Acta Hortic. 1256. ISHS 2019. DOI 10.17660/ActaHortic.2019.1256.30 Proc. VI International Conference Postharvest Unlimited Eds.: D. Valero et al. 217 Postharvest fruit quality in ethylene insensitive mutants of zucchini squash A. Garcı́a 1 , J.L. Valenzuela 1 , S. Manzano 1 , G. Cebrián 1 , J. Romero 1 , E. Aguado 1 , D. Garrido 2 and M. Jamilena 1,a 1 Departments of Biology and Agronomy, Agri-food Campus of International Excellence (CeiA3), and CIEMBITAL, University of Almerı́a, 04120 Almerı́a, Spain; 2 Department of Plant Physiology, Faculty of Sciences, University of Granada, Granada, Spain. Abstract Three ethylene insensitive mutants (Ein1, Ein2 and Ein3) were isolated from an EMS mutant library of zucchini squash by screening for a negative triple response of etiolated seedlings to ethylene. The ethylene insensitive mutations were isolated from other mutations in each one of the lines by backcrossing (BC) with the background genotype. To gain insight into the involvement of ethylene in postharvest fruit quality, WT and mutant fruit from BC3 generation was compared for different fruit quality parameters during 14 days of cold storage, including loss of weight and firmness, chilling injury (CI), and ethylene and CO2 production. The oxidative status of the fruit was also analysed. The mutations stimulated the production of ethylene in rewarmed fruit after cold storage but, given that ethylene response pathway was partially blocked in the mutants, some fruit quality parameters were improved, concomitantly with a reduction of oxidative stress metabolites such as hydrogen peroxide and malonyl dialdehyde (MDA). The Ein1 and Ein3 mutant fruit exhibited reduced chilling injury, and Ein1 also reduced the fruit respiration rate during cold storage. Weight loss was not altered in any of the ethylene mutants. The involvement of ethylene in postharvest deterioration of zucchini fruit quality, including CI and oxidative damage, is discussed. Keywords: chilling injury, ethylene, oxidative stress INTRODUCTION The maintenance of the postharvest quality of the zucchini fruit during transportation and commercialization depends on its tolerance to cold storage. The fruits of most zucchini cultivars are, however, very sensitive to chilling injury (DF), which results into different fruit symptoms, including pitting, weight loss and softening (Martı́nez- Téllez et al., 2002; Megı́as et al., 2014). Although the zucchini fruit is non-climacteric, we have previously shown that the cold tolerance of some cultivars is associated with a decrease in ethylene production and metabolites associated with oxidative stress (Megı́as et al., 2014, 2015, 2016; Palma et al., 2016). At the University of Almerı́a we have developed a ethylmethanesulfonate (EMS) collection of 3,800 mutant lines. Since we know that ethylene negatively regulates the postharvest quality and CI the zucchini fruit (Megı́as et al., 2014, 2015, 2016), ethylene insensitive mutants could be a source of variation for improving postharvest fruit quality in zucchini breeding programs. After a massive screening of an M2 mutant collection by using the ethylene triple response test, three mutant families have been identified that show ethylene insensitivity: Ein1, Ein2 and Ein3. The objective of this work was to study the effects of these mutations on cold-induced ethylene production, oxidative stress metabolites, and postharvest fruit quality. a E-mail: mjamille@ual.es