Improved stomatal regulation and ion partitioning boosts salt tolerance in grafted melon

Abstract

Grafted plants are often more tolerant to salinity than nongrafted controls. In order to distinguish differential response components in grafted melon (Cucumis melo L.), salt stress was imposed on several rootstock–scion combinations in four experiments. The rootstock used was an interspecific squash (Cucurbita maxima Duch. × Cucurbita moschate Duch.), RS841, combined with two cantaloupe (C. melo var. cantalupensis) cultivars, namely London and Brennus, against both self-grafted and nongrafted controls. Physiological, morphological and biochemical adaptations to 0, 40 and 80 mM NaCl were monitored. Upon salinity, plant biomass and leaf area were improved by grafting per se, since self-grafted plants performed similarly to the heterografted ones. However, improvements in the exclusion of Na+ and the uptake of K+ were due only to the rootstock genotype, since ionic composition was similar in self-grafted and nongrafted plants. These results indicate that the favourable effects of grafting on plant growth cannot be ascribed to a more efficient exclusion of Na+ or enhanced nutrient uptake. On the other hand, growth improvements in both self- and heterografted plants were associated with a more efficient control of stomatal functions (changes in stomatal index and water relations), which may indicate that the grafting incision may alter hormonal signalling between roots and shoots.

Global DNA methylation changes in Cucurbitaceae inter-species grafting

“…Recently, grafting of watermelon onto specific rootstocks resulted in significant increase of lycopene content in watermelon fruits and enhanced resistance to soil-borne diseases (Mohamed et al 2012), whereas different rootstock-scion combinations lead to alterations in the content of plant nutrients in leaves and fruits of watermelon grafts (Yetisir et al 2013). In addition, cucumber and melon grafted onto pumpkin rootstocks were shown to exhibit enhanced tolerance to increased salinity , Orsini et al 2013). …”

Salt-tolerant rootstock increases yield of pepper under salinity through maintenance of photosynthetic performance and sinks strength

“…Tomato and melon are the two commonest herbaceous species in which the grafting practice has been efficiently applied to obtain salt-tolerant plants (Estañ et al, 2005, Edelstein et al, 2011, Orsini et al, 2013. In melon, the favorable effects of grafting on plant growth cannot be ascribed to a more efficient exclusion of Na + or enhanced nutrient uptake but they were associated with a more efficient control of stomatal functions (changes in stomatal index and water relations), which may indicate that the rootstock may alter hormonal signalling between root and shoot (Orsini et al, 2013). As far as we know, very few studies on grafted pepper plants have been conducted to elucidate whether or not salt tolerance might be conferred by rootstocks.…”

Ionic partitioning and stomatal regulation

“…As only grafting and salinity presented significant interactions, results from all experiments were jointly discussed, thus offering innovative elements for the comprehension of the effect of grafting on the plant physiological response to the stress. In the present manuscript, additional results obtained from one of the experiments conducted at Bologna University, Italy (experiment 1#) 7 are discussed, with the aim of further elucidating how the differential stomatal and ionic response observed in self-grafted vs. interspecific grafting may lead to similar performances upon salt stress (0, 40, and 80 mM NaCl, starting from 10 Days After Transplanting, DAT, and lasting 30 d). Similarly to other experiments presented in the manuscript, 2 melon cultivars (namely Brennus, ZKI, Hungary, and London, Nunhems, The Netherlands) were used, altogether with a squash rootstock (Rs841, Monsanto, USA).…”

“…9,10 The increased CO 2 assimilation per unit water used was a consequence of the changes in the stomatal morphology (mainly through increase in the stomatal index, SI), 11 rather than stomatal closure, which, on the other hand, turned out to be the main response to salinity in non-grafted plants. 7 Clearly, the improved response of grafted plants to salinity followed a binary pathway: signaling (possibly mediated by wound-related hormones, i.e., ABA and ethylene) resulted in a physiological pre-adaptation to the stress, most efficient when rootstock and scion belonged to the same species. On the other hand, the interspecific rootstock efficiently operated as a toxic-ions filter, thus resulting in lower accumulation in the epigeous plant organs.…”

“…Although these rootstocks have proven to improve crop's performances in presence of biotic 5,6 and abiotic 4 stresses, whether the beneficial effects should be attributed to the rootstock genotype rather than grafting per se is still a controversial matter among scientists. In a recent publication, 7 the comprehension of the role of grafting in improving the response to salinity in melon was addressed. The manuscript reported on the effects associated to cultivar, grafting, and salinity over 4 experiments in a range of different environmental conditions.…”