Allelochemicals Biologica... - Name

68
ANA LUISA ANAYA
effects on microbial composition of the soybean rhizosphere were also determined by
identifying microorganisms. Bacteria strains were identified rising fatty acid analysis,
and fungus identification was done rising standard morphological measurements and
appropriate taxonomic keys. Results showed that most amendments alone or in
combination with benzaldehyde reduced damage from plant parasitic nematodes.
Benzaldehyde applied alone or in combination with the amendments exerted a selective
action on the activity and composition of microbial populations in the soybean
rhizosphere. In control soils the bacterial flora was predominantly Gram-negative,
while in soils amended with velvetbean or kudzu alone or with benzaldehyde. Grampositive
bacteria were dominant. Mycoflora promoted by the different amendments or
combinations with benzaldehyde included species of Aspergillus, Myrothecium,
Penicillium, and Trichoderma.
Calvet et al. (2001) evaluated the survival of two species of plant parasitic
nematodes: the root-lesion nematode Pratylenchus brachyurus, and the root-knot
nematode Meloidogyne javanica, in saturated atmospheres of 12 natural chemical
compounds. The infectivity of two isolates of arbuscular mycorrhizal fungi: Glomus
mosseae and Glomus intraradices, under identical experimental conditions, was also
determined. All the compounds tested exerted a highly significant control against M.
javanica and among them, benzaldehyde, salicilaldehyde, borneol, p-anisaldehyde
and cinnamaldehyde caused a mortality rate above 50% over P. brachyurus. The
infectivity of G. intraradices was inhibited by cinnamaldehyde, salicilaldehyde, thymol,
carvacrol, p-anisaldehyde, and benzaldehyde, while only cinnamaldehyde and thymol
significantly inhibited mycorrhizal colonization by G. mosseae.
When soybean plant responses to Meloidogyne incognita infestation were
compared to resistant (Bryan) and susceptible (Brim) cultivars at 0, 1, 3, 10, 20, and
34 days after infestation, Qiu and collaborators (1997) observed that the resistant
cultivar had higher chitinase activity than the susceptible cultivar at every sample
time beginning at the third day. Results from isoelectric focusing gel electrophoresis
analyses indicated that three acidic chitinase isozymes with isoelectric points (pIs) of
4.8, 4.4, and 4.2 accumulated to a greater extent in the resistant compared to the
susceptible cultivar following challenge. SDS-PAGE analysis of root proteins revealed
that two proteins with molecular weights of approximately 31 and 46 kD accumulated
more rapidly and to a higher level in the resistant than in the susceptible cultivar.
Additionally, three major protein bands (33, 22, and 20 kD) with chitinase activity
were detected with a modified SDS-PAGE analysis in which glycolchitin was added
into the gel matrix. These results indicate that higher chitinase activity and early
induction of specific chitinase isozymes may be associated with resistance to rootknot
nematode in soybean.
Antagonists, most likely favored by selected cover crops, include mainly fungal
egg parasites, trapping fungi, endoparasitic fungi, fungal parasites of females,
endomycorrhizal fungi, planthealth promoting rhizobacteria, and obligate bacterial
parasites. There are several hypotheses on how cover crops can enhance nematodeantagonistic
activities. A series of ecological events may be involved. The decomposing