Effect of pesticides on leguminous plants: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 96

inhibition of nodule formation (rhizobial bacterium)
but other pesticides, namely Lorsban, Decis, Karate
and Ripcord were considered safe for the rhizobial
population. For Azotobacter, Lorsban was seen to have no
side effect on the nodulation process whereas other four
pesticides (Pyrifos, Decis, Karate and Ripcord) were
observed to have a negative impact on nodulation
(Khan et al., 2009). In Vigna sinensis L., Phaseolus vulgaris
L. and Lupinus albus L., a decline in the nodulation pro-
cess was observed after treating the plants with Afugan,
Brominal, Gramoxone, Selecron and sumi oil (Abd-Alla
et al., 2000). Atrazine, isoproturon and metribuzin
application to Vigna radiata resulted in a reduction of
nodule number (Khan et al., 2006). Application of the
pesticide fipronil to Pisum sativum, Cicer arietinum, Lens
esculentum and Vigna radiata has caused a reduction in
nodule formation. This pesticide also has a negative
effect on the leghaemoglobin content of nodules
(Ahemad & Khan, 2011c).

which in turn diminishes the fixed nitrogen content and
plant yield (Fox et al., 2007). The pesticide tebuconazole
negatively affected the symbiotic association between pea
and Rhizobium , consequently decreasing the growth,
nutrient uptake and seed yield of the plants (Ahemad &
Khan, 2011d). The survival and viability of Bradyrhizobium
on peanut seeds was inhibited by the pesticides Vitavax
and benomyl. Due to this, the symbiosis of Bradyrhizobium
with peanut was inhibited, resulting in the reduction in
nitrogen fixation and seed yield of the plants (Hashem et
al., 1997). All these studies demonstrate that pesticide
stress weakens the association between legumes and
nitrogen-fixing bacteria, which in turn decreases nodu-
lation and nitrogenase activity. Under these conditions,
the amount of fixed nitrogen declines, which reduces
the yield of the host plants (Figure 6.1).

6.4 pesticide tolerance in legumes

6.3.4.2 Effect on nitrogenase activity
A decline in nitrogenase activity was observed in the
legume Medicago sativa L. under pesticide stress (methyl
parathion, DDT, bisphenol A and pentachlorophenol),
which resulted in a reduction of nitrogen content and
yield of the plant (Fox et al., 2007). Reduced nitrogenase
activity was noted in Cicer arietinum, Lens esculentum,
Pisum sativum and Vigna radiata after pyriproxyfen appli-
cation. This was due to the decline in leghaemoglobin
content inside root nodules (Ahemed, 2014). In Medicago
sativa, a significant reduction in nitrogenase activity was
observed after treating the plant with DDT, methyl
parathion, pentachlorophenol and chrysin (Fox et al.,
2007). Decline in nitrogenase activity of the bacteria
Rhizobium and Bradyrhizobium was seen in the legumes
Trifolium pratense, Medicago sativa and Ornithopus compres-
sus after the use of the pesticides Funaben T and Pivot
100SL. In Arachis hypogaea, application of endosulfan
(conc. 250 ppm) resulted in decreased nitrogenase
activity (Darure et al., 2012).
Effective symbiosis by rhizobia enhanced nodulation
and nitrogen fixation, and the availability of more
nitrogen to the plants increased their yield (Graham &
Vance, 2000). Differences in nodule number induced dif-
ferences in the fixed nitrogen and affected the yield of
the host plant (Amijee & Giller, 1998). It has been dem-
onstrated that pesticides result in the reduction of
attachment of rhizobia to the roots of leguminous plants,

Rhizobacteria enhance the plant growth and produc-
tivity by the production of siderophores, phytohormones,
antibiotics, etc. They also decrease ethylene concentration
and induce systemic resistance (Lugtenberg & Kamilova,
2009; Zaidi et al., 2009; Tank & Saraf, 2010). Rhizobacteria
may degrade or hydrolyse pesticides enzymatically
(Herman et al., 2005; Yang & Lee, 2008). The symbiotic
association between rhizobia and bradyrhizobia enhances
nitrogen fixation throughout the root length, which
reduces the requirement for inorganic nitrogen and
improves the soil nitrogen content (Sanginga et al.,
1996; Bellone et al., 1997). Rhizobium increases the
nitrogen-fixing capacity of plants through symbiotic
association with them (Fox et al., 2007). Legume plants
were inoculated with competent rhizobial strains to
enhance the nodulation and nitrogen fixation (Ahemad &
Khan, 2009). Phosphorus is one of the most important
elements for plant growth and productivity. Some
rhizobial strains of Bradyrhizobium and Rhizobium legu-
minosarum bv. phaseoli can solubilize insoluble phosphate
and enhance plant growth (Halder & Chakrabartty,
1993). When Rhizobium and phosphate-solubilizing
bacteria were used together, a synergistic effect on grain
yield and symbiotic effectiveness of mungbean was
observed. Phosphate-solubilizing bacteria improved the
symbiotic effectiveness and competitive ability of inocu-
lated Rhizobium sp. under field conditions in lentil
(Kumar & Chandra, 2008). Symbiotic bradyrhizobia