F2 Selection Research Articles

Genetic Analysis of Vitamin C Content in Rapeseed Seedlings by the Major Gene Plus Polygene Mixed Effect Model.

Rapeseed (Brassica napus L.) seedlings are rich in vitamin C (Vc), which is beneficial for humans. Understanding the genetic variance in Vc content has practical significance for the breeding of "oil-vegetable dual-purpose" rapeseed. In this study, the joint segregation analysis of a mixed genetic model of the major gene plus polygene was conducted on the Vc content in rapeseed seedlings. Six generations, including two parents, P1 (high Vc content) and P2 (low Vc content), F1, and the populations of F2, BC1P1, and BC1P2 from two crosses were investigated. Genetic analysis revealed that the genetic model MX2-A-AD was the most fitting genetic model, which indicates that Vc content is controlled by two additive major genes plus additive and dominance polygenes. In addition, the whole heritability in F2 and BC1P1 was higher than that in BC1P2. The largest coefficient of variation for Vc content appeared in the F2 generation. Therefore, for Vc content, the method of single cross recross or single backcross are suggested to transfer major genes, and the selection in F2 would be more efficient than that in other generations. Our findings provide a theoretical basis for the quantitative trait locus (QTL) mapping and breeding of Vc content in rapeseed seedlings.

Reproducible Quantitative Trait Loci for Resistance to Soft Rot Caused by Dickeya dianthicola Derived from the Wild Potato Solanum microdontum (PI 458355) Are Located on Chromosomes 1, 3, and 5.

The potato wild relative Solanum microdontum is a breeder-friendly source of genetic resistance to soft rot. Our objectives were to (i) identify loci associated with soft rot resistance in S. microdontum germplasm and (ii) develop bi-parental populations in a self-compatible S. tuberosum genetic background to recover segregating F2 progenies, construct a linkage map, and identify quantitative trait loci (QTLs). Under objective (i), tubers from 103 S. microdontum genotypes from the United States Potato Genebank were inoculated with a high virulence strain of Dickeya dianthicola, and lesion size was measured after a 24-h incubation period at 30°C. Association analysis using 3,490 polymorphic Infinium array SNP markers identified soft rot resistance loci on chromosomes 1, 2, 3, 5, 7, 8, 11, and 12. Under objective (ii), a resistant S. microdontum accession PI 458355 was crossed with a highly fertile, self-compatible, diploid S. tuberosum pollen parent (PI 654351) to generate segregating F2 populations. Composite interval mapping was conducted using a genetic linkage map with 970 GBS-based SNP markers. Reproducible QTLs were detected on chromosomes 1, 3, and 5, explaining 11, 13, and 23% of the phenotypic variation, respectively. Homozygous S. microdontum alleles at the QTL on chromosome 5 and heterozygous or homozygous S. microdontum alleles at QTLs on chromosomes 1 and 3 significantly decrease lesion size compared with the homozygous S. tuberosum parent. The germplasm created in these studies provides a resource for studying traits from S. microdontum, and we can use the advanced F2 selections for future potato improvement. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Registration of R16‐45 as a flood‐tolerant, high‐yielding soybean germplasm line

AbstractR16‐45 (Reg. no. GP‐526, PI 704118) is a high‐yielding soybean [Glycine max (L.) Merr.] breeding line with flood tolerance at early reproductive stages released as germplasm by the Arkansas Agricultural Experiment Station in 2023. It is an F2 selection from the cross between the flood‐tolerant breeding line R07‐6669 and the high‐yielding Arkansas cultivar ‘UA 5612’. R16‐45 is a conventional (non‐genetically modified) soybean with a relative maturity of 5.6. Plants have determinate growth habit, white flower color, and buff hilum color. It has gray pubescence, tan pod wall at maturity, and yellow cotyledons with a dull yellow seed coat. R16‐45 showed high yield potential and broad adaptability across 17 environments in Arkansas and other southern states, with an average of 4145 kg ha−1 (95.3% of the checks’ mean). Six years of field evaluations for flooding tolerance showed that R16‐45 is consistently tolerant to 8‐to‐10‐day flooding stress at the R1/R2 growth stages (average flood damage score of 3.6, compared with 6.0 from the reference checks). In addition, R16‐45 is resistant to stem canker. Given substantial yield losses associated with flooding stress and stem canker, R16‐45 is a valuable germplasm source for public and private soybean breeding programs attempting to incorporate novel genetic diversity into their breeding pipeline.

