Effects of Polyploidy on Physiological Performance of Acclimatized Solanum betaceum Cav. Plants under Water Deficit

The urgent need to identify stress-tolerant genotypes and understand their inherent genetic plasticity is one of the major targets of research and breeding programs. Species that are cultivated in areas that are prone to drought need to be able to tolerate water stress (WS) while still displaying features that are economically valuable. Tamarillo (Solanum betaceum) is a solanaceous fruit crop with increasing agronomic interest due to the nutritional properties of its edible fruits and its biotechnological potential. Several protocols have been established for the in vitro culture of this species and controlled hybridization, as well as for the induction of tetraploidy. Nevertheless, the impact of WS on S. betaceum performance has been poorly studied, and nothing is known about the role of ploidy status on this response. Since no morphological differences were noticed between diploids and tetraploids at the end of the acclimatization period, we hypothesized that ploidy level may have a role in plant drought responses. Thus, micropropagated and acclimatized tamarillo diploid (2n = 2x = 24) and tetraploid (4n = 4x = 48) plants were exposed to WS, and several physiological parameters were evaluated, such as plant growth, water potential, photosynthetic performance, sugars, proline, and MDA levels. Water stress did not affect plant growth in both diploids and tetraploids, but it induced stomatal closure and reduced the net CO2 assimilation rate. Water stress also reduced the photosynthetic efficiency of PSII, but no differences were found in the total chlorophyll content. From all the parameters analyzed, tetraploid plants showed a better response under water shortage conditions when considering water potential (WP). Metabolite analysis indicated no significant differences in the accumulation of soluble sugars and MDA in WS plants but a significant increase in proline accumulation in diploids exposed to WS. These observed differences in parameters such as WP and proline accumulation point to mechanisms of osmoregulation and stress signaling that differ between diploid and tetraploid plants, particularly in WS conditions, demonstrating that tetraploids can adapt better to water shortage conditions than their diploid counterparts.