Water relations and carbohydrate partitioning of four greenhouse-grown olive genotypes under long-term drought

Abstract

Olive plants of broad-leaved 'Minuta' (MN) and 'Nocellara del Belice' (NB) and narrow-leaved 'Passulunara' (PA) and 'Biancolilla Siracusana' (BS) were studied to evaluate their responses to drought. In a greenhouse, two-year-old rooted cuttings were irrigated to field capacity (WW) or with 20% of WW evapotranspiration (DS) for over three months. Subsequently, all pots were rewatered to field capacity for 20 days. Gravimetric soil water content (SWC), leaf relative water content (RWC), stomatal conductance (gs), and leaf carbohydrates, percentage of leaf drop and shoot elongation were determined throughout the trial. In WW, SWC fluctuated between 80 and 100% of field capacity, whereas in DS, SWC decreased sharply reaching a minimum level around 30-35% of field capacity after two months of drought. At this time, drought induced a significant reduction of: (a) RWC in PA and BS, (b) gs in MN, NB, and PA, and (c) shoot elongation (-23%) in PA. Conversely, drought increased leaf drop in all genotypes, especially in MN and NB. RWC and gs levels were mostly restored after rewatering. Initially, drought induced an increase of mannitol and total carbohydrates in MN and a decrease in NB. At more advanced drought stages, mannitol and total carbohydrates decreased in PA and BS. NB exhibited a general increase of the (mannitol + glucose)/sucrose ratio in response to drought. The two broad-leaved genotypes (MN and NB) maintained similar leaf hydration levels in DS and WW plants proving to be generally intolerant to dehydration, whereas the two narrow-leaved genotypes (PA and BS) tolerated a fair degree of dehydration

Physiological and biochemical responses of young olive trees (Olea europaea L.) to water stress during flowering

“…Our data showed a positive relationship between RWC and ψ w in olive leaves, indicating that RWC is a good estimate of plant water status. The same finding was previously reported by Dichio et al [33] and Lo Bianco et al [6]. Moriana et al [46] recommended ψ w as a useful tool for monitoring the response of the water status of olive plants to irrigation.…”

“…The effectiveness of water use in response to limited resources is often assessed by the water status, gas exchange and some biochemical changes. Several studies have been conducted on young trees growing in pots to assess their behavior in stressed environments [3][4][5][6][7].…”

A Cultivar-Sensitive Approach for the Continuous Monitoring of Olive (Olea europaea L.) Tree Water Status by Fruit and Leaf Sensing

“…In MN trees, a clear shift from state I to II was not observed, despite the slight tendency to enter state II at 219 and 221 DOY, with no apparent differences among irrigation levels ( Figure 8F). This suggests that MN leaves can maintain high cell turgor, probably by reduced cell wall elasticity or osmotic adjustments, as found in other olive genotypes (Bacelar et al, 2009;Dichio et al, 2009;Lo Bianco and Scalisi, 2017).…”

“…The different mechanisms in the two cultivars were observed in an -ON year, and it would be interesting to further study tree responses in -OFF years, as Dell'Amico et al 2012and Girón et al (2015) observed that in "Manzanillo" trees crop load influenced the ability of fruit and leaves to act as sinks for water. Changes in osmotic adjustments (Dichio et al, 1997(Dichio et al, , 2009Lo Bianco and Scalisi, 2017) and cell-wall elasticity (Xiloyannis et al, 1993;Bacelar et al, 2009) along water deficit gradients have been reported for leaves. However, to the best of our knowledge, no consideration has been previously given to concomitant changes of similar drought tolerance mechanisms in fruit.…”

“…The physiological responses of plants to decreasing water availability are various and depend on evolutionary adaptation and acclimation to new climatic conditions. The olive species (Olea europaea L.) has a very wide genetic pool, and includes genotypes that can respond to drought using different mechanisms of leaf dehydration tolerance and leaf morphological and structural adaptations (Bacelar et al, 2004(Bacelar et al, , 2006Ennajeh et al, 2010;Lo Bianco and Scalisi, 2017;Scalisi et al, 2019a). Gucci et al (2000) and Lo Bianco and found different leaf stomatal regulation among olive cultivars.…”