الفهرس 
Root-knot diseasesOnly 14 pages are availabe for public view
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Abstract
Tomato (Lycopersicon esculentum L.) is considered one of the most important economic vegetable crops in Egypt occupying the second place after potatoes where it is used either fresh or processed. It is a good source of vitamins A, B, C, minerals and carbohydrates. Recently, it started gaining more medicinal value because of the antioxidant property of ascorbic acid and lycopene content that may help counteract aging and many types of cancer. It is attacked by several fungal, bacterial, viral and nematode diseases. Root-knot nematodes (RKNs) are one of the most important pests on tomato and many crops worldwide and in Egypt, especially in newly reclaimed sandy areas causing great harmful effects on plants and losses in quality and quantity of yield. The use of chemicals to control plant parasitic nematodes were an expensive and environmentally hazardous approach and may also suppress the populations of beneficial antagonistic microorganisms in agricultural soil as well as the negative effects on human, animals and the environment. Thus, there is a need to develop alternative strategies to manage plant parasitic nematodes, especially Meloidogyne spp. Therefore, this study aimed to evaluate some safe treatments against RKNs.
Results obtained from the present investigation can be summarized as follows:-
Four different yeast isolates (Pichia guilliermondii ATCC 9058, Saccharromyces cereviciae, Candida albicans ATCC 10231 and Saccharromyces spp.) were evaluated against root-knot nematodes (RKNs) under laboratory conditions. Results showed that all treatments have the ability to inhibit egg-hatching and kill second-stage juveniles (J2s). The yeast isolate, P. guilliermondii ATCC 9058, achieved the highest percentage of egg-hatching inhibition and J2s mortality, followed by S. cereviciae, while Saccharomyces spp. was the least effective.
Eight different wild weeds (Atriplex lindleyi (Moq.) subsp. inflata (F. Muell) P.G., Chenopodium album, Hyoscyamus muticus, Mesembryanthemum nodiflorum, Pluchea dioscoridis, Senecio squalidus, Zygophyllum qatarense and Amaranthus ascendens) were evaluated against RKNs under laboratory conditions. Results showed that all treatments have the ability to inhibit egg-hatching and kill second-stage juveniles (J2s). Atriplex lindleyi (Moq.) subsp. inflata (F. Muell) P.G., achieved the highest percentage of egg-hatching inhibition and J2s mortality, followed by C. album, while A. ascendens was the least effective.
The yeast isolates were evaluated as soil amendments against Meloidogyne spp. on tomato under greenhouse conditions at the three different application times (one week prior, one week post and at the same time of seedlings transplanting) and different concentrations 1,2 and 4% of soil weight. Results indicated that all treatments at the three different application timings and concentrations had a significant effect on nematode parameters (number of galls, egg masses, females and number of juveniles (J2s)/250g soil, gall index, nematode final population and reproduction factor) and plant growth parameters (shoot and root fresh weights, shoot and root lengths as well as plant dry weight). The most effective application time was one week prior to seedlings transplanting, followed by at the same time of seedlings transplanting, while one-week post seedlings transplanting was the least effective. Pichia guilliermondii ATCC 9058, at 4% of soil weight concentration, followed by S. cereviciae, at 4% of soil weight concentration, demonstrated the highest reduction in nematode parameters and the highest increase in growth parameters and the activities of two enzymes peroxidase and polyphenol oxidase while the least effective treatment was Saccharomyces spp. at 1% of soil weight concentration compared with nematode alone treatment.
The weeds were evaluated as soil amendments one-week post seedlings transplanting against Meloidogyne spp. on tomato under greenhouse conditions with three different application shapes (fresh, powder and aqueous extract) and different concentrations (1,2 and 4% of soil weight). Results indicated that all treatments with the three different forms and concentrations had a significant effect on nematode parameters and plant growth parameters. The most effective form was the powder, followed by the fresh, while the aqueous extract was the least effective. Atriplex lindleyi (Moq.) subsp. inflata (F. Muell) P.G. at 4% of soil weight concentration, followed by C. album at 4% of soil weight concentration, demonstrated the highest reduction in nematode parameters and the highest increase in growth parameters and the activities of two enzymes peroxidase and polyphenol oxidase while the least effective treatment was A. ascendens at 1% of soil weight concentration compared with nematode alone treatment.
Integrating the best treatments, P. guilliermondii ATCC 9058 with A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. with the three forms (powder, fresh and aqueous extract) as soil amendment one week prior to seedlings transplanting at 4% of soil weight for both treatments compared to the nematicide Nemaphos. Results referred to the fact that generally, Nemaphos treatment recorded complete destruction to the nematode population with a 100% reduction in nematode parameters. The combination of the yeast and the weed were more effective than the separate in controlling Meloidogyne spp. on tomato. Nemaphos followed by the combination consisting of P. guilliermondii ATCC 9058 and the powder shape of A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. recorded the highest reduction in reducing nematode parameters followed by the combination consisting of P. guilliermondii ATCC 9058 and the fresh shape of A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. while the least reduction in these nematode parameters was recorded by the combination consisted of P. guilliermondii ATCC 9058 and the aqueous extract of A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. The most effective combination consisted of P. guilliermondii ATCC 9058 and the powder shape of A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. achieved a close proportion in reducing nematode parameters to the nematicide Nemaphos but the combination proved to be the most effective in enhancing plant growth parameters much greater than Nemaphos.
Results showed that there is a strong correlation between data obtained from the laboratory and the greenhouse. This correlation strongly supports our hypothesis that yeasts and wild weeds could play an important role in management of root-knot nematodes in tomatoes.
The results of our study suggest that the biocontrol agents P. guilliermondii ATCC 9058 and A. lindleyi (Moq.) subsp. inflata (F. Muell) P.G. as soil amendment treatments separately or combined suppressed galls and egg-masses formation of Meloidogyne spp. showing high nematicidal activity under greenhouse conditions and promoting the growth of tomato plants over the untreated control. They can be used as effective biocontrol agents to protect tomato plants from Meloidogyne spp. and can be stably used to control root-knot nematodes in the field under organic agriculture and Global GAP agricultural systems instead of these expensive and hazardous carcinogenic nematicides which have a toxic effect on flora and fauna of environment and can work for fulfilling the demand of global food production through sustainable nematode management by the involvement of organic farming system. Such a strategy could also lead to improved water quality and reduced environmental contamination, besides, reducing the hazards of pesticide residues in food and soil.
One of the main advantages of wild weeds amendments is that they may be easily and cheaply produced by farmers and in small scale industries as chopped leaf and stem, powder or partially purified extracts. Application of plant materials to soil is an inexpensive and effective technique and its easy adaptability will give additional advantages leading to acceptance of this technology by farmers. However, the commercial applications of these novel treatments require further investigation.
All mechanisms can potentially be involved in the nematode biocontrol process and understanding these processes could lead to the development of improved biocontrol application methods. Nevertheless, it is not known whether the nematicidal activity was due to a single compound or a complex of compounds and/or compounds interactions. future research needs to be made to evaluate the eventual hazardous effects of the tested combination such as toxicity to beneficial soil organisms, isolation and purification of the active compounds with further bioassay tests using isolated compounds in single and/or complex forms. Economic considerations are important in commercial agriculture, so that it should be included.