Relationship between root respiration and seedling age in tomato cultivars infested by Meloidogyne incognita

Measurements were made of respiration in the roots of tomato cultivars susceptible and resistant to Meloidogyne incognita. Nematode infestation of the susceptible cv. Roma VF caused an initial stimulation of the total respiration with an increase in the CN-sensitivity; the effect decreased and then disappeared as the seedlings aged. In the resistant cv. Rossol nematode infestation initially caused an inhibition of total respiration and a decrease in the CN-sensitivity; respiration and CN-sensitivity increased with seedling age. The activity of the alternative respiration pathway (m-chlorobenzhydroxamic acid-sensitive) was unchanged by nematode infestation in the resistant cultivar and increased markedly in the susceptible cultivar during the early stages of infestation.     

Effect of seaweed concentrate on the establishment and yield of greenhouse tomato plants

Seaweed concentrate prepared fromEcklonia maxima (Osbeck) Papenfuss, when applied as a soil drench, significantly improved the growth of tomato seedlings. Application as a foliar spray had no effect on young plants. In a second experiment SWC-treated plants exhibited early fruit ripening and a total fruit fresh weight increase of 17%. The number of harvested fruit were improved by about 10%. In this instance foliar applied SWC was more beneficial than SWC applied to the soil. The significance of these findings is discussed.author for correspondence     

Synergism between Gibberellin and Auxin in the Growth of Intact Tomato

Gibberellin A_4&7 was more effective than gibberellic acid in increasing shoot elongation when applied to the apex of intact Lycopersicum esculentum seedlings of Tiny Tim, a dwarf cultivar, and Winsall, a tall cultivar. After 14 days, gibberellic acid and gibberellin A_4&7 stimulated growth of the dwarf more than the tall tomato. In tall tomato the application of indole-3-acetic acid alone (6.1 μg/plant) showed an inhibitory growth effect, but when applied with 17.5 μg per plant of gibberellic acid, it had a synergistic effect at 7 days but not at 14 days. When the auxin concentration was reduced to 0.61 μg per plant a synergistic effect was observed on tall plants at 7 and 14 days between indole-3-acetic acid and gibberellic acid. Application of gibberellin A_4&7 with auxin did not give a synergistic response in tall or dwarf tomato.     

丛枝菌根真菌对不同番茄品种抗根结线虫病的影响

【背景】根结线虫病害严重制约我国设施蔬菜的生产。丛枝菌根真菌(Arbuscular Mycorrhizal Fungi,AMF)作为土壤中最重要的有益真菌之一,可以促进植物生长,提高植物抗病性,减轻土传真菌和线虫病害的发生。在蔬菜保护地栽培中,AMF对于植物线虫病防治作用的研究受到了广泛关注。【目的】针对番茄生产中危害最严重的南方根结线虫(Meliodogyne incognita)病害问题,研究AMF和番茄品种不同组合的抗线虫效应,以期为菌根真菌作为生物防治剂和生物菌肥应用于实际生产提供技术基础。【方法】在灭菌土壤中,人工接种根结线虫,比较不同菌种Rhizophagus intraradices(Ri)、Acaulosporamellea(Am)及菌种组合Rhizophagusintraradices+Acaulosporamellea(Ri+Am)在不同番茄品种(感病品种蒙特卡罗和抗线虫品种仙客1号)上对南方根结线虫侵染和繁殖的影响,研究AMF对根结线虫的拮抗效应。另外,采用南方根结线虫连作发病的土壤,在感病品种蒙特卡洛上接种AMF混合菌种Ri+Am,番茄苗移栽入连作土壤中,测定各生长指标和调查根结和卵块数量,评价接种AMF处理对根结线虫病的防治效果。【结果】在灭菌土壤中,普通番茄品种蒙特卡罗的菌根效应显著优于抗线虫番茄品种仙客1号,表现为前者单位根重的根结和卵块的数量均比对照显著降低,而后者仅降低了卵块数量;蒙特卡罗上接种Ri+Am混合菌种的效果优于接种单一菌种Am和Ri;而仙客1号上接种Ri的效果更好。接种线虫也显著影响了AMF的侵染,而且对抗性品种仙客1号的影响更为明显。但除了接种Am的处理,大多数处理收获时菌根侵染率仍维持较高的水平(70%以上)。在连作土壤中,感病品种蒙特卡罗接种混合菌种Ri+Am具有较好的抗/耐线虫效应,主要表现为促进植株生长,显著降低根结和卵块数量,但菌根侵染率较灭菌土壤低,约为40%。【结论】综合以上结果,表明菌根化苗能够在一定程度上减轻根结线虫病的危害。土壤灭菌条件下,在感病和抗线虫番茄品种上接种AMF能够减轻线虫的侵染和繁殖,而且在感病品种上的防治效果更加显著。在连作土壤中,在番茄感病品种上接种AMF也表现较好的抗线虫效果。     

