部分葡萄品种和砧木抗葡萄根瘤蚜性能鉴定

为了检测我国葡萄品种和砧木对中国生态型葡萄根瘤蚜Daktulosphaira viticola (Fitch) 的抗性,在实验室条件下采用离体根接种法鉴定了10个葡萄砧木、18个葡萄栽培品种,测定了根瘤蚜存活率、发育历期、产卵量、种群龄期结构指数和成虫大小等指标。结果表明： 砧木品种SO4,5BB,1103P,420A,Lot,101-14MG,3309C,140Ru和110R抗根瘤蚜,接种后蚜虫陆续死亡,尤其是SO4,5BB,1103P和420A对根瘤蚜高抗,使根瘤蚜滞育仅发育至1龄。我国当作砧木使用的贝达不抗根瘤蚜,接种后蚜虫存活率始终保持在38.82％～47.5%,日产卵量达9.01;欧美杂交种中的康克、康拜尔和卡它巴对根瘤蚜稍有抗性,根瘤蚜日产卵量在6.00～6.85粒之间,其中康克、康拜尔葡萄上蚜虫的存活率随时间的延长而明显降低,由最初的60％下降至25％～30％; 欧美杂交种中的黑虎香和白香蕉虽然在一定程度上能够限制根瘤蚜的存活和发育进程,但对根瘤蚜的繁殖量没有影响。所有供试欧亚种和欧美杂交种的栽培品种都对根瘤蚜高度敏感,接种后第29 d 蚜虫存活率仍保持在40％～60％,且前后变化较小,日产卵量变化于7～12.35粒之间,总产卵量均在190粒以上。由此可见,我国供试栽培品种均不抗根瘤蚜,在根瘤蚜疫区需要用抗性砧木嫁接苗建园。     

Resistance of pepper germplasm to Meloidogyne incognita

In this work, we have evaluated the host suitability of 29 pepper genotypes of Capsicum annuum and 9 of the related cultivated species C. chinense (4), C. frutescens (4) and C. pubescens (1) to Meloidogyne incognita in field conditions. The presence/absence of resistance genes in the pepper germplasm were also assessed using PCR‐specific markers linked to the N, Me1‐Mech2, Me3‐Me4 and Me7‐Mech1 genes. Intraspecific variability for M. incognita resistance was found. According to gall index (GI) and reproduction index (RI) the most resistant genotypes, which may contribute to nematode management, include three of C. frutescens (Fru‐2, Fru‐3 and Fru‐4) and seven of C. annuum (Ca‐3, Ca‐4, Ca‐5, Ca‐11, Ca‐15, Ca‐24 and Ca‐25). No egg masses or eggs were found in Fru‐3 and Fru‐4 genotypes as occurred in the resistant controls ‘SCM’, ‘CH’ and ‘Charlot’. The amplification of markers linked to resistance genes in genotypes with a suitable degree of resistance, together with the differences found between genotypes with regard to the gene and/or number of amplified markers, make this germplasm a valuable tool for further characterisation and pepper breeding.     

Host-induced silencing of Mi-msp-1 confers resistance to root-knot nematode Meloidogyne incognita in eggplant

RNA interference (RNAi)-based host-induced gene silencing (HIGS) is emerging as a novel, efficient and target-specific tool to combat phytonematode infection in crop plants. Mi-msp-1, an effector gene expressed in the subventral pharyngeal gland cells of Meloidogyne incognita plays an important role in the parasitic process. Mi-msp-1 effector is conserved in few of the species of root-knot nematodes (RKNs) and does not share considerable homology with the other phytonematodes, thereby making it a suitable target for HIGS with minimal off-target effects. Six putative eggplant transformants harbouring a single copy RNAi transgene of Mi-msp-1 was generated. Stable expression of the transgene was detected in T₁, T₂ and T₃ transgenic lines for which a detrimental effect on RKN penetration, development and reproduction was documented upon challenge infection with nematode juveniles. The post-parasitic nematode stages extracted from the transgenic plants showed long-term RNAi effect in terms of targeted downregulation of Mi-msp-1. These findings suggest that HIGS of Mi-msp-1 enhances nematode resistance in eggplant and protect the plant against RKN parasitism at very early stage.

     

The multi-year effects of repeatedly growing cotton with moderate resistance to Meloidogyne incognita

Meloidogyne incognita causes more damage to cotton in the US than any other pathogen. The objective of this study was to document the cumulative effect of moderate resistance on M. incognita population density, root galling, and yield suppression in the southern United States on a moderately resistant cotton genotype grown continuously for three years. Cotton genotypes were Phytogen PH98-3196 (77% suppression of M. incognita), Acala NemX (85% suppression of M. incognita), and Delta and Pine Land DP458 B/R (susceptible standard, 0% suppression). Cotton was grown in fumigated and non-fumigated plots to measure yield loss. Each genotype and nematicide combination was planted in the same place for three years at two sites to document cumulative effects. In 2006, following three years of the different genotypes, all plots at one site were planted with susceptible cotton to document residual effects of planting resistant genotypes. Root galling and nematode population densities in the soil were significantly lower, and percentage yield suppression was numerically lower, when moderately resistant cotton was grown compared to the susceptible standard in both fields in all three years. Differences between susceptible and moderately resistant genotypes are established quickly (after only one season) and then either maintained at similar levels or slightly increased in subsequent years depending on initial nematode levels. However, when susceptible cotton was grown following three years of the moderately resistant genotypes, the nematode suppression provided by moderate resistance was undetectable by the end of the first season. Moderately resistant cotton genotypes are more beneficial than previously reported and should be pursued for nematode management. Rotation of moderately resistant and susceptible cotton could be used along with nematicides to manage root-knot nematodes in a continuous cotton cropping system and reduce selection pressure on the nematodes.     

Overexpression of sense and antisense ced-9 in tobacco plants confers resistance to Meloidogyne incognita

Transgenic tobacco plants expressing the Caenorhabditis elegans programmed cell death gene ced-9, in both sense and antisense orientations, were produced using Agrobacterium tumefaciens-mediated transformation. The generated transgenic tobacco plants were tested for resistance to the root-knot nematode Meloidogyne incognita by measuring gall formation, size of galls generated, and the ability of juvenile-2 (J2) to hatch. Results showed that expression of ced-9 gene in either sense (ced-9F) or antisense (ced-9R) orientation in hemizygous transgenic tobacco plants induced prevention of M. incognita proliferation (as measured by gall number reduction) and J2 hatching. Furthermore, the results also showed that ced-9R in homozygous transgenic tobacco plants prevented J2 hatching, whereas ced-9F homozygous transgenic tobacco plants lost nematicidal function. Although our study demonstrates that expression of either ced-9R or ced-9F genes in tobacco plants significantly reduces infection by M. incognita, further investigation is required to understand the specific mechanisms involved for this control. It is possible that the nematode resistance seen with both sense (ced-9F) and antisense (ced-9R) sequences is the result of two independent mechanisms, one acting on invading nematodes and the other acting during embryogenesis of M. incognita, ultimately resulting in plant protection.     

Symptomless Resistance of Alfalfa to Meloidogyne incognita acrita

Penetration, development and migration of the cotton root-knot nematode, Meloidogyne incognita acrita, in resistant and susceptible alfalfa varieties was compared. Larvae entered both resistant and susceptible plants in approximately the same numbