Root-knot Nematode Development Research Articles

Influence of insectocompost obtained by cultivation of the during beetle <i>Ulomoides dermestoides</i> on the ecological-trophic composition and development of soil and phytoparasitic nematodes

The purpose of the research is to study the effect of insect compost obtained as a result of the vital activity of insects of the Coleoptera order Ulomoides dermestoides on the quantitative and qualitative composition of soil nematodes of various ecological and trophic groups, as well as on the morphological and physiological state of plants and infection of tomato plants with root-knot nematodes.Materials and methods. Under laboratory conditions, soil containing a diverse fauna of nematodes was treated with 1% dry and 0.5; 0.75 and 1% aqueous solutions of biocompost. Insect compost was obtained by keeping the U. dermestoides on a dry nutrient mixture. Then a mixture of lawn grasses was sown in the ground. After 30 days, the composition of nematodes was analyzed. The ability of insect compost to suppress parasitic nematode species was studied using the tomato-knot nematode model system. Tomatoes were infected with Meloidogyne incognita at a rate of 500 larvae (J2) per plant and simultaneously treated with a 0.5% aqueous biocompost solution.Results and discussion. The insect compost U. dermestoides has an effect on quantitative and qualitative indicators in the community of soil nematodes, increasing the number of predatory and saprobiotic nematodes and displacing parasitic ones. And due to the content of various biologically active compounds, it affects the development of rootknot nematodes in tomato roots. When tomatoes are treated with an aqueous solution of insect compost, the infection score and the number of nematodes that penetrate the roots are reduced. The introduction of compost when growing a mixture of lawn grasses and tomatoes can improve the condition of the plants.

STUDY ON PENETRATION, LIFE CYCLE AND DEVELOPMENT OF ROOTKNOT NEMATODE, MELOIDOGYNE INCOGNITA IN FIELD PEA

STUDY ON PENETRATION, LIFE CYCLE AND DEVELOPMENT OF ROOTKNOT NEMATODE, MELOIDOGYNE INCOGNITA IN FIELD PEA

Studies on the Growth and Development of Root-Knot Nematode Meloidogyne incognita of Phaseolus vulgaris in Tissue Culture Media

The study was conducted to study the growth and development of root-knot nematode, Meloidogyne incognita of Phaseolus vulgaris in tissue culture media. The data revealed the developmental common bean cv. Paulista of M.S media as the following: the seed swelling stage after three days, the radical appearance stage after five days. The cotyledons leaves appear after six days, the cotyledon leaves appear after eight days, and the seedling stage after twelve days. The life cycle of M. incognita completed about thirty-seven days in root tissues of Paulista cultivar. Microscopic examinations of the infected bean roots revealed the following: Second-stage juveniles of M. incognita penetrated the roots within 24 hrs after nematode inoculation. Third-stage juveniles were observed in roots (six-eight) days after nematode inoculation. While, fourth stage juveniles were observed in roots 12-14 days after nematode inoculation. The pre-adult females were seen inside roots within twenty days after nematode inoculation. The adult females were seen inside roots within twenty-seven days after nematode inoculation. Egg laying females with deposit egg masses of M. incognita was observed thirty-seven days after nematode inoculation.

Metagenomic insights into the changes in the rhizosphere microbial community caused by the root-knot nematode Meloidogyne incognita in tobacco

Root-knot nematode (RKN) disease is a destructive soil disease that affects crop health and causes huge losses in crop production. To explore the relationships between soil environments, rhizobacterial communities, and plant health, rhizosphere bacterial communities were analyzed using metagenomic sequencing in tobacco samples with different grades of RKN disease. The results showed that the community structure and function of the plant rhizosphere were significantly correlated to the RKN disease. RKN density and urease content were key factors affecting the rhizosphere bacterial community. Urease accelerated the catabolism of urea and led to the production of high concentrations of ammonia, which directly suppressed the development of RKNs or by improving the nutritional and growth status of microorganisms that were antagonistic to RKNs. Further experiments showed that the suppression role of ammonia should be attributed to the direct inhibition of NH3. The bacterial members that were positively correlated with RKN density, contained many plant cell wall degrading enzymes, which might destroy plant cell walls and promote the colonization of RKN in tobacco roots. The analysis of metatranscriptome and metabolism demonstrated the role of these cell wall degrading enzymes. This study offers a comprehensive insight into the relationships between RKNs, bacteria, and soil environmental factors and provides new ideas for the biological control of RKNs.

