Vegetative growth, superoxide dismutase activity and ion concentration of salt-stressed watermelon as influenced by rootstock

Abstract

SUMMARYWatermelon is a crop with a high water demand and is frequently grown under conditions of higher than normal root-zone salinity. In the present study, seedlings of watermelon (cv. Fantasy, Citrullus lanatus (Thunb.) Matsum & Nakai) were grown either ungrafted or grafted on three rootstocks: Strong Tosa, S1 (both Cucurbita maxima×Cucurbita moschata), or Emphasis (Lagenaria siceraria). All the plants were exposed to an NaCl-induced salinity stress (electrical conductivity, EC=2·2, 4·0, or 6·0 dS/m). The vegetative growth of all the plants substantially reduced after 2 weeks of exposure to 6·0 dS/m; however, growth of the plants grafted on Strong Tosa reduced less than that of the others. The leaf water content and specific leaf area (SLA, m2/g) decreased with an increasing salinity in grafted plants, but not in ungrafted plants. Salinity induced an increase of superoxide dismutase (SOD) activity in grafted plants up to two-fold depending on the rootstock, whereas it had no effect on this enzyme activity in ungrafted plants. Leaf Na+ concentration increased with increasing salinity in ungrafted and S1 grafted plants, whereas there was no significant leaf Na+ accumulation in Emphasis and Strong Tosa grafted plants. Leaf K+ concentration was affected by the rootstock but not by salinity, thus, the ability to keep a high K+/Na+ ratio was achieved mainly by limiting leaf Na+ concentration. The rootstock determined the leaf Cl− accumulation, with lower overall concentrations found if plants were grafted on the S1 rootstock than on Emphasis or ungrafted plants. Salinity significantly decreased the leaf NO3− concentration on Emphasis grafted plants only, while the NO3−/Cl− ratio was reduced in all the rootstocks. The capacity of Strong Tosa to withstand salt stress better than other tested rootstocks was probably due to the ability to induce anatomical adaptation (SLA) and SOD activity in response to salt stress, and also to the efficiency of Na+ exclusion from the shoot.

Tomato salt tolerance: impact of grafting and water compositionon yield and ion relations

“…Furthermore, the grafted plants (with Maxifort rootstock) did not exclude Cl -more efficiently than the nongrafted plants. These results are in contrast to those reported earlier for other grafting combinations of Jaguar cv tomato (Estan et al, 2005), watermelon (Goreta et al, 2008), and cucumber (Huang et al, 2009). They all reported that grafting decreased Cl -(as well as decreased Na + and higher yields) as compared to nongrafted under salt stress.…”

“…These data indicate that increased Na + concentrations have a role in the response of tomato to salt stress. Earlier, Estan et al (2005) for tomato, Goreta et al (2008) Grafted and nongrafted plants had comparable Cl -leaf concentrations, as shown in Table 3 (only one salinity level was statistically significantly different). These data indicate that Cl -accumulation does not explain the greater yield of grafted tomato plants as compared to nongrafted plants under saline conditions.…”

“…Increased tolerance to salinity was related to reduced Na + in the vegetation with no change in Cl - (Goreta et al, 2008), reduced concentrations of Na + and Cl - (Estan et al, 2005), and increased K + with lower Na + and Cl - (Huang et al, 2009). Edelstein et al (2011), in a study with one salt level (EC 1.9 dS m -1 ), determined that melon grafted on pumpkin rootstock decreased plant Na + relative to nongrafted and self-grafted melon, while plant Cl -concentrations were similar among the rootstocks.…”

“…Watermelon grafted onto an apparently more salt tolerant rootstock demonstrated increased vegetative growth relative to nongrafted plants in a 2-week-long study with NaCl as the salinizing solution (Goreta et al, 2008). Huang et al (2009) examined the effect of grafting on cucumber salinized with NaCl.…”

Assessment of watermelon accessions for salt tolerance using stress tolerance indices

“…Yasar, Uzal and Yasar (2013) carried out a study examining the salt stress-tolerance of watermelon genotypes and indicated that the plants selectively took up Na + and K + ion under salt stress conditions, and the resistant genotypes promoted the uptake of K + ions rather than Na + ions. Moreover, under salinity stress conditions, with increasing salt concentration, the K + ion concentration increases in salt tolerant plants (Goreta et al, 2008;Yetisir;Uygur, 2009). Therefore, the K/Na ratio represents the tolerance level of a genotype.…”