub), and 4x (Tub)-4x (diplandrous tetraploid-DTO)] were evaluated under short-day conditions in Brazil. Two 4x-4x (intra-Tub) cultivars (`Bintje' and `Delta') were used as standards. The 4x-2x (FDR) and 4x-4x (DTO) strategies were equivalent for all traits but they presented superior performance when compared to the 4x-4x (intra Tub) scheme(as a group) for total tuber yield (TTY), commercial yield (CY), and plant vigor (PV). No differences among breeding schemes were observed for three other traits: eye depth (ED), plant uniformity (PU), and haulm maturity (HM). As a group, the 4x-2x (FDR) and 4x-4x (DTO) strategies were similar to the two standard cultivar for all traits but HM. However, eight families [six 4x-2x (FDR) and two 4x-4x (DTO)] had significantly superior performance for TTY when compared with the standard cultivars. For CY, the best 4x-4x (DTO) and the best 4x-2x (FDR) families outyielded `Bintje' by161% and 128%, respectively. No major differences were observed between breeding schemes for TTY and CY when comparing families derived from one single cultivar (`Chiquita') as 4x female parent. However, superior families, based upon multi trait selection criteria, could be obtained only with the 2n-pollen-based strategies. It was possible to select high yielding 4x-2x (FDR) and 4x-4x (DTO) families with favorable trait combinations (e.g., high yielding with ED scores similar to the standards). Individual DTO clones selected within these families may represent outstanding parental materials for crosses with tropical-adapted commercial cultivars. This initial comparison of progenies and cultivars derived from these breeding strategies suggests that 4x-2x (FDR) and 4x-4x (DTO) schemes could be viable alternatives to the conventional 4x-4 × crosses also in tropical/subtropical areas of the world. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adaptation to day length and yield stability of families from 4x×2x crosses in potato

Summary The objectives of this research were to evaluate the response to day length and the yield stability of environments of 4x families from 4x×2x crosses in potato. Twenty families from crosses between 4x female parents with different genetic backgrounds and 2x parents, which formed 2n pollen by first division restitution and were selected under short days, were evaluated in four locations in Peru (short days) and during two years at Rhinelander, USA (long days). Results from the USA indicate that the 4x progeny from 4x×2x crosses were very late maturing and poor yielding.Further, vine maturity, tuber size and tuber number are highly correlated with the percentage of Tuberosum germplasm in the parentage. Results from Peru indicate that most 4x×2x families had high tuber yield, stability for yield and high dry matter content. The lack of correlation between rank order of the parental value, based on progeny testing, of the male and female parents among short day locations and between short and long day environments indicates that selection of parents must be done in each location in which the final product, either a family or a clone, will be used.International Potato Center (CIP)     

Combining ability of common bean (Phaseolus vulgaris) genotypes for root traits across diverse environments

Root system architecture is important for common bean (Phaseolus vulgaris) adaptability to diverse environments. Beans employ complex adaptive root mechanisms for coping with multiple stresses in production environments. Understanding genetic control of root traits is central to improvement of common bean for adaptation to marginal environments. The objectives of this study were to (i) determine combining ability of root and agronomic traits and (ii) estimate the heritability and genetic correlation of root and agronomic traits in common bean. Four bean lines with superior root traits were crossed with four locally adapted varieties in a North Carolina II mating scheme to generate 16 crosses. The 16 F₁s were selfed and advanced to F₂ generation. Eight parents and their F₂ progenies were evaluated in an alpha-Lattice design with two replications. General and specific combing ability mean squares were significant (p ≤ .05) for all traits measured. General predictability ratios ranged from .47 to .68 across locations suggesting that both additive and non-additive gene action modulate root traits and seed yield. Positive and significant (p ≤ .05) phenotypic and genetic correlations revealed significant association between root traits and yield. Moderate to high heritability estimates of between .43 and .67 were realized. Such estimates point to possible deployment of a successful selection programme. Genotype AFR398 displayed significant positive GCA effects among its crosses for both root and agronomic traits hence a potential candidate genotype for inclusion in a bean genetic improvement programme for marginal environments.     