Cross adaptation of potato plants to low temperatures and potato cyst nematode infestation

Effect of short-term (2 h a day) and long-term (6 days) exposure to low temperature (5°C) on cold tolerance was investigated in two cultivars of potato (Solanum tuberosum L.): resistant (Sudarynya) and susceptible (Nevskii) to potato cyst nematode (Globodera rostochiensis Woll.). The extent of their infestation and changes in the expression of the genes of resistance to nematode (H1 and Gro1-4) were also analyzed. In both cultivars, exposure to low temperature enhanced cold resistance of potato plants. Enhancing cold resistance of cv. Sudarynya induced by a short-term exposure to chilling did not affect the extent of nematode infestation, whereas in susceptible cv. Nevskii, the extent of infestation decreased by almost three times. The level of expression of H1 gene in the leaves of the susceptible cultivar rose almost twofold both after short-term and long exposure to chilling, while in the resistant cultivar, gene expression increased only after a short-term effect of cold. The level of Gro1-4 gene expression increased after both temperature treatments only in the resistant cv. Sudarynya. Thus, the expression of genes for potato resistance to nematode infestation became more active in the susceptible cultivar as regards the gene H1 and in the resistant cultivar, regarding the gene Gro1-4. In the nematode-susceptible cv. Nevskii, the level of infestation decreased and cold resistance increased, apparently indicating cross adaptation to two factors of different nature.     

Effect of 28-homobrassinolide on susceptible and resistant cultivars of tomato after nematode inoculation

In vitro effects of 28-homobrassinolide (HBl) were evaluated on morphological and biochemical parameters of susceptible (Pusa Ruby) and resistant (PNR-7) cultivars of tomato, 5 days after nematode inoculation. In susceptible cultivar, nematode invasion reduced the plant growth while growth was enhanced after brassinosteroid treatment. In case of resistant plants, nematodes were not able to invade the roots and here also, pre-sowing treatment of seeds with HBl further enhanced the growth of plants. An increase in specific activities of antioxidative enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase, glutathione peroxidase and superoxide dismutase) was observed in susceptible plants treated with HBl. In resistant cultivar, nematode inoculation increased the specific activities which were further enhanced with HBl treatment. The results obtained in the present study indicated the ameliorative effects on tomato varieties treated with HBl even after nematode stress. Thus, suggesting a possible role of HBl in lessening the oxidative stress generated during nematode invasion and boosting the resistance capacity of plants.     

