RESUMEN
An experiment to evaluate the control of soybean cyst nematodes compared 1-year, 2-year, and 3-year nonhost rotations with continuous soybeans (Glycine max) in 0.2-ha plots. In a second 1-year rotation, the plots were planted to soybean or corn (Zea mays) after fumigation in the spring with a split application of 1,3-dichloropropene (748.2 liters/ha). The effects of the nematicide were apparent the first year. Soybean yield was 1,482 kg/ha compared to 233 kg/ha in the untreated plots. In the second year, the highest yielding plants (2,035 kg/ha) were those following 1 year of corn that had been treated the previous year; plants in untreated plots yielded 288 kg/ha. Average yield of soybean following 1 year of corn was 957 kg/ha compared to 288 kg/ha for continuous soybean. In the third year, the effects of the nematicide were still evident. Soybean plants in plots treated the first year, followed by corn, then soybean, yielded 1,044 kg/ha compared to 761 kg/ ha for soybean following 1 year of corn and 991 kg/ha for soybean following 2 years of corn. Plots planted to soybean for 3 consecutive years yielded 337 kg/ha. Nematicidal effects were no longer evident during the fourth year. Yields were most improved by the greatest number of years in the nonhost crop; highest yields in descending order were from plants following 3 years of corn, 2 years of corn, and 1 year of corn. Plots planted to soybean for 4 consecutive years yielded 130 kg/ha. Highly significant negative correlations occurred each year between initial nematode population densities and seed yield.
RESUMEN
Quantitative techniques were used to analyze and determine optimal potential profitability of 3-year rotations of cotton, Gossypium hirsutum cv. Coker 315, and soybean, Glycine max cv. Centennial, with increasing population densities of Hoplolaimus columbus. Data collected from naturally infested on-farm research plots were combined with economic information to construct a microcomputer spreadsheet analysis of the cropping system. Nonlinear mathematical functions were fitted to field data to represent damage functions and population dynamic curves. Maximum yield losses due to H. columbus were estimated to be 20% on cotton and 42% on soybean. Maximum at-harvest population densities were calculated to be 182/100 cm(3) soil for cotton and 149/100 cm(3) soil for soybean. Projected net incomes ranged from a $17.74/ha net loss for the soybean-cotton-soybean sequence to a net profit of $46.80/ha for the cotton-soybean-cotton sequence. The relative profitability of various rotations changed as nematode densities increased, indicating economic thresholds for recommending alternative crop sequences. The utility and power of quantitative optimization was demonstrated for comparisons of rotations under different economic assumptions and with other management alternatives.
RESUMEN
The influence o f various crop rotations and nematode inoculum levels on subsequent population densities of Meloidogyne incognita races 1 and 3 were studied in microplots. Ten different 3-year sequences o f cotton, corn, peanut, or soybean, all with cotton as the 3rd-year crop, were grown in microplots infested with each race. Cotton monoculture, two seasons o f corn, or cotton followed by corn resulted in high race 3 population densities and severe root galling on cotton the 3rd year. Peanut for 2 years preceding cotton most effectively decreased the race 3 population and root galls on cotton the 3rd year. Race 1 did not significantly influence cotton growth or yield at initial populations of up to 5,000 eggs/500 cm(3) soil. At 5,000 eggs/500 cm(3), cotton growth was suppressed by race 3 but yield was not affected.
RESUMEN
Root gall induction and egg production by the four recognized host races and two cytological races of Meloidogyne incognita were compared on cotton Gossypium hirsutum cvs. Deltapine 16 (root-knot susceptible) and Auburn 634 (highly resistant). The 12 nematode populations included in the study were from various parts of the world. No population increases occurred on the highly resistant cultivar. After 45 days, populations of host races 1 and 2 induced slight root galling on both cuhivars with only limited reproduction. Host race 4 populations induced moderate root galling with higher reproduction on Deltapine 16 than that of race 1 or race 2 populations. Host race 3 populations induced severe root galling with population density increases of 7-30-fold. In a complementary study, 24 cotton cultivars or breeding lines were compared for suitability as hosts for a typical population of M. incognita race 3. The poorest hosts, 'Aubnru 623,' 'Auburn 634,' and 'McNair 220,' yielded fewer eggs after 45 days than were added initially. The best hosts - 'M-8.' 'DES 24-8,' 'McNair 235,' and 'Coker 20l' - yielded > 5 times as many eggs as were added initially.
