Roots Of Cultivars Research Articles

2,4-D attenuates salinity-induced toxicity by mediating anatomical changes, antioxidant capacity and cation transporters in the roots of rice cultivars

Growth regulator herbicides are widely used in paddy fields to control weeds, however their role in conferring environmental stress tolerance in the crop plants are still elusive. In this study, the effects of recommended dose of 2,4-dichlorophenoxyacetic acid (2,4-D) on growth, oxidative damage, antioxidant defense, regulation of cation transporter genes and anatomical changes in the roots of rice cultivars XS 134 (salt resistant) and ZJ 88 (salt sensitive) were investigated under different levels of saline stress. Individual treatments of saline stress and 2,4-D application induced oxidative damage as evidenced by decreased root growth, enhanced ROS production, more membrane damage and Na+ accumulation in sensitive cultivar compared to the tolerant cultivar. Conversely, combined treatments of 2,4-D and saline stress significantly alleviated the growth inhibition and oxidative stress in roots of rice cultivars by modulating lignin and callose deposition, redox states of AsA, GSH, and related enzyme activities involved in the antioxidant defense system. The expression analysis of nine cation transporter genes showed altered and differential gene expression in salt-stressed roots of sensitive and resistant cultivars. Together, these results suggest that 2,4-D differentially regulates the Na+ and K+ levels, ROS production, antioxidant defense, anatomical changes and cation transporters/genes in roots of rice cultivars.

Genotype-dependent regulation of drought-responsive genes in tolerant and sensitive sugarcane cultivars

Drought is the most damaging among the major abiotic stresses. Transcriptomic studies allow a global overview of expressed genes, providing the basis for molecular markers development. Here, the HT-SuperSAGE technique allowed the evaluation of four drought-tolerant cultivars and four-sensitive cultivars, after 24h of irrigation suppression. We identified 9831 induced unitags from roots of the tolerant cultivars with different regulations by the -sensitive cultivars after the applied stress. These unitags allowed a proposal of 15 genes, whose expressed profiles were validated by RT-qPCR, evaluating each cultivar independently. These genes covered broad metabolic processes: ethylene stress attenuation (ACCD); root growth (β-EXP8); protein degradation [ubiquitination pathway (E2, 20SPβ4); plant proteases (AP, C13)]; oxidative detoxification (TRX); fatty acid synthesis (ACC); amino acid transport (AAT), and carbohydrate metabolism [glycolysis (PFK, TPI, FBA); TCA cycle (LDP, MDH); pentose phosphate pathway (TKT)]. The expressed profiles showed a genotype-dependent regulation of the target genes. Two drought-tolerant cultivars (SP83-2847; CTC6) presented each one, nine of the induced genes. Among the -sensitive cultivars, CTC13 induced only one, while SP90-1636 induced two genes. These genes should help breeders to identify accessions managing drought stress tolerance responses, showing better ethylene stress attenuation, energy allocation, amino acid transport, and protein homeostasis.

Effects of Surface Charge and Functional Groups on the Adsorption and Binding Forms of Cu and Cd on Roots of indica and japonica Rice Cultivars.

This work was designed to understand the mechanisms of adsorption of copper (Cu) and cadmium (Cd) on roots of indica and japonica varieties of rice. Six varieties each of indica and japonica rice were grown in hydroponics and the chemical properties of the root surface were analyzed, including surface charges and functional groups (-COO- groups) as measured by the streaming potential and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Binding forms of heavy metals adsorbed on rice roots were identified using sequential extraction methods. In rice roots exposed to Cu and Cd solutions, Cu existed mainly in both exchangeable and complexed forms, whereas Cd existed mainly in the exchangeable form. The amounts of exchangeable Cu and Cd and total adsorbed metal cations on the roots of indica varieties were significantly greater than those on the roots of japonica varieties, and the higher negative charges and the larger number of functional groups on the roots of indica varieties were responsible for their higher adsorption capacity and greater binding strength for Cu and Cd. Surface charge and functional groups on roots play an important role in the adsorption of Cu and Cd on the rice roots.

