Long-term high temperature effect on field-grown pumpkins (Cucurbita maxima Duchesne and Cucurbita moschata Duchesne)

Abstract

Temperature stress during reproductive phase of life is among environmental constrains with the most adverse effect on pumpkins, at least in the fields of South and East Europe. The growing season (May-September) of 2017 was characterized by 56 days of high (>30 °C) and 21 days of extremely high (>35 °C) maximum daily temperatures, differing from the temperate season of 2016 (33 and 0 days), and from the 1981-2010 averages of 32.4 and 3.3 days, respectively. This was an opportunity to analyze the effects of the stress on pumpkin quality and agronomic traits. The investigation was undertaken on field-grown Cucurbita maxima and Cucurbita moschata collections, each comprising 41 genetically divergent accessions. All appropriate agro-technical procedures, including irrigation, were applied in both seasons of the experiment (2016, 2017); therefore high temperature was the only stress to which the plants were exposed. The most affected by the stress was carotenoid content, which was 64.1% (C. maxima) and 75.4% (C. moschata) lower comparing to the values noted in the temperate season. Concerning other quality traits, protein content was 44.6% reduced in C. moschata, and slightly (6.1%) increased in C. maxima. Dry weight and total soluble solids contents were moderately increased in both species; and sugar content in C. moschata only. Refractive index and pH were unaffected by the stress. Concerning agronomic traits, temperature stress decreased the fruit weight (23.1, 17.3%) and therefore the yield of both C. maxima (27.0%) and C. moschata (16.1%), exhibiting no significant effect on number of fruits per plant.