Carla Cassaniti

Do conditions during dormancy influence germination of Suaeda maritima

BACKGROUND AND AIMS Seeds of annual halophytes such as Suaeda maritima experience fluctuating salinity, hydration, hypoxia and temperature during dormancy. Germination then occurs in one flush of 2-3 weeks after about 5 months of winter dormancy during which time the seeds can remain in saline, often waterlogged soil. The aim of this study was to investigate the effect of simulated natural conditions during dormancy on germination and to compare this with germination following the usual conditions of storing seeds dry. The effects of hydration, salinity, hypoxia and temperature regimes imposed during dormancy on germination were investigated. Also looked at were the effects of seed size on germination and the interaction between salinity during dormancy and salinity at the time of germination. METHODS Various pre-treatments were imposed on samples of seeds that had been stored dry or wet for different periods of time during the 5 months of natural dormancy. Subsequent germination tests were carried out in conditions that simulated those found in the spring when germination occurs naturally. Various salinities were imposed at germination for a test of interaction between storage salinity and salinity at germination. KEY RESULTS A temperature of about 15 degrees C was needed for germination and large seeds germinated earlier and better than small seeds. Cold seawater pre-treatment was necessary for good germination; the longer the saline pre-treatment during the natural dormancy period the better the germination. There appeared to be no effect of any specific ion of the seawater pre-treatment on germination and severe hypoxia did not prevent good germination. A short period of freezing stimulated early germination in dry-stored seed. Storage in cold saline or equivalent osmotic medium appeared to inhibit germination during the natural dormancy period and predispose the seed to germinate when the temperature rose and the salinity fell. Seeds that were stored in cold wet conditions germinated better in saline conditions than those stored dry. CONCLUSIONS The conditions under which seeds of S. maritima are stored affect their subsequent germination. Under natural conditions seeds remain dormant in highly saline, anoxic mud and then germinate when the temperature rises above about 15 degrees C and the salinity is reduced.

The Response of Ornamental Plants to Saline Irrigation Water

Salinity affects about one third of irrigated land, causing a significant reduction in crop productivity (Flowers & Yeo, 1995; Ravindran et al., 2007). For this reason researchers have paid considerable attention to this important environmental problem over the last decades. Few studies, however, have dealt specifically with ornamental plants used in landscapes, despite the fact that salt stress causes serious damage in these species (Cassaniti et al., 2009a; Marosz, 2004). Salinity is of rising importance in landscaping because of the increase of green areas in the urban environment where the scarcity of water has led to the reuse of wastewaters for irrigation (McCammon et al., 2009; Navarro et al., 2008). Salinity is also a reality in coastal gardens and landscapes, where plants are damaged by aerosols originating from the sea (Ferrante et al., 2011) and in countries where large amounts of de-icing salts are applied to roadways during the winter months (Townsend & Kwolek, 1987). Although water is used for purposes other than irrigation, “a landscape may serve as a visual indicator of water use to the general public due to its visual exposure” (Thayer, 1976). While in the past only good quality water (in some States of the USA, homeowners used approximately 60% of potable water to irrigate landscapes; Utah Division of Water Resources, 2003) was used for landscaping and/or floriculture (Tab. 1), nowadays the ecological sensitivity widely diffused in landscape management and planning (Botequilla Leitao & Ahern, 2002) determines the need to explore alternative water sources for irrigation. Landscape water conservation consequently requires making choices of plant species able to tolerate salt stress in order to allow the use of low quality water. Alternative water sources might be recycled water, treated municipal effluent and brackish groundwater, all of which generally have higher levels of salts compared with potable waters (Niu et al., 2007b). Treated effluent may also contain nutrients essential for plant growth; if water quality is good (not too saline), treated effluent can improve plant growth and reduce fertilizer requirements (Gori et al., 2000; Quist et al., 1999); application of industrial and municipal wastewater to land can be an environmentally safe water management strategy (Rodriguez, 2005; Ruiz et al., 2006). The potential physical, chemical or biological problems that are associated with effluent water applied to edible crops (Kirkam, 1986) are of lesser concern for landscape plant production (Gori et al., 2000).

