Inheritance of very high linoleic acid content and its relationship with nuclear male sterility in safflower

Safflower (Carthamus tinctorius L.) possesses the highest amount of linoleic acid among the 10 major vegetable oil crops of the world. Very high linoleic acid content is controlled by recessive alleles at a single locus Li. However, deviated segregations from the expected monogenic inheritance have been observed in crosses involving nuclear male‐sterile (NMS) lines. The present research was undertaken to study the inheritance of very high linoleic acid content in safflower and its relationship with nuclear male sterility. F₁, F₂, F₃, BC₁F₁ and BC₁F₂ seed generations were evaluated in a cross between CR‐142 (a line with very high linoleic acid content, 88%) and CL1 (an NMS line with wild‐type linoleic acid content, 74%). The genetics of linoleic acid content in male‐sterile plants was determined by testcrossing with CR‐142. The results confirmed monogenic inheritance. The analysis of the F₃ and BC₁F₂ to CL1 seed generations demonstrated a repulsion‐phase linkage between Li and Ms loci, the latter conferring the NMS trait. The recombination rate between Li and Ms was estimated to be 0.09.     

Development of cytoplasmic-genic male sterility in safflower

An interspecific cross was made between Carthamaus oxyacantha and the cultivated species C. tinctorius to develop a cytoplasmic‐genic male sterility (CMS) system in safflower. C. oxyacantha was the donor of sterile cytoplasm. The 3: 1 segregation pattern observed in BC₁F₂ suggested single gene control with dominance of male‐fertility over male‐sterility. The information obtained from crossing male sterile X male fertile plants in BC₁F₃ and BC₁F₄ generations showed statistically significant single gene (1: 1) segregation for male sterility vs. male fertility. The results demonstrated that C. tinctorius possesses a nuclear fertility restorer gene and that a single dominant allele restored fertility (Rf) in progeny carrying CMS cytoplasm of C. oxyacantha. Male sterility occurred with the homozygous recessive condition (rfrf) in a sterile C. oxyacantha cytoplasm background and not in the normal cytoplasm of C. tinctorius. The genetic background of different restorer lines of C. tinctorius having normal cytoplasm did not effect fertility restoration. The absence of male sterile plants in C. tinctorius populations ruled out the possibility of genetic male sterility. Normal meiosis in F₁ and BC₁F₂ ruled out a cytogenetic basis for the occurrence of male sterility.     

Construction and characterization of 3-S Lines, an alternative population for mapping studies in rice (Oryza sativa L.)

Most traits of agronomic importance in rice are quantitative in nature and are controlled by polygenes, called quantitative trait loci (QTL). Understanding the nature and effect of QTLs are important for rice breeding to achieve higher yield and stability. Single segment substitution lines (SSSLs or 3-S Lines) were developed through simple sequence repeats (SSR) marker-facilitated backcrossing methods for Hua-Jing-Xian 74 (HJX74) with the donor segment from six elite germplasm and was characterized. Complete genome survey was carried out with 258 polymorphic SSR markers. Polymorphism of the donors with the recurrent parent varied between 32.98 and 60.73% with an average of 47.81%. Japonica donors were more polymorphic than indica donors. Number of substitution segments per plant decreased with the advancement of backcross generations. In BC₂F_1, BC₃F₁, BC₃F₂ and BC₃F₃ the average number of substitution segment per plant were 12.5, 5.98, 1.69 and 1.46, respectively. Average size of substitution segments also decreased with the number of times plants were backcrossed and selfed. In BC₂F₁, BC₃F₁, BC₃F₂ and BC₃F_3, average size of the segments was 25.43, 22.38, 20.78 and 18.15 cM, respectively. The rate of reduction of segment size was more in backcross (11.99%) than selfing (7.15%) generations. Percent recovery of recurrent parent genome in BC₂F₁, BC₃F₁, BC₃F₂ and BC₃F₃ was 82.24, 92.55, 98.04 and 98.52%, respectively. A total of 111 SSSLs comprising of 43 unique types were developed in BC₃F₂ and BC₃F₃. The estimated length of the segments in SSSLs ranged from 2.00 to 64.80 cM with an average of 21.75 cM, and 6.05 to 48.90 cM with an average of 20.95 cM in BC₃F₂ and BC₃F₃, respectively. Total length of all substitution segments was 2367.5 cM that covered 704.50 cM (39.25%) of the entire rice genome. Effective development and successful utilization of 3-S Lines for analysis of QTLs and mapping of genes established the suitability of the SSR marker facilitated backcross breeding approach for 3-S Lines development and its utilization.     

