Gametogenesis and the Chromosomes of Meloidogyne nataliei: Not Typical of Other Root-knot Nematodes

Studies of oogenesis and spermatogenesis revealed that Meloidogyne nataliei is a diploid, amphimictic species with four (n), relatively large chromosomes, and possibly with an XX ♀-XY ♂ mechanism of sex determination. It differs considerably from all other amphimictic, or meiotically parthenogenetic, species of Meloidogyne which have 13-18 smaller chromosomes and from Meloidogyne (Hypsoperine) spartinae which has seven. Consequently, the taxonomic position of M. nataliei needs to be re-evaluated. The chromosomes of M. nataliei and their behavior during gametogenesis resemble more closely chromosomes of the genus Heterodera than those of the genus Meloidogyne. This resemblance, however, may not imply a closer phyletic relationship of M. nataliei to heteroderid nematodes.     

Inhibition of Acetylcholinesterases from Aphelenchus avenae by Carbofuran and Fenamiphos

Exposure to carbofuran and fenamiphos for 72 hours reduced the numbers of active Aphelenchus avenae in aqueous suspension by > 75%. When nematicides were removed, many A. avenae exposed to carbofuran resumed normal movement but A. avenae treated with fenamiphos did not recover. Acetylcholinesterase (AChE) activity was suppressed by > 95% in nematodes treated with carbofuran or fenamiphos. However, 48 hours after treated nematodes had been placed in water, AChE activity in carbofuran treated populations was 98% of the levels in control nematodes. Nematodes that had been treated with fenamiphos showed only slight AChE recovery. The antidotes, atropine sulfate and 2-PAM, were largely ineffective in counteracting the toxic effects of the nematicides.     

Influence of Aphelenchus avenae on Vesicular-arbuscular Endomycorrhizal Growth Response in Cotton

The influence of Aphelenchus avenae on the relationship between cotton (Gossypium hirsutum ''Stoneville 213'') and Gigaspora margarita or Glomus etunicatus was assessed by its effect on the mycorrhizal stimulation of plant growth and microorganism reproduction. The mycophagous nematode usually did not suppress stimulation of shoot growth resulting from mycorrhizae (G. margarita) at inoculum levels of 3,000 or 6,000 nematodes per pot, but retarded root growth at 6,000 per pot. When the nematode inoculum was increased to 10, 40, or 80 thousand, G. margarita stimulation of shoot or root growth was retarded at the two higher rates. Shoot growth enhancement by G. etunicatus was suppressed by 10 thousand A. avenae but not by 40 or 80 thousand. A. avenae reproduced better when the nematode was added 3 wk after G. margarita than with simultaneous inoculations. Sporulation of both fungi was affected little by the mycophagous nematode. The high numbers of A. avenae required for an antagonistic effect probably precludes the occurrence of any significant interaction between these two organisms under field conditions.     

Sensitivity of Acetylcholinesterases from Aphelenchus avenae to Organophosphorous and Carbamate Pesticides

The sensitivities of acetylcholinesterases (ACHE) from the nematode Aphelenchus avenae and the house fly Musca domestica to various pesticides were compared using a colorimetric assay. ACHE from A. avenae were generally less sensitive than ACHE from M. domestica to inhibition by organophosphorous and carbamate pesticides. Carbamates were somewhat more inhibiting than organophosphorous pesticides to nematode ACHE. In vivo tests with concentrations of various pesticides up to 500 ppm in sand caused less than 100% mortality of nematodes.     

Morphometric and Serologic Comparisons of a Number of Populations of Cyst Nematodes

Thirty-five populations of Heterodera glycines and populations of 15 other Heterodera, Globodera, and Punctodera species were studied morphometrically and some were compared serologically. There was a wide range of each measurement within each nematode population. Except for one soybean cyst nematode population from Indiana, which was a tetraploid and considerably larger than the others, morphometric measurements overlapped. In a discriminant function comparison most of the populations were closely grouped but at least three were rather distinctly separated. Morphometrically H. fici, H. cruciferae, H. schachtii, and H. trifolii were closely associated with H. glycines. Serology indicated a close relationship between H. glycines, H. lespedezae, H. trifolii, H. schachtii, and the Heterodera sp. from Rumex, while H. betulae appeared to be more distantly related.     

