Effect of Nonhost Cultivars on Heterodera schachtii Population Dynamics

Broadcast plantings of nonhost cultivars (alfalfa, barley, bean, onion, potato, and wheat) in soil in redwood boxes (4.2 × 30 × 14 cm) infested with Heterodera schachtii reduced the initial nematode populations (P = 0.05). The reduction was greater with sugarbeets, a host, than with all other cropping treatments except onion, bean, and fallow (P = 0.05). After 80 days, when the root growth of all treatments had completely penetrated the soil, the nematode population was lower under onion than under wheat and barley (P = 0.05). The terminal nematode population (160 days) was lowest under onion, followed by bean, potato, fallow, and alfalfa. The nematode population was less under onion than under fallow, alfalfa, barley, and wheat (P = 0.05). Bean, potato, and fallow nematode populations were less than barley populations (P = 0.05). When broadcast plantings of these cultivars were simulated in microplots, the terminal population (100 days) was significantly lower under onion and bean than fallow (P = 0.05). However, no significant differences in reduction of H. schachtii population density were obtained when commercial row plantings of these crops were simulated in microplots. H. schachtii suppressed growth of barley, tomato, and sugarbeet, but not of bean, onion, alfalfa, or wheat in the greenhouse. Only the growth of sugarbeet was suppressed significantly in the field (P = 0.05).     

Pathological Interaction of a Combination of Heterodera schachtii and Meloidogyne hapla on Tomato

Increased culturing of a tomato population of Heterodera schachtii (UT1C) on tomato for 480 days (eight inoculation periods of 60 days each) significantly increased virulence to ''Stone Improved'' tomato. A synergistic relationship existed between Meloidogyne hapla and H. schaehtii on tomato. A combination of H. schachtii (UTIC) and M. hapla significantly reduced tomato root weights by 65, 64, and 61% below root weights of untreated controls, and single inoculations of M. hapla and H. schachtii, respectively. This corresponded to root reductions of 42, 44, and 46% from a combination of H. schachtii (UT1B) and M. hapla. Antagonism existed between H. schachtii and M. hapla with regard to infection courts and feeding sites. The root-knot galling index dropped from 6.0 with a single inoculation of M. hapla to 4.3 and 3.3 with combined inoculations of M. hapla plus UT1B and M. hapla plus UTIC cyst nematode populations. The pathological virulence of H. schachtii to sugarbeet was not lost by extended culturing on tomato; there were no differences in penetration, maturation, and reproduction between sugarbeet populations continually cultured on sugarbeet and the population continually cultured on tomato.     

Interaction of Ditylenchus dipsaci and Meloidogyne hapla on Resistant and Susceptible Plant Species

Numbers ofDitylenchus dipsaci or Meloidogyne hapla invading Ranger alfalfa, Tender crop bean, Stone Improved tomato, AH-14 sugarbeet, Yellow sweet clover, and Wasatch wheat from single inoculations were not significantly different from numbers by invasion of combined inoculations. D. dipsaci was recovered only from shoot and M. hapla only from root tissue. Combined inoculations did not affect reproduction of either D. dipsaci or M. hapla. D. dipsaci suppressed shoot growth of all species at 15-30 C, and M. hapla suppressed shoot growth of tomato, sugarbeet, and sweet clover at 20, 25, and 30 C. There was a positive correlation (P < 0.05) between shoot and root growth suppression by D. dipsaci on all cultivars except wheat at 20 C and tomato at 30 C. M. hapla suppressed (P < 0.05) root growth of sugarbeet at 20-50 C and wheat at 30 C. Growth suppression was synergistic in combined inoculations of sweet clover shoot growth at 15 C and root growth at 20-30 C, wheat root growth at 15 and 20 C, and tomato root growth at 15-30 C (P < 0.05) D. dipsaci invasions caused mortality of alfalfa and sweet clover at 15-30 C and sugarbeet at 20-30 C. Mortality rates of alfalfa and sweet clover increased synergistically (P < 0.05) from combined inoculations.     