The control of genetic parameters on grain yield and its components in hexaploid wheat

Controlling of genetical parameters on grain yield and its components were study in six generation (P1,P2,F1,F2,B1 and B2) for two crosses of hexaploid wheat, Triticum aestivum L. (Iba-99 x Reyna-27) and (Abochareeb-3 x Jawaher-20) to estimate: gene action parameters, components of genetic variance, environmental variance, average degree of dominance, broad sense heritability, narrow sense heritability and expected genetic advance from selection in F2. Two models were applied in analyzing the component of generation means and the total phenotypic variance for studied traits in six generations for each cross were analyzed. The results showed that: The three parameter genetics models were adequate for the inheritance of spike number and grain yield in tow crosses and there were significant additive, dominance and epistatic effects on the other traits. Over dominance for studied traits, but partial for 100 grain weight in the first cross, plant height and spike length in the second cross. Narrow sense heritability and expected genetic advance were high for most traits.

The effect of individual selection on sperm motility in tropical abalone Haliotis squamata

High-quality broodstock is required to support successful cultivation activities of the tropical abalone. This study aimed to find out the structure of the sperm under the influence of individual selection. A total of 50 eggs per batch were measured in egg diameter, calculated by the degree of fertilization and hatching rate. Sperm collection is carried out from the natural spawning of male abalone from the wild (F0) and the selected offspring from individual Fillial-1, F2, and F3 selections. Samples of sperm were collected by artificial spawning and analyzed using the Sperm Class Analyzer® CASA System. The results showed that the wild abalone (F0) had the highest hatching rate but was not significantly different from other derivatives (P > 0.05). The average spermatozoa was 2.39 million cells/m, with the highest spermatozoa (F0) of 7.110 million cells/ml. The most increased sperm motility and rapid velocity were in the wild (89.78%; 34.00%) and the lowest of F2 (22.00; 4.00%). A significant difference in sperm motility and rapid velocity were found between F0 and other treatment. The consequences of individual selection will aid in studying reproductive factors and sperm motility, which are most likely crucial in tropical abalone fertilization.

Новый экологически пластичный сорт рапса ярового Эребус

The spring rapeseed variety Erebus was developed in 2007–2018 by individual selection in F2 from the hybrid combination LK-443-04 × LK-654-06. Ac-cording to the competitive variety trials conducted by the All-Russian Research Rapeseed Institute during 2013-2018, variety Erebus had better results than standard variety Rif in seed yield by 0.12 t/ha or 5.8% and in oil yield the results were higher by 0.08 t/ha. The content of glucosinolates in the seeds was 2.8 µmol/g lower than that one of variety Rif. In 2022, Erebus has been included in the National List of Varieties (Patent № 11441) and approved for pro-duction use in the Central (3), Volga-Vyatsky (4), Central Chernozem (5), Middle Volga (7), Ural (9), West Siberian (10), East Siberian (11) and Far East (12) regions of the Russian Federation.

Consequence of cyclic pollen selection for heat tolerance on the performance of different generations in maize (Zea mays L.)

The reproductive stage in many crops, including maize, is very sensitive to heat stress and the genetic overlap between gametophytic and sporophytic phase gives an opportunity to select superior stress tolerant genotype at gametophytic stage. An attempt was made to evaluate the response of cyclic pollen selection in the F1 and F2 generations on the performance of F3 generation progenies for seed yield and yield contributing traits under natural heat stress conditions. In this direction three groups of F3 progenies, namely (i) pollen selection in F1 and F2 generations (GG), (ii) pollen selection only in F2 generation (CG), (iii) no pollen selection in F1 and F2 generations (CC) were screened for heat stress at Agricultural Research Station (ARS), Bheemarayanagudi. The GG progenies recorded significantly higher chlorophyll content, more number of pollen grains per anther and less pollen sterility compared to CG and CC group of progenies under heat stress. Further, the F4 progenies obtained through cyclic pollen selection (in F1, F2 and F3) were also tested for heat stress tolerance at seedling stage. The significant improvement for heat stress tolerance was recorded in F4 progenies derived through cyclic pollen selection as compared to control (no pollen selection for heat tolerance in any generation) F4 progenies. The results indicated that cyclic pollen selection in F1, F2 and F3 generations improved the heat stress tolerance of the progenies in the succeeding generations. To provide genetic evidence for the effect of pollen selection for heat tolerance, the control F2 (C) and selected F2 (G) populations were compared for the segregation of SSR markers. The selected F2 (G) population showed significant deviation from normal Mendelian ratio of 1:2:1 and showed skewness towards the alleles selected from male parent. The results provide strong evidence for an increase in the frequency of parental alleles in the progenies that impart heat stress tolerance.

