Comparison of the damage potential and yield loss of the rice root–knot nematode, Meloidogyne graminicola, on lowland and upland rice varieties from Myanmar
Date
2015Author
Win, Pa Pa
De Waele, Dirk
Kyi, Pyone Pyone
Maung, Zin Thu Zar
Myint, Yi Yi
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In Asia, the rice root-knot nematode, Meloidogyne graminicola, is an important pathogen of
Asian rice (Oryza sativa) in most rice producing countries including Myanmar. In the first part of our
study, the damage potential of M. graminicola on commonly cultivated newly released high-yielding
lowland rice varieties and upland rice varieties (traditional, improved and aerobic), which are being
grown in different regions in the summer-irrigated lowland and rainfed upland rice ecosystems in
Myanmar, was investigated under screenhouse conditions. In the second part of our study, a field
experiment was carried out in the Ayeyarwady River Delta, the major lowland rice producing area of
Myanmar, to investigate the impact of M. graminicola on plant growth and yield of the same lowland rice
varieties included in the screenhouse experiment in a naturally-infested farmer’s field. None of the 15
lowland varieties and none of the nine upland varieties included in the screenhouse experiments was
resistant to M. graminicola. Although differences in susceptibility were observed among the lowland and
upland varieties, and between the two types (lowland and upland) of rice varieties, with an Mf–eggs
(multiplication factor of the second-stage juveniles without counting the eggs) ranging from 13.2 to 52.8
for the lowland varieties vs 39.8 to 108.4 for the upland varieties, all varieties included in our study can
be considered as highly susceptible to M. graminicola when the nematode population densities are
assessed at harvest. Also in the field experiment, all the 15 lowland varieties were susceptible to M.
graminicola infection. This part of our study shows that upland rice varieties are more susceptible to M
graminicola infection than lowland rice varieties. The percentage reduction in lowland and upland
varieties was very similar in six out of the ten plant growth and yield-contributing traits measured. The
highest differences in percentage reduction were observed for fresh root weight (41.0 vs 26.1% for the
lowland and upland varieties, respectively), number of tillers per plant (29.1 vs 14.1%, respectively),
percentage filled grains per plant (11.7 vs 0.8%, respectively) and filled grain weight per plant (34.7 vs
47.6 g, respectively). Within the two types of rice varieties significant differences in percentage reduction
of plant growth traits between uninoculated and inoculated plants were observed among the rice varieties,
so we suggest that the effect of M. graminicola infection on the different vegetative and reproductive
plant growth stages of rice varieties is highly genotype-dependent and that no general conclusions can be
made. In the screenhouse experiments, infection with M. graminicola caused on average a yield reduction
with 31.1% in the lowland rice varieties vs 44.9% in the upland rice varieties, which indicates that in the
upland varieties the higher nematode population densities per root unit (1 g) and per root system resulted
in a higher yield loss compared with the lowland varieties. In the field experiment, carbofuran treatment
resulted, on average, in a 16.5% increase in yield of the lowland rice varieties
URI
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