| dc.description.abstract | Studies were carried out in the laboratory, greenhouse and in the field to determine the
possibility of optimizing the C:N ratios in organic soil amendments for the control of
root-knot nematodes. Amendments with high eN ratios were combined with those
with low C:N ratios to attain an optimum level of between 13 and 20. Amendments
whose C:N ratios fell within the optimum range were treated as separate entries.
Seventeen organic amendments and amendment combinations were screened in the
greenhouse for their effectiveness in root-knot nematode control in tomato cv. Cal J.
The amendments included sawdust, pyrethrum marc, pig manure, cow manure, sheep
manure, chicken manure, neem cake powder, Calliandra, Leuceana, pyrethrum marc
colonized by Aspergillus niger, pyrethrum marc colonised by Trichoderma spp.,
Calliandra + sawdust, Leuceana + sawdust, Calliandra + sheep nure, Leuceana + pig
manure, cow manure + neem cake powder and chicken manure + cow manure. All the
organic amendments evaluated significantly (P=0.05) suppressed Meloidogyne spp.
populations in soil and also significantly (J>=0.05) reduced the severity of galling.
Control of root -knot disease was not limited to the amendments with C:N ratios within
or below the optimum range. Pyrethrum marc, pyrethr urn marc colonized by A. niger,
pyrethrum marc colonized by Trichoderma and pig manure had C:N ratios above the
optimum but were highly effective in root-knot disease control. On the other hand,
sheep manure and cow manure had their C:N ratios within the optimum range but had
lesser levels of root -knot disease control.
Among the various types of animal manures, chicken manure had the highest level of
disease control as measured by galling indices followed by pig manure while control
with cow manure and sheep manure was lowest. The green manures, Leuceana and
Calliandra, also effected a significant (P=0.05) reduction in disease severity as
measured by galling indices. Sawdust gave a significant (P=0.05) reduction in galling
index as compared to the unamended soil but the level of disease control was lowest
compared to other amendments. Neem powder, pyrethrum marc, pyrethrum marc
colonized by Trichoderma spp. and pyrethrum marc colonized by A, niger although
highly effective in root-knot disease control were found to be phytotoxic.
Neem powder, pyrethrum marc, pyrethrum marc colonized by A. -niger, pyrethrum
marc colonized by Trichoderma spp. and chicken manure significantly (P=0.05)
delayed seedling emergence. Use of water extracts from organic amendments in seed
germination tests showed that the delay in emergence was due to inhibition of
germination by the extracts from these amendments.
Three organic amendments were selected from the 17 for further experiments on
determination of the most effective rate and time of application. Selection was based
on the level of control, the type (source) of the amendment and its availability.
Chicken manure was selected among the animal manures, Calliandra from the green
manures and pyrethrum marc from the agricultural waste. Three levels of application
were used, 2.5% weightof amendment to weight of soil (w/w), 5.0% (w/w) and 7.5%
(w/w). Increase in rate of application resulted in an increase in disease control, except
for Calliandra where galling increased after 5.0% (w/w) level of application.
Growth retardation and phytotoxicity also increased with increase in application rates
of pyrethrum marc. Amendments applied at planting were more effective in disease
control than those applied two or four weeks before planting.
Water extracts from organic amendments were found to be highly toxic to root-knot
nematode juveniles with most of the juveniles being immobilized within 10 hours of
exposure to the extracts.
Twelve of the most effective and readily available organic amendments were selected
from the 17 and evaluated in a root-knot nematode infested field for their effectiveness
in disease control using tomato cv. Cal - J. Except for Calliandra, Calliandra + sheep
manure and cow manure where the control was not significant (P=0.05), all the other
organic amendments used in the field significantly (P=0.05) reduced the galling indices
compared to the control. Pyrethrum marc colonized by A. niger had the highest
reduction followed by pyrethrum marc colonized by Trichoderma, Leuceana + prg
manure, chicken manure, pyrethrum marc, chicken manure + cow manure and pig
manure. | en |