Rhizobium specificity of Trifolium ambiguum M. Bieb × T. repens L. hybrid clovers

Growth of full-sib families of an F₁ interspecific hybrid between Trifolium ambiguum M.Bieb and T. repens L, and two generations of backcross hybrids (BC₁F₂ and BC₂F₁) with T. repens as the recurrent parent, were compared to their parental species. Plants were grown in a N-free medium and inoculated with Rhizobium leguminosarum biovar trifolii rhizobia effective on T. ambiguum or T. repens. Hybridisation produced progeny that nodulated with rhizobia from either T. ambiguum or T. repens, but plant growth varied. Mean weights of T. repens and hybrids, particularly F₁ and BC₁F₂, were higher when inoculated with a mixture of strains isolated from field grown T. repens than with the New Zealand inoculant strain for T. repens. When inoculated with the mix of rhizobia from T. repens, mean weights were 242, 189, 132, 125, and 100 mg/plant for T. repens, BC₂F₁, BC₁F₂, F₁ and T. ambiguum, respectively. However, although the mean weight of BC₂F₁ lines was significantly less than T. repens, there was considerable variation in individual full-sib families indicating the potential to select within BC₂F₁ hybrids for high plant growth/symbiotic nitrogen fixation. The weight of T. ambiguumplants inoculated with the New Zealand inoculant strain for hexaploid T. ambiguum was similar to T. repens inoculated with the mix of rhizobia from T. repens (253 and 242 mg/plant, respectively). Mean fresh weights of F₁ hybrid plants were similar when inoculated with rhizobia for T. ambiguum or T. repens (125 and 130 mg/plant, respectively). However, weight of T. repens, BC₁F₂ and BC₂F₁ hybrids inoculated with rhizobia for T. ambiguum were all less than 90 mg/plant. There was a significant relationship between plant fresh weight and ethylene production. The results indicate that measuring weights of inoculated plants growing in N-free media is a rapid initial method of screening a range of plant germplasm for plant growth/symbiotic nitrogen fixation rates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Successful backcrosses of somatic hybrids between Sinapis alba and Brassica oleracea with the Brassica oleracea parent

Somatic hybrids between Sinapis alba (2n= 24) and Brassica oleracea (2n= 18) have been backcrossed with the B. oleracea parent. Whereas backcrosses with the diploid B. oleracea parent were unsuccessful, 344 BC₁ seeds could be obtained from inter-valence crosses with tetraploid B. oleracea (2n= 4x= 36). The investigated 96 BC₁ plants segregated for morphological traits and for fertility. They were backcrossed with diploid B. oleracea or self-pollinated, depending on their male fertility. The BC₁F₂ and BC₂ progenies segregated well for the morphological traits. Disturbances were observed especially in the generative phase (flower development and pollen fertility). Both male fertile and male sterile BC₁F₂ and BC₂ plants were obtained and backcrossed or self-pollinated with the B. oleracea parent. The presence of either one of the parental or the cybrid organelle genomes was detected. In the progenies, a stable maternal inheritance of the organelle genome patterns was observed. Isozyme analyses revealed polymorphism for the leucine aminopeptidase (LAP) which was used for the identification of S. alba genes in the progenies. Cytological investigations showed a clear differentiation between the BC₁F₂ and BC₂ plants. Whereas the BC₁F₂ plants possess large numbers of chromosomes ranging from 34 to 40, the BC₂ material was strongly reduced to chromosome numbers ranging from 20 to 22. Preliminary investigation of the meiosis suggests the possibility of introgressions of S. alba-DNA into the B. oleracea genome.     