A Novel Penicillium sp. Causes Rot in Stored Sugar Beet Roots in Idaho.

Penicillium vulpinum along with a number of other fungi can lead to rot of stored sugar beet roots. However, Penicillium isolates associated with necrotic lesions on roots from a recent sugar beet storage study were determined to be different from P. vulpinum and other recognized Penicillium species. Phylogenies based on sequencing of the internal transcribed spacer (ITS)-5.8S, β-tubulin (BenA), and RNA polymerase II second largest subunit (RPB2) DNA regions indicate that these isolates are novel, but most closely related to the following Penicillium spp. in the section Fasiculata: P. aurantiogriseum, P. camemberti, and P. freii. Macro- and micromorphological data also support designating these isolates as a new species for which we propose the name, Penicillium cellarum sp. nov. Inoculation studies with the P. cellarum isolates on roots of the commercial sugar beet cultivar B-7 led to the formation of necrotic lesions 23 to 25 mm in diameter after 86 days in storage. These lesions were similar to those observed on sugar beet roots in commercial storage piles. These data indicate that P. cellarum is a pathogen which can cause root rot in stored sugar beet roots.

Identification of Light-Independent Anthocyanin Biosynthesis Mutants Induced by Ethyl Methane Sulfonate in Turnip "Tsuda" (Brassica rapa).

The epidermis of swollen storage roots in purple cultivars of turnip “Tsuda” (Brassica rapa) accumulates anthocyanin in a light-dependent manner, especially in response to UV-A light, of which the mechanism is unclear. In this study, we mutagenized 15,000 seeds by 0.5% (v/v) ethyl methane sulfonate (EMS) and obtained 14 mutants with abnormal anthocyanin production in their epidermis of swollen storage roots. These mutants were classified into two groups: the red mutants with constitutive anthocyanin accumulation in their epidermis of storage roots even in underground parts in darkness and the white mutants without anthocyanin accumulation in the epidermis of storage roots in aboveground parts exposed to sunlight. Test cross analysis demonstrated that w9, w68, w204, r15, r21, r30 and r57 contained different mutations responsible for their phenotypic variations. Further genetic analysis of four target mutants (w9, w68, w204 and r15) indicated that each of them was controlled by a different recessive gene. Intriguingly, the expression profiles of anthocyanin biosynthesis genes, including structural and regulatory genes, coincided with their anthocyanin levels in the epidermis of storage roots in the four target mutants. We proposed that potential genes responsible for the mutations should be upstream factors of the anthocyanin biosynthesis pathway in turnips, which provided resources to further investigate the mechanisms of light-induced anthocyanin accumulation.

Effect of different growing media on the rooting of pomegranate (Punica granatum L.) cv. 'Phulearakta' cuttings

To identify the most efficient growing medium for root and shoot development in stem cuttings of pomegranate cv. ‘Phulearakta’ under arid conditions, a greenhouse experiment was conducted in randomized complete block design with three replications during 2014-15 at ICAR-CIAH, Bikaner. About 15-20 cm long hard wood cuttings, 0.5-1.0 cm diameter and having three to four buds were separated from the healthy trees and planted in mid-January. Detached cuttings were treated with 2500 ppm of IBA (3- Indole butyric acid) using quick dip technique (for 5 seconds) and planted in five rooting substrates i.e.sand, vermiculite, perlite, cocopeat and garden soil (control) alone and in combination at 1:1 (v/v). The response of perlite + vermiculite medium was best in terms of rooting (82.33 per cent), number of roots (32.67 per cutting), fresh and dry weight of roots (0.61 mg and 2.08 mg), shoots per cutting (80.33) and survival (76.0 per cent) than the other medium used. Vermiculite + Coco peat 1:1 (v/v) combination also resulted in rooting in more than 80 per cent of cuttings whereas cuttings raised in garden soil and sand showed very low rooting. Based on the findings, it appears that Perlite + vermiculite 1:1 (v/v) and vermiculite + cocopeat may be appropriate alternatives to the conventially used substrate, i.e., garden soil for the better rooting and establishment of pomegranate cultivar 'PhuleArakta' cuttings.