Interaction of Meloidogyne incognita (Kofoid & White, 1919) (Nemata: Meloidogynidae) and Fusarium oxysporum f. sp. radicis-lycopersici Jarvis & Shoemaker in tomato F1 hybrids with differing levels of resistance to these pathogens

The interaction of Meloidogyne incognita (Kofoid & White, 1919) (Rhabditida: Meloidogynidae) and Fusarium oxysporum f. sp. radicis-lycopersici Jarvis & Shoemaker (FORL) on nematode reproduction and wilt severity was investigated in tomato hybrids in this study. The study included with five combinations of individual, simultaneous and sequential inoculations of M. incognita and FORL to tomato F1 hybrids Adel, Alberty, Armstrong, Body, Gülizar and Kaplan in January-May 2021 under controlled conditions. The experiment was completed after 60 days. Simultaneous inoculation increased M. incognita galls and egg masses in Adel, Armstrong, Body, and Gülizar. The highest gall and egg mass numbers occurred with FORL inoculation 10 days after M. incognita inoculation (N+10 FORL) in Alberty and Kaplan. The highest disease incidence occurred in all tomato hybrids at the application of N+10 FORL and was followed by Gülizar, Kaplan, Body, Alberty, Armstrong and Adel. Meloidogyne incognita showed high reproductive rates in Alberty and Body, and FORL resistance was overcome with treatment N+10 FORL. Meloidogyne incognita was unable to reproduce in Adel and Armstrong and thus no disease was seen. The results indicated that the development of root-knot nematodes is a significant factor affecting the durability of FORL resistance.

Effect of plant age on development of root-knot nematode (M. javanica) on coriander

Coriander is one of the most important and nutritive seed spice crops grown all over the world. The production of coriander is affected by various biotic and abiotic factors. Among the diseases of coriander, nematode diseases are also most important. Root-knot nematodes are dangerous and economically very important pest of cultivated crops in the world. In view of this, a pot experiment was conducted to test the effect of plant age on development of Meloidogyne javanica on coriander.The pots were filled with sterilized sandy loamy soil. Root-knot nematodes (J2 stage) were inoculated in each pot at the time of germination, 7, 14, 21 and 28 days after germination.Results showed that as the nematode inoculum interval after germination was extended, the plant growth characteristics were also greatly improved. Similarly, increased nematode inoculum interval after germination considerably reduced nematode reproduction. But, No. of eggs/egg mass was found almost similar in among all plant ages (i.e., from at the time of germination, 7, 14, 21 and 28 days after germination).

Effects of Roots-Applied Resistance Inducers on Penetration and Development of Root-Knot Nematode in Sugar-Beet

Effects of Roots-Applied Resistance Inducers on Penetration and Development of Root-Knot Nematode in Sugar-Beet

English

Root-knot nematodes (Meloidogyne spp.) are soil-borne pathogens that can cause severe damage to agricultural production. The most common approaches to prevent root-knot nematode infections are based on crop rotation with non-host plants, use of chemical insecticides, biological control methods, and use of nematode-antagonistic or trap plants. Marigolds (Tagetes erecta) are used as nematode-killing plants, but there is controversy over the mechanism through which they control root-knot nematodes. This study confirmed that marigold root-exudates are lethal to root-knot nematodes, illustrated that marigolds act as trap plants for root-knot nematodes when planted close to nematode host plants such as tomato. We investigated the rates of infection and development of nematode larvae injected into the marigold root system to evaluate whether marigolds could act as a non-host plant for root-knot nematodes. We found that aqueous solutions of marigold root-exudates showed strong lethal and inhibitory effects on sec-stage juveniles and eggs of root-knot nematodes. Marigold roots secreted substances that attracted nematodes from the surrounding environment. Furthermore, marigold root cells contained substances that had a strong inhibitory effect on the development of root-knot nematodes, resulting in diapause in nematodes, and inhibition of further infection. Herein we report a preliminary exploration of the antagonistic mechanism in marigolds for controlling the growth and development of root-knot nematodes. Our research provides basis for promoting the use of marigold for the control of nematodes as an important part of sustainable cropping strategies that rely on biological pest control. © 2021 Friends Science Publishers