Production of intergeneric hybrids between Brassica juncea and Diplotaxis virgata through ovary culture, and the cytology and crossability of their progenies

The cytogenetic study was investigated in the intergeneric F₁ hybrid, F₂and backcross progenies (BC₁). The plants used were Brassica juncea(2n=36) and Diplotaxis virgata(2n=18). Three intergeneric F₁ hybrids between two species were produced through ovary culture. They showed 36 chromosomes. It might consist one genome of B. juncea and two genomes of D. virgata. The morphology of the leaves resembled that of B. juncea. The color of the petals was yellow that was like in D. virgata. The size of the petal was similar to that of B. juncea. The mean pollen fertility was15.3% and the chromosome associations in the first meiotic division were(0–1)_IV+(0–2)_III+(8–12)_II+(12–20)_I. Many F₂ and BC₁seeds were harvested after open pollination and backcross of the F₁ hybrids withB. juncea, respectively. The F₂seedlings showed different chromosome constitutions and the range was from 28 to54 chromosomes. Most seedlings had 38chromosomes followed by 36, 40 and 54. The BC₁ seedlings also showed different chromosome constitutions and the range was from 29 to 62. Most seedlings had both 40and 54 chromosomes followed by 36, 46 and52. In the first meiotic division of F₂ and BC₁ plants, a high frequency of bivalent associations was observed in all the various kinds of somatic chromosomes. Many F₃ and BC₂ seeds were obtained by self-pollination and open pollination of both F₂ and BC₁ plants, and by backcrossing both F₂ and BC₁plants with B. juncea, respectively,especially, three type progeny with 36, 40or 54 chromosomes. The somatic chromosomes of the F₃ and BC₂ plants were further investigated. The bridge plants between B. juncea and D. virgata with 36 chromosomes may be utilized for breeding of other Brassica crops as well as B. juncea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytogenetic study of Helianthus laevigatus and its F1 and BC1F1 hybrids with cultivated sunflower, Helianthus annuus

Although the wild sunflower species Helianthus laevigatus has not been extensively studied it may be considered for sunflower breeding as a potential source of desirable genes for Sclerotinia stalk rot resistance and high contents of proteins and linoleic acid in the seed. A set of six H. laevigatus populations was crossed to cultivated sun~ower lines and produced nine F₁ (2-14 plants) and 66 BC₁F₁ hybrid combinations (1-13 plants). Male sterility occurred in F₁ and BC₁F₁ hybrid combinations and pollen viability was lower in the progenies than in the parents (51.6-77.2%in F₁ and in F₁ and 4.8-34.0% in BC₁F₁). Meiosis was normal in the H. laevigatus populations It was found that this tetraploid species also occurred in a hexaploid form Numerous irregularities were observed in the meiosis of the F₁ interspecific hybrids During diakinesis, quadrivalents and hexavalents were recorded in addition to bivalents Dislocated chromosomes and chromosome bridges were present in the other phases The chromosome number in F₁ was 68 (tetraploid). Irregularities in chromosome pairing were observed in the interspecific hybrids at BC₁F₁. There were many univalents, and trivalents quadrivalents and hexavalents were also present The chromosome number in the BC₁F₁ generation ranged from 34 to 60. The occurrence of meiotic irregularities in the F₁ and BC₁F₁ interspecific hybrids indicates that H. laevigatus and the cultivated sunflower differ in genome constitution.     

Introgression of resistance to Columbia and Northern root-knot nematodes fromSolanum bulbocastanum into cultivated potato

Summary Resistance toMeliodogyne chitwoodi races 1 (MC1) and 2 (MC2) andM. hapla (MH) derived fromSolanum bulbocastanum was introduced into the cultivated potato gene pool through somatic fusion. The initial F₁ hybrids showed resistance to the three nematodes. Resistance to reproduction on roots by MC1 was accompanied by resistance to tuber damage in F₁ clones. Tuber damage sometimes occurred, however, in hybrids of BC₁ progeny resistant to reproduction on roots when MC2 and MH were the challenging nematodes. Resistance to reproduction was transferred into BC₁ individuals, but a greater proportion of BC₁ progeny was resistant to MC1 than to MC2 or MH. Resistance to MC1 appears to be dominant and discretely inherited. F₁ and BC₁ progeny were pollen sterile, but seed were produced from crosses using cultivated tetraploid pollen sources. Approximately 11 and 33 per cent of pollinations produced berries on F₁ and BC₁ pistillate parents, respectively. Seed yield increased fourfold overall in crosses with F₁ compared to BC₁ individuals.Abbreviations MC1 Meloidogyne chitwoodi race 1 - MC2 Meloidogyne chitwoodi race 2 - MH Meloidogyne hapla - Rf Reproductive factor     