Combining ability and patterns of inheritance for plant and fruit traits in Japanese quince (Chaenomeles japonica)

Phenotypic variation and pattern ofinheritance was investigated for plant andfruit traits in Japanese quince (Chaenomeles japonica, Maloideae). Japanesequince is a minor fruit crop in Latvia andLithuania, and is presently being developedfor production of juice, aroma and fruitfibre in Sweden and Finland. General andspecific combining ability was estimatedfor five plant vegetative traits, eightfruit yield and morphology traits, and fivefruit biochemistry traits in a studypopulation consisting of 14 hybridfamilies. Thorniness seems to be controlledprimarily by a single locus. All othertraits studied appear to be governedprimarily by additive genes, as judged fromgeneral combining ability estimates.Significant specific combining ability(SCA) was detected for yield, plant heightand some fruit traits. However, therelative contribution of SCA to the overallgenetic variance was in general low. Anefficient breeding strategy for Japanesequince could therefore be based onrecurrent selection.     

Combining ability estimates for yield and fibre quality traits in 4 × 13 line × tester crosses of Gossypium hirsutum

The aim of this study was to estimate the general combining ability of the parents and specific combining ability of hybrids considered for the development of high yielding and better quality cultivars. Seventeen genotypes and 52 F₁ hybrids obtained by crossing 4 lines and 13 testers in line × tester mating system during 2003 were sown in randomized complete block design in 2004. Line × Tester analysis revealed significant GCA and SCA effects for all the traits except fibre elongation. Preponderance of non-additive gene action was obtained for seed cotton yield per␣plant and majority of its component traits including fibre traits. Among the parents: PIL-8 for days to 50% flowering, CCH-526612 for boll weight, CITH-77 for number of open bolls per plant and CNH-36 for seed cotton yield per plant were detected with higher general combining ability. Parent, CCH-526612 for 2.5% span length, fibre strength and fibre elongation and AKH-9618 for micronaire value, fibre strength and fibre elongation were good combiners for fibre quality traits. The F₁s achieved high seed cotton yield by producing more number of open bolls. The high yielding hybrids with acceptable fibre quality traits were: CISV-24 × LH-1995, H-1242 × PIL-8 and RS-2283 × SGNR-2 deducted with significant SCA effects for seed cotton yield and fibre characteristics; 2.5% span length and fibre strength. These cross combinations involved at least one parent with high or average GCA effect for a particular trait.     

A diallel crossing approach aimed on selection for ripening time and yield in breeding of new strawberry (Fragaria × ananassa Duch.) cultivars

The extension of the ripening season in open field production is of high economic interest for strawberry growers. Therefore, targeted breeding for extreme early or late ripening cultivars with high yield potential is of particular interest. Thirteen strawberry cultivars were crossed in a reciprocal way without selfing, and the 144 resulting F₁ populations were evaluated in a field trial over a period of two consecutive years. The data were analysed using a mixed‐model approach adapted for diallel crossing designs using SAS 9.3. The variability in the crossing approach is mainly based on the general combining ability (GCA) of the cultivars (additive effects). Specific and reciprocal combining abilities (non‐additive effects) appear less important. The highest GCAs for the trait Marketable Yield were found for the cultivars ‘Polka’ and ‘Yamaska’. The trait Earliness is bilateral with significantly low GCAs for early ripening in ‘Clery’ and ‘Daroyal’ and significantly high GCAs for late ripening in ‘Yamaska’ and ‘Florence’. Crosses with these cultivars are likely to deliver populations with both high yield and an extended ripening period.     

Correlation between late blight resistance and foliage maturity type in potato

The genetics of race-non-specific foliage resistance against Phytophthora infestans, of foliage maturity type, and of their association in potato (Solanum tuberosum) were studied. Six progenies were derived from a half-diallel set of crosses between diploid potato clones that represented a broad pool within the genus Solanum and were free of any of the 11 known R genes for late blight resistance. The progenies were evaluated for resistance to late blight and for foliage maturity type, and five of them showed a significant correlation between the two traits. The correlation did not account for all variation that was present for both traits, as reflected in the analysis in which the relative AUDPC values were adjusted for foliage maturity type. The present study adds to previous results: resistance against P. infestans always coincides with late foliage maturity. However, the results also indicate that some selection for late blight resistance without affecting the foliage maturity type should be possible.     

Optimising potato breeding. I. The genotypic,environmental and genotype-environment coefficients of variation for tuber yield and other traits in potato (Solanum tuberosum L.) under different experimental conditions

Summary Coefficients of variation for genotypic differences, genotype-location, genotype-year and genotype-location-year interaction were computed from reported data of potato trials in order to use them in a decision support system. The obtained coefficients of variation not only varied considerably between traits, but also between trials within traits. It is argued that only parameter values representative for the pertaining breeding situation should be used for optimising a selection programme.     