Root nematode infection enhances leaf defense against whitefly in tomato

The foliar response to different herbivores sharing the same hosts is an important topic for the study of plant-insect interactions. Plants evolve local and systemic resistant strategies to cope with herbivores. Many researchers have characterized the mechanisms of leaf responses to insect infestation; however, the fact that roots serve as systemic resistance modulators to leaf herbivores has been widely ignored. Here, we report that tomato (Solanum lycopersicum) plants infected with southern root-knot nematodes (Meloidogyne incognita)—which feed on the roots to form nodules—enhanced leaf defenses against aboveground attackers, specifically, the whitefly (Bemisia tabaci). Our results show that nematode infection reduced the whitefly population abundance because of conferring a stronger SA-dependent defense pathway against whitefly than in tomato plants without nematode infection. Meanwhile, nematode-infected tomato plant also activated the foliar JA-dependent defense pathway at 4 h after whitefly infestation. However, the foliar JA-dependent defense under whitefly infestation alone was suppressed, with the JA content being nearly 30 % lower than that in tomato plants co-infected with nematodes and whiteflies. Furthermore, nematode infection significantly decreased the plant nitrogen concentration in leaves and roots. As a result, nematode infection reduced the number of whiteflies by enhancing foliar SA-dependent defense, activating JA-dependent defense and decreasing nitrogen nutrition. Our results suggest that underground nematode infection significantly enhances the defense ability of tomato plants against whitefly.     

Interaction of Glomus mosseae and Paecilomyces lilacinus on Meloidogyne javanica of tomato

The effects of Glomus mosseae and Paecilomyces lilacinus on Meloidogyne javanica of tomato were tested in a greenhouse experiment. Chicken layer manure was used as a carrier substrate for the inoculum of P. lilacinus. The following parameters were used: gall index, average number of galls per root system, plant height, shoot and root weights. Inoculation of tomato plants with G. mosseae did not markedly increase the growth of infected plants with M. javanica. Inoculation of plants with G. mosseae and P. lilacinus together or separately resulted in similar shoots and plant heights. The highest root development was achieved when mycorrhizal plants were inoculated with P. lilacinus to control root-knot nematode. Inoculation of tomato plants with G. mosseae suppressed gall index and the average number of galls per root system by 52% and 66%, respectively, compared with seedlings inoculated with M. javanica alone. Biological control with both G. mosseae and P. lilacinus together or separately in the presence of layer manure completely inhibited root infection with M. javanica. Mycorrhizal colonization was not affected by the layer manure treatment or by root inoculation with P. lilacinus. Addition of layer manure had a beneficial effect on plant growth and reduced M. javanica infection.     

Plant Species, Host Age and Host Genotype Effects on Meloidogyne incognita Biocontrol by Pseudomonas fluorescens Strain CHA0 and its Genetically-Modified Derivatives

Pseudomonas fluorescens strain CHA0 and its antibiotic overproducing derivative CHA0/pME3424 repeatedly reduced Meloidogyne incognita galling on tomato, brinjal, mungbean and soya bean roots but not in chilli. An antibiotic‐deficient derivative, CHA89, did not reduce nematode invasion in any of the plant species tested. When plant species were compared, bacterial inoculants afforded better protection to tomato, mungbean and soya bean roots against root‐knot nematodes than to brinjal and chilli. Antibiotic overproducing strain CHA0/pME3424 markedly reduced fresh shoot weights of chilli and mungbean while antibiotic‐deficient strain CHA89 enhanced fresh shoot weights of mungbean. While strains CHA0 had no significant impact on fresh root weights of any of the plant species, strain CHA0/pME3424 consistently reduced fresh root weights of brinjal and mungbean. In none of the plant species the bacterial strains had an influence on protein contents of the leaves. Regardless of the plant species, the three bacterial strains did not differ markedly in their rhizosphere colonization pattern. However, colonization was highest in brinjal rhizosphere and lowest in the mungbean rhizosphere. A slight host genotype effect on the biocontrol performance of the bacterial inoculants was also detected at cultivar level. When five soya bean cultivars were compared, biocontrol bacteria exhibited best suppression of the root‐knot nematode in cv. Ajmeri. Antibiotic overproducing strain CHA0/pME3424 substantially reduced fresh shoot weights of the soya bean cultivars Centuray 84 and NARC‐I while strain CHA89 enhanced shoot weights of the cultivars Ajmeri, William‐82 and NARC‐II. Wild type strain CHA0 had no significant impact on fresh shoot weights of any of the soya bean cultivars. Strain CHA0/pME3424 reduced fresh weights of root of Century 84, NARC‐I and NARC‐II while strain CHA89 increased root weights. Bacterial rhizosphere colonization was highest in variety NARC‐I and lowest in variety Ajmeri. Plant age had a significant impact on the biocontrol performance of bacterial inoculants against nematodes. The biocontrol effect of all bacterial strains was more prominent during early growth stage (7 days after nematode inoculation). A strong negative correlation between bacterial rhizosphere colonization and nematode invasion in soya bean roots was observed.     

