Environmental stresses such as chilling temperatures can reduce seed germination rate, seedling emergence rate, flower and fruit development, marketable yield, and postharvest fruit storage longevity in cucumber (Cucumis sativus L.) (Staub and Bacher, 1997; Staub and Wehner, 1996). Chilling temperatures occur in unpredictable patterns, making it difficult to implement management practices for crop protection. Moreover, response of cucumber seedlings to chilling depends on pre- and postchilling environment. Therefore, breeding for tolerance to chilling is an attractive management tool to minimize crop loss.
Chilling injury at the first true-leaf stage in cucumber is controlled by simple plastidic (maternal; Chung et al., 2003) and nuclear (parental; Kozik and Wehner, 2008) factors. While Chung et al. (2007) identified three putative plastidic single-nucleotide polymorphisms (SNPs) associated with chilling tolerance in processing cucumber ‘Chipper’, Kozik and Wehner (2008) characterized one dominant nuclear gene, Ch, in line NC-76 (derived from PI 246930). The response of chilling tolerant ‘Chipper’ and line NC-76 seedlings challenged at 4 °C for 5.5 h under 270 µmol·m−2·s−1 photosynthetic photon flux irradiance are similar (Gordon and Staub, 2011).
No chilling-tolerant U.S.-processing cucumber varieties are commercially available. Although the processing cultivar Chipper (released in 1968 from Clemson University, Clemson, SC) possesses plastid genes for chilling tolerance in the seedling stage, its yield and quality are substantially lower than current cultivars. Therefore, experiments were undertaken to introgress the plastid chilling tolerance of ‘Chipper’ (donor parent) into the commercially acceptable processing cucumber line M29 [recurrent parent; experimental inbred line (S11), North Carolina State University, Raleigh, NC] via backcrossing and self-pollination (Gordon and Staub, 2013). As a result, a series of three advanced backcross (ABL; BC5) and 10 inbred backcross (IBL; BC2S3–5) chilling-tolerant U.S. processing lines possessing acceptable yield and quality traits are being released by the Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA). The chilling tolerance of backcross progeny is characterized by their response to chilling stress (5.5 h at 4 °C in 270 µmol·s−2·m−2 cool white lighting) at the first true-leaf stage under controlled environmental conditions. These lines provide chilling-tolerant genetic stocks suitable for immediate use by cucumber improvement programs.
Origin
Breeding lines were developed through initial reciprocal matings made between chilling tolerant ‘Chipper’ (CH is used hereafter to indicate tolerant cytoplasmic constitution) and chilling sensitive processing line M29 (M designates sensitive constitution) to produce F1 progeny for backcrossing to the recurrent parent, line M29 (Gordon and Staub, 2013). NCSU M 29 was developed from the cross of two accessions, PI 222783 (‘Khiar Sabz’) × PI 222985 (‘Khiar’). These PIs were crossed in 1980 and their progeny selected for cold germination ability in 1982–1986 in controlled-germination chambers, and finished as an S11 inbred. Chilling-sensitive and tolerant advanced backcross (ABL; BC1-BC5) and inbred backcross (IBL; BC2S1–5) lines were created from F1 reciprocal chilling-sensitive and tolerant lines by backcrossing to a cloned recurrent parent of the alternate chilling response type [i.e., tolerant (‘Chipper’) and sensitive (M29), respectively] parental line. Exact reciprocal F1 progeny for comparative genotypic and phenotypic analyses were developed by crossing ‘Chipper’ and M29 to produce germplasm in chilling-tolerant (CH; ‘Chipper’ × M29) and in sensitive (M; M29 × ‘Chipper’) maternal plastidic backgrounds.
Reciprocal F1s intended to produce chilling-tolerant ABL were backcrossed to their paternal genetic donor five times to produce BC1-BC5 progeny. For production of IBL, 240 randomly chosen reciprocal ABL BC2 progeny (i.e., 120 chilling-sensitive ABL BC2, and 120 chilling-tolerant ABL BC2) were self-pollinated five times to produce the sensitive and tolerant [containing the M29 plastid (MIBL), and tolerant ‘Chipper’ plastid (CHIBL), respectively] BC2S5 progeny. Attrition due to seedling death and lack of seed set during reciprocal backcrossing yielded a set (BC1-BC5) of 10 ABL (i.e., five each—chilling tolerant and sensitive) and 163 (i.e., 57 CHIBL and 106 MIBL) IBL for molecular genotyping, chilling tolerance testing, and field evaluation.
