Agriculture Reference
In-Depth Information
[5]. However, the bicarbonate mode of action is not well understood. Some of its
effects have been related to its pH buffering capacity (bicarbonate can maintain a
high pH in the medium, which can diminish Fe solubility and Fe
3+
reduction) but,
besides these pH-mediated effects, bicarbonate can also inhibit the induction of
Fe responses [5].
Fe deficiency is widely reported in several legume crops, like soybean,
peanut and dry bean. Field pea is reported as a moderately sensitive crop [7],
although Fe chlorosis is a worldwide agricultural problem in this species, as
indicated by research works in different countries [8-13]. Most of these
research works are aimed to study the variability in tolerance to calcareous
soils among different pea genotypes and the physiological mechanisms behind
the tolerance [8-13].
For the screening of pea genotypes tolerant to calcareous soils, several
methodological approaches are employed, similar to the ones used for other
dicot plants. The most direct one is to compare the behaviour of different
genotypes when grown in calcareous soils, either in pots or in the field [11].
Another common approach is to compare the genotypes when grown in
nutrient solution with bicarbonate, that simulate the conditions of calcareous
soils [8-13]. For pea, the bicarbonate concentrations more frequently used
ranged from 10 to 15 mM [8-13]. The parameters commonly used to compare
the behaviour of the different genotypes are chlorosis score, chlorophyll
content in young leaves, Fe concentration, active Fe concentration (it not the
total Fe), and shoot and root growth [8-13]. It has been found that the root to
shoot ratio increases upon bicarbonate treatment, and some authors have tried
to relate this parameter to the tolerance (frequently, sensitive cultivars have
higher root to shoot ratios under bicarbonate treatment than the tolerant ones
[8]) but other ones have not found such a relationship [11]. Finally, an
approach that could be more frequently used in the future is the identification
of physiological traits related to the tolerance to Fe deficiency. Some traits that
can be used in pea to discriminate between tolerant and sensitive genotypes are
the following ones. First, traits associated with Fe acquisition by roots, such as
acidification capacity and capacity to enhance ferric reductase activity [9,12].
One of the problems with these traits is that they should be determined several
times because they change daily [11-12]. In the case of the ferric reductase
activity, some works have found a relationship with the tolerance to chlorosis
but some others have not [11-12]. Other possible traits for screening are the
ones related to Fe translocation from roots to shoots, such as citrate
concentration, and to Fe signaling, such as ethylene production [12-13].
Finally, some authors have found that the tolerant cultivars have greater ability