Host Suitability and Susceptibility of Glycine max cv. Bedford to Race 1 of Heterodera glycines

Populations of Heterodera glycines identifiable as race 1 reproduced on the race 1 resistant ''Bedford'' soybean. A Beaufort County, North Carolina, population had an index of parasitism of 112% on Bedford in greenhouse tests. Indices of parasitism for this population on race 1 resistant cultivars Pickett 71, Centennial, and Forrest were less than 10%. The Beaufort County population had significantly greater reproduction on Bedford in microplots than did populations of race 3 or race 4. In field tests, a race 1 population suppressed yields of Bedford but not yields of Centennial. Based on these data, Bedford is no longer recommended in North Carolina as a race 1 resistant cultivar.     

Development of Four Populations of Meloidogyne hapla on Two Cultivars,of Cucumber at Different Temperatures

The infectivity and development of four populations of Meloidogyne hapla were compared, at three temperatures, on tomato and two varieties of cucumber. A population from Canada produced few root-galls on cucumber and, except at 24 C, no larvae developed into adult females and produced egg masses. In contrast, a population with 45 chromosomes from America produced many galls on cucumber and small proportions of larvae became females and produced egg masses at 20 and 24 C. At 18 C this population produced no egg masses on cucumber, but a population from Britain and one from America with 17 chromosomes produced more egg masses at this temperature than at 20 or 24 C. Dissection of the galls showed that on cucumber many larvae died or their growth and development was slowed.     

Relationship Between Morphology and Parasitism in Two Populations of Meloidogyne incognita

The reliability of morphological characters and host differential plants for distinguishing between two populations of Meloidogyne incognita was studied. Population A (originally from North Carolina) had incognita-type perineal patterns. A single egg mass subpopulation of population A had a mixture of incognita and acrita perineal patterns with 33% of the patterns atypical for either species. Population B (from Georgia) had predominantly acrita-type patterns with only about 5% atypical patterns. The head shapes of males from both populations were mainly M. incognita. On the basis of stylet length, both populations conformed to M. incognita acrita. Both populations were identified as M. incognita race 1 by reaction on the North Carolina differential hosts. Reactions on azalea and pepper gave no clear identification of the populations. We concluded that there is no relation between perineal pattern, male head shape, and parasitism of host differentials with the two populations studied.     

Esterase and Malate Dehydrogenase Phenotypes in Portuguese Populations of Meloidogyne Species

Nonspecific esterases and malate dehydrogenases of 1-5 females from 40 root-knot nematode populations from Portugal were analyzed by electrophoresis in 0.4-mm-thick polyacrylamide gels. Fourteen major bands of esterase activity were detected, corresponding to 10 distinct phenotypes, Meloidogyne javanica and M. hapla had distinct species-specific phenotypes. Two phenotypes occurred in M. arenaria. The most variability was found among M. incognita populations. Of the remaining two phenotypes, one was associated with M. hispanica and the other belonged to a new species. Three malate dehydrogenase phenotypes were discerned on the basis of particular combinations of the eight main bands of activity found. As previously found, esterases were more useful than malate dehydrogenases in identification of the major Meloidogyne species. The host plant had no effect on the nematode esterase or malate dehydrogenase phenotypes.     

Nematode Temperature Responses: a Niche Dimension In Populations of Bacterial-Feeding Nematodes

The optimum temperatures for population development were determined for six species of bacterial-feeding nematodes from among eight temperatures, ranging from 5 to 40 C. Four of the species are cohabiting species. The range of temperatures over which population development occurs (temperature niche breadth) is different for the cohabiting species. This difference may be a means of reducing competition between species, thus increasing temperatures over which habitats can be exploited.     

Resistant Host Responses to Ten California Populations of Meloidogyne incognita

Resistant and susceptible cultivars of tomato, lima beans, cotton, and alfalfa were tested with 10 populations of Meloidogyne incognita from different California locations. Nine of the populations differed in aggressiveness on the nine cultivars tested. Two populations were especially aggressive toward resistant tomato cultivars.     