Line Evaluation
Initially, progeny within the F1 and BC1-BC5 generations of the two ABL chilling response types were phenotyped for chilling response in the University of Wisconsin Biotron-controlled environmental facility (Madison, WI) to confirm their predicted chilling response based on their cytoplasmic constitutions (Gordon, 2009; Gordon and Staub, 2011; Gordon and Staub, 2013). Subsequently, both chilling-tolerant and chilling-sensitive ABL [i.e., BC1-BC5 generations (5) in each of 2 lineages] and CHIBL (i.e., 10 of 57 BC2S4–5 generated from 1 BC2) were genotyped using 11 simple sequence repeat (SSR) codominant markers, and then evaluated in field plots for their general horticultural performance (i.e., yield and quality) and general combining ability (GCA) for four economically important traits. Genetic relationships among ABL, CHIBL, and parents were determined on the basis of Principal Component Analysis (PCA). Predictably, PCA results indicated that ABL were genotypically similar to line M29 and IBL were genetically diverse, but more similar to M29 than to ‘Chipper’.
To estimate GCA estimation, ABL and CHIBL were crossed with elite processing cultigens (i.e., lines H-19, 7012, WI 1983G, 5551, Gy 14, and ‘Addis’) (Gordon and Staub, 2013). Parents, progeny (BC, and F1), and control cultivar Vlasset were evaluated for days to anthesis, sex expression type, fruit length (L):diameter (D) ratio (L:D), and yield in replicated trials at each of four harvests in 2006 and five harvests in 2007, at the University of Wisconsin Experiment Station at Hancock, WI. In addition, 44 CHIBL were also evaluated for these traits to determine their horticultural acceptability. Some ABL (10) and IBL (12) differed from their nonrecurrent and both parents, respectively, in many of the traits measured. The phenotypic variation among IBL was remarkably broad (Table 1).
Descriptive statistics of yield component traits of cucumber (Cucumis sativus L.) ‘Vlasset’, advanced backcross (ABL; BC3-BC5), and inbred backcross (IBL; BC2S4) lines, and their parents as assessed at Hancock WI field trials in 2006 and 2007 (mean values represent replication averages taken over four harvests in each of two plantings).
Description
On the basis of genotypic and phenotypic analysis, large portions of the nuclear genome of the recurrent parent (and its phenotype) were recovered by the BC2 generation, with nearly complete recovery of recurrent parental traits and its nuclear genome occurring by the BC3 in ABL (Gordon and Staub, 2013). The GCA of IBL was significant (P < 0.001) for yield, fruit size, fruit length, fruit diameter, and L:D ratio. Given their GCA, and genotypic and phenotypic characteristics when compared with their parents and the control cultivars, three chilling-tolerant ABL (designated ‘Gabrielle’ ARS CHBC3, ‘Saira’ ARS CHBC4, and ‘Kodie’ ARS CHBC5), and 10 chilling-tolerant IBL (designated ARS CHBC2S4-10, -14, -17, -34, -64, -81, -96, -101, -105, and CHBC2S5-28) are being released for commercial use (Table 1). The ABL and IBL are intended for the development of elite chilling-tolerant cultivars (Fig. 1). The quality (e.g., size) and yield characteristics of chilling-tolerant ABL Gabrielle, Saira, and Kodie and some IBL (e.g., CHBC2S4-14 and -17) are similar to or better than the control cultivar Vlasset under Wisconsin growing conditions.
Fruits of chilling tolerant (4 °C) cucumber (Cucumis sativus L.) advanced backcross lines (ABL) ‘Gabrielle’ (Panel A; ARS-ABL CHBC3), ‘Saira’ (Panel B; ARS-ABL CHBC4), and ‘Kodie’ (Panel C; ARS-ABL CHBC5), and tolerant inbred backcross lines (IBL) CHBC2S4-28 (Panel D), CHBC2S4-81 (Panel E), and CHBC2S4-105 (Panel F). Plastid chilling tolerance derived from ‘Chipper’ (CH) as the donor parent.