Characterisation of root-knot nematode resistance in black oat, Avena strigosa, ‘Terara’

Summary The mechanism of root-knot nematode (RKN) resistance in black oat ‘Terara’ and its stability under high temperatures were examined. To investigate the suppressive mechanism, we observed root invasion and development of RKN in ‘Terara’. Juveniles of Meloidogyne incognita, M. arenaria and M. javanica successfully invaded roots of ‘Terara’ 3 days after inoculation (DAI), whereas juveniles of M. hapla were hardly observed in black oat roots. The total number of M. incognita and the ratio of successfully developing juveniles were significantly lower in roots of ‘Terara’ than a susceptible cultivar from 7 DAI. A number of M. incognita developed to sausage-shaped juveniles in ‘Terara’; however, juveniles beyond that stage were seldom observed. Histological observation of feeding sites suggested the poor development of giant cells was involved in this arrested development. Juveniles of M. arenaria and M. javanica also only developed to the sausage-shaped stage at 21 DAI. These observations indicated that ‘Terara’ and resistant common oat cultivars suppressed RKN in a similar way. The effect of high temperature on resistance was evaluated using ‘Terara’ cultivated at 30°C throughout the experiment and at 32°C for the initial 5 DAI. The number of egg masses of M. incognita under the 32°C treatment was slightly higher than the 25°C control. However, it was still suppressed to 4.9% of the susceptible cultivar.

Soil Types and their Physio – Chemical Properties for Population Development of Root Knot Nematode (Meloidogyne spp.) in Tomato (Solanum lycopersicum)

Root Knot Nematodes (RKN) (Meloidogyne spp.) is the major soil borne microorganisms causing severe losses in vegetable production in Sri Lanka. This experiment was conducted to determine the effect of the fourteen different soil types and their physio-chemical properties for population development of Meloidogyne spp on tomato crop. The population of RKN showed significant differences among different soil types. The maximum nematode population (Root Galling Index of 7.25, Number of knots of 165.25) were recorded in Red Yellow Podzolic – Imperfectly Drained soil with higher organic carbon (11.54%), phosphorus (3.30 ppm), potassium (369 ppm), sand (77.06%), moisture content (16.22%) and it was not significantly difference between Red Yellow Podzolic – Imperfectly Drained soil and Regosol. The minimum nematode population (Root Galling Index of 2.75, Number of knots of 51.75) was recorded in Reddish Brown Latosol – Imperfectly Drained soil with organic carbon (4.1% w/w), phosphorus (0.58 ppm), sand (64.66%), and moisture content (6.19%). Analysis of correlation coefficient showed that population of Meloidogyne spp. significantly positive correlated with phosphorus, potassium, nitrogen, EC, soil moisture and sand percentage while significantly negative correlated with the silt + clay percentage, soil temperature and soil pH. There was no significant correlation recorded with soil organic carbon content as it was clearly indicated that all the samples had very low percentage of organic carbon in compared to suppressive soils. Therefore, the study concludes all soil physic-chemical properties except organic carbon have direct effect on the development of population of Meloidogyne spp. and it is varied with the different soil types, hence it is vital to contemplate soil type and its physio-chemical properties when executing Integrated Nematode management programs for Meloidogyne spp. However, further Investigations are required to study the direct effect of soil organic carbon on development of population of Meloidogyne spp.

KETEPATAN WAKTU APLIKASI Paecilomyces lilacinus DALAM MENGENDALIKAN NEMATODA BENGKAK AKAR (Meloidogyne spp.) PADA TANAMAN TOMAT