Cuticle Formation in Hemicycliophora arenaria,Aphelenchus avenae and HirschmannIella gracilis

The onset of molting in all stages of Hemicycliophora arenaria was preceded by the appearance of numerous, discrete globular structures which were termed "molting bodies" because they were present in the hypodermis only during the production of the new cuticle. In all parasitic stages the molt commenced with the separation of the cuticle from the hypodermis from which the new sheath and cuticle were differentiated. Following completion of the new sheath and cuticle most of the old outer covering was apparently absorbed before ecdysis. Electronmicrographs of body wall cross sections in molting L4 male specimens revealed the final molt to be a double molt in which an additional sixth cuticle was produced. Since both a new sheath and cuticle were produced during the molt of each stage, the sheath must be considered as an integral part of the cuticle and not as a residual cuticle or the result of an incomplete additional molt. Molting in Aphelenchus avenae and Hirschmanniella gracilis was less complex and "molting bodies" were not observed. After cuticle separation the hypodermis gave rise to a new trilaminate zone, the future cortex, and (later) the matrix and striated basal layers.     

Resistance of Anhydrobiotic Aphelenchus avenae to Methyl Bromide Fumigation

The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes.     

Regulation of the sperm‐to‐oocyte transition in Caenorhabditis briggsae hermaphrodites by the Cbr‐met‐2 and Cbr‐fem‐3 genes

In Caenorhabditis briggsae hermaphrodites, spermatogenesis begins in the L4 larval stage and persists into early adulthood. Oogenesis begins after spermatogenesis; the sperm‐to‐oocyte transition is irreversible. The timing of this transition is believed to have evolved in response to selection to maximize the intrinsic growth rate. Sperm‐to‐oocyte transitions occurred early in Cbr‐met‐2 and Cbr‐fem‐3 mutants. These early transitions resulted in reduced brood sizes, but had little or no impact on the intrinsic growth rate. In Cbr‐met‐2; Cbr‐fem‐3 doubly mutant hermaphrodites, the transition to oogenesis occurred even earlier and brood size was further reduced, indicating that Cbr‐met‐2 and Cbr‐fem‐3 regulate the sperm‐to‐oocyte transition through separate pathways. Mutations in Cbr‐met‐2 also resulted in an increase in the frequency of males in mutant populations. These increased male frequencies were not caused by increased rates of X nondisjunction during oogenesis in mutant hermaphrodites. Rather, increases in the rates of outcrossing in mutant populations likely were an indirect effect of reduced brood sizes derived from self‐fertilization. Based on these observations, it is possible that the timing of the sperm‐to‐oocyte transition in C. briggsae evolved in response to sexual selection on hermaphrodites to limit rates of outcrossing. Mutations in the orthologous Caenorhabditis elegans gene, Cel‐met‐2, did not impact the timing of the sperm‐to‐oocyte transition, consistent with the independent evolution of hermaphroditic reproduction in these species. Although brood sizes were reduced in Cel‐met‐2 mutant strains, increased male frequencies were not observed. Cbr‐ and Cel‐met‐2 mutations also differed in terms of germline mortality, observed in C. elegans, but not in C. briggsae.     

Ethanol Production and Utilization by Aphelenchus avenae and Caenorhabditis sp.

In microaerobic and anaerobic environments the principal glycolytic end-product of A. avenae and Caenorhabditis sp. was lactic acid during the first 12-16 hr, after which it was ethanol. Upon return to aerobiosis, ¹⁴C-labeled ethanol in the medium was utilized by the nematodes; ¹⁴CO₂ and some ¹⁴C-labeled glycogen was detected. Total dry weight loss of non-feeding nematodes was 25% greater in the absence of alcohol than in the presence of ethanol or n-propanol. Physical movement and respiration increased and reproduction was extended by alcohol in the bathing solution.     