Statistical investigation of selection in f2 on the basis of x2 method in solving issues related to mendel's laws

Statistical investigation of selection in f2 on the basis of x2 method in solving issues related to mendel's laws

Selection for Yield, Rust Resistance and Quality Traits in Early Generations of Giza 171 X Sids 12 Cross of Bread Wheat

The F2 and F3 populations resulting from Giza171 × Sids12 hybrid were used from 2015/2016 to 2018/2019 seasons at Sakha Agricultural Research Station to study the inheritance of some agronomic characters and resistance to rusts diseases and select new bread wheat families with high yield potential and good grain quality. Giza171 was preferable for yield and its components, while Sids12 was desirable for earliness characters. The ranges of the F2 and F3 populations went out the means of its parents for the studied characters. All characters showed moderate to high values of broad sense heritability in F2 and F3 generations. The best responsive characters to selection in F2 were No. spikes plant-1 and grain yield plant-1, while days to maturity was the least responsive character. F3 families hadhighly significant variations for all studied characters. Correlation coefficients referred that grain filling rate, followed by No. spikes m-2, then kernels weight spike-1, later the No. kernels spike-1 had the most impact on grain yield in F3 families. The resistance of yellow and leaf rusts was controlled by two dominant genes and stem rust was controlled by two complementary dominant genes. Thirteen promising families were high yielding, resistant to the three rusts and have appropriate height were selected to promote to the next advanced of segregating generations and five of them were preferable for grain quality of wheat.

Proposed Research for Innovative Solutions for Chickpeas and Beans in a Climate Change Scenario: The Mediterranean Basin

In order to gain insight into the complex molecular networks driving legume adaptation caused by climate change, it is necessary to deeply characterize the existing germplasm in response to the environmental constraint predicted to worsen in the near future: drought. In this study, we propose to perform a three-year deep agronomic characterization of local genotypes of selected legumes in abiotic stressing conditions through controlled and field experiments conducted in several countries of the Mediterranean basin (Italy, Spain, Algeria, Tunisia, Turkey, Lebanon, and Croatia). These phenotypic analyses will be integrated with a multi-omic approach aiming at identifying the key players involved in the modulation of the analyzed traits that includes the analysis of the plant methylome, transcriptome, and proteome. Following this approach, we propose to deliver epigenomic markers linked with rapid adaptation mechanisms in response to drought. Besides, new genetic variability by breeding could be created in stressing conditions and produce the basis for the obtainment of more productive cultivars in worsening environments. The epigenetic marks identified in “omic” activities will be validated in molecular marker-assisted selection in F2–F4 populations. Finally, specific rhizobia strains for the best evaluated genotypes will be identified in order to enhance symbiotic nitrogen fixation in drought stress conditions with selected cultivars.

Determination of drought tolerance related traits in <i>Helianthus argophyllus</i>, <i>Helianthus annuus</i>, and their hybrids

Drought is a major constraint for sunflower (Helianthus annuus) production worldwide. Drought tolerance traits have been identified in the related wild species Helianthus argophyllus. This study was initiated to develop sunflower drought-tolerant genotypes by crossing cultivated sunflower with this species and analyze drought tolerance traits in the H. annuus and H. argophyllus populations, H. annuus intraspecific hybrids, and H. annuus × H. argophyllus interspecific hybrids along with the commercial hybrid Hysun-33 under three stress regimes: exogenous application of ABA, both by foliar spray and irrigation, and 5% PEG-induced osmotic stress. H. argophyllus populations had a significantly lower leaf area and higher water-use efficiency and leaf cuticular wax content under all treatments, and maintained a higher net photosynthetic rate and stomatal conductance under osmotic stress. Small leaf area and high cuticular waxes content of the wild species were, however, not inherited in interspecific hybrids which suggested for selection in F2 for these traits. Therefore, transgressive plants were selected in the F2 population to establish F3 plant progenies with silver-leafed canopy of H. argophyllus which showed higher achene yield under stress condition. These results are discussed with a view to using H. argophyllus to improve drought tolerance in cultivated sunflower.