Root-knot nematodes (Meloidogyne spp.) have been reported to be one of the primary pathogens that decreased tomato production in Indonesia. Biological control of root-knot nematodes by using parasitic fungus as like as Paecilomyces lilacinus is still limited. An effective application of parasitic fungi could be successful by managing a suitability application time. The study aimed to determine the suitability of the application time of the P.lilacinus in controlling root-knot nematodes on tomato. The study was conducted in farmers' land that was infected by root-knot nematodes. The experiment was done in a randomized block design with applying P.lilacinus isolates on 12, 8, and 4 days before planting, planting time, and 4, 8, 12 days after planting. All treatments were repeated four times. The application of P. lilacinus onto tomato root at planting time was better at suppressing the development of root-knot nematode compared to applications made before or after planting. P. lilacinus was able to suppress the number of root-knot (66.08%), the number of egg groups (77.33%), the number of eggs (26.79%), and the number of nematodes in the soil (82.20%). Keywords: Application time, Meloidogyne spp., Paecilomyces lilacinus, tomato

Small RNA Sequencing Reveals Regulatory Roles of MicroRNAs in the Development of Meloidogyne incognita.

MicroRNAs (miRNAs) are an extensive class of small regulatory RNAs. Knowing the specific expression and functions of miRNAs during root-knot nematode (RKN) (Meloidogyne incognita) development could provide fundamental information about RKN development as well as a means to design new strategies to control RKN infection, a major problem of many important crops. Employing high throughput deep sequencing, we identified a total of 45 conserved and novel miRNAs from two developmental stages of RKN, eggs and J2 juveniles, during their infection of cotton (Gossypium hirsutum L.). Twenty-one of the miRNAs were differentially expressed between the two stages. Compared with their expression in eggs, two miRNAs were upregulated (miR252 and miRN19), whereas 19 miRNAs were downregulated in J2 juveniles. Nine miRNAs were expressed at high levels, with >1000 reads per mapped million (RPM) sequenced reads in both eggs and J2 juveniles (miR1, miR124, miR2-3p, miR252, miR279, miR57-5p, miR7904, miR87, and miR92). Three miRNAs were only expressed in eggs (miR4738, miRN3, and miRN5). These differentially expressed miRNAs may control RKN development by regulating specific protein-coding genes in pathways associated with RKN growth and development.

English

The reaction of four wheat RbcS RNAi mutants and wild type to the infection of M. incognita was investigated in a greenhouse pot experiment using plant growth parameters as well as nematode reproduction. Obtained results revealed that all estimated growth parameters of lines under study were reduced by M. incognita infection to various extents. RSS13.2 line showed the highest percentage of reduction of plant total fresh weight, length, and shoot dry weight. It did act as good host for root-knot nematode; therefore, it was classified as susceptible host. In addition, the lowest reduction percentage of fresh and dry weights was observed in RSS8.5 line although it showed high values for nematode development and reproduction parameters; therefore, it seemed to be as a tolerant host. The maximum reduction in chlorophyll content was recorded in RSS7.6 line, whereas, the minimum was obtained from RSS11.5 line. It was evident that none of the five tested wheat lines was immune to M. incognita infection. The lowest numbers of second stage juveniles, galls, and egg-masses were observed in soil and on roots of RSS11.5 line although its plant growth was slightly affected; therefore, it is considered as partially resistant line. It could be concluded from the results of this study that, RNAi mutants of the RbcS were partially effective in suppressing root-knot nematode development. © 2019 Friends Science Publishers

Penetration and post-infection development of root-knot nematodes in watermelon

Meloidogyne javanica has showed less reproductive success than M. incognita in watermelon genotypes. This study was conducted to elucidate the low reproduction of M. javanica in watermelon. The post-infection development of M. javanica in watermelon ‘Sugar Baby’ was determined at progressively higher initial population (Pi) levels at two time points during the life cycle. Plants were inoculated with 0, 25, 50, 100, 200, and 300 second-stage juveniles (J2)/plant. The increase in Pi was correlated with the penetration rates (R2= 0.603, p<0.001) and total numbers of nematodes in the root (R2 =0.963, p< 0.001) but there was no correlation between the Pi and the reproduction factor (eggs/plant/Pi). The population in the roots at 26 days post-inoculation (dpi) consisted primarily of third-stage juveniles (J3) with a small presence of J2 and fourth stages, and egg-laying females. The dominance of the J3, when egg-laying females are expected, point to the malfunction of the feeding sites that failed to support nematode development beyond the J3 stage. The similarities in egg-laying females at 26 and 60 dpi imply the disruption of the life cycle. Watermelon compensated for M. javanica parasitism by increasing vine length (19% to 33%) and dry top weight (40%) in comparison with the non-inoculated plants. The area under the vine length progress curve was significantly larger as the Pi progressively increased (R²=0.417, p<0.001). Physiological variation was detected between the M. incognita populations. M. arenaria had less ability to invade watermelon roots than did M. incognita and M. javanica.