Population Dynamics of Heterodera schachtii on Tomato and Sugar Beet

Experiments showed that development of male and female Heterodera schachtii on tomato and sugarbeet are disproportionately influenced by the nematode inoculum level and root size, which together determine the density of invading larvae. Slight overcrowding favored development of males over females, whereas severe overcrowding equally affected development of males and females. Differential population changes of host-selected races on tested cultivars was attributable to selective development of male and female nematodes.     

Control of Heterodera carotae,Ditylenchus dipsaci,and Meloidogyne javanica with Fumigant and Nonfumigant Nematicides

Five field trials were conducted in Italy in 1983 and 1984 to test the efficacy of isazofos and benfuracarb in controlling Heterodera carotae on carrot, Ditylenchus dipsaci on onion, and Meloidogyne javanica on tomato. Methyl isothiocyanate (MIT) was tested against H. carotae and M. javanica. Single (10 kg a.i./ha) and split (5 + 5 kg a.i./ha) applications of isazofos gave yield increases of carrot and onion similar to those obtained with DD (300 liters/ha) and aldicarb (10 kg a.i./ha). Population densities of H. carotae in carrot roots at harvest and of M. javanica in tomato roots 2 months after transplanting were also suppressed by isazofos. Benfuracarb (10 kg a.i./ha increased onion yields in a field infested with D. dipsaci, but it was not effective against H. carotae or M. javanica. The efficacy of MIT at 400 and 600 liters/ha was similar to that of MIT + DD (Di-Trapex) at 300 liters/ha. Both nematicides inhibited hatch of H. carotae eggs and decreased the soil population density of M. javanica.     

Induced tolerance of Sclerotium cepivorum to antibiotics in the presence of onion exudates

The onion white rot pathogen Sclerotium cepivorum was cultured on agar media containing 2% malt extract and one of the antifungal antibiotics, endomycin, griseofulvin, venturicidin and cycloheximide at concentrations that reduced but did not prevent growth of mycelium. When onion seeds or agar discs impregnated with diffusates from onion bulbs were placed on the antibiotic media, radial growth of the fungus was greatly increased, and there was a profuse development of aerial mycelium. Gaseous diffusates from onion tissue and from impregnated agar discs were also effective. On the antibiotic media, tomato, cabbage and radish seeds did not stimulate the growth of S. cepivorum and the onion exudates did not stimulate the growth of four other fungi. This and other evidence is considered to show that the stimulation of growth of S. cepivorum was not caused by any direct effect on the antibiotics but by a tolerance of the fungus to them, which was specifically induced by an exudate from its host plant. The phenomenon may be related to the reported reversal by onion extracts of the inhibitory effects of soil mycostasis on germination of sclerotia of the fungus.     

Effect of distillery effluent on seed germination in some vegetable crops

A laboratory experiment was conducted to study the effect of different concentrations (0%, 5%, 10%, 15%, 20%, 25%, 50%, 75% and 100%) of distillery effluent (raw spent wash) on seed germination (%), speed of germination, peak value and germination value in some vegetable crops: tomato, chilli, bottle gourd, cucumber and onion. The distillery effluent did not show any inhibitory effect on seed germination at low concentration except in tomato, but in onion the germination was significantly higher (84%) at 10% concentration as against 63% in the control. Irrespective of the crop species, at highest concentrations (75% and 100%), complete failure of germination was observed. The speed of germination, peak value and germination value also followed a similar trend. We found that a concentration of 5% was critical for seed germination in tomato and bottle gourd, and 25% in the rest of the crops. Based on the tolerance to distillery effluent, the crops studied have been arranged in the following order: cucumber > chilli > onion > bottle gourd > tomato. We conclude that the effect of the distillery effluent is crop-specific and due care should be taken before using the distillery effluent for pre-sowing irrigation purposes.     

