White-spot lesions (WSL) associated with orthodontic appliances are a cosmetic problem and increase risk for cavities. We characterized the microbiota of WSL, accounting for confounding due to gingivitis. Participants were 60 children with fixed appliances, aged between 10 and 19 yrs, half with WSL. Plaque samples were assayed by a 16S rRNA-based microarray (HOMIM) and by PCR. Mean gingival index was positively associated with WSL (p = 0.018). Taxa associated with WSL by microarray included Granulicatella elegans (p = 0.01), Veillonellaceae sp. HOT 155 (p < 0.01), and Bifidobacterium Cluster 1 (p = 0.11), and by qPCR, Streptococcus mutans (p = 0.008) and Scardovia wiggsiae (p = 0.04) Taxa associated with gingivitis by microarray included: Gemella sanguinis (p = 0.002), Actinomyces sp. HOT 448 (p = 0.003), Prevotella cluster IV (p = 0.021), and Streptococcus sp. HOT 071/070 (p = 0.023); and levels of S. mutans (p = 0.02) and Bifidobacteriaceae (p = 0.012) by qPCR. Species’ associations with WSL were minimally changed with adjustment for gingivitis level. Partial least-squares discriminant analysis yielded good discrimination between children with and those without WSL. Granulicatella, Veillonellaceae and Bifidobacteriaceae, in addition to S. mutans and S. wiggsiae, were associated with the presence of WSL in adolescents undergoing orthodontic treatment. Many taxa showed a stronger association with gingivitis than with WSL.
orthodontic; adolescents; white-spot lesions; microbial ecology; Scardovia wiggsiae; HOMIM
Symptoms of anxiety and depression are common in older people, but the relative importance of factors operating in early and later life in influencing risk is unclear, particularly in the case of anxiety.
We used data from five cohorts in the Healthy Ageing across the Life Course (HALCyon) collaborative research programme : the Aberdeen Birth Cohort 1936, the Caerphilly Prospective Study, the Hertfordshire Ageing Study, the Hertfordshire Cohort Study and the Lothian Birth Cohort 1921. We used logistic regression to examine the relationship between factors from early and later life and risk of anxiety or depression, defined as scores of 8 or more on the subscales of the Hospital Anxiety and Depression Scale, and meta-analysis to obtain an overall estimate of the effect of each.
Greater neuroticism, poorer cognitive or physical function, greater disability and taking more medications were associated in cross-sectional analyses with an increased overall likelihood of anxiety or depression. Associations between lower social class, either in childhood or currently, history of heart disease, stroke or diabetes and increased risk of anxiety or depression were attenuated and no longer statistically significant after adjustment for potential confounding or mediating variables. There was no association between birth weight and anxiety or depression in later life.
Anxiety and depression in later life are both strongly linked to personality, cognitive and physical function, disability and state of health, measured concurrently. Possible mechanisms that might underlie these associations are discussed.
Anxiety; cohort studies; depression; elderly; life course
Few sources of resistance to root-knot nematodes (Meloidogyne incognita) in upland cotton (Gossypium hirsutum) have been utilized to develop resistant cultivars, making this resistance vulnerable to virulence in the pathogen population. The objectives of this study were to determine the inheritance of resistance in five primitive accessions of G. hirsutum (TX1174, TX1440, TX2076, TX2079, and TX2107) and to determine allelic relations with the genes for resistance in the genotypes Clevewilt-6 (CW) and Wild Mexico Jack Jones (WMJJ). A half-diallel experimental design was used to create 28 populations from crosses among these seven sources of resistance and the susceptible cultivar DeltaPine 90 (DP90). Resistance to M. incognita was measured as eggs per g roots in the parents, F1 and F2 generations of each cross. The resistance in CW and WMJJ was inherited as recessive traits, as reported previously for CW, whereas the resistance in the TX accessions was inherited as a dominant trait. Chi square analysis of segregation of resistance in the F2 was used to estimate the numbers of genes that conditioned resistance. Resistance in CW and WMJJ appeared to be a multigenic trait whereas the resistance in the TX accessions best fit either a one or two gene model. The TX accessions were screened with nine SSR markers linked to resistance loci in other cotton genotypes. The TX accessions lacked the allele amplified by SSR marker CR316 and linked to resistance in CW and other resistant genotypes derived from this source. Four of five TX genotypes lacked the amplification products from the marker BNL1231 that is also associated with the resistant allele on Chromosome 11 in WMJJ, CW, NemX, M120 RNR and Auburn 634 RNR. However, all five TX genotypes produced the same amplification products from three SSR markers linked to the resistant allele on Chromosome 14 in M120 RNR and M240 RNR. The TX accessions have unique resistance genes that are likely to be useful in efforts to develop resistant cotton cultivars with increased durability.
