Drought Tolerance Mechanisms in Plants: Physiological Responses Associated with Water Deficit Stress in Solanum lycopersicum

Drought is among the top largest causes of agricultural productivity losses globally. Tomato (Solanum lycopersicum L.) is a commercially important crop considerably hampered by drought. It is considered a drought sensitive crop with a yield response factor (Ky) 1.05. Although advancements in molecular research and plant breeding have led to release of drought tolerant cultivars in most developed countries, breeding efforts have focused on yield as the core selection index particularly in Sub-Saharan Africa (SSA) with less regard for drought tolerance. Several studies, however, have documented various physiological, morphological and biochemical adaptive drought tolerance and avoidance strategies in tomatoes and other crop species. It is argued that selection efficiency for drought tolerance breeding programs would be improved if physiological traits linked to drought tolerance are considered. This review presents an overview of previous research efforts in understanding physiological responses to drought, in crop species with particular attention to Solanum lycopersicum (Tomato). It further highlights research gaps, identifying unexplored domains and suggesting recommendations for future investigation.