Abstract:
Worldwide, root-knot (Meloidogyne species) nematodes are considered to be the
most important and damaging genus in crop husbandry. The existence of a wide
host range, over 2000 plants, and several biological races, makes the management
of this nematode genus difficult with nematode-resistant crop Hybrid Sorghum
Sudan grass (Sorghum bicolor × Sorghum Sundanese) has been classified as being
resistant to certain Meloidogyne species and races, with a wide range of uses in crop
rotation intended to manage nematode population densities. However, due to the
ability of nematodes to enter chemiobiosis when gradually exposed to chemicals,
this hybrid might not be effective in managing nematode population densities for the
subsequent highly susceptible sweet potato (Ipomoea batatas L.) cultivars. The
objective of the study was to determine whether hybrid Sorghum-Sudan grass would
suppress M. javanica (Trial 1), M. incognita race 2 (Trial 2) and M. incognita race 4
(Trial 3) population densities, allowing a nematode susceptible sweet potato cv.
′Beauregard′ as successor crop to be cultivated without suffering nematode damage.
The hybrid Sorghum-Sudan grass study was conducted under greenhouse
conditions, with seven inoculation levels, namely, 0; 5; 25; 125; 625; 3 125 and 15
625 eggs and second-stage juveniles (J2) of each nematode species or race,
arranged in randomised complete block design, with six replications and validated in
time. Plant growth, foliar nutrient elements and nematodes were collected at 56 days
after inoculation and prepared for analysis using standard methods. The
reproductive factor (RF) at all levels was zero, whereas nematode inoculation at all
levels did not have any effect on plant growth of the hybrid Sorghum-Sudan grass.
However, the nematode levels affected the accumulation of nutrient elements and
the quality of forage. After cultivating the susceptible sweet potato cultivar in pots
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previously with hybrid Sorghum-Sudan grass at increasing levels of M. javanica
alone, that is in Trial 1, similar results were observed with respect to RF and lack of
nematode damage to plant growth. Consequently, the hybrid was suitable for use in
crop rotation with sweet potato for the purpose of managing nematode population
densities of thermophilic Meloidogyne species and/or races.