Allelic relationships; cotton; Gossypium hirsutum; host resistance; inheritance of resistance; Meloidogyne incognita; molecular markers; root-knot nematode
We developed and tested three dimensional (3-D) indices for quantifying severity of deformational plagiocephaly (DP).
We evaluated the extent to which infants with and without DP (as determined by clinic referral and two experts’ ratings) could be correctly classified.
Infants ages 4–11 months, including 154 with diagnosed DP and 100 infants without a history of DP or other craniofacial condition. After excluding participants with discrepant expert ratings, data from 90 infants with DP and 50 infants without DP were retained.
Two-dimensional histograms of surface normal vector angles were extracted from 3-D mesh data and used to compute the severity scores below.
Left Posterior Flattening Score (LPFS), Right Posterior Flattening Score (RPFS), Asymmetry Score (AS), Absolute Asymmetry Score (AAS) and an approximation of a previously described 2-D measure, the Oblique Cranial Length Ratio (aOCLR). Two-dimensional histograms localized the posterior flatness for each participant.
We fit receiver operating characteristic curves and calculated the area under the curves (AUC) to evaluate the relative accuracy of DP classification using the above measures.
The AUC statistics were: AAS=91%; LPFS=97%, RPFS=91%; AS=99%, and aOCLR=79%.
Novel 3-D-based plagiocephaly posterior severity scores provided better sensitivity and specificity in the discrimination of plagiocephalic and typical head shapes than the 2-D measurements provided by a close approximation of OCLR. These indices will allow for more precise quantification of the DP phenotype in future studies on the prevalence of this condition, which may lead to improved clinical care.
plagiocephaly; head shape
The susceptibility of 22 plant species to Meloidogyne marylandi and M. incognita was examined in three greenhouse experiments. Inoculum of M. marylandi was eggs from cultures maintained on Zoysia matrella “Cavalier” or Cynodon dactylon x C. trasvaalensis “Tifdwarf”. Inoculum of M. incognita was eggs from cultures maintained on Solanum lycopersicum ‘Rutgers’. In each host test the inoculum density was 2,000 nematode eggs/pot. None of the three dicot species tested (Gossypium hirsutum, Arachis hypogaea, and S. lycopersicum) were hosts for M. marylandi but, as expected, M. incognita had high levels of reproduction on G. hirsutum and S. lycopersicum. Meloidogyne marylandi reproduced on all of the 19 grass species (Poaceae) tested but reproduction varied greatly (P = 0.05) among these hosts. The following grasses were identified for the first time as hosts for M. marylandi: Buchloe dactyloides (buffalograss), Echinochloa colona (jungle rice), Eragostis curvula (weeping lovegrass), Paspalum dilatatum (dallisgrass), P. notatum (bahiagrass), Sorghastrum, nutans (indiangrass), Tripsacum dactyloides (eastern gamagrass), and Zoysia matrella (zoysiagrass). No reproduction of M. incognita was observed on B. dactyloides, Cyndon dactylon (common bermudagrass), E. curvula, P. vaginatum (seashore paspalum), S. nutans, T. dactyloides, Z. matrella or Z. japonica. Reproduction of M. incognita was less than reproduction of M. marylandi on the other grass species, except for the Zea mays inbred line B73 on which M. incognita had greater reproduction than did M. marylandi (P = 0.05) and Stenotaphrum secundatum (St. Augustinegrass) on which M. incognita and M. marylandi had similar levels of reproduction.
dicots; grasses; Meloidgyne marylandi; M. incognita; hosts; Poaceae; root-knot nematode
The importance of plant-parasitic nematodes as yield-limiting pathogens of cotton has received increased recognition and attention in the United States in the recent past. This paper summarizes the remarks made during a symposium of the same title that was held in July 2007 at the joint meeting of the Society of Nematologists and the American Phytopathological Society in San Diego, California. Although several cultural practices, including crop rotation, can be effective in suppressing the populations of the important nematode pathogens of cotton, the economic realities of cotton production limit their use. The use of nematicides is also limited by issues of efficacy and economics. There is a need for development of chemistries that will address these limitations. Also needed are systems that would enable precise nematicide application in terms of rate and placement only in areas where nematode population densities warrant application. Substantial progress is being made in the identification, characterization and mapping of loci for resistance to Meloidogyne incognita and Rotylenchulus reniformis. These data will lead to efficient marker-assisted selection systems that will likely result in development and release of nematode-resistant cotton cultivars with superior yield potential and high fiber quality.
Objectives: Increased white matter (WM) lesions on magnetic resonance imaging (MRI) are associated with worse cognitive function in older people. Enlarged perivascular spaces (EPVS) commonly coexist with and share some risk factors for WM lesions but are not quantified in published scales. It is not known whether the extent of EPVS is also associated with cognitive function. We tested the hypothesis that more EPVS would be associated with worse cognitive function.
Methods: Ninety seven healthy men (65–70 years), not on medications, underwent MRI scanning and comprehensive cognitive testing. EPVS were quantified in both the basal ganglia/centrum semiovale and the hippocampus, and WM lesions were measured.
Results: Scores on published WM lesion rating scales intercorrelated highly significantly and positively (ρ = 0.61 to 0.91, p<0.0001). A summary (WML) factor derived from principal components analysis of the WM scales correlated with EPVS in the basal ganglia/centrum semiovale (ρ = 0.48, p<0.0001) but not in the hippocampus. EPVS scores in the basal ganglia/centrum semiovale correlated significantly and negatively with non-verbal reasoning (ρ = –0.21, p = 0.038) and general visuospatial ability (ρ = –0.22, p = 0.032), adjusted for prior intelligence. The WML factor correlated significantly and negatively with visuospatial ability, as previously reported, and showed an unexpected positive correlation with one test of verbal memory (list-learning).
Conclusions: These findings suggest that increased EPVS are correlated with worse cognitive function. Future studies examining changes in WM with ageing should consider incorporating measures of EPVS and examine the sequence of EPVS and WM lesion development over time. More work is needed to develop valid and reliable measures of EPVS.
Abamectin is nematicidal to Meloidogyne incognita and Rotylenchulus reniformis, but the duration and length of cotton taproot protection from nematode infection by abamectin-treated seed is unknown. Based on the position of initial root-gall formation along the developing taproot from 21 to 35 d after planting, infection by M. incognita was reduced by abamectin seed treatment. Penetration of developing taproots by both nematode species was suppressed at taproot length of 5 cm by abamectin-treated seed, but root penetration increased rapidly with taproot development. Based on an assay of nematode mobility to measure abamectin toxicity, the mortality of M. incognita associated with a 2-d-old emerging cotton radicle was lower than mortality associated with the seed coat, indicating that more abamectin was on the seed coat than on the radicle. Thus, the limited protection of early stage root development suggested that only a small portion of abamectin applied to the seed was transferred to the developing root system.
abamectin; avermectin; cotton; Gossypium hirsutum; Meloidogyne incognita; nematicide; reniform nematode; root-knot nematode; Rotylenchulus reniformis; seed treatment
Avermectins are macrocyclic lactones produced by Streptomyces avermitilis. Abamectin is a blend of B1a and B1b avermectins that is being used as a seed treatment to control plant-parasitic nematodes on cotton and some vegetable crops. No LD50 values, data on nematode recovery following brief exposure, or effects of sublethal concentrations on infectivity of the plant-parasitic nematodes Meloidogyne incognita or Rotylenchulus reniformis are available. Using an assay of nematode mobility, LD50 values of 1.56 μg/ml and 32.9 μg/ml were calculated based on 2 hr exposure for M. incognita and R. reniformis, respectively. There was no recovery of either nematode after exposure for 1 hr. Mortality of M. incognita continued to increase following a 1 hr exposure, whereas R. reniformis mortality remained unchanged at 24 hr after the nematodes were removed from the abamectin solution. Sublethal concentrations of 1.56 to 0.39 μg/ml for M. incognita and 32.9 to 8.2 μg/ml for R. reniformis reduced infectivity of each nematode on tomato roots. The toxicity of abamectin to these nematodes was comparable to that of aldicarb.
abamectin; avermectin; LD50; Lycopersicon esculentum; Meloidogyne incognita; nematicide; Rotylenchulus reniformis; reniform nematode; root-knot nematode; seed treatment; tomato
Nine sources of resistance to Rotylenchulus reniformis in Gossypium (cotton) were tested by measuring population density (Pf) and root-length density 0 to 122 cm deep. A Pf in the plow layer less than the autumn sample treatment threshold used by consultants was considered the minimum criterion for acceptable resistance, regardless of population density at planting (Pi). Other criteria were ample roots and a Pf lower than on the susceptible control, as in pot studies. In a Texas field in 2001 and 2002, no resistant accessions had Pf less than the control but all did in microplots into which nematodes from Louisiana were introduced. An environmental chamber experiment ruled out nematode genetic variance and implicated unknown soil factors. Pf in field experiments in Louisiana, Mississippi, and Alabama were below threshold for zero, six and four of the accessions and above threshold in the control. Gossypium arboreum A2–87 and G. barbadense GB-713 were the most resistant accessions. Results indicate that cultivars developed from these sources will suppress R. reniformis populations but less than in pots in a single season.
cotton; Gossypium; nematode; reniform; resistance; Rotylenchulus reniformis
Objective: To investigate the relations between premorbid and current mental ability, mood, and white matter signal abnormalities detected by T2 weighted brain magnetic resonance imaging (MRI) and impairment of balance and mobility in older adults.
Methods: 97 subjects from the Aberdeen 1921 birth cohort underwent brain MRI, evaluation of balance, and measurement of gait speed. White matter hyperintensities detected on T2 weighted MRI scans were rated by three independent raters on three variables: white matter lesions; periventricular lesions; and brain stem lesions.
Results: Decreased gait speed was correlated with impaired visual acuity (p = 0.020), shorter stature (p = 0.008), a lower childhood IQ (p = 0.030), a lower current Raven's progressive matrices score (Raven score) (p < 0.001), a higher hospital anxiety and depression scale (HADS) score (p = 0.004), and an increased grade of brain stem lesions on MRI. Inability to balance was correlated with Raven score (p = 0.042), brain stem lesions (p = 0.003), white matter lesions (p = 0.003), and periventricular lesions (p = 0.038). Binary logistic regression identified brain stem lesions (odds ratio (OR) 0.22; 95% confidence interval 0.09 to 0.54) and HADS depression score (OR 0.75; 0.58 to 0.97) as the only significant associations with balance. Structural equation modelling detected an association between two latent traits representing white matter disease and an integrating function, respectively.
Conclusions: In this cohort, white matter lesions, periventricular lesions, and brain stem lesions were associated with impaired balance. Current mental ability was strongly related to gait speed. There appears to be a concordance between motor skills and intellect in old age, which is degraded by white matter disease.
Objectives: Patients with type II diabetes are at increased risk of cognitive impairment. The retinal and renal complications of diabetes follow microvascular damage permitting small arterioles to leak, hence the cerebral damage might also follow loss of blood–brain barrier (BBB) integrity. Magnetic resonance (MR) brain imaging with intravenous gadolinium (Gd) diethylenetriamine pentaacetic acid (Gd-DTPA) was used to identify increased BBB permeability.
Methods: Ten well controlled type II diabetic patients aged 65–70 years and 10 controls underwent MR brain imaging with fluid attenuated inversion recovery (FLAIR); T1 weighted (T1W) volumetric imaging before; and T1W volumetric imaging at 5, 15, 30, 45, 60, and 90 minutes after intravenous Gd-DTPA. The T1W image before Gd-DTPA was subtracted from the images at each time point after Gd-DTPA. Net signal intensity was plotted against time for different brain regions. White matter hyperintensities were scored from the FLAIR image.