Gametogenesis and reproductive periodicity of the “biologically vulnerable” giant Caribbean sea anemone,Condylactis gigantea,in Florida

The giant Caribbean sea anemone, Condylactis gigantea, is an ecologically important member of the benthic community. It provides habitat for many species, including symbiotic cleaner shrimps, and is recognized by reef fishes as a cleaning station cue. Numbers of C. gigantea in Florida have recently declined, possibly due to deteriorating environmental conditions and increasing harvest pressure. A previous research finding indicating that C. gigantea spawns in the late spring has been questioned by fishers for the aquarium trade industry. We therefore examined specimens of C. gigantea collected monthly from October 2011 to September 2012 in the Florida Keys to characterize the reproductive cycle, also measuring several physical and chemical parameters of concurrently collected water samples. We ascertained that the anemone is gonochoric and has a 1:1 sex ratio. Within and between individuals, at the same time and place, spermatogenesis was synchronous, whereas oocyte development was asynchronous. Low‐level spawning occurred between October and April with a peak in May, in good agreement with earlier research. Water quality at both sites showed no discernible change over the study period. Conservation efforts directed at population management could benefit this anemone.     

Morphological Comparison of Second-Stage Juveniles of Six Populations of Meloidogyne hapla by SEM

External morphology of second-stage juveniles of six populations of Meloidogyne hapla, hclonging to two cytological races (A and B), and one population each of M. arenaria, M. incognita, and M. javanica was compared by scanning electron microscopy (SEM). Race A of M. hapla included three facultatively parthenogenetic populations with haploid chromosome numbers of 15. 16, and 17; race B consisted of three mitotically parthenogenetic populations with somalic chromosome numhers of 45, 45, and 48. The mitotically parthenogenetic populations of M. arenaria, M. incognita, and M. javanica had 54, 41-43, and 44 chromosomes, respectively. Observations were made on head structures, lateral field, excretory pore, anal opening, and tail. Head morphology, including shape and proportion of labial disc and lips, expression of labial and cephalic sensilla, and markings on head region, was distinctly different for each species. M. hapla populations of race A were distinct from each other but showed much intrapopulatiou variation in head morphology. Populations of race B were different from those of race A and were very stable and quite similar in head morphology. Considerable inter- and intrapopulatiou variation made the structure of the lateral field, excretory pore, anal opening, and tail of little value in distinguishing species or populations. The results are discussed in relation to earlier SEM observations on the genus Helerodera.     

Infection of Seedlings of Alfalfa and Red Clover by Concomitant Populations of Meloidogyne incognita and Pratylenchus penetrans

Invasion of 2-day-old seedlings of ''Buffalo'' alfalfa and ''Kenland'' red clover by larvae of M. incognita and adults of P. penetrans, during 1-3 day periods of incubation at 24 C, was investigated in 50-mm petri dishes on 1% agar. Penetration by both nematodes increased arithmetically with increased numbers in inocula. P. penetrans invaded alfalfa more readily than red cover, but M. incognita invaded red clover more readily than alfalfa. Both nematodes inhibited root-elongation of alfalfa more than that of red clover. In combinations of 10 and 50 of both nematodes, invasion of both plants by both nematodes was the same as for each nematode alone. Penetration by M. incognita into alfalfa, but not into red clover, was significantly reduced when combinations of 50 M. incognita and 200 P. penetrans were inoculated simultaneously. In the presence of large numbers of entrant P. penetrans in both plants, penetration by M. incognita was highly significantly reduced. Penetration by P. penetrans was unaffected in the reciprocal situations.     

植物雌配子体发育研究进展

高等植物雌配子体的形成涉及孢原细胞和大孢子母细胞的确立与分化、大孢子发生、功能大孢子以及胚囊的形成和发育等多种复杂调控过程。随着当代生物技术及功能基因组学的发展,近年对雌配子体发育的研究已从细胞学描述逐渐过渡到对基因和发育调控分子机理的探索。以拟南芥、水稻和玉米等模式植物为材料进行的相关研究,丰富了人们对于植物雌配子体和其它有性生殖过程遗传调控机理的认识。本文着重阐述了植物雌配子体发生和发育过程,并综述了这一领域最新研究进展。