Some isolates of the nematophagous fungus Pochonia chlamydosporia promote root growth and reduce flowering time of tomato

The fungal parasite of nematode eggs Pochonia chlamydosporia is also a root endophyte known to promote growth of some plants. In this study, we analysed the effect of nine P. chlamydosporia isolates from worldwide origin on tomato growth. Experiments were performed at different scales (Petri dish, growth chamber and greenhouse conditions) and developmental stages (seedlings, plantlets and plants). Seven P. chlamydosporia isolates significantly (P < 0.05) increased the number of secondary roots and six of those increased total weight of tomato seedlings. Six P. chlamydosporia isolates also increased root weight of tomato plantlets. Root colonisation varied between different isolates of this fungus. Again P. chlamydosporia significantly increased root growth of tomato plants under greenhouse conditions and reduced flowering and fruiting times (up to 5 and 12 days, respectively) versus uninoculated tomato plants. P. chlamydosporia increased mature fruit weight in tomato plants. The basis of the mechanisms for growth, flowering and yield promotion in tomato by the fungus are unknown. However, we found that P. chlamydosporia can produce Indole‐3‐acetic acid and solubilise mineral phosphate. These results suggest that plant hormones or nutrient ability could play an important role. Our results put forward the agronomic importance of P. chlamydosporia as biocontrol agent of plant parasitic nematodes with tomato growth promoting capabilities.     

Influence of different Inocula of Meloidogyne arenaria on plant growth parameters and nematode multiplication in balsam (Impatiens balsamina)

Pathogenic effect of root-knot nematode Meloidogyne arenaria was studied on balsam (Impatiens balsamina) by inoculating the different inoculum levels of root-knot nematode. It was observed that the inoculum levels up to 2000 J₂ of root-knot nematode did not show significant reduction in plant growth characters as compared to control. Although the significant reduction in plant growth characters was recorded at and above 3000 J₂ of root-knot nematode, progressive increase in the host infestation as indicated by the number of galls as well as the population of root-knot nematode was recorded with an increase in the level of inoculum. However, the rate of nematode multiplication was reduced with the increase in the inoculum density of M. arenaria. It can be concluded from these results that the damaging threshold level of M. arenaria on balsam was found to be as 3000 J₂/plant.     

Involvement of salicylic acid in induction of nematode resistance in plants

The role of salicylic acid (SA) as a possible signaling component in the case of the infection of plants with nematodes has been studied using a model system consisting of the tomato (Lycopersicon esculentum (Mill.) and race 1 of the gall eelworm Meloidogyne incognita (Kofoid and White, 1919; Chitwood, 1949). The preplanting SA treatment of tomato seeds results in an increased nematode resistance of susceptible tomato cultivars; the protective effect is higher in the case of SA combined with chitosan, a biogenic elicitor of plant resistance. The studied preparations stimulate the growth and development of the plants. The increase in the resistance of tomato plants is related to the increased activity of phenylalanine ammonia-lyase and an increased SA content in plant tissues infected with nematodes; both these factors significantly influence nematode development.     

