Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2013
Publication Date: 9/10/2013
Citation: 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 phenotytpe. Euphytica. 195:217-234.
Interpretive Summary: Many horticultural crop species that have origins in tropical or subtropical growing regions are geing grown in temperate climates where environmental conditions (i.e., temperature, photoperiod) are at or exceed their natural limits. Frequently, when temperatures drop below a critical threshold, such plant species can be damaged. Chilling injury, for example, can critically impede plants during vegetative and reproductive growth, and, thereby, greatly reduce yield potential especially in immature plants. For instance, the U.S. cotton industry suffered a $60 million (US) loss in 1980 as early spring temperatures fell to unexpected lows, significantly damaging developing seedlings. Likewise, chilling damage can dramatically reduce yield in cucumber. Cucumber germplasm exhibits genetic variation in response to chilling temperatures, but chilling tolerance does not exist in modern U.S. processing cucumber cultivars. Therefore, a project was initiated to develop cucumber genetic stocks that can be used by commercial seed companies to introduce chilling tolerance modern cucumber. Using previously identified chilling tolerant exotic plants, chilling tolerance was introduced into commercially acceptable cucumber (by traditional cross breeding) to produce genetic stocks that can be readily used by commercial seed companies. Refined commercial chiling tolerant cultivars derived from these stocks will increase the managerial effectiveness of the growers and assist in making them more globally competitive by reducing the risk of crop failure due to chilling temperatures.
Technical Abstract: Environmental stresses such as chilling temperatures can decrease germination, emergence, flower and fruit development, marketable yield, and postharvest fruit storage longevity in cucumber (Cucumis sativus L.). While response to chilling injury in cucumber is controlled by simple plastidic (maternal) and nuclear (paternal) factors, no chilling tolerant U.S. processing varieties are commercially available. Furthermore, even though three single nucleotide polymorphic (SNP) sites have been identified as plastid components associated with chilling tolerance in cucumber, it is not known how these factors interact with nuclear factors controlling economically important traits. Therefore, an experiment was designed to evaluate the rate of recovery of the chilling susceptible (cytoplasm) genotype during introgression backcrossing (IB), where it was used as a recurrent parent after the initial mating to a line possessing chilling tolerant cytoplasm (donor parent). Phenotypic yield and quality trait data were collected on processing type backcross progeny (BC1-5 and BC2S3) derived from an initial 'Chipper' (tolerant) x line M 29 (susceptible) mating, and rate of progression to the recurrent parent was determined by simple sequence repeat (SSR) marker and morphological trait analyses. Substantial degrees of the recurrent parent phenotype and nuclear genome were recovered by the BC2 generation (P = 0.001), with nearly complete recovery of recurrent parental traits and its nuclear genome occurring by the BC3. General combining ability (GCA) of derived BC2S3 lines was significant for yield, yield/plant, length (L), diameter (D), and L:D ratios. The BC2S3 line GCA and rate of progression towards the recurrent parent for economically important traits suggests that elite chilling tolerant cucumber germplasm can be developed rapidly through IB and marker genotyping.