Knock-down of heat-shock protein 90 and isocitrate lyase gene expression reduced root-knot nematode reproduction.

Crop losses caused by nematode infections are estimated to be valued at USD 157 billion per year. Meloidogyne incognita, a root-knot nematode (RKN), is considered to be one of the most important plant pathogens due to its worldwide distribution and the austere damage it can cause to a large variety of agronomically important crops. RNA interference (RNAi), a gene silencing process, has proven to be a valuable biotechnology alternative method for RKN control. In this study, the RNAi approach was applied, using fragments of M. incognita genes that encode for two essential molecules, heat-shock protein 90 (HSP90) and isocitrate lyase (ICL). Plant-mediated RNAi of these genes led to a significant level of resistance against M. incognita in the transgenic Nicotiana tabacum plants. Bioassays of plants expressing HSP90 dsRNA demonstrated a delay in gall formation and up to 46% reduction in eggs compared with wild-type plants. A reduction in the level of HSP90 transcripts was observed in recovered eggs from plants expressing dsRNA, indicating that gene silencing persisted and was passed along to first progeny. The ICL knock-down had no clear effect on gall formation but resulted in up to 77% reduction in egg oviposition compared with wild-type plants. Our data suggest that both genes may be involved in RKN development and reproduction. Thus, in this paper, we describe essential candidate genes that could be applied to generate genetically modified crops, using the RNAi strategy to control RKN parasitism.

Evaluation of Some Botanicals and Trichoderma harzianum for the Management of Tomato Root-knot Nematode (Meloidogyne incognita (Kofoid and White) Chit Wood)

Root-knot nematode disease caused by Meloidogyne incognita (Kofoid and White) Chit wood) is one of the major constraints for successful cultivation of tomato (Lycopersicon esculentum Mill.) in Ethiopia. Hence, the present study was conducted to evaluate the effect of leaf and seed extracts of four botanicals viz., Rape seed (Brassica napus L.), Lantana (Lantana camara L.), African marigold (Tagetes erecta L.) and Neem (Azadirachta indica L.) at 5% and 10% concentrations and T. harzianum at 5% plus control were tested on root-knot nematode under in vitro and also to evaluate their against root-knot nematode development and their role on plant growth parameters of tomato under in vivo condition. Plant extracts were more effective and significantly inhibited egg hatching and immobilizing the J2 larval mortality of M. incognita than T. harzianum. Aqueous extract of all the tested plants inhibited egg hatching of nematode and resulted 84.67-100% mortality of the J2 juveniles of M. incognita in vitro at the 10% concentration after 72 h of exposure time. There were no significant differences among the treatments of rape seed leaf (84.7%) at 10% concentration and Lantana camara (87%), African marigold (86.3%) and Neem leaf (85%) at 5% concentration after 72 h. Aqueous seed extracts of A. indica more significantly inhibited egg hatching and larva mortality of the J2 of M. incognita in vitro at the 10% concentration and immobilized by 89, 93 and 100% after 24, 48 and 72 h of exposures, respectively, while at similar concentration of T. erecta, B. napus and L. camara leaf extracts exhibited 92, 89 and 93.2% inhibition of egg hatching and 75, 62.1 and 73% larval mortality, respectively. The effect of different botanicals and T. harzianum singly and in combination were studied for the management of tomato root-knot nematode under greenhouse condition. There was a significant difference in the reduction of root-knot nematode incidence, root-knot nematode population, nematode reproduction rate (NRR), number of galls and egg masses per plant were recorded. In pot culture condition, the application of leaf extract of individual plant in the presence of the nematode significantly enhanced the growth of tomato seedlings in comparison to the control. A significant increase in plant height, shoot weight and root weight of the seedlings were observed at the 10% concentration of leaf extracts in comparison to control. There was a significant difference in the reduction of root-knot nematode population, nematode reduction rate, number of galls and egg masses per plant of L. camara combined with T. harzianum. The mean fruit weight and total yield were observed highest in the combination treatment of L. camara combined with T. harzianum. This study results revealed that the test plants are readily available to farmers at no cost and able to reduce nematode population below economic threshold.