Membrane chemical stability and seed longevity

Here, we investigate the relationships between the chemical stability of the membrane surface and seed longevity. Dry embryos of long-lived tomato and short-lived onion seeds were labeled with 5-doxyl-stearic acid (5-DS). Temperature-induced loss of the electron spin resonance signal caused by chemical conversion of 5-DS to nonparamagnetic species was used to characterize the membrane surface chemical stability. No difference was found between temperature plots of 5-DS signal intensity in dry onion and tomato below 345 K. Above this temperature, the 5-DS signal remained unchanged in tomato embryos and irreversibly disappeared in onion seeds. The role of the physical state and chemical status of the membrane environment in the chemical stability of membrane surfaces was estimated for model systems containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) dried alone or in the presence of trehalose or glucose. Fourier transform infrared spectroscopy was used to follow temperature-induced structural changes in dry POPC. Spin-label technique was used to relate the chemical stability of 5-DS with the dynamic properties of the bilayer and 5-DS motion behavior. In all the models, the decrease in 5-DS signal intensity was always observed above T _m for the membrane surface. The 5-DS signal was irreversibly lost at high temperature when dry POPC was embedded in a glucose matrix. The loss of 5-DS signal was moderate when POPC was dried alone or in the presence of trehalose. Comparison of model and in vivo data shows that the differences in longevity between onion and tomato seeds are caused by differences in the chemical status of the membrane surface rather than the degree of its immobilization.     

Cropping system influences Tomato spotted wilt virus disease development,thrips population and yield of tomato (Lycopersicon esculentum)

Yield of tomato is limited by many diseases including Tomato spotted wilt virus disease. This study was conducted in the field at Kenya Agriculture Research Institute Njoro, Kenya, in 2004 and 2006 to determine the effect of intercropping on disease development, thrips population and yield of tomato variety Cal J grown under four intercrop systems involving kale, onion, maize and sole tomato. The experimental design was a Randomised Complete Block Design (RCBD) replicated three times. Disease scores on tomato–maize differed significantly from tomato–kale and tomato–onion in both years of the study. Maize cropping system had a low significant thrips population from the other cropping systems. Tomato–maize intercrop produced the lowest fruit weights and marketable yield in 2004 and 2006, while yield of onion, kale and maize in intercrops were not significantly different from their monocrops. Land equivalent ratio was >1 in all the cropping systems.     

Ethylene Production by Meloidogyne spp.-Infected Plants

Gall size and rates of ethylene production by various hosts infected with Meloidogyne javanica and by excised tomato root cultures infected with M. javanica or M. hapla were measured. Infection with M. javanica increased the rate of ethylene production in dicotyledonous plants (cabbage, pea, carrot, cucumber, carnation, and tomato), but not in infected monocotyledonous plants (corn, wheat, and onion). Nematode infection induced large galls on roots of dicotyledonous, but not monocotyledonous, plants. Excised tomato roots in culture infected with M. javanica produced ethylene at high rates and formed large galls, whereas roots infected with M. hapla produced ethylene at low rates and induced smaller galls.     

Monoxenic maintenance and reproduction of root-knot nematode (Meloidogyne hapla) on multiple-species in vitro root culture systems

The ability of tomato root tips transformed with Agrobacterium rhizogenes and non-transformed onion and dandelion root tips to regenerate and provide suitable monoxenic hosts for the maintenance of root-knot nematode (Meloidogyne hapla) was investigated. Populations of M. hapla were successfully established on all root culture systems examined, but the onion root culture was overall the most effective method for long-term maintenance and reproduction of M. hapla. The use of a pre-induction medium containing the hormone !-naphthaleneacetic acid was necessary for the production of onion root culture systems but was not required for the establishment of tomato or dandelion root cultures. Differences in nematode reproduction were observed on tomato when multiple populations of M. hapla were used for inoculations.     