RESUMEN
Microplot and greenhouse experiments were conducted to evaluate the effects of soil incorporation of the nematophagous fungus Arthrobotrys conoides and green alfalfa mulch on the population dynamics of Meloidogyne incognita on corn. Reproduction of M. incognita and the incidence of root galling were reduced by the addition of A. conoides and/or green alfalfa in all tests. Numbers of juveniles were reduced by as much as 84%, and eggs were fewest in early to mid-season soil samples from microplots. Yields increased in treatments with A. conoides and/or green alfalfa in greenhouse tests and in the microplot tests in 1979. No interaction was found between the fungus and green alfalfa in the reduction of the nematode population.
RESUMEN
The development of Meloidogyne platani on sycamore was followed for 40 days (22-28 C). Juveniles penetrated the feeder roots behind the root cap and invaded the vascular cylinder within 3 days after inoculation. All subsequent development of the nematodes and host effects occurred only within the stele. The second juvenile molt and sex differentiation occurred by the 17th day. Young females were observed by the 26th day. Eggs were observed inside the roots by the 35th day and were exposed to the surface of galls by the 40th day. In pathogenicity studies, a significant negative correlation was shown to exist between fresh shoot and root weights and inoculum density. Besides sycamore, white ash was the only hardwood species tested to become infected. Of the herbacious plants tested, tobacco was heavily galled, tomato and watermelon moderately galled, and pepper only slightly galled. Egg production was moderate on tobacco, slight on tomato and watermelon, and absent on pepper.
RESUMEN
In greenhouse experiments, the effect of Arthrobotrys conoides on Meloidogyne incognita population densities as affected by soil temperature, inoculum density, and green alfalfa was determined. The effect on M. incognita population densities was greater at a soil temperature of 25 C than at 18 or 32 C. Nematode control by A. conoides was most effective when the fungus was introduced into the soil 2 wk prior to nematode inoculation and planting of corn. Inoculum density of A. conoides was positively correlated with plant shoot weight (r = 0.81) and negatively correlated with numbers of Meloidogyne juveniles (r = -0.96), eggs (-0.89) and galls per gram of root (-0.91). A. conoides was not isolated from green alfalfa, but was isolated from alfalfa-amended soil to which no fungus had been added.
RESUMEN
Nematology on a world basis has experienced phenomenal growth during the last 25 years. Major influences responsible for this growth are discussed. Education of nematologists has been most evident in only a few developed nations. Some developing countries are now beginning to train nationals as nematologists. Research programs in developed countries are more intensive than in developing nations, largely because of available resources and priorities given to solving nematological problems. Developed nations have been able to take advantage of technological advances almost immediately, whereas in developing nations the lack of resources and constraints imposed by certain social or political conditions has made this difficult. Indications are that emphasis in training nematologists in developed countries may have reached a plateau, while in developing nations provisions for training and research are on the increase.
RESUMEN
Meloidogyne megatyla n. sp. is described from Pinus taeda in North Carolina. Stylet knobs are distinctively high in proportion to width, giving an especially massive appearance to the knobs of larvae and males. Mean larval length is 416 mum and stylet length is 14.6 mum. The perineal pattern is composed of smooth striae, with a high arch, and is often somewhat rectangular. The relationship of M. megatyla to other Meloidogyne species is unclear, although a comparison is made with Meloidogyne incognita and Meloidogyne mali. Galling was slight; only about 50 eggs were produced per egg mass, and under greenhouse conditions a single generation may take more than 10 weeks. Meloidogyne megatyla n. sp. did not reproduce on any of the differential hosts commonly used to distinguish among Meloidogyne species.
RESUMEN
Root-knot nematodes are widely distributed throughout the world. Their distribution and economic importance are purported to be related to biological and environmental factors favorable to Meloidogyne spp. A scheme for comparing Meloidogyne spp. with two other genera of diverse biological characteristics is presented to support this hypothesis. It is further suggested that a probability index can be developed to predict the likelihood of a given nematode species being transported, established, and becoming economically important in regions of the world where i t does not already occur.