Characterization of donor genome contents of backcross progenies detected by SSR markers in rice

Backcrossing is a trait introgression method of renewed importance in crops. The evolution of introgressed or substituted segments through backcross generations has been analyzed theoretically using simulations. In this study, the content of donor genomes, including donor segment number (DSN), donor segment length (DSL), and donor genome size (DGS), were directly analyzed in six crosses over three successive backcrosses using a set of single sequence repeat (SSR) markers covering the entire rice genome. The results of this analysis demonstrated that the average DSN in each genome was 8.39 in BC₂F₁, 4.13 in BC₃F₁, and 2.41 in BC₄F₁, decreasing nearly by half with each backcrossing. The average DSL was 33.43 cM (centiMorgans) in BC₂F₁, 29.04 cM in BC₃F₁, and 25.07 cM in BC₄F₁, display a progressive decrease slightly greater than 10% in each additional backcross generation. Meanwhile the average DGS was 280.51 cM in BC₂F₁, 119.97 cM in BC₃F₁, and 60.53 cM in BC₄F₁, decreasing 57.2% from BC₂F₁ to BC₃F₁ and 50.4% from BC₃F₁ to BC₄F₁. This revealed that the reduction in DGS was approximately 50% with each backcrossing. These results provide a guide for introgression or substitution of target chromosome segments from donors into recipients in backcross programs. Zhang-Ying Xi and Feng-Hua He contributed equally to this work.     

Backcross variability for grain yield in oat species crosses (Avena sativa L. x A. sterilis L.)

Summary Avena sterilis introductions from the Middle East were useful sources of genes for improving the grain yield of adapted A. sativa cultivars for midwestern US. Introgression of genes from A. sterilis materials into A. sativa oat breeding populations was readily accomplished through a backcrossing procedure. Backcrossing successfully accomplished the recombination required to introgress complexly inherited traits. The BC₁F₂, BC₂F₂, BC₃F₂, and BC₄F₂ generations appeared to be best for selecting high-yielding transgressive segregates from the A. sativa x A. sterilis crosses.Journal Paper No. J-7919 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50010. Project No. 1752.     

A major gene for low temperature germinability in rice (Oryza sativa L.)

Low temperature-induced retardation of seedling growth is a common problem in temperate rice-growing areas, at high altitudes of tropical and sub-tropical areas, and in areas with a cold irrigation water supply. Studies on low temperature germinability have revealed complex inheritance of the trait. The purpose of this study was to identify the gene(s) for low temperature germinability using Italica Livorno as a donor parent. The frequency distributions for the germination rate at 15 °C in the F₂ and BC₁F₁ populations showed continuous segregation, suggesting that low temperature germinability was under polygenic control. Since some lines in the BC₁F₁ population showed vigorous low temperature germinability similar to that of Italica Livorno, backcrosses until the BC₅F₁ generation was carried out using Hayamasari as the recurrent parent. Clear segregations of low temperature germinability were observed in the BC₅F₁ and BC₅F₂ populations. The distribution of low temperature germinability fitted a single-gene segregation, indicating that a single dominant gene with a large effect was transferred to Hayamasari. This gene is tentatively symbolized as Ltg(t). Low temperature germinability of near isogenic lines for Ltg(t) was similar to that of Italica Livorno. Ltg(t) should greatly contribute to the improvement and manipulation of low temperature germinability in rice breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Potential of wild germplasm for increasing yield of grain sorghum

Summary Sorghum [Sorghum bicolor (L.) Moench] backcross populations containing 3 to 50% wild germplasm were evaluated in south central India for grain yield and nine related traits. No individual BC₀F₂- to BC₂F₂-derived lines were high transgressive segregates for grain yield. Only 1.5% of all BC₃F₂- or BC₄F₂-derived lines were transgressive segragates, with 26% higher mean grain yield than their respective recurrent parents. The ten highest-yielding BC₂F₂- to BC₄F₂-derived lines per mating having parent CK60B yielded an average of 14% more than CK60B, which was, at the 5% level, a statistically significant difference. However, the increased yield was associated with increased plant height. The highest-yilding lines from RS/R/A2725 x virgatum and RS/R/A2725 x verticilliflorum were an average of 13.5% higher-yielding than RS/R/A2725 (a significant difference) and were equal in plant height. Selection increased BC₂ mean grain yields by 6 to 27%. Population mean yield, mean yield of selected lines, and frequency of high-yielding lines were highest in the BC₄.Journal paper no. 380, ICRISAT, Patancheru, India; Journal paper no. J-11114, Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, USA.     

