One species, pathogen and stress intensity. Alkalinity

One of the first studies in stress
combination, especially alkalinity and salinity was performed  by (Rabhi et al. 2007) using  Medicago ciliaris. The shared responses
are general physiological adaptation of plants and can guard them against
multiple individual stresses. Some unique adaptation strategies tailored for
stress combinations have been identified in the recent reports (Mittler 2006;
Prasch and Sonnewald 2013). Among different stress combinations that
occur in field conditions, heat and drought stress and their interaction with
pathogens are the most studied (Mittler 2006; Pandey et al. 2015; Ramegowda
and Senthil-Kumar 2015). Plant adaptation strategy to a combination
of two stresses consists of both “shared” and “unique” response. Shared
responses refer to the molecular and physiological responses which are common
to the two different stresses and unique responses are the ones which are
specific to the individual stresses or the stress combinations (Rizhsky et al. 2002). Appearance of many abiotic stresses such as
heat, salinity, alkalinity and drought change the reaction of plant to certain
stress. The outcomes of these
interactions can either provide resistance or susceptibility toward any of the
two stresses depending on the plant species, pathogen and stress intensity.
Alkalinity (high soil pH) often co-occurs with salinity (high soil NaCl
concentrations) in the landscape: many saline soils are also alkaline due to
the presence of sodium carbonates (Rengasamy 2010). Like salinity, alkalinity exacerbates water
loss, interfering with stomatal closure due to the accumulation of sodium ions (Bernstein 1975). Soils of high pH often have poor structure,
affecting their hydraulic conductivity and the plants’ water uptake, and
causing hypoxia in the root zone (Bernstein 1975). Both these factors affect water use
efficiency, which is also one of the major stresses for plants in saline
environments. Plants equipped to deal with salinity and alkalinity employ
osmotic adjustments that are not found in plants without tolerance to either
stresses or which make tolerant plants naturally resistant to water stress.
Furthermore, both salinity and alkalinity affect photosynthesis and metabolism through
a range of physiological and molecular processes (Suriyan et al. 2009). It is therefore possible that because of the
shared challenges, salt and alkaline tolerance have evolved in closely related
lineages that possess traits enabling the evolution of mechanisms of tolerance
to either stress. Saline and alkaline stress occur normally in the north
African fields where both stress are there, in my current study we tested
several M. truncatula accessions to
combined stress to have a contrasting lines that have the ability to tolerate
combined stress. Under particular biotic or abiotic stress condition, developed
in controlled growth condition in the laboratory have failed to show enhanced
tolerance when tested in the field, therefore this gap might explain why many
of the transgenic plants with enhance tolerance to stress failed. A focus
on molecular, physiological and metabolic aspects of stress combination is
vital to bridge this gap and facilitate the development of crops and plants
with enhanced tolerance to field stress conditions.