GC–MS Analysis of Cell Wall-Bound Phenolic Compounds and Lignin Quantification in Date Palm Cultivars that are Resistant or Susceptible to Fusarium oxysporum f. sp. albedinis

This study aimed to collect data about the interactions that occur between the date palm (Phoenix dactylifera L.) and Fusarium oxysporum f. sp. albedinis (F.o.a), the causal agent of bayoud disease. Alkaline hydrolysis was carried out using the root parietal residue of three cultivars of date palm, among which two are susceptible (Deglet Nour (DN) and Tggaza (TG)) and one is resistant (Takerbucht (TK)) to bayoud disease. Gas chromatography coupled with mass spectrometry (GC–MS) analysis revealed that p-hydroxybenzoic acid is the major phenolic compound of cell wall-bound phenolics. In uninfected palm groves, the resistant date palm cultivar contained a high level of p-hydroxybenzoic acid; however, in palm groves infested with F.o.a, a significant decrease in p-hydroxybenzoic acid was observed. In the roots of susceptible cultivars with bayoud symptoms, we noted a qualitative and quantitative increase in phenolic compounds, with a remarkable increase inp-hydroxybenzoic acid content during the infection of susceptible cultivars. We investigated lignin content in roots. An increase in total lignin content was observed in both cultivars collected from palm groves infested by F.o.a, but more accumulated in the roots of the resistant cultivar than in those of the susceptible cultivars. Our findings indicate that p-hydroxybenzoic acid plays an important role in date palm defense mechanisms against F.o.a. However, its accumulation in susceptible cultivars as a response to pathogens did not block the progression of the parasite and thus was not an effective mode of resistance. Susceptible cultivars used phenolic compounds from the benzoic series for their defense, while resistant cultivars used lignification that reinforced the cell wall.

Dual Cultures of Meloidogyne javanica and Grapevine Rootstocks on Artificial Media

Grapevine rootstock cultivars were cultured on more than one artificial medium. Meloidogyne javanica was inoculated on the roots of different cultivars on seven media and penetration and development were recorded. Plate cultures of roots allowed microscopic examination of nematode development. Nematode reproduction occurred on susceptible rootstocks only, suggesting similar results for field and in vitro screening. However, root and nematode development was low and inconsistent, indicating problems which will have to be resolved before general application of the technique.

Differential gene expression in banana roots in response to Fusarium wilt

Banana wilt disease, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a devastating disease in the banana industry. The molecular mechanism underlying the wilt resistance of AAA-type banana cultivars has not been fully characterized. Our objective was to analyse the genes differentially expressed in roots during the time of flower bud differentiation in plants grown in fields infested with Foc TR4. We compared the Foc TR4-tolerant ‘Formosana’ banana and the susceptible ‘Brazil’ banana. cDNA libraries were constructed from RNA isolated from the roots of both cultivars, and generated approximately 40 million and 35 million high-quality reads, respectively. We mapped 28 353 810 ‘Formosana’ reads and 26 917 421 ‘Brazil’ reads to the banana genome. A search of the NR (non-redundant) database resulted in the annotation of 34 408 genes. Additionally, 107 genes were differentially expressed between the two cultivars. Among the 48 differentially expressed genes with known functions, 41 were expressed more highly in ‘Formosana’ than in ‘Brazil’. These genes were divided into several categories, including specific resistance mechanism-related enzyme genes and phytoalexin synthesis-related genes. The expression levels of eight genes were validated by a quantitative real-time polymerase chain reaction. Our results indicate that ‘Formosana’ may enhance its tolerance to Foc TR4 by increasing the expression of defence-related genes (possibly constitutively). This cultivar also exhibits up-regulated expression of non-specific stress-related genes, which may enhance its overall disease tolerance. This study provides important transcript-level details potentially useful for clarifying the molecular mechanism underlying the disease resistance of Cavendish banana cultivars.

Ralstonia solanacearum Differentially Colonizes Roots of Resistant and Susceptible Tomato Plants.