Results: The signal intensity/time curves showed that brain signal intensity increased more in the diabetic group than controls during the first 15 minutes after Gd-DTPA, particularly in the basal ganglia (p=0.018). Signal intensity in controls peaked at five minutes and diabetics at 15 minutes. Subjects with more white matter hyperintensities had greater signal increase after Gd-DTPA, whether diabetic or not (p=0.001).
Conclusions: Increased BBB permeability with MR imaging was detected in patients with type II diabetes or white matter hyperintensities. Increased permeability of the BBB might account for some of the cerebral effects of type II diabetes, and so possibly also for the effect of other conditions that affect the microvasculature (like hypertension), on the brain.
The techniques of laser capture microdissection and quantitative RT-PCR were investigated as methods for measuring mRNA in giant cells induced by Meloidogyne javanica. Laser capture microdissection allowed precise sampling of giant cells at 1 to 3 weeks after inoculation. The expression of three genes (a water channel protein gene Rb7, a plasma membrane H+-ATPase (LHA4), and a hexose kinase (HXK1) was measured based on mRNA extracted from tissue samples and quantitated using reversetranscription real-time PCR. These genes were chosen arbitrarily to represent different aspects of primary metabolism. The amount of HXK1 mRNA in giant cells was not different from that in root meristem or cortical cells when compared on the basis of number of molecules per unit tissue volume, and was similar at all sample times. Amount of mRNA for LHA4 and Rb7 was much greater in giant cells than in cortical cells, but only Rb7 was also greater in giant cells than in root meristem cells. Numbers of mRNA molecules of LHA4 increased linearly in giant cells from 1 to 3 weeks after inoculation, whereas the amount of Rb7 mRNA was similar at 1 and 2 weeks after inoculation but increased at 3 weeks after inoculation. The amount of mRNA for these two genes was similar at all sample times in cortical and root-tip cells. Apparent up regulation of some genes in giant cells may be due primarily to the increased number of copies of the gene in giant cells, whereas for other genes up regulation may also involve increased transcription of the increased number of copies of the gene.
gene expression; giant cells; HXK1; LAH4; laser capture microdissection; Meloidogyne javanica; mRNA; RB7; root-knot nematodes; real-time PCR; reverse transcription
A single dominant gene for resistance to Meloidogyne arenaria was identified previously in two peanut cultivars, Arachis hypogaea 'COAN' and 'NemaTAM'. The interspecific Arachis hybrid TxAG-6 was the source of this resistance and the donor parent in a backcross breeding program to introgress resistance into cultivated peanut. To determine if other resistance genes were present in TxAG-6 and derived breeding populations from the third backcross generation (BC₃), F₂ individuals were evaluated for the resistance phenotype. The ratio of the resistant and susceptible individuals for all F₂ populations fit the expected ratio for resistance being governed by one dominant gene and one recessive gene. Evaluation of the F₃ generation from four susceptible F₂ individuals (two from TxAG-6 × A. hypogaea and two from the BC₃ population) confirmed that a recessive gene for resistance to M. arenaria was present in each of the tested populations. The identification of a second gene for resistance in the A. hypogaea germplasm may improve the durability of the resistance phenotype.
Arachis hypogaea; durable resistance; Meloidogyne arenaria; peanut; recessive inheritance; resistance genes; root-knot nematode
AIMS—To examine the relation
between birth weight and cognitive function at age 11 years, and to
examine whether this relation is independent of social class.
study based on birth records from 1921 and cognitive function measured
while at school at age 11 in 1932.Subjects were 985 live singletons
born in the Edinburgh Royal Maternity and Simpson Memorial Hospital
in 1921. Moray House Test scores from the Scottish Mental Survey 1932 were traced on 449of these children.
RESULTS—Mean score on Moray House
Test increased from 30.6 at a birth weight of <2500 g to 44.7 at
4001-4500 g, after correcting for gestational age, maternal age,
parity, social class, and legitimacy of birth. Multiple regression
showed that 15.6% of the variance in Moray House Test score is
contributed by a combination of social class (6.6%), birth weight
(3.8%), child's exact age (2.4%), maternal parity (2.0%), and
illegitimacy (1.5%). Structural equation modelling confirmed the
independent contribution from each of these variables in predicting
cognitive ability. A model in which birth weight acted as a mediator of
social class had poor fit statistics.
