poster - International Conference of Agricultural Engineering

FIGURE 3: SPAD index in cowpea as a function of salinity of irrigation water. Campina
Grande, Paraíba, Brazil, 2012.
irrigation, where saline stress showed influence on the accumulation of chlorophyll in the
leaves. According to these authors, the levels of biochemical constituents of the leaves as
photosynthetic pigments, are reduced by salinity, and this effect is compounded by the length
and level of exposure to stress condition. In response to conditions of high soil salinity, the
plants develop various physiological and biochemical alterations (Munns & Tester, 2008). In
plants subjected to salinity decreases in chlorophyll concentration can be attributed to
increased activity of the enzyme that degrades the chlorophyll chlorophyllase (Sharma &
Hall, 1991). Campbell et al. (2008) showed that the increase in the salinity significantly
reduced levels of chlorophyll a, b and total. Under which of the biochemical point of view,
observed reductions in chlorophyll content in plants under salt stress, appear to be related to
reduced ability of plants to synthesize or further degradation of pigments.
The number of nodules of all genotypes of cowpea plants submitted to increasing levels of
salinity of irrigation water, was adversely affected, the largest decrease in the order of 75%
and observed for genotype MNC01-649F-1-3 (data not shown). According to other authors,
the effect of salt on nodulation varies depending on the host legume species (Cordovilla et
al., 1999). In studies with pea and bean, Bohlool & Singleton, (1984) evaluated the effect of
salt stress on nodulation and plant growth and observed that there was an inhibition of
nodulation in both species. However, according to the authors, the pea had a higher
sensitivity to salt stress than the beans. Previously, Singleton & Bohlool, (1984) evaluated
the nodulation of soybean under different salinity levels and observed that the plants were
sensitive to increasing salinity levels.
4. Conclusions
No significant interaction between factors and between both genotypes, however there was a
decrease in the values obtained in response to increasing salinity of irrigation water. Salt
stress caused a decrease in pigmentation of the leaves and nodulation of cowpea.