Effect of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 to soybean

Screenhouse studies were conducted to investigate the effects of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 on soybean and the influence of the nematode on wilt incidence and growth of soybean. The interaction of each fungus with the nematode resulted in reduced shoot and root growth. Final nematode population was also reduced with concomitant inoculation of nematode and fungus or inoculation of fungus before nematode. While M. incognita suppressed wilt incidence in two nematode-susceptible cultivars of soybean (TGX 1485-2D and TGX 1440-IE), it had limited effect on wilt incidence in the nematode resistant cultivar of soybean (TGX 1448-2E). When F. oxysporumwas inoculated with the nematode, the mean number of nematodes that penetrated soybean roots decreased by 75% in TGX 1448-2E, 68% in TGX 1485-1D and 65% in TGX 1440-1E. Similarly when the soil was treated with S. rolfsii, the number decreased by 78% in TGX 1448-2E, 77% in TGX 1485-1D and 68% in TGX 1440-1E. The nematode did not develop beyond second-stage juvenile in TGX-1448-2E.     

Effects of dual inoculation of mycorrhiza and endophytic,rhizospheric or parasitic bacteria on the root-knot nematode disease of tomato

The effects of mycorrhisation and inoculation with soil bacteria on the disease caused by Meloidogyne incognita on tomato were studied in pots under greenhouse conditions. Efficacy in promoting plant growth and reducing disease severity and final nematode densities were evaluated for two arbuscular mycorrhizal fungi (AMF; Funneliformis mosseae and Rhizophagus irregularis), three soil bacteria with different living strategies (the endophyte Bacillus megaterium, a rhizospheric Pseudomonas putida and the hyperparasite of nematodes Pasteuria penetrans) and combinations of the fungi and bacteria. In M. incognita-infested plants, F. mosseae increased tomato growth more than R. irregularis, and plants inoculated with B. megaterium presented higher shoot fresh weight than with P. putida or P. penetrans, but dual inoculation did not improve tomato growth more than single inoculations. Disease severity and final nematode densities were reduced by F. mosseae compared to non-mycorrhizal plants. B. megaterium and P. penetrans reduced both the root galling and the final nematode densities compared to treatments without bacteria. P. penetrans reduced final nematode densities more than B. megaterium or P. putida. Dual inoculation of AMF and P. penetrans showed the highest efficacy in reducing the final nematode densities in tomato.     

Interaction of Vesicular-Arbuscular Mycorrhizae and Cultivars of Alfalfa Susceptible and Resistant to Meloidogyne hapla

The interaction between vesicular-arbuscular mycorrhizal (VAM) fungi and the root-knot nematode (Meloidogyne hapla) was investigated using both nematode-susceptible (Grasslands Wairau) and nematode-resistant (Nevada Synthetic XX) cultivars of alfalfa (Medicago sativa) at four levels of applied phosphate. Mycorrhizal inoculation improved plant growth and reduced nematode numbers and adult development in roots in dually infected cultures of the susceptible cultivar. The tolerance of plants to nematode infection and development when preinfected with mycorrhizal fungi was no greater than when they were inoculated with nematodes and mycorrhizal fungi simultaneously. Growth of plants of the resistant cultivar was unaffected by nematode inoculation but was improved by mycorrhizal inoculation. Numbers of nematode juveniles were lower in the roots of the resistant than of the susceptible cultivar and were further reduced by mycorrhizal inoculation, although no adult nematodes developed in any resistant cultivar treatment. Inoculation of alfalfa with VAM fungi increased the tolerance and resistance of a cultivar susceptible to M. hapla and improved the resistance of a resistant cultivar.     