CONCLUSION—In this 1921 birth
cohort, social class and birth weight have independent effects on
cognitive function at age 11. Future research will relate these
childhood data to health and cognition in old age.
Meloidogyne haplanaria n. sp. is described and illustrated from specimens parasitizing peanut in Texas. The perineal pattern of the female is rounded to oval with a dorsal arch that is high and rounded except for striae near the vulva, which are low with rounded shoulders. The striae are distinctly forked in the lateral field, and punctations often occur as a small group near the tail tip and singly within the whole perineal pattern. The female stylet is 13-16 µm long and has broad, distinctly set-off knobs. The excretory pore opens 40-118 µm from the head, approximately halfway between the anterior end and the metacorpus. Males are 1.2-2.4 µm in length and have a high, wide head cap that slopes posteriorly. The labial disc and medial lips are partially fused to form an elongated lip structure. In some specimens the labial disk is distinctly separated from the lips by a groove. The stylet is 17-22 µm long and has wide knobs that are rounded and distinctly set off from the shaft. Mean second-stage juvenile length is 419 µm. The head region is not annulated, and the large labial disc and crescent-shaped medial lips are fused to form a dumbbell-shaped head cap. The stylet is 9-12 µm long and has rounded, posteriorly sloping knobs. The slender tail, 58-74 µm long, has a distinct, inflated rectum and a slightly rounded tip. The hyaline tail terminus is 11-16 µm long. The isozyme phenotypes for esterase and malic dehydrogenase do not correspond to any other recognized Meloidogyne species. Tomato and peanut are good hosts; corn and wheat are very poor hosts; and cotton, tobacco, pepper, and watermelon are nonhosts.
esterase phenotype; malate dehydrogenase phenotype; scanning electron microscopy; taxonomy
Resistance to Meloidogyne arenaria in the peanut cultivar COAN is inherited as a single, dominant gene. The mechanism of resistance to M. arenaria in COAN was evaluated in three experiments. In the first experiment the number of second-stage juveniles (J2) of M. arenaria penetrating roots of the susceptible cultivar Florunner was higher than the number of J2 penetrating roots of the resistant peanut cultivar COAN (P < 0.05). In a second experiment it was determined that the root size and number of potential infection courts (root tips) were similar for the two peanut cultivars. The number of nematodes emigrating from roots of COAN after penetration was greater than emigrated from roots of Florunner (P < 0.05). Necrotic host tissue was rarely observed in roots of COAN infected with M. arenaria, suggesting that resistance to M. arenaria does not involve a necrotic, hypersensitive response. Most of the J2 observed in roots of COAN were restricted to the cortical tissue, with only 1 of 90 J2 observed being associated with the vascular cylinder, whereas in Florunner >70% of the J2 were associated with vascular tissues. Resistance in COAN may be due to constitutive factors in the roots.
Arachis hypogaea; emigration; host resistance; hypersensitive reaction; Meloidogyne arenaria; peanut; penetration; root-knot nematode
Several cotton genotypes with resistance to Meloidogyne incognita have been released in recent years. To estimate the durability of this resistance, galling severity on these resistant genotypes by M. incognita was measured. Nematode isolates (115 total) were collected from cotton fields in 14 Texas counties in August and September 1996 and 1997. Four additional isolates from Maryland, Mississippi, and North Carolina were also tested. The isolates were evaluated in 12 greenhouse experiments for their ability to gall roots of the resistant cotton genotypes M315, Acala NemX, and Stoneville LA887 and the susceptible cultivar Deltapine 90. Numbers of galls on each genotype by each isolate were counted 60 days after inoculation with 10,000 eggs/plant. M315 consistently had the fewest galls for each nematode isolate, whereas Deltapine 90 had the greatest number of galls. Numbers of galls on NemX and LA887 were usually intermediate and more variable. For each separate experiment, analysis of variance indicated that the effects of nematode isolates, cotton genotypes, and isolate-genotype interaction were significant (P < 0.05). In two of the experiments, nematode reproduction was also measured and galling was positively correlated (r = 0.68 and 0.86) with egg production by M. incognita. Nematode isolates from one field exhibited higher root galling and reproduction (P < 0.05) on resistant genotypes than other isolates, suggesting a need for gene deployment systems that will enhance the durability of resistance.