Ralstonia solanacearum is the causal agent of bacterial wilt and infects over 200 plant species in 50 families. The soilborne bacterium is lethal to many solanaceous species, including tomato. Although resistant plants can carry high pathogen loads (between 105 and 108 CFU/g fresh weight), the disease is best controlled by the use of resistant cultivars, particularly resistant rootstocks. How these plants have latent infections yet maintain resistance is not clear. R. solanacearum first infects the plant through the root system and, thus, early root colonization events may be key to understanding resistance. We hypothesized that the distribution and timing of bacterial invasion differed in roots of resistant and susceptible tomato cultivars. Here, we use a combination of scanning electron microscopy and light microscopy to investigate R. solanacearum colonization in roots of soil-grown resistant and susceptible tomato cultivars at multiple time points after inoculation. Our results show that colonization of the root vascular cylinder is delayed in resistant 'Hawaii7996' and that, once bacteria enter the root vascular tissues, colonization in the vasculature is spatially restricted. Our data suggest that resistance is due, in part, to the ability of the resistant cultivar to restrict bacterial root colonization in space and time.

Phytochelatins play key roles for the difference in root arsenic accumulation of different Triticum aestivum cultivars in comparison with arsenate uptake kinetics and reduction

In the previous studies, we have found that arsenic (As) accumulation in roots of bread wheat (Triticum aestivum L.) seedlings were significantly different among different wheat cultivars, and As(V) tolerant wheat cultivars have much higher capacities of root As accumulation. However, the reason for the difference remains unclear. Four wheat cultivars with high (MM45 and FM8) or low (QF1 and HM29) levels of arsenic (As) accumulation were selected to investigate the relationship between root As(V) uptake kinetics and root As accumulation. MM45 and HM29 were also used to examine As(V) reduction ability and non-protein thiol (cysteine [Cys], glutathione [GSH], and phytochelatins [PCs]) concentrations in wheat seedlings. MM45 had the lowest Michaelis–Menten constant (Km) and maximum influx rate (Vmax). No difference in the Km values was found among the three other cultivars. No difference in As(V) reduction capacity was observed between MM45 and HM29. GSH and PC2 were significantly induced by 10 μM As(V) in roots of wheat seedlings, particularly in MM45. Synthesis of GSH and PCs was completely suppressed in the presence of l-buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine synthetase. BSO markedly decreased the As tolerance of wheat seedlings and decreased the accumulation of As in roots, but increased As accumulation in shoots. No significant difference in As concentrations was found between MM45 and HM29 under the BSO treatment. GSH and PCs are the reason why As accumulation and As(V) tolerance differ in roots of different wheat cultivars.

Investigation of the changes in low molecular weight organic acids and other physiological parameters by nitric oxide application in two wheat cultivars exposed to boron stress

ABSTRACTBoron (B) is one of the essential nutrients for the growth of plants, but its high concentrations are toxic for plants. Thus, B toxicity is a big challenge in crop cultivation. Nitric oxide (NO) is a small signaling molecule that has cytoprotective roles in plants. We investigated whether exogenous sodium nitroprusside (SNP), which is a NO donor, may succeed to alleviate B-induced toxicity in wheat cultivars. Seedlings were grown for 10 days in a growth chamber at 25°C with 16 hr light–8 hr dark photo cycle. After high B application, the effects of SNP on growth parameters; electrolyte leakage (EL); changes in reactive oxygen species [contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline]; the activities of antioxidant enzymes [glutathione peroxidase (GSHPx), glutathione reductase (GR), and glutathione S-transferase (GST)] and nitrate reductase (NR); and low molecular weight organic acid (LMWOAs) contents and also chlorophyll and total carotenoid contents were investigated in both shoots and roots of two different wheat cultivars. All experiments were carried out in triplicate. 0.2 mM SNP application ameliorated the chlorophyll and total carotenoid contents, and growth parameters such as shoot length, root length, and fresh weight in both wheat cultivars exposed to B stress. SNP reduced the B-induced lipid peroxidation, EL, and proline and H2O2 content in wheat cultivars. SNP application also increased the activities of NR and antioxidant enzymes, including GSHPx, GR, and GST in wheat cultivars exposed to B toxicity. All of the tested LMWOAs including succinic, propionic, butyric, oxalic, formic, malic, malonic, and benzoic acids were increased by SNP treatment in the shoots and roots of both wheat cultivars exposed to B toxicity. In conclusion, results obtained from this study have demonstrated that interactive effects of SNP with B considerably reduced the toxic effects of B in wheat cultivars.

