Expression of Tolerance for Meloidogyne graminicola in Rice Cultivars as Affected by Soil Type and Flooding.

The effects of different water regimes on the pathogenicity of Meloidogyne graminicola on six rice cultivars were determined in two soil types in three greenhouse experiments. Two water regimes, simulating continuous flooding and intermittent flooding, were used with five of the cultivars. All cultivars were susceptible to the nematode, but IR72 and IR74 were more tolerant than IR20 and IR29 under intermittent flooding. All were tolerant under continuous flooding. UPLRi-5 was grown under multiple water regimes: no flooding; continuous flooding; flooding starting at maximum tillering, panicle initiation, or booting stage; and flooding from sowing until maximum tillering or booting. In sandy loam soil, M. graminicola reduced stem and leaf dry weight, root dry weight, and grain weight under all water regimes. In clay loam soil, the nematode reduced root weight when the soil was not flooded or flooded only for a short time, from panicle initiation, or booting to maturity, and from sowing to maximum tillering. In clay loam soil, stem and leaf dry weight, as well as grain weight, were reduced by the nematode under all water regimes except continuous flooding or when the soil was flooded from sowing to booting stage. These results indicate that rice cultivar tolerance of M. graminicola varies with water regime and that yield losses due to M. graminicola may be prevented or minimized when the rice crop is flooded early and kept flooded until a late stage of development.

Interpreting Upland Rice Yield and Pratylenchus zeae Relationships: Correspondence Analyses.

Correspondence analyses were used to explore the relationships between yield and populations of Pratylenchus zeae in an upland rice field and in a greenhouse experiment. Initial soil (Pi) and final root (Pf) population densities of P. zeae, and yield (Y) of rice cv. UPL Ri5 were determined at 490 spots in the field. Very low Y was linked to very high Pf. Low Y was linked to medium or high Pi and medium Pf. Medium to very high Y were clustered with undetectable Pi and very low or high Pf. All yield levels were independent of very high Pi. In the greenhouse experiment where seven nematode inoculum levels and three fertilizer levels were evaluated, low Y was associated with medium or high Pf and high Y with high or low Pf. The analyses indicated that nematode-yield interaction involved a complex, dynamic process, in which the root-carrying capacity probably was a determining factor. Correspondence analysis, which does not require assumptions on the shape of nematode population-yield relationships or on variable distributions, revealed meaningful associations in these complex data sets.

Sampling approaches for extensive surveys in nematology.

Extensive surveys of the frequency and abundance of plant-parasitic nematodes over large geographic areas provide useful data of unknown reliability. Time, cost, and logistical constraints may limit the sampling intensity that can be invested at any survey site. We developed a computer program to evaluate the probability of detection and the reliability of population estimates obtained by different strategies for collecting one sample of 10 cores from a field. We used data from two fields that had been sampled systematically and extensively as the basis for our analyses. Our analyses indicate that, at least for those two fields, it is possible to have a high probability of detecting the presence of nematode species and to reliably estimate abundance, with a single 10-core soil sample from a field. When species were rare or not uniformly distributed in a field, the probability of detection and reliability of the population estimate were correlated with the distance between core removal sites. Increasing the prescribed distance between cores resulted in the composite sample representing a wider range of microenvironments in the field.

Use of Green Manure Crops in Control of Hirschmanniella mucronata and H. oryzae in Irrigated Rice.

Four field experiments were conducted to study the effect of Sesbania rostrata and Aeschynomene afraspera as rotational and green manure crops on the population dynamics of Hirschmanniella mucronata and H. oryzae, and subsequent rice yields. The sequential cropping of the legumes with rice controlled both nematode species. In two experiments, yield of rice was related to the nematode population denisites at planting and harvesting of the second rice crop (R(2) = 0.391, P < 0.001, and R(2) = 0.57, P < 0.001), regardless of the treatments. Rice yield increases were attributed to nutritional effect of the green manure and the reduction of the nematode populations or the modification of a factor(s) linked to the nematode populations induced by their cropping. As the two leguminous crops do not generate direct return, using them to control the rice-root nematodes was not economical, despite the significant yield increase obtained.

Influence of photoperiod and temperature on migrations of meloidogyne juveniles.

Photoperiod influences the migration of M. incognita juveniles toward tomato roots. Approximately 33% migrated vertically 20 cm in 7 days to roots when 12 h dark were alternated with 12 h light. Only 7% migrated when light was constant for 24 h. Vertical migration of M. incognita juveniles was studied at 14, 16, 18, 20, and 22 C. The migration of M. incognita juveniles begins at about 18 C and reaches its maximum at 22 C. The migration of M. hapla and M. incognita juveniles were compared at 14, 18, and 22 C. Juveniles of M. hapla were able to migrate at a lower temperature than those of M. incognita. With M. hapla, there was no significant difference in migration between 18 and 22 C.

Effect of Soil Texture and the Clay Component on Migration of Meloidogyne incognita Second-stage Juveniles.

The vertical migration of M. incognita juveniles introduced at 20 cm from the roots was studied in five natural soils, 100% silica sand, 95% silica sand with 5% clay, 90% silica sand with 10% clay, and 95% silica sand with 5% clay as a concentrated layer. In natural soils the percentage of juveniles capable of migrating 20 cm and penetrating the roots decreased when the percentage of clay and silt increased. No migration occurred in silica sand without clay particles; when 5 or 10% of clay were mixed to silica sand, 34 and 26%, respectively, of the juveniles were able to migrate 20 cm. Clay separated from silica sand in which tomatoes were grown was attractive for juveniles. It is suggested that clay particles aid in the migration of root-knot juveniles over long distances to plant roots by absorbing and holding root exudates or bacterial by-products which form a concentration gradient enabling nematodes to locate roots.

Genetic investigations on chronic forms of infantile and juvenile spinal muscular atrophy.

A material of 247 cases selected from 260 cases of spinal muscular atrophy in the Warsaw Department of Neurology in 1960-1974 was analyzed. The size of sibships was established and calculations were made of the mean distribution of the age at onset, also according to sex, for the different clinical forms, genetical proportions by the method of siblings and of probands, and coefficient of sib-sib correlation for the material as a whole and separately for males, females and male-female pairs. The analysis shows the course of the disease to differ between the sexes and to be mild in males more often than in females, as is particularly noticeable in the higher age groups. Cases of Kugelberg-Welander's disease are predominantly male. The hypothesis is advanced that a proportion of male patients have a sex-linked modifying gene of a fairly high frequency (possibly of the range of 1 in 5 males, and 1 in 25, in the homozygous state, in females). Although it would not disprove conclusively the nosological distinctness of different forms of infantile and juvenile spinal muscular atrophy, the existence of the modifying gene, if proved, would tend rather to add to the likelihood of their constituting a single recessive autosomal disease.