Control of plant-parasitic nematodes by Paecilomyces lilacinus and Monacrosporium lysipagum in pot trials

The common soil inhabiting nematophagous fungus Paecilomyces lilacinus (Thom) Samson and the nematode trapping fungus Monacrosporium lysipagum (Drechsler) Subram were assayed for their ability to reduce the populations of three economically important plant-parasitic nematodes in pot trials. The fungi were tested individually and in combination against the root-knot nematode Meloidogyne javanica (Treub) Chitwood, cereal cyst nematode Heterodera avenae Wollenweber, or burrowing nematode Radopholus similis (Cobb) Thorne on tomato, barley and tissue cultured banana plants, respectively. In all cases, nematode populations were controlled substantially by both individual and combined applications of the fungi. Combined application of P. lilacinus and M. lysipagum reduced 62% of galls and 94% of M.␣javanica juveniles on tomato when compared to the experiment with no fungi added. Sixty five percent of H. avenae cysts were reduced on barley by combined application of fungi. Control of R. similis on banana, both in the roots and in the soil, was greatest when M. lysipagum was applied alone (86%) or in combination with P. lilacinus (96%), using a strategy where the fungi were inoculated twice in 18 weeks growth period. Overall, combined application of P. lilacinus and M. lysipagum was the most effective treatment in controlling nematode populations, although in some cases M. lysipagum alone was as effective as the combined application of fungi, particularly against M. javanica.     

Über die Kallosebildung in Siebröhren von Kartoffelpflanzen in Abhängigkeit von Blattrollvirusinfektion und chemisch-physikalischen Bedingungen

All the cultivars of tomato tested were found to be infected with the root‐knot nematode, Meloidogyne incognita, however, to varying extent. There was also reducton in plant growth parameters accordingly. Further reduction in plant growth of tomato cultivars was recorded when plants also received the treatment with the heavy metal, lead, notwithstanding the fact that the presence of lead also reduced the root‐knot development. Tomato cv. Arka Vikas showed minimum reduction in plant growth with single or combined treatment with the nematode and the heavy metal.     

Role of cyanide production by Pseudomonas fluorescens CHA0 in the suppression of root-knot nematode, Meloidogyne javanica in tomato

Summary Pseudomonas fluorescens strain CHA0 produces hydrogen cyanide (HCN), a secondary metabolite that accounts largely for the biocontrol ability of this strain. In this study, we examined the role of HCN production by CHA0 as an antagonistic factor that contributes to biocontrol of Meloidogyne javanica, the root-knot nematode, in situ. Culture filtrate of CHA0, resulting from 1/10-strength nutrient broth yeast extract medium amended with glycine, inhibited egg hatch and caused mortality of M. javanica juveniles in vitro. The bacterium cultured under high oxygen-tension conditions exhibited better inhibitory effects towards nematodes, compared to its cultivation under excess oxygen situation. Growth medium amended with 0.50 or 1.0 mM FeEDDHA further improved hatch inhibition and nematicidal activity of the strain CHA0. Strain CHA77, an HCN-negative mutant, failed to exert such toxic effects, and in this strain, antinematode activity was not influenced by culture conditions. Exogenous cyanide also inhibited egg hatch and caused mortality of M. javanica juveniles in vitro. Strains CHA0 or CHA77 applied in unsterilized sandy-loam soil as drench, caused marked suppression of root-knot disease development incited by M. javanica in tomato seedlings. However, efficacy of CHA77 was noticeably lower compared to its wild type counterpart CHA0. An increased bioavailability of iron following EDTA application in soil substantially improved nematode biocontrol potential of CHA0 but not that of CHA77. Soil infestation with M. javanica eggs resulted in significantly lower nematode population densities and root-knot disease compared to the juveniles used as root-knot disease-inducing agents. Strain CHA0 significantly suppressed nematode populations and inhibited galling in tomato roots grown in soil inoculated with eggs or juveniles and treated with or without EDTA. Strain CHA0 exhibited greater biocontrol potential in soil inoculated with eggs and treated with EDTA. To demonstrate that HCN synthesis by the strain CHA0 acts as the inducing agent of systemic resistance in tomato, efficacy of the strain CHA0 was compared with CHA77 in a split root trial. The split-root experiment, guaranteeing a spatial separation of the inducing agent and the challenging pathogen, showed that HCN production by CHA0 is not crucial in the induction of systemic resistance in tomato against M. javanica, because the HCN-negative-mutant CHA77 induced the same level of resistance as the wild type but exogenous cyanide in the form of KCN failed to trigger the resistance reaction. In the root section where both nematode and the bacterium were present, strain CHA0 reduced nematode penetration to a greater extent than CHA77, suggesting that for effective control of M. javanica, a direct contact between HCN-producing CHA0 and the nematode is essential.     