Endophytic Bacterium Pseudomonas fluorescens RG11 May Transform Tryptophan to Melatonin and Promote Endogenous Melatonin Levels in the Roots of Four Grape Cultivars.

Endophytes have been verified to synthesize melatonin in vitro and promote abiotic stress-induced production of endogenous melatonin in grape (Vitis vinifera L.) roots. This study aimed to further characterize the biotransformation of tryptophan to melatonin in the endophytic bacterium Pseudomonas fluorescens RG11 and to investigate its capacity for enhancing endogenous melatonin levels in the roots of different grape cultivars. Using ultra performance liquid chromatography-tandem mass spectrometry combined with 15N double-labeled L-tryptophan as the precursor for melatonin, we detected isotope-labeled 5-hydroxytryptophan, serotonin, N-acetylserotonin, and melatonin, but tryptamine was not detected during the in vitro incubation of P. fluorescens RG11. Furthermore, the production capacity of these four compounds peaked during the exponential growth phase. RG11 colonization increased the endogenous levels of 5-hydroxytryptophan, N-acetylserotonin, and melatonin, but reduced those of tryptamine and serotonin, in the roots of the Red Globe grape cultivar under salt stress conditions. Quantitative real-time PCR revealed that RG11 reduced the transcription of grapevine tryptophan decarboxylase and serotonin N-acetyltransferase genes when compared to the un-inoculated control. These results correlated with decreased reactive oxygen species bursts and cell damage, which were alleviated by RG11 colonization under salt stress conditions. Additionally, RG11 promoted plant growth and enhanced the levels of endogenous melatonin in different grape cultivars. Intraspecific variation in the levels of melatonin precursors was found among four grape cultivars, and the associated root crude extracts appeared to significantly induce RG11 melatonin biosynthesis in vitro. Overall, this study provides useful information that enhances the existing knowledge of a potential melatonin synthesis pathway in rhizobacteria, and it reveals plant–rhizobacterium interactions that affect melatonin biosynthesis in plants subjected to abiotic stress conditions.

蒸したサツマイモの肉質と未糖化残存デンプンに及ぼす<i>β</i>-アミラーゼ活性の影響

蒸したサツマイモの肉質と未糖化残存デンプンに及ぼす<i>β</i>-アミラーゼ活性の影響

Protective Role of Pre-treatment with Different Phenolic Acids in Wheat Seedlings Against Heat Stress Induced Oxidative Damage

The present study appraised the effects of pre-treatment with different phenolic compounds viz. gallic acid (GA), ferulic acid (FA), p-coumaric acid (p-CA), caffeic acid (CF) and salicylic acid (SA) on antioxidant defense system of two contrasting wheat cultivars grown under heat stress. HD 2967 is relatively thermotolerant cultivar whereas PBW 550 is relatively heat sensitive cultivar. In comparison to control, shoot and root lengths of HD 2967 were reduced by about 32% under heat stress whereas in PBW 550, shoot and root lengths were inhibited by more than 45%. Pre-treatment with phenolic acids enhanced the shoot and root lengths and biomass of growing tissues and maximum increase in the growth of HD 2967 was reported with p-CA, CF pre-treatments. Free radical scavenging capacities of stressed seedlings were significantly improved by pre-treatment with GA. MDA and H2O2 contents increased in both the cultivars on exposure to heat stress but the increase was more in the sensitive cultivar. In roots of thermotolerant cultivar, SA and CF pre-treatments were more effective in reducing lipid peroxidation whereas in case of PBW550, pre-treatments with all the phenolic acids reduced MDA content by more than 20%. Pre-treatment with different phenolic acids especially SA and CF reduced H2O2 content in HD2967 whereas, in the shoots and roots of PBW 550 maximum decrease was reported on pre-treatment with GA, SA, p-CA and CF. Pre-treatment with CF stimulated SOD, CAT, APX and GR activities in the stressed roots of HD 2967 and SOD, POX and GR activities in the roots of PBW 550. Therefore, this study revealed that pre-treatments with phenolic acids especially CF have the potential to activate ascorbate glutathione cycle in stressed HD 2967 seedlings as revealed by ascorbate peroxidase and glutathione reductase enzymes. Further, it can be inferred that application of these phenolic acids protects the heat stressed seedlings by playing a dual role i.e. in activation of the antioxidant machinery as well as in the regulation of the growth.