cotton; durable resistance; Gossypium hirsutum; host resistance; Meloidogyne incognita; nematode; root knot
Segregation of resistance to Meloidogyne arenaria in six BC₅F₂ peanut breeding populations was examined in greenhouse tests. Chi-square analysis indicated that segregation of resistance was consistent with resistance being conditioned by a single gene in three breeding populations (TP259-3, TP262-3, and TP271-2), whereas two resistance genes may be present in the breeding populations TP259-2, TP263-2, and TP268-3. Nematode development in clonally propagated lines of resistant individuals of TP262-3 and TP263-2 was compared to that of the susceptible cultivar Florunner. Juvenile nematodes readily penetrated roots of all peanut genotypes, but rate of development was slower (P = 0.05) in the resistant genotypes than in Florunner. Host cell necrosis indicative of a hypersensitive response was not consistently observed in resistant genotypes of either population. Three RFLP loci linked to resistance at distances of 4.2 to 11.0 centiMorgans were identified. Resistant and susceptible alleles for RFLP loci R2430E and R2545E were quite distinct and are useful for identifying individuals homozygous for resistance in segregating populations.
Arachis hypogaea; genetics; host resistance; Meloidogyne arenaria; molecular markers; nematode; peanut; RFLP; root-knot nematode
Resistance to a peanut-parasitic population of Meloidogyne javanica and an undescribed Meloidogyne sp. in peanut breeding lines selected for resistance to Meloidogyne javanica was examined in greenhouse tests. The interspecific hybrid TxAG-7 was resistant to reproduction of Meloidogyne javanica, M. javanica, and Meloidogyne sp. An Meloidogyne javanica-resistant selection from the second backcross (BC) of TxAG-7 to the susceptible cultivar Florunner also was resistant to M. javanica but appeared to be segregating for resistance to the Meloidogyne sp. When reproduction of M. javanica and Meloidogyne javanica were compared on five BC4F3 peanut breeding lines, each derived from Meloidogyne javanica-susceptible BC4F2 individuals, all five lines segregated for resistance to M. javanica, whereas four of the lines appeared to be susceptible to Meloidogyne javanica. These data indicate that several peanut lines selected for resistance to Meloidogyne javanica also contain genes for resistance to populations of M. javanica and the undescribed Meloidogyne sp. that are parasitic on peanut. Further, differences in segregation patterns suggest that resistance to each Meloidogyne sp. is conditioned by different genes.
Arachis hypogaea; genetics; Meloidogyne arenaria; Meloidogyne javanica; Meloidogyne sp.; nematode; peanut; resistance; root-knot nematode
The yield response of Florunner peanut to different initial population (Pi) densities of Meloidogyne arenaria, M. javanica, and an undescribed Meloidogyne species (isolate 93-13a) was determined in microplots in 1995 and 1996. Seven Pi's (0, 0.5, 1, 5, 10, 50, and 100 eggs and J2/500 cm³ soil) were used for each Meloidogyne species in both years. The three species reproduced abundantly on Florunner in both years. In 1995, mean reproduction differed among the three species; mean Rf values were 10,253 for isolate 93-13, 4,256 for M. arenaria, and 513 for M. javanica. In 1996, the reproduction of M. arenaria (mean Rf = 7,820) and isolate 93-13a (mean Rf = 7,506) were similar, and both had greater reproduction on peanut than did M. javanica (mean Rf = 2,325). All three nematode species caused root and pod galling, and a positive relationship was observed between Pi and the percentage of pods galled. Meloidogyne arenaria caused a higher percentage of pod galling than did M. javanica or isolate 93-13a. A negative linear relationship between log₁₀ (Pi + 1) and pod yield was observed for all three nematode species each year. The yield response slopes were similar except for that of M. javanica, which was less negative than that of isolate 93-13a in 1995, and less negative than that of M. arenaria and isolate 93-13a in 1996.
Arachis hypogaea; damage function; Meloidogyne arenaria; Meloidogyne javanica; Meloidogyne spp.; nematode; peanut; root-knot nematode