오이 뿌리혹선충병에 대한 효율적인 저항성 검정법 확립

연작 재배로 인하여 뿌리혹선충(Meloidogyne incognita)과 같은 식물 기생 선충에 의한 피해는 오이 재배 면적이 늘어나면서 크게 늘어나고 있다. 이러한 생산량의 감소 피해를 해결하기 위한 친환경적인 방제 방법으로 경종적 방제의 저항성 품종을 이용한 재배가 점차 증가되고 있다. 본 연구에서는 새로운 저항성 육종 소재를 찾기 위한 효율적인 저항성 검정 방법을 확립하기 위하여, 뿌리혹선충 M. incognita를 이용한 오이의 선충병 발생 정도를 접종원 농도, 오이 생육 시기 및 이식 시기 등의 다양한 발병 조건에 따라 오이 4개 품종('드레곤삼척', 아시아스트라이크', '네박자', '하늘백다다기')을 대상으로 조사하였다. 접종원의 접종 농도가 증가 할수록 오이의 뿌리혹선충병 발생은 농도 의존적으로 증가되었지만, 오이의 생육 시기 및 이식 시기에 따른 오이의 뿌리혹선충병 발생은 유의한 차이가 없었다. 따라서, 오이 품종의 뿌리혹선충병 저항성 검정 조건으로 온실(<TEX>$25{\pm}5^{\circ}C$</TEX>)에서 파종 후 21일간 재배하고, 이식한지 7일 후에 5,000개의 뿌리혹선충 알 접종으로 45일 이후에 병 조사를 하는 것이 적합함을 알 수 있었다. 적정한 발병 조건에 따라 시판 중인 오이 45개 품종의 뿌리혹선충에 대한 저항성 정도를 조사한 결과, 대목 6개 품종에서 난낭수 100개 이하의 뿌리혹선충병 발생 정도를 보였고, 특히 '유니온' 대목 품종은 중간 저항성으로 조사되었다. 그 외 실험한 모든 품종들은 유사한 정도의 높은 감수성을 나타냈다. 이들 결과들을 바탕으로 M. incognita에 대한 오이 품종의 저항성 정도를 검정하기 위한 효율적인 방법을 제안하고자 한다. Root-knot nematodes represent a significant problem in cucumber, causing reduction in yield and quality. To develop screening methods for resistance of cucumber to root-knot nematode Meloidogyne incognita, development of root-knot nematode of four cucumber cultivars ('Dragonsamchuk', 'Asiastrike', 'Nebakja' and 'Hanelbakdadaki') according to several conditions such as inoculum concentration, plant growth stage and transplanting period was investigated by the number of galls and egg masses produced in each seedling 45 days after inoculation. There was no difference in galls and egg masses according to the tested condition except for inoculum concentration. Reproduction of the nematode on all the tested cultivars according to inoculum concentration increased in a dose-dependent manner. On the basis of the result, the optimum conditions for root-knot development on the cultivars is to transplant period of 1 week, inoculum concentration of 5,000 eggs/plant and plant growth stage of 3-week-old in a greenhouse (<TEX>$25{\pm}5^{\circ}C$</TEX>). In addition, under optimum conditions, resistance of 45 commercial cucumber cultivars was evaluated. One rootstock cultivar, Union was moderately resistant to the root-knot nematode. However, no significant difference was in the resistance of the others cultivar. According to the result, we suggest an efficient screening method for new resistant cucumber to the root-knot nematode, M. incognita.

