Osmotic and toxic ion effects on seedling emergence and nutrition of citrus rootstocks

Abstract

The effects of isosmotic solutions of sodium chloride (NaCl), polyethylene glycol (PEG), and mannitol with or without supplemental calcium (Ca) were compared to separate osmotic effects from toxic ion effects of salts on seed imbibition, seedling emergence, and the early stage of seedling growth of three citrus rootstocks. The rate of seed imbibition was relatively low for sour orange (SO) in PEG treatments which caused a delay in seedling emergence. These results of PEG supported earlier findings which suggested the existence of a critical level of hydration that seeds must reach before germination can proceed. Final percent emergence (FPE) was reduced the most by NaCl and mannitol compared with PEG. Furthermore, Ca addition to mannitol and NaCl solutions improved FPE in Cleopatra mandarin (CM) and trifoliate orange (TO). These results demonstrated that the effects of mannitol and NaCl on FPE went beyond the osmotic effects. Seedling growth was reduced the most by mannitol not only due to its uptake and transport to the leaves and stems where it caused dehydration and visible leaf injury but also to reduction in shoot Ca and potassium (K) concentrations. This study showed that the effects of salts on seed imbibition and time to emergence of the first seedling was primarily osmotic, while their effects on FPE and seedling growth was mainly toxic.

Effect of seed coat removal and controlled-release fertilizer application on plant emergence and vegetative growth of two citrus rootstocks

“…There was no effect of controlled-release fertilizer concentrations on plant emergence ( figure 1). Citrus rootstock germination has been affected by high osmotic or salinity levels in the substrate [12,13]. In the present case, the salinity index of the fertilizer is probably not high enough to decrease germination at the concentrations tested.…”

Osmotic and Autotoxic Effects of Leaf Extracts on Germination and Seedling Growth of Alfalfa

“…Later, as the cotyledons slow in water uptake and expansion, Phase II begins, and the embryo axis, mainly the root, is likely the major sink for water and the toxin. Similar to citrus (Zekri, 1993), the effects of the autotoxin are mainly osmotic during the imbibition period but mainly toxic after Phase II begins. The toxin likely reduces RER while within the seed to further delay Gt 50 (Chon et al, 2003).…”

PEG stress altered citrus root and leaf mineral concentrations

“…The effects of PEG-induced water stress on growth, root density, seedling emergence, and plant water relations including leaf water potential, stomatal conductance and root hydraulic conductivity of citrus rootstocks have been investigated (Zekri, 1987;Zekri and Parsons, 1989,1990a, 1990bZekri, 1991bZekri, , 1993. However, none of these studies has shown the relationship between nutrient accumulation and concentration in the roots and nutrient translocation to the leaves.…”