Effectiveness of selection, parent-offspring correlation and regression in bacterial blight resistance genes introgressed rice segregating population

ABSTRACT: The effectiveness of early generation selection was practiced in bacterial blight resistance genes introgressed F2 and F2:3 population of the cross CB 174 R × IRBB 60 in rice. F2 Selection have been proved to be robust and effective tool in crop improvement program. Selection differential was positive for all studied traits. Selection response was high for number of grains, thus indicating the effectiveness of selection for these character. Realized heritability was found high for number of grains and thousand grain weight, suggested that direct selection was effective. Expected selection response and predicted genetic gain was high for number of grains. Parent-offspring correlation showed low but significance association for number of productive tillers (r=0.47**, P<0.01), single plant yield (r=0.35**, P<0.01) and (r=0.30*, P<0.05) panicle length in F2 and F2:3 generation indicates that selection was fruitful in early generation. Statistically regression coefficient was not significant linear dependence of the mean of F2 and F2:3 generation.

Registration of 40 Converted Germplasm Sources from the Reinstated Sorghum Conversion Program

Forty sources of late‐maturing sorghum [Sorghum bicolor (L.) Moench] germplasm registered with the National Plant Germplasm System as genetic stocks (Reg. No. GS‐744, PI 674473 to Reg. No. GS‐783, PI 674512) were converted to early‐maturing, dwarf‐height BC1F3 families and released by the National Sorghum Foundation, the United Sorghum Checkoff Program, the USDA‐ARS, and NuSeed/MMR Genetics in 2014. The sorghum working groups represented include zerazera, caudatum, conspicuum, durra, nandyal, nigricans, guineense, caudatum‐kafir, caudatum‐guineense, caudatum‐nigricans, caudatum‐durra, durra‐kafir, durra‐bicolor, caffrorum‐bicolor, and durra‐dochna. Conversion was accomplished by crossing late‐maturing tropical accessions to inbred BTx406 in a short‐day nursery with selection of early‐maturing, short genotypes within F2 segregating populations in a long‐day nursery. Early‐flowering short F2 selections were genotyped, and one F2 plant with the greatest proportion of the exotic genome from each accession was backcrossed to the plant introduction. The resulting BC1F1 was self‐pollinated, and selections of early‐maturing, short genotypes within BC1F2 segregating populations were made. Early‐flowering, short BC1F2 selections were genotyped, and one BC1F2 plant with the greatest proportion of the exotic genome was self‐pollinated. The BC1F2:3 families, RSC02‐BC1‐10‐F3bk to RSC149‐BC1‐12‐F3bk, represent new sources of germplasm from the USDA‐ARS sorghum collection readily usable in temperate zones worldwide.

Broadening genetic diversity in Brassica napus canola: Development of canola-quality spring B. napus from B. napus×B. oleracea var. alboglabra interspecific crosses

Rahman, H., Bennett, R. A. and Seguin-Swartz, G. 2015. Broadening genetic diversity in Brassica napus canola: Development of canola-quality spring B. napus from B. napus × B. oleracea var. alboglabra interspecific crosses. Can. J. Plant Sci. 95: 29-41. The narrow genetic base in spring Brassica napus (AACC) canola is a limitation for continued improvement of this crop. This research focused on broadening of genetic diversity in spring canola by using B. oleracea (CC). Seeds of B. oleracea contain high levels of erucic acid and glucosinolates, which are undesired in canola. Therefore, inheritance of these traits and the prospect of developing spring canola with allelic diversity introgressed from B. oleracea were investigated in B. napus×B. oleracea interspecific progenies. Zero-erucic plants in F2 generation occurred at a lower frequency than expected based on segregation involving only the C-genome erucic acid alleles. Selection in F2 to F3 focused on zero erucic acid, while focus in later generation was...