Citation: HortScience 50, 8; 10.21273/HORTSCI.50.8.1252
Fruits of chilling tolerant (4 °C) cucumber (Cucumis sativus L.) advanced backcross lines (ABL) ‘Gabrielle’ (Panel A; ARS-ABL CHBC3), ‘Saira’ (Panel B; ARS-ABL CHBC4), and ‘Kodie’ (Panel C; ARS-ABL CHBC5), and tolerant inbred backcross lines (IBL) CHBC2S4-28 (Panel D), CHBC2S4-81 (Panel E), and CHBC2S4-105 (Panel F). Plastid chilling tolerance derived from ‘Chipper’ (CH) as the donor parent.
Citation: HortScience 50, 8; 10.21273/HORTSCI.50.8.1252
Fruits of chilling tolerant (4 °C) cucumber (Cucumis sativus L.) advanced backcross lines (ABL) ‘Gabrielle’ (Panel A; ARS-ABL CHBC3), ‘Saira’ (Panel B; ARS-ABL CHBC4), and ‘Kodie’ (Panel C; ARS-ABL CHBC5), and tolerant inbred backcross lines (IBL) CHBC2S4-28 (Panel D), CHBC2S4-81 (Panel E), and CHBC2S4-105 (Panel F). Plastid chilling tolerance derived from ‘Chipper’ (CH) as the donor parent.
Citation: HortScience 50, 8; 10.21273/HORTSCI.50.8.1252
Though not tested directly for chilling tolerance, all IBLs were molecularly genotyped against the set of three previously described plastidic tolerance-associated SNPs (Chung et al., 2007; Gordon and Staub, 2013). Their phenotypic response to chilling (resistant or sensitive) is predictable based upon previous chilling studies conducted on the original parents and other chilling-tolerant germplasm. With the presence of the tolerant plastid and SNP-based genotype assessment, as well as the known nuclear response to chilling of the recurrent parent (susceptible; M29), the ABLs and IBLs resulting from the initial ‘Chipper’ × M29 cross are chilling tolerant (i.e., no visible necrotic symptoms) at the first true-leaf stage under the chilling conditions under which the parents were evaluated (i.e., 5.5 h at 4 °C).
Availability
Seed of chilling tolerant ABL and IBL from a hand-pollinated greenhouse increase may be obtained by addressing requests to P.W. Simon, Vegetable Crops Research, U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin, Madison, WI 53706.
Literature Cited
Chung, S.M., Staub, J.E. & Fazio, G. 2003 Inheritance of chilling injury: A maternally inherited trait in cucumber J. Amer. Soc. Hort. Sci. 128 526 530
Chung, S.M., Gordon, V.S. & Staub, J.E. 2007 Sequencing of cucumber (Cucumis sativus L.) chloroplast genomes identifies differences between chilling tolerant and susceptible cucumber lines Genome 50 215 225
Gordon, V.S. 2009 Characterizing plastome variation and its contribution to chilling injury tolerance in cucumber (Cucumis sativus L.). PhD Diss. University of Wisconsin, Madison (OCoLC: Ocn648006186). 20 July 2015. <http://search.proquest.com/docview/305029867?accountid=14761>
Gordon, V.S. & Staub, J.E. 2011 Comparative analysis of chilling response in cucumber through plastidic and nuclear genetic effects component analysis J. Amer. Soc. Hort. Sci. 136 256 264
Gordon, V.S. & Staub, J.E. 2013 Backcross introgression of plastomic factors controlling chilling tolerance into elite cucumber (Cucumis sativus L.) germplasm: Early generation recovery of recurrent parent phenotype Euphytica 195 217 234
Kozik, E.U. & Wehner, T.C. 2008 A single dominant gene ch for chilling resistance in cucumber seedlings J. Amer. Soc. Hort. Sci. 133 225 227
Staub, J.E. & Wehner, T.C. 1996 Noninfectious disorders: Temperature stress, p. 66. In: T.A. Zitter, D.L. Hopkins, and C.E. Thomas (eds.). Compendium of cucurbit diseases Part II. APS Press, St. Paul, MN
Staub, J.E. & Bacher, J. 1997 Cucumber as a processed vegetable. In: D.S. Smith, J.N. Cash, W.-K. Nip, Y.H. Hui (eds.). Processing vegetables: Science and technology IV. Technomic Publishing Co., Inc. Lancaster, PA