Effect of potato used as a trap crop on potato cyst nematodes and other soil pathogens and on the growth of a subsequent main potato crop

A field experiment in which main‐crop potatoes were grown every other year was conducted on a sandy soil from 1994 to 1999. The aim of the experiment was to control soil‐borne pathogens of potato with ecologically sound methods. Potato grown as a trap crop from the end of April to the end of June (8 wk) was used to control potato cyst nematodes (PCN) (Globodera pallida), and its effects on other important soil pathogens and on the growth of a subsequent potato crop were also assessed. Additional experimental treatments were a potato crop from which the haulm was removed and a green manure crop. Three potato cultivars with different degrees of resistance to PCN were grown as the main crop. Duplicate sets of the experiment were run concurrently. The PCN were effectively controlled by the potato trap crop. When a highly resistant potato cultivar was grown as a main crop after the trap crop, the post‐harvest soil infestation was very low. When a moderately resistant cultivar was grown after the trap crop the soil infestation also remained low. When the trap crop was alternated with a susceptible potato cultivar as a main crop, soil infestation increased slightly, but the degree of control when compared with no trap crop averaged 96%. Soil infestation with root‐knot nematodes (mainly Meloidogyne hapla) increased when potato was grown as a trap crop, but soil infestation with the root‐lesion nematode Pratylenchus crenatus was not affected. Stem canker caused by Rhizoctonia solani was not affected by the trap crop but black scurf (sclerotia of R. solani) on tubers was reduced. Soil infestation with Verticillium dahliae declined in one of the duplicate sets of the experiment but not in the other. However, stem infections by V. dahliae were significantly decreased in both sets, although the effect depended on the PCN‐resistance level of the potato cultivar. When a highly resistant potato cultivar was grown Verticillium stem infections were not significantly affected, they were decreased with a moderately resistant cultivar but the decrease was most pronounced with a PCN‐susceptible cultivar. Senescence of a following potato crop was not influenced by the trap crop when a highly PCN‐resistant cultivar was grown, but it was delayed in the case of a moderately resistant or a susceptible cultivar, resulting in higher tuber yields for those cultivars. The experiment proved that a trap crop can be an alternative to chemical soil disinfection but, for several reasons, the potato itself is not an ideal crop for this purpose; a trap crop other than potato must be developed.     

Use of chitin for controlling plant plant-parasitic nematodes

Summary Bean and tomato seedlings, treated with different amounts of ammonia and chitin, and inoculated with the root-knot nematode,Meloidogyne javanica, were reared in two consecutive 35-day growth of shoot and root and the condition of the root systems of both plant species and degree of infection byM. javanica were decreased by increasing amounts of ammonia. Chitin caused a relatively small reduction in gall formation but almost no changes in fresh shoot weights. The effect of chitin on plant growth and nematode attack were also compared in irradiated and non-irradiated soil. In the first cycle galling index of the chitin treated plant was similar to that of untreated plants maintained in the irradiated soil conditions, while in the non-irradiated soil, chitin treatment reduced galling index. In the second cycle, chitin treatment reduced galling index in both irradiated and non-irradiated soils, especially in the latter, where galling index greatly decreased compared with the non-treated plants. Differences in fresh shoot weight between nematode-infected and nematode-free plants amended with chitin were greater under non-irradiated than irradiated conditions, especially in the second cycle. In non-irradiated soil, a higher level of chitinolytic microorganisms, particularly actinomycetes, was found in the second cycle. Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel. No. 1520-E, 1985 series.