Efficiency of marker-assisted selection for ascochyta blight in chickpea

SUMMARYThe extent to which markers have been used in chickpea breeding programmes has not been clearly determined. In the current study, phenotypic and marker-assisted selection (MAS) were employed to select blight resistant genotypes, comparing the effectiveness of both methods. The phenotypic evaluation showed that the resistance could be recessive in the material employed. However, the high distorted segregation towards the susceptible parent detected on linkage group four (LG4) could also explain the phenotype distribution of resistance. Phenotypic selection in F2:4and F2:5generations lead to an increase in the frequency of the allele associated with the resistance of the markers CaETR and GAA47, indicating the usefulness of these markers for MAS. The markers TA72 and SCY17 could be also useful for MAS but the high distorted segregation towards the susceptible parent in the region where these markers are located could explain their low effectiveness. The costs associated with phenotypic selection and MAS for ascochyta blight resistance during three cycles of selection are presented in the current study, showing that MAS was more expensive than phenotypic selection. Nevertheless, the use of markers reduced the time taken to select resistant lines. The markers analysed in the current study were useful to select genotypes resistant to ascochyta blight in chickpea breeding programmes, allowing pyramiding genes or quantitative trait loci (QTL) related to different pathotypes. It is recommended that MAS should be employed in early generations of chickpea breeding programmes for the four QTL analysed because this makes it possible to develop populations with a high frequency of the favourable alleles conferring resistance to blight.

Registration of Partially Converted Germplasm from 44 Accessions of the USDA‐ARS Ethiopian and Sudanese Sorghum Collections

Forty‐four sources of late‐maturing sorghum [Sorghum bicolor (L.) Moench] germplasm registered with National Plant Germplasm System as genetic stocks (Reg. No. GS‐655, PI 665639 to Reg. No. GS‐698, PI 665682) were converted to early‐maturing, dwarf‐height F3 families and were released by the National Sorghum Foundation, the United Sorghum Checkoff Program, the USDA‐ARS, and MMR Genetics in 2012. The sorghum working groups represented in these partially converted materials include zerazera, caudatum, caudatum‐kafir, caudatum‐guineense, caudatum‐nigricans, caudatum‐durra, nandyal, durra, durra‐kafir, and durra‐bicolor. Conversion was accomplished by crossing photoperiod‐sensitive tropical accessions to elite line BTx406 during the winter in Puerto Vallarta, Mexico with selection of early‐maturing, short (generally 2‐ or 3‐dwarf) genotypes within F2 segregating populations under long‐day, summer conditions in Vega, TX. Early‐flowering short F2 selections were genotyped by sequencing, and five F2 plants with the greatest proportion of the exotic genome from each accession were selfed in Puerto Vallarta. The resulting F2:3 germplasm families, RSC02‐3sel(bulk) to RSC149‐3sel(bulk), represent new sources of germplasm from the USDA‐ARS collection of a height and maturity readily usable to temperate‐zone areas of the world. This germplasm will be useful in breeding programs by providing new genetic diversity from tropical accessions currently not available for use in hybrids.

Registration of ‘B2’ Connecticut Broadleaf Cigar‐Wrapper Tobacco Resistant to Fusarium Wilt, Tobacco Mosaic Virus, Cyst Nematodes, and Blue Mold

‘B2’ Connecticut broadleaf cigar‐wrapper tobacco (Nicotiana tabacum L.) (Reg. No. CV‐124, PI 664300) is a male‐sterile hybrid released by the Connecticut Agricultural Experiment Station and is resistant to Fusarium wilt, Tobacco mosaic virus (TMV), the tobacco cyst nematode [TCN; Globodera tabacum tabacum (Lownsbery and Lownsbery 1954) Stone 1973], and blue mold [caused by Peronospora tabacina de Bary Adam 1933 (= Peronospora hyoscyami de Bary 1863 f. sp. tabacina Skalicky 1964)]. Initial crosses were made in 1987 between VA‐81 and PD4 flue‐cured tobacco and three broadleaf inbreds resistant to Fusarium wilt [caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. nicotianae (J. Johnson) W.C. Snyder & H.N. Hans.] and TMV. F2 selections were backcrossed twice to broadleaf lines, inbred and selected across 12 generations using bulk modified single‐seed descent with 2% of plants (20 plants of 1000) selected most years; selection for TMV and TCN resistance was conducted in greenhouse screens with fewer plants. Lines were field selected for reduced ozone weather fleck. One F12 selection was backcrossed again to the broadleaf cultivar ‘Scantic’ and inbred via pedigree selection across 10 generations with field and greenhouse selection. Progeny testing was used to select F8 plants homozygous for resistance to TCN and for hypersensitive TMV resistance from Nicotiana glutinosa L. A superior male‐fertile inbred (MF‐2) resulting from 27 generations of selection for broadleaf characteristics with 8 cycles of selection each for Fusarium wilt, TMV and TCN resistance was identified and crossed with a male‐sterile CT broadleaf line resistant to TMV and Fusarium wilt (MS‐1) to produce the F1 male‐sterile hybrid B2.