Inheritance of black leaf mold resistance in tomato

Summary Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC₁F₂-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC₁F₂-358-4-13 and CL5915-93D₄-1-0-3). For each cross, six generations, i.e. P₁, P₂, F₁, F₂, BC₁F₁ and BC₁F₂ were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F₂ in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC₁F₂ data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.     

Comparing mating designs to restore seed production of interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum

Interspecific hybrids between Trifolium uniflorum and cultivated white clover (Trifolium repens) have highly useful characteristics for temperate pastoral systems derived from both parent species. However, the early hybrids (F₁ and BC₁) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC₁F₁ generation produced lower‐than‐expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover corrected these deficiencies and created new variation. Seed numbers were also returned to near target levels by recurrent selection within the BC₁ generation. Thus, it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. The BC₁F₂ and BC₂F₁ generations produced high seed numbers per plant, along with reasonable variation. Both of these second‐generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits.     

Introgression of Cajanus platycarpus genome into cultivated pigeonpea, C. cajan

Summary Cajanus platycarpus, an incompatible wild species from the tertiary gene pool of pigeonpea (C. cajan (L.) Millspaugh), has many desirable characteristics for the improvement of cultivated varieties. To necessitate such transfers, embryo rescue techniques were used to obtain F₁ hybrids. The F₁ hybrids were treated with colchicine to obtain tetraploid hybrids, that were selfed to obtain F₂, F₃ and F₄ progenies. All of the hybrids and subsequent progenies had an intermediate morphology between the two parents. Backcrossing of the tetraploid hybrids with cultivated pigeonpea was not possible given embryo abortion, with smaller aborted embryos than those obtained in the F₀ parental cross.As a route of introgression, diploid F₁ hybrids were backcrossed with cultivated pigeonpea and BC₁ progeny obtained by in vitro culture of aborting embryos. BC₂ plants were obtained by normal, mature seed germination. Although embryo rescue techniques had to be used to obtain F₁ and BC₁ plants, it was possible to produce BC₂ and subsequent generations through direct mature seed. Every backcross to cultivated pigeonpea increased pollen fertility and the formation of mature seeds.Special project assistant till December, 2003.     

Interspecific hybrids between helianthus PetiolarisNutt. and H. Annuus L.: Effect of backcrossing on meiosis

Summary Interspecific substitutions of the nucleus of Helianthus annuus (2n=34) into the cytoplasm of H. petiolaris (2n=34) were obtained by successive backcrossing using cultivated sunflower, H. annuus, as the recurrent pollen parent.Meiosis in the F₁ was characterized by multivalents, suggesting that 10 of the 34 chromosomes were heterozygous for chromosomal interchanges. An additional pair of chromosomes also contained a paracentric inversion. Continued backcrossing resulted in rapid elimination of the meiotic aberrations evident in the F₁. In the BC₁, 1 of 11 plants had normal meiosis and by the BC₂, only 13 of 54 plants had meiotic aberrations similar to those of the F₁. However, trisomic progeny (2n=35) were found in 3 of the 11 BC₁ plants and 20 of the 54 BC₂ plants. No meiotic aberrations were observed in BC₃ or BC₄ plants. Plants with indehiscent anthers, and considered to be male sterile (M.S.), first occurred in the BC₁ and, by the BC₂, 51 of 54 plants were M.S. All 19 BC₃ and 16 BC₄ plants were M.S. Preliminary investigations suggest that the pollen from such plants is sterile and that the sterility is cytoplasmic rather than genetic.Disc-flower measurements were a useful technique for selecting samples at the correct stage of microsporogenesis, but could not be used to distinguish between successive backcrosses.     

