potassium due changes in plasma-membrane permeability
to ions (Cocucci et al. 1983). Indeed, rice resistance to
brown spot is affected by ophiobolin A, which decreases
the content of phenolics and the activities of peroxidase and
phenylalanine ammonia-lyase (Vidhyasekaran et al. 1992).
Lesions caused by B. oryzae reduce the leaf photosynthetic
area and the efficient use of nutrients, which ultimately
decreases the number of tillering nodes (Lee 1992). The
number and the weight of grains per panicle can also be
dramatically reduced (Aluko 1975).
Brown spot disease also leads to a reduction in the total
photosynthetic pigments in rice leaves (Abdel-Fattha et al.
2007; Shabana et al. 2008). The content of leaf pigments
and membrane integrity are crucial for maintenance of the
net CO 2 assimilation rate (A) in plants (Matsuda et al.
2004). Plazek et al. (2004) showed that cold-induced
resistance to B. sorokiniana in barley had a significant
connection between the quantum yield of photosystem II
and host resistance. Reduction on the content of leaf
pigments can be caused by several pathogens such as
Exsorohilum turcicum on maize (Chauhan et al. 1997),
Alternaria alternata on tomato (Abbas et al. 1995), and B.
sorokiniana on Poa pratiensis (Hodges and Campbell
1999). Wheat resistance to B. sorokiniana was associated
with the strength of the epidermal cell-wall and low
electrolyte leakage (Ibeagha et al. 2005). Cold-induced
resistance of barley to B. sorokiniana correlated with a
decrease in cell membrane permeability (Plazek and Zur
2004). The non-host selective toxins produced by B.
sorokiniana disrupt membrane potential and induce chlo-
rophyll loss by directly damaging the chloroplasts with a
concurrent release of ethane (Hodges and Campbell 1999).
No information is available concerning the effect of B.
oryzae infection on rice leaves at the cellular level and its
effect on photosynthetic parameters. Thus, the aim of this
study was to investigate, in vivo, the damage to cell
membranes caused by B. oryzae infection and the changes
on some photosynthetic parameters.