Plant selection in F2 segregating populations of papaya from commercial hybrids

The objective of this paper was to estimate the genetic parameters and additive genetic values in segregating populations of papaya using the mixed model methodology. Two F2 populations from Tainung and Calimosa hybrids were evaluated. The experimental design was an augmented block with four replicates, and Golden and Calimosa cultivars were the common treatment. Estimates of individual heritability were high for fruit length (FL) and weight (FW), moderate for fruit diameter (FD), and low for total soluble solids (TSS) and fruit firmness (FF). Considering FF and TSS as main traits for selection, genotypes of Calimosa-F2 population showed better performance to FF, but worse concerning TSS. It was selected 18.3% and 24.6% of plants from Tainung-F2 and Calimosa-F2 populations, respectively. Negative correlation between TSS and FF was not able to reduce the genetic gains. The segregating populations from Calimosa hybrid are more promising for the selection of papaya lines.

Response to Early Generation Selection for Resistance to Rice Kernel Fissuring

ABSTRACTThe value of milled rice (Oryza sativa L.) depends on the percent whole versus broken kernels after milling. Kernel fissures caused by pre‐ or postharvest stresses are the leading cause of breakage on milling. ‘Cypress’ is known to be more fissure resistant (FR) than most cultivars, but breeding success has been limited by a lack of ability to identify FR among F2 and F3 progeny. An induced‐fissuring method wherein small samples of seed are evaluated for fissure rates after controlled exposure to humid laboratory conditions can distinguish FR among pure‐breeding rice cultivars. To measure the efficacy of the induced‐fissuring system for evaluating FR among segregating breeding progeny, we applied divergent selection for FR and fissure susceptibility (FS) on seed harvested from ∼300 Cypress (FR) × ‘LaGrue’ (FS) F2 plants and evaluated selection success using seed from F2:3 plants grown in Arkansas and Texas. A second round of divergent selection was made among F3 progeny followed by F3:4 progeny testing. Fissure susceptible F2:3 progeny fissured twice as much as FR progeny, with an average response to selection of 13.5%. Response to F3 selection was smaller (averaging 2.6%), suggesting some fixation of alleles due to the F2 selections. Narrow‐sense heritabilities (h2) were 0.54 and 0.73 for the FR and FS F2 selections, respectively. This study documented successful early‐generation selection for FR, opening new opportunity for breeders to develop rice cultivars improved for this important trait.

Genetic Analysis of Cryotolerance in Cotton During the Overwintering Period Using Mixed Model of Major Gene and Polygene

The joint analysis of the mixed genetic model of major gene and polygene was conducted to study the inheritance of cryotolerance in cotton during the overwintering period. H077 (G. hirsutum L., weak cryotolerance) and H113 (G. barbadence L., strong cryotolerance) were used as parents. Cryotolerance of six generation populations including P1, P2, F1, B1, B2, and F2, from each of the two reciprocal crosses H077×H113 and H113×H077 were all investigated. The results showed that cryotolerance in cotton during the overwintering period was accorded with two additive major genes and additive-dominance polygene genetic model. For cross H077×H113, the heritabilities of major genes in B1, B2, and F2 were 83.62, 76.84, and 90.56%, respectively; and the heritability of polygene could only be detected in B2, which was 7.76%. For cross H113×H077, the heritabilities of major genes in B1, B2, and F2 were 67.42, 68.95, and 83.40%, respectively; and the heritability of polygene was only detected in F2, which was 6.51%. In addition, the whole heritability in F2 was always higher than that in B1 and B2 in each cross. Therefore, for the cryotolerance breeding of perennial cotton, the method of single cross recombination or single backcross should be adopted to transfer major genes, and the selection in F2 would be more efficient than that in other generations.