Root interactions and tomato growth in tomato/potato onion companion-cropping system under different phosphorus levels

When two plants interact, changes in plant growth are usually related to variations in root distribution and phosphorus (P) levels. However, root distributions and root tendencies are difficult to study because root systems grow beneath the soil surface. In this study, a transparent root box was used to observe interactions between root systems in situ, and the relation between tomato growth and root proliferation at different depths and distance from the rows at no P added and 120?mg kg^-1 P added levels were also tested. We found that tomato shoot and total biomass increased and roots grew deeper when companion cropped with potato onion under both P levels. Moreover, tomato roots tended to grow away from the potato onion roots. Our results suggest that a deeper and more evasive root distribution may be related to the increased plant growth of tomato when companion cropped with potato onion.     

Current Status of the Availability,Development, and Use of Host Plant Resistance to Nematodes

Host plant resistance (HPR) to nematodes has been identified in many major crops and related wild germplasm. Most HPR is to the more specialized, sedentary endoparasitic genera and species, e.g., Globodera, Heterodera, Meloidogyne, Nacobbus, Rotylenchulus, and Tylenchulus. Some HPR has been developed or identified also to certain migratory endoparasites (Aphelenchoides, Ditylenchus, Pratylenchus, Radopholus) in a few hosts. Commercial use of HPR remains limited, despite its benefits to crop production when deployed appropriately. Restricted use and availability of HPR result from problems associated with transfer of resistance into acceptable cultivars. Difficulties occur in gene transfer to acceptable cultivars because of incompatibility barriers to hybridization or linkage to undesirable traits, for example in cucurbitaceous and solanaceous crops and sugarbeet. Specificity of HPR to only one species, or one or few pathotypes, as it relates to resistance durability and nematode virulence, and HPR response to abiotic factors such as high soil temperature, also limit availability and utility. A scheme for HPR development is presented to emphasize nematology research and information requirements for expanding HPR use in nematode control programs, for example in common bean, sugarbeet, and tomato. Nonbiological factors that influence HPR usage are discussed, including heavy reliance on nematicide programs, low priority of nematode HPR in many breeding programs, and insufficient breeder-nematologist collaboration.     

Relations between harmful effects on plants and on animals of toxins produced by species of Fusarium

642 isolates ofFusarium belonging to 49 species and 14 sections were tested for the toxicity of their culture extracts when applied to rabbit skin and for their pathogenicity to the seedlings of 10 field crops. It was found that as the grade of animal toxicity of the isolates increased their phytotoxicity under the condition of these tests likewise increased both with regard to the number of plants killed and the number of hosts affected by the isolate. The hosts succumbing to the largest number of isolates were tomato, eggplant and onion.     

Development of Heterodera schachtii on Large Rooted Crop Plants and the Significance of Root Debris as Substratum for Increasing Field Infestations

Heterodera schachtii developed to maturity and reproduced on the lateral roots of defoliated sugarbeet which were buried to a depth of 2.5 cm in sterilized soil and inoculated with cysts. Nematodes did not develop on detached lateral roots or on roots of young defoliated beets which did not have a large tap root. The storage roots of large rooted plants were sliced, placed in small jars, inoculated with cysts, covered with moist granulated agar or soil and incubated at 24°C 12-62 days. The sugarbeet nematode developed in root slices of sugarbeet, red table beet, icicle and globe radish, turnip and rutabaga. Only a few males developed on slices of potato tubers. Neither males nor females developed on root slices of carrot, salsify or parsnip. H. schachtii also developed on the cut surfaces of growing sugarbeet and radish.     