RESUMEN
Among 17 species and cultivars of plants exposed to Anguina plantaginis, only Plantago aristata (bracted plantain) was a host. Larvae penetrated the emerging apical meristem; reproduces and migrated progressively; caused twisting and galling of leaves, looping andspiraling of peduncles, and transformation of floral structures into galls. Extreme infections caused stunting and death of entire plants. Hypertrophy and hyperplasia of leaf mesophyll, cell separation and disintegration, and xylem wall thickening in older galls occurred. Only third-stage larvae were infective, and they exhibited cryptobiosis under adverse conditions.
RESUMEN
Treated and nontreated field plots were assayed, and the population density of each plant-parasitic nematode present was compared with crop growth and yield and with the population densities of other nematode species in the same plots. The strongest correlations between nematode population densities and growth responses occurred when soil assays for nematodes were made 55-73 days after planting. Belonolairnus longicaudatus was the most damaging parasite on peanut, Arachis hypogaea, as evidenced by high negative correlations between population densities and plant growth responses. Criconemoides ornatus, Meloidogyne hapla, Helicotylenchus dihystera, Trichodorus christie, Tylenchorhynchus claytoni, and Pratylenchus brachyurus were involved to varying degrees, depending on previous crop and initial densities of these nematodes. Hoplolaimus galeatus and Xiphinema americanum did not appear to affect crop response. The negative correlation of Trichodorus christiei to yield of soybean, Glycine max, was higher than that of Belonolairnus longicaudatus, although both contributed to yield losses. Similar correlation analyses showed that apparent antagonistic or synergistic population-density relationships among nematodes under field conditions depend on the time of sampling and the composition of the nematode community under study.
RESUMEN
Morphological changes occurring during post-infection development and the influence of temperature on the life cycle of Heterodera lespedezae are reported. Morphological development was similar to that of H. schachtii. Each post-infection stage had a distinct styler, and fed actively. Detailed observations were made of cuticle formation and markings, esophageal glands, and reproductive system. Certain developmental phases, such as matrix deposition and oviposition, appeared to be correlated with color changes of the adult female body. The effect of temperature on nematode development was observed in a phytotron at day/night temperatures of 18/14, 18/18, 22/18, 26/22, 26/26, and 30/26 C; the optimum was 26/26 C. More time was required to complete the life cycle at the three lower temperatures than at the three higher temperatures.
RESUMEN
Soluble-protein and eight enzyme profiles obtained by polyacrylamide-gel electrophoresis were compared between Meloidogyne incognita and M. arenaria. Esterase, malate dehydrogenase, and alpha-glycerophosphate dehydrogenase patterns were distinctly characteristic for each species. Peroxidase and alpha-glycerophosphate dehydrogenase isoenzyme patterns varied when nematodes were propagated on different host plants. Similar profiles were obtained for two populations within each species. Antigenic proteins of these two species were compared following separation by electrophoresis.
RESUMEN
Various taxonomically useful profiles of four dehydrogenases (lactate, malate, glucose-6-phosphate, and a-glycerophosphate) and three hydrolases (acid and alkaline phosphatase and esterase) were detected in whole nematode homogenates of Meloidogynejavanica, M. hapla, M. incognita, M. arenaria, Ditylenchus dipsaci, D. triformis, Heterodera glycines, and Aphelenchus avenae. The enzyme profiles were stable in populations cultured on several different hosts. A tentative enzymically-determined phylogeny of Meloidogyne is given.
RESUMEN
Disc-electrophoretic separation of soluble proteins from whole nematode homogenates yielded band profiles useful for distinguishing selected species of Meloidogyne and Ditylenchus, and the genera Heterodera, and Aphelenchus. Certain protein bands were common to all the species of Meloidogyne, whereas other bands were specific. Meloidogyne spp. and Heterodera glycines shared some protein similarities, but other genera differed distinctly. Protein profiles of Meloidogyne spp. were not significantly altered by the host on which the nematode was cultured.