Genetics of grains per spike in durum wheat under normal and late planting conditions

Parental, F₁, F₂, BC₁, BC₂, BC₁₁, BC₁₂, BC₂₁, BC₂₂, BC₁ self and BC₂ selfed generations of three crosses involving six cultivars of durum wheat (Triticum durum Desf.) were studied for grains per spike under normal and late sown environments to analyze the nature of gene effects. A 10-parameter model did not fully account for the differences among the generation means. In two cases more complex interactions or linkage were involved in the inheritance of grains per spike in durum. Both digenic and trigenic epistatic interactions had a role in controlling the inheritance of grains per spike, however, trigenic interactions contributed more than digenic interactions. Non-fixable gene effects were many times higher than fixable ones in all three crosses and in both sowing environments indicating a major role of non-additive gene effects in the inheritance of this trait. Duplicate epistasis between sets of three genes under both environments was recorded for the cross Raj 911 × DWL 5002. Epistatic interactions, particularly the trigenic ones, contributed the maximum significant heterosis. Epistatic interactions involving dominance in the F₂ generations caused significant inbreeding depression. Selective diallel mating and/or biparental mating could be used for amelioration of grains per spike in durum wheat.     

Conversion of the genic male sterility (GMS) system of bell pepper (Capsicum annuum L.) to cytoplasmic male sterility (CMS)

Non‐pungent bell pepper (Capsicum annuum L.) lacks the cytoplasmic male sterility (CMS) nuclear restorer allele, Rf, and CMS cannot be employed in its F₁ hybrid seed production. To demonstrate that the genic male sterility (GMS) system in non‐pungent bell pepper can be converted to the CMS male sterility system, the conversion of GMS to CMS for non‐pungent bell pepper line GC3 was conducted by introgression of S‐type cytoplasm and the Rf allele from tropical pungent donors. After morphological traits were evaluated, two lines from BC₁F₁ containing S‐type cytoplasm and four lines from BC₂F₂ containing Rf allele, phenotypically similar to GC3, were obtained and could be employed as CMS male sterile lines and restorer lines for non‐pungent bell pepper. Four molecular markers potentially linked to traits of interest were also evaluated in BC₁F₁ and BC₁F₂ populations. This is the first time that GMS has been successfully converted to CMS in bell pepper, a significant contribution for bell pepper hybrid seed production.     

Development of Bruchid-Resistant Mungbean Line Using Wild Mungbean Germplasm in Thailand

A mungbean (V. radiata) line (BC₃F₃ generation) which is resistant to two species of bruchid beetles (Callosobruchus chinensis and C. maculatus) was successfully developed in Thailand using a wild mungbean variety (V. radiata var. sublobata). One accession (TC1966) of wild mungbean was found to be completely resistant to C. chinensis and C. maculatus occurring at Chainat Field Crops Research Center in Thailand. The resistance was controlled by a single dominant gene (R). A breeding program to develop a bruchid-resistant mungbean cultivar with good agronomic characters under the environmental conditions of Thailand was initiated in 1987.‘Chainat 60’ (‘CN60’), a recommended mungbean cultivar in Thailand, was crossed with TC1966 to incorporate the resistance gene. Agronomic characters of the hybrids were improved by recurrent backcrossing using ‘CN60’ as a pollen parent. Seed yield per plant, days to flowering, and seed size of the bruchid-resistant BC₃F₂ population reached the level of ‘CN60’ after three consecutive backcrossings. Bruchid-resistant line (BC₃F₃, R/R) was selected from individual BC₃F₂ plants.     

Tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum obtained through manipulation of ploidy and endosperm balance number (EBN)

The objectives of this study were to evaluate the tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F₁ triploid, BC₁ pentaploid‐near pentaploid and BC₂ tetraploid–near tetraploid hybrids. The F₁ triploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overcome. Indeed, the triploids produced 2n eggs, thus giving a compatible maternal to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) × 4x(3EBN) crosses. The tolerance to low temperatures of BC₁ and BC₂ hybrids was lower than that of the F₁. However, a number of genotypes were identified which were able to withstand temperatures down to ‐5°C. Some BC₂ hybrids were also tested for their tolerance to tuber soft rot, and some resistant hybrids were detected. A number of them combined the capacity for cold acclimatization with tolerance to tuber soft rot. These hybrids have an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum.