Genetic transformation using foreign genes and the subsequent development of transgenic plants has been employed to develop enhanced elite germplasm. Although some skepticism exits regarding pollen tube-mediated gene transfer (PTT), reports demonstrating improved transformation efficiency with PTT systems are increasing and encouraging and the adoption of increasingly refined pollenmediated methodologies may lead to species-dependent improvements in breeding. Here, we highlight PTT technology as an alternative to genetic transformation.

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Abstract:The responses to chilling temperature of 12 Korean cucumber varieties was compared to those of two U.S.A. (previously determined cold tolerant NC76 and 'Chipper'), and Chinese and Japanese germplasms. Seedlings of each entry were exposed to 4°C (Experiment 1) and 1°C (Experiments 2 and 3) at the first-true leaf stage for eight and nine hours, respectively, under 80% relative humidity (RH) and 149 μmoles･m -2 ･s -1 photosynthetic photon flux (PPF). The chilling response [damage rating (DR)] of each accession was based on visual ratings (1 to 5) after treatment, where 1 = no damage, 2 = slight, 3 = moderate, 4 = advanced, and 5 = severe damage. Predictably the cumulative average DR of chilling tolerant line NC76 and 'Chipper' after chilling was 1 and 1.1, respectively. Korean 'Nacdongchungjang' was most sensitive to chilling temperatures [DR = 2.3] when compared to the other entries examined. The sensitivity to chilling of 'Nacdongchungjang' was followed by Chinese 'Dongguan' [DR = 1.7]. In contrast, 'Saeronchungjang' (DR = 1) and 'Janghyungnachap' (DR = 1) were the most chilling tolerant of the Korean accessions examined and equivalent to the response of line NC76 and 'Chipper'. Nevertheless, chloroplast type genotyping of these accessions with known chilling-linked sdCAPS genomic markers revealed genotypic differences between chilling tolerant lines (NC76 and 'Chipper') and all Korean lines examined.

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