Phenotypic plasticity in Cucurbita maxima and C. moschata seedlings as a measure of drought stress tolerance under pot screening

Abstract

A pot screening approach was used to identify mannitol stress tolerance indicating traits that were reliable and easy to determine, in two Cucurbita species. A population of C. maxima seedlings with trimmed roots were exposed to 0–800 mM mannitol for 20 days and the mannitol concentration required to inhibit root regrowth by 50±0.51% was established through a linear regression analysis (LD50 = 453 mM, -1.11 MPa). The established LD50 was then used to screen a population of C. moschata seedlings in addition to a second population of C. maxima. When exposed to 453 mM mannitol for 10 days, both species were able to regrow roots, maintain biomass production, chlorophyll content, high water status, membrane stability and accumulate proline as an osmoprotectant. Even with a good water status, stress exposure for 20 days compromised the biomass production, chlorophyll content, membrane stability and encouraged a surge in proline content. Based on their phenotypic plasticity indices, traits such as root regrowth, fresh weight, dry weight, relative chlorophyll content, electrolyte leakage and proline content were identified as potential indicators of stress tolerance at day 10 of mannitol stress. Meanwhile, root regrowth and proline content were the only traits identified as good indicators of stress tolerance at day 20 of mannitol stress. The biochemical, morphological and physiological traits of tested populations had varying degrees of plasticity under stress and this should be considered when screening and identifying drought resilient seedlings prior to labourious field tests.