Effects of salt stress imposed during two growth phases on cauliflower production and quality

BACKGROUND Cultivation of cauliflower is diffused in Mediterranean areas where water salinity results in the need to identify alternative irrigation sources or management strategies. Using saline water during two growth phases (from transplanting to visible appearance of inflorescence or from appearance of inflorescence to head harvest), the present study aimed to identify the growth period that is more suitable for irrigation with low quality water in relation to cauliflower production and quality. RESULTS Salinity affected cauliflower growth mainly when imposed in the first growth phase. The growth reduction depended mainly on ion-specific effects, although slight nutrient imbalances as a result of Na+ and Cl- antagonisms were observed. The use of non-saline water in the first or second growth period reduced both the osmotic and toxic effects of salinity. When salinity was applied during inflorescence growth, yield was reduced because of a restriction of water accumulation in the head. CONCLUSION The results of the present study demonstrate the possibility of producing marketable cauliflower heads under conditions of salinity by timing the application of the best quality water during the first growth phase to improve fruit quality and during the second phase to reduce the negative effects of salinity on yield.

The influence of rootstock on growth and ion concentrations in pepper (Capsicum annuum L.) under saline conditions

SUMMARY A study was conducted to evaluate the influence of rootstock on the growth and ion concentrations in pepper (Capsicum annuum L.) plants under salt stress. Pepper plants (‘Ibleor’) were grafted onto three different rootstocks (‘Atlante’, ‘Galaxy’, and ‘Robusto’). Non-grafted ‘Ibleor’ plants were also studied as controls. Treatments consisted of a non-saline nutrient solution or two iso-osmotic saline plus nutrient treatments (30 mM NaCl and 20.5 mM Na2SO4). Grafting did not enhance the growth of pepper plants under non-saline conditions, whereas reductions in growth due to salinity were attenuated in grafted plants compared to non-grafted plants. The different levels of tolerance of the three rootstocks to salinity did not appear to be related to the capacity of each genotype to maintain leaf turgor by osmotic adjustments, but did appear to be associated primarily with a reduced uptake of toxic ions and, therefore, to a lower concentration of these ions in the grafted plants. The nutritional status of plants exposed to either saline treatment was influenced only slightly by grafting.

Arsenic uptake and partitioning in grafted tomato plants

Arsenic is a toxic and cancerogenic metalloid that poses a threat to food crop consumption. Previous studies have shown that grafting vegetables onto certain rootstocks may restrict the uptake of some toxic metals, such as cadmium, lead, and so on, but these studies did not investigate the uptake of arsenic. The aim of this work was to determine the following: i) if grafting can influence and reduce arsenic translocation in the root and/or aerial organs; ii) how tomato plants irrigated with arsenic-enriched nutrient solution (100 μg·L-1) accumulate this metalloid; and iii) if arsenic poses a potential risk to fruit quality. We found that differences in plant growth and the qualitative traits of fruits were mainly related to the adopted rootstock rather than to the addition of arsenic. Grafting influenced metalloid accumulation in roots and its translocation from roots to shoots and fruits. Tomato plants accumulated arsenic in their roots, and only a small portion was translocated to shoots and fruits, making the risk for human consumption negligible. Therefore, the uptake of this toxic element and its translocation are influenced by the rootstock utilized.

Tomato and eggplant scions influence the effect of rootstock under Na2SO4 salinity

A short-term experiment was conducted to investigate whether the effect of rootstock on plant response to salinity depends on the solanaceous species used as scion. Tomato cv. ‘Ikram’ and eggplant cv. ‘Black Bell’ were grafted onto two tomato interspecific hybrids (‘Beaufort’ and ‘He-Man’). Plants were grown in an open soilless cultivation system and supplied with two nutrient solutions: non-saline control and a saline solution (adding 15 mM Na2SO4, 3.7 dS m−1). Plant dry biomass production and partitioning were influenced by salinity, but its effect was depending on the rootstock/scion combination. ‘Beaufort’ eliminated the deleterious effect of salinity when tomato was used as scion, but reduced (−29.6%) the shoot biomass of eggplant. ‘He-Man’ had a different effect on scion growth under saline conditions: shoot biomass was less reduced in eggplant (−20.6%) than in tomato (−26.8%). Under salt stress, ‘Beaufort’ reduced the accumulation of Na+ in tomato leaves more than in eggplant, whereas no differences were observed between tomato and eggplant grafted onto ‘He-Man’. Stem Na+ accumulation followed a different pattern. The increase of Na+ in the stems was similar for tomato and eggplant grafted onto ‘Beaufort’, whereas stems of tomato accumulated more Na+ compared to eggplant grafted onto ‘He-Man’. The opposite response of the tested rootstocks to salt stress when the scion was either tomato or eggplant seems to be partially related to the capacity of the rootstock and scion to exclude Na+ from the shoot. However, the results of nutrient accumulation within plant tissues imply that other mechanisms in addition to ion competition are involved in the salt resistance of grafted plants.