Expression of tomato salicylic acid (SA)‐responsive pathogenesis‐related genes in Mi‐1‐mediated and SA‐induced resistance to root‐knot nematodes

The expression pattern of pathogenesis-related genes PR-1, PR-2 and PR-5, considered as markers for salicylic acid (SA)-dependent systemic acquired resistance (SAR), was examined in the roots and shoots of tomato plants pre-treated with SA and subsequently infected with root-knot nematodes (RKNs) (Meloidogyne incognita). PR-1 was up-regulated in both roots and shoots of SA-treated plants, whereas the expression of PR-5 was enhanced only in roots. The over-expression of PR-1 in the whole plant occurred as soon as 1 day after SA treatment. Up-regulation of the PR-1 gene was considered to be the main marker of SAR elicitation. One day after treatment, plants were inoculated with active juveniles (J2s) of M. incognita. The number of J2s that entered the roots and started to develop was significantly lower in SA-treated than in untreated plants at 5 and 15 days after inoculation. The expression pattern of PR-1, PR-2 and PR-5 was also examined in the roots and shoots of susceptible and Mi-1-carrying resistant tomato plants infected by RKNs. Nematode infection produced a down-regulation of PR genes in both roots and shoots of SA-treated and untreated plants, and in roots of Mi-carrying resistant plants. Moreover, in resistant infected plants, PR gene expression, in particular PR-1 gene expression, was highly induced in shoots. Thus, nematode infection was demonstrated to elicit SAR in shoots of resistant plants. The data presented in this study show that the repression of host defence SA signalling is associated with the successful development of RKNs, and that SA exogenously added as a soil drench is able to trigger a SAR-like response to RKNs in tomato.

Ectopic expression of Kip‐related proteins restrains root‐knot nematode‐feeding site expansion

The development of nematode feeding sites induced by root-knot nematodes involves the synchronized activation of cell cycle processes such as acytokinetic mitoses and DNA amplification. A number of key cell cycle genes are reported to be critical for nematode feeding site development. However, it remains unknown whether plant cyclin-dependent kinase (CDK) inhibitors such as the Arabidopsis interactor/inhibitor of CDK (ICK)/Kip-related protein (KRP) family are involved in nematode feeding site development. This study demonstrates the involvement of Arabidopsis ICK2/KRP2 and ICK1/KRP1 in the control of mitosis to endoreduplication in galls induced by the root-knot nematode Meloidogyne incognita. Using ICK/KRP promoter-GUS fusions and mRNA in situ hybridizations, we showed that ICK2/KRP2, ICK3/KRP5 and ICK4/KRP6 are expressed in galls after nematode infection. Loss-of-function mutants have minor effects on gall development and nematode reproduction. Conversely, overexpression of both ICK1/KRP1 and ICK2/KRP2 impaired mitosis in giant cells and blocked neighboring cell proliferation, resulting in a drastic reduction of gall size. Studying the dynamics of protein expression demonstrated that protein levels of ICK2/KRP2 are tightly regulated during giant cell development and reliant on the presence of the nematode. This work demonstrates that impeding cell cycle progression by means of ICK1/KRP1 and ICK2/KRP2 overexpression severely restricts gall development, leading to a marked limitation of root-knot nematode development and reduced numbers of offspring.

Effect of plant elicitors on the reproduction of the root-knot nematode Meloidogyne chitwoodi on susceptible hosts

Sustainable strategies for plant-parasitic nematode control are required to reduce dependence on chemical nematicides. Foliar application of various compounds can induce a systemic defence response that reduces nematode infestation. The effects of benzothiadiazole (BTH), β-aminobutyric acid (BABA), jasmonates (cis-jasmone and methyl jasmonate) and salicylic acid (SA) in the development and reproduction of the root-knot nematode Meloidogyne chitwoodi in tomato plants were assessed. The effects of BTH and of the jasmonates were further tested on potato plants. Pot assays were conducted using tomato plants cv. Tiny Tim or potato cv. Desiree treated with foliar sprays and inoculated with 300 second stage juveniles. Nematode development and reproduction were assessed 21 and 45 days after inoculation. Treatment with SA had a negative effect on nematode development in tomato plants but did not affect reproduction and methyl jasmonate treatment was the most effective in reducing nematode penetration (58 %). Nematode development was significantly affected in potato plants sprayed with cis-jasmone. Nematode penetration was reduced by 90, 67 and 81 % in plants treated with BTH, cis-jasmone and methyl jasmonate respectively, although the reproduction factor (Rf) was only significantly lower in the BTH treatment (Rf = 7.6) when compared to the control (Rf = 18.1). Our results suggest that both the SA and JA pathways play an important role in plant defence mechanisms against root-knot nematode development and reproduction for both plants, and should be considered in the design of integrated pest management approaches.