Effect of Ash Pond Soil and Amendments on the Growth and Arbuscular Mycorrhizal Colonization of Allium cepa and Germination of Arachis hypogaea,Lycopersicon esculentum,and Vigna mungo Seeds

The effect of fly ash pond soil on the growth and yield of onion (Allium cepa var. microaggregatum) plants grown in pots was investigated. The fly ash pond soil was amended with combinations of red soil and press mud, a waste product from sugar mills. Water-holding capacity of ash pond soil amended with press mud increased; however, addition of press mud delayed onion bulb development. Onion bulb germination took place rapidly in ash pond soil; however, subsequent bulb development declined. The addition of red soil and press mud increased the growth and yield of onion plants. In all the soils and amendments, onion plant roots were colonized by native arbuscular mycorrhizal species. Both vesicles and arbuscules were present in the roots. Colonization was low in ash pond soil but increased with the addition of red soil. Effect of fly ash pond soil on germination of groundnut (Arachis hypogaea), tomato (Lycopersicon esculentum), and black gram (Vigna mungo) seeds was evaluated and compared with red soil in the laboratory. Ash pond soil increased the germination of tomato seeds but did not affect the germination of groundnut and black gram seeds.     

In-Vitro and In-Vivo Effects of Aldicarb on Survival and Development of Heterodera schachtii

Aqueous solutions of 5-500 μg/ml aldicarb inhibited hatching of Heterodera schachtii. Addition of hatching agents, zinc chloride, or sugarbeet root diffusate, to the aldicarb solutions did not decrease the inhibition of hatching. When cysts were removed from the aldicarb solufions and then treated for 4 wk in sugarbeet root diffusate, larvae hatched and emerged. Treatments of newly hatched larvae of H. schachtii with 5-100 μg/ml aldicarb depressed later development of larvae on sugarbeet (Beta vulgaris). Similar treatments with aldicarb sulfoxide had less effect on larval development, and aldicarb sulfone had no effect. Numbers of treated larvae that survived and developed were inversely proportional to concentration (0.1-5.0 μg/ml) and duration (0-14 days) of aldicarb treatments. Development of H. schachtii on sugarbeet grown in aldicarb-treated soil was inversely proportional to the concentration of aldicarb in the tested range of 0.75 - 3.0 μg aldicarb/g of soil. Transfer of nematode-infected plants to soil with aldicarb retarded nematode development, whereas transfer of plants first grownin treated soil to nematode-infested soil only slightly suppressed nematode development. Development of H. schachtii was inhibited in slices of storage roots of table beet (B. vulgaris), sugarbeet and turnip, (Brassica rapa), that had grown in soil treated with aldicarb.     

Effect of Azospirilla Lectins on Germination Capacity of Seeds

We studied the effect of lectins of Azospirillum brasilense Sp 7 on germination capacity of tomato, cucumber, pea, wheat, and onion seeds. The lectins proved to inhibit seed germination. We studied the effect of different concentrations of lectins from four azospirilla strains on the rate of wheat seed germination. Both inhibiting and stimulating effects were demonstrated. Lectin-induced changes in the mitotic state of plant cells were demonstrated with histological sections of the root growing point in onion.     

Host Suitability of Rapeseed for Heterodera schachtii

Because rapeseed, especially canola, has the potential to be grown in rotation with sugarbeet in the north-central region of the United States, this study was initiated to assess its susceptibility to infection by Heterodera schachtii and to develop a screening method for Brassica germplasm. Existing methodology was adapted for growing Brassica juncea, B. napus, B. rapa, Brassica hybrids, and sugarbeet, Beta vulgaris, in H. schachtii-infested soil to count the females that developed on the roots. Cysts on sugarbeet contained a mean of 130 eggs compared with 240 for B. napus, lowest for the Brassica. Viability of eggs produced was assessed in soil planted with Brassica and sugarbeet and infested with with 0, 100, 1,000, 3,000, and 5,000 eggs to count resulting females and cysts. Number of females (y) was related linearly to infestation rate (x) by the regression equations y = 2.82 + 0.07(x) for the Brassica lines (R² = 0.79; P < 0.001) and y = 0.43 + 0.04(x) for sugarbeet (R² = 0.69; P < 0.007). These data indicated the potential for H. schachtii population increase if the two crops are used in rotation. All of the 111 germplasm lines tested were susceptible. The methodology developed during this research would benefit attempts to develop rapeseed cultivars resistant to H. schachtii.