Assessment of water stress tolerance in eleven pomegranate cultivars based on agronomic traits

Abstract

The aim of this study was to assess eleven Mediterranean pomegranate cultivars for drought tolerance based on their responses to severe water stress. The experiment was performed under field conditions in Sais Plain (NW Morocco) on twelve-year-old pomegranate trees (Punica granatum L.), under drip irrigation. For each cultivar, two treatments were applied from fruit set to harvest: a control treatment irrigated at 100 % of seasonal ETc (FI), and a continuous deficit treatment irrigated at 50 % of ETc (CDI). The measurements concerned fruit yield, fruit weight, aril content, aril weight, seed weight, juice content, shoot length, leaf area, foliage density, wood density and concentration of chlorophyll-a and chlorophyll-b. Results showed clear differences among pomegranate cultivars in response to water stress. The most frequent effects of water stress were recorded on yield, fruit weight and chlorophyll pigment contents. Fruit yield was not affected in Zheri Automne cultivar, while it was significantly decreased under CDI in all other cultivars by 14 % in Bzou to 51% in Ounk Hmam. A significant decrease of fruit weight was observed in six cultivars, with a rate of 13 % in Gordo de Jativa cultivar to 24 % in average for Grenade Jaune, Grenade Rouge and Ounk Hmam. These last cultivars were the only ones affected in juice content by 9–11%. Regarding CDI effect on vegetative growth, it was recorded a high decrease of shoot length in the cultivars Gjeibi (78 %), Sefri (64 %) and Mollar Osin Hueso (38 %). The cultivars ranking for drought tolerance based on mean ratios of all traits between CDI and FI treatments was drawn according to cluster analysis, combined to a scoring method. It was thus retained that the most drought tolerant cultivar was Zheri Automne, followed by Djebali and Bzou, while Grenade Rouge cultivar was the most sensitive.