Transmission of a Bacillus thuringiensis cry3Aa transgene from diploid to tetraploid potato using 4x-2x hybridization: effect of ploidy increase on transgene expression and implications for TPS hybrid production

The study examined the effect of ploidy elevation through unreduced gametes on transgene expression in potato. Tetraploid transgenic progenies were obtained from one tetraploid potato cultivar crossed with 2n pollen producing diploid clones harbouring an exogenous transgene (cry3Aa). Both single‐ and multiple‐insert diploid transgenic lines that were regenerated by Agrobacterium tumefaciens leaf disc inoculation were used in crosses. A DAS‐ELISA system and no‐choice feeding bioassay enabled characterization of the parental lines as either ‘high’ or low’ expressers of the Cry3Aa protein. High Cry3Aa expression was observed for both single‐insert transgenic diploids and their 4x‐2x progeny. On the contrary, 68% of 4x‐2x progeny derived from a multiple‐insert, diploid transgenic had significantly reduced Cry3Aa expression compared with the parent, with 32% demonstrating nearly complete silencing of the transgene. Multiple copies of a transgene, like homologous native genes, may be susceptible to transgene silencing following polyploidization. Therefore, incorporation of exogenous transgenes into a true potato seed (TPS) production system is feasible if a single‐insert diploid parent is used. Gene‐centromere mapping of the cry3Aa transgene demonstrated that a non‐transgenic refuge might be naturally created in a TPS hybrid system through genetic recombination.     

Cytometric and morphometric identification of diploid, tetraploid and pentaploid plants derived from Actinidia arguta (2n = 4x) crossed with A. deliciosa (2n = 6x)

Interspecific crosses between Actinidia arguta (In = 4x) and A. deliciosa (2n = 6x) were carried out in order to transfer cold resistance from a wild to the cultivated kiwifruit species. Of the 65 progenies obtained and analysed by flow cytometry, 16 were diploid, one was tetraploid and 48 were, as expected, pentaploid. Morphologically, the diploids can be distinguished from the pentaploids by their longer lamina. The existence of 5x progenies confirms the existence of gene flow between A. arguta and A. deliciosa, whereas the existence of 2x and 4x progenies provides evidence for parthenogenesis within the Actinidia genus following an interspecific cross. The study demonstrates the utility of flow cytometry for genomic analysis of progenies derived from interspecific crosses. Possible uses of both sexual and parthenogenetic progenies in the breeding and genetics of kiwifruit are discussed.     

Mapping of a gene (Vir) for a non-glaucous, viridescent phenotype in bread wheat derived from Triticum dicoccoides, and its association with yield variation

The introgression of desirable genes or alleles from the wild relatives of hexaploid wheat can be a valuable source of genetic variation for wheat breeders to enhance modern varieties. The UK Group 1 bread making variety Shamrock is an example where the introgression of genetic material from wild emmer (Triticum dicoccoides) has been used to develop a modern cultivar. A striking character of Shamrock is its unique viridescent colour compared to other UK wheats, a trait that coincides with a non-glaucous phenotype. A doubled haploid population segregating for the trait (Shamrock × Shango) was examined to map the location of Vir, and analyse any associated pleiotropic effects. The viridescence gene located to the distal end of the short arm of chromosome 2B. QTL analysis of productivity traits shows an association between Vir and a significant delay in senescence, resulting in an extension of the grain filling period. A stable yield QTL, accounting for up to a quarter of the variation in one case, was also identified at or near Vir, indicating significant yield benefits either by linkage or pleiotropy.     

Inheritance pattern of mungbean yellow mosaic disease resistance and gene action for different traits in mungbean (Vigna radiata (L.) Wilczek) under protected and unprotected field conditions

Understanding of mungbean yellow mosaic disease resistance is crucial to develop resistant varieties to combat worldwide threat of the disease epidemics. This study was aimed to determine nature of disease resistance in terms of number of genes governing it and genetics of related traits. Experimental site was located on 31.43°N and 73.06°E with an elevation of 186 m, and evaluation trials were conducted during spring season due to high disease epidemics in this season. Two contrasting genotypes, that is, NM 6‐68‐2 (resistant) and NM 1‐32‐1 (highly susceptible), were crossed to raise six populations, that is, P₁, P₂, F₁, F₂, BC₁ and BC₂ for evaluation under protected and unprotected field conditions using chi‐square test and generation mean and variance analysis. It was discovered that disease resistance was governed by two major genes with additive effects. Disease resistance can easily be incorporated through backcrossing and direct selection following hybridization. Direct selection should be practised at earlier generation for plant height, chlorophyll contents and number of seeds per pod due to preponderance of additive effects whereas at later generations for seed yield per plant, 100 seed weight, harvest index, number of pods per plant and pod length due to involvement of duplicate epistasis.