The Effects of Cadmium Exposure on Cadmium Fractionation and Enzyme Activities in the Rhizosphere of Two Radish Cultivars (Raphanus sativus L.).

The effects of increasing Cd additions on plant growth and Cd fractionation and enzyme activities in rhizosphere soil of two radish cultivars were investigated. The results showed that Cd concentrations in shoot and root of cultivar 4 were both higher than for cultivar 19 under different Cd levels. Compared with cultivar 19, the total, shoot and root biomasses of cultivar 4 were significantly reduced with increasing Cd levels. A decrease in soil pH was observed for cultivar 4. The exchangeable Cd concentration of soil from cultivar 4 was significantly higher than for soil from cultivar 19, while the carbonate-bound Cd concentration of soil from cultivar 4 was significantly lower than for cultivar 19. Enzyme activities, especially acid phosphatase activity, were more susceptible to Cd in soil from cultivar 4. These results indicated that cultivar 19 exhibits a stronger ability to adapt to Cd stress than cultivar 4.

COLONIZATION CAPABILITY OF TRICHODERMA VIRIDE (T1SK) ON SEVERAL BANANA CULTIVAR ROOTS AND ITS EFFECT AGAINST DEVELOPMENT OF FUSARIUM WILT DISEASE AND PLANT GROWTH

Fusarium wilt desease caused by Fusarium oxysporum f.sp. cubence (Foc) one the important desease on banana around the world. The purpose of this research was to recognize surface and endophytic colonization capability of Trichoderma viride (T1sk) on several banana cultivar roots and its effect against Fusarium wilt disease and increasing banana seedling growth. The experiment was divided into 2 parts that were colonization effect against Fusarium wilt disease development and colonization capability of T. viride (T1sk) on roots of several banana cultivars. The parameters observed were: 1) surface and endophytic colonization capability of T. viride (T1sk) on various banana seedling roots, 2) incubation period, 3) percentage of symptomatic leaves, 4) increase of leaves amount, 5) increase of plant height, 6) Stem circle and 7)dry weight of banana seedling biomass. The result showed that highest surface colonization capability of T. viride (T1sk) found in Barangan and Kepok cultivars and endophyte colonization found in Kepok cultivar. The surface colonization capability of T viride (T1sk) on the roots of Barangan and kepok reached 93, 33% and the ability of being endophyte 43, 33% and 38, 33% could reduce Fusarium wilt disease on banana seedling and increase seedling growth.

Biochemical and plant nutrient alterations induced by Meloidogyne javanica and Fusarium oxysporum f.Sp.radicis lycopersici co-infection on tomato cultivars with differing level of resistance to M. javanica

The experiment was conducted to assess plant nutrient levels and biochemical changes in tomato roots Solanum lycopersicum Mill. cultivars in response to Fusarium oxysporum f.sp. radicis lycopersici (FORL) and/or Meloidogyne javanica (RKN) infection. The enzyme activity, total sugar concentration, total phenol and protein content in tomato roots of resistant (Firenze), intermediate resistant (Colibri) and susceptible cultivar (Riogrande) at seven days post infection by FORL and RKN were measured. Tomato plants (45 days post-inoculation) were quantified by atomic spectrometry for Cu, Zn, Fe, Mn, Mg, K and Ca contents in roots. At seven days post infection, defense responses involving enzymes were observed in tomato roots. Peroxidase (POX), catalase (CAT), polyphenoloxidase (PPO) and superoxide dismutase (SOD) enzymes activities were enhanced after pathogen infection and this increase was greater with synergetic infection by RKN and FORL and more in the resistant cultivar when compared to the susceptible one. Total protein content, sugar concentration and total phenol content variations were correlated to pathogen co-infection and not to the resistance level of the tomato. It was concluded that synergetic infection by FORL and RKN induced plant defense response especially in resistant cultivars. Those responses diverged with single or dual infection by pathogens and with resistance level on host plant. The nematode-fungi disease complex had great impact on unbalancing nutrients contents in roots by reducing significantly (P < 0.05) the contents of Cu, Zn, Fe, Mn, Mg and K. However, The Ca content was increased in roots. All tomato cultivars responded similarly on changing nutrient content independently with resistance level.

Interrelations between commercial beetroot (Beta vulgaris) cultivars and Meloidogyne species

ABSTRACTMost beetroot (Beta vulgaris) cultivars in South Africa are exotic and were specifically bred for root-knot (Meloidogyne species) nematode populations in their countries of origin. Due to the widespread distribution of different Meloidogyne species and races, exotic cultivars should be matched with nematode populations in importing countries. The objective of this study was to determine the interrelations between exotic beetroot cultivars ‘Detroit Red Dark’ and ‘Crimson Globe’ with Meloidogyne species in the predominant beetroot-producing regions in South Africa. Different inoculum series of M. incognita and M. javanica were used on the two beetroot cultivars. At 56 days after initiating the treatments, roots of both cultivars had small undeveloped root galls, with the reproductive factor values of M. incognita on ‘Detroit Dark Red’ being above and below unity at low (≤125 inoculation) and high (≥250 inoculation) nematode levels, respectively. Growth of ‘Detroit Dark Red’ was significantly stimulated and inhibited at low and high nematode infection levels, respectively. In contrast, RF values for M. javanica on ‘Crimson Globe’ were below unity, without any significant effects on plant growth. In conclusion, ‘Detroit Dark Red’ was tolerant to M. incognita, whereas ‘Crimson Globe’ was resistant to M. javanica.

Chip Technologies for Screening Chemical and Biological Agents Against Plant-Parasitic Nematodes.

Plant-parasitic nematodes cause substantial damage to agricultural crops worldwide. Long-term management of these pests requires novel strategies to reduce infection of host plants. Disruption of nematode chemotaxis to root systems has been proposed as a potential management approach, and novel assays are needed to test the chemotactic behavior of nematodes against a wide range of synthetic chemicals and root exudates. Two microfluidic chips were developed that measure the attraction or repulsion of nematodes to chemicals ("chemical chip") and young plant roots ("root chip"). The chip designs allowed for chemical concentration gradients to be maintained up to 24 h, the nematodes to remain physically separate from the chemical reservoirs, and for images of nematode populations to be captured using either a microscope or a flatbed scanner. In the experiments using the chemical chips, seven ionic solutions were tested on second-stage juveniles (J2s) of Meloidogyne incognita and Heterodera glycines. Results were consistent with previous reports of repellency of M. incognita to a majority of the ionic solutions, including NH4NO3, KNO3, KCl, MgCl2, and CaCl2. H. glycines was found to be attracted to both NH4NO3 and KNO3, which has not been reported previously. A software program was written to aid in monitoring the location of nematodes at regular time intervals using the root chip. In experiments with the root chip, H. glycines J2s were attracted to roots of 3-day-old, susceptible (cultivar Williams 82) soybean seedlings, and attraction of H. glycines to susceptible soybean was similar across the length of the root. Attraction to resistant (cultivar Jack) soybean seedlings relative to the water only control was inconsistent across runs, and H. glycines J2s were not preferentially attracted to the roots of resistant or susceptible cultivars when both were placed on opposite sides of the same root chip. The chips developed allow for direct tests of plant-parasitic nematode chemotaxis to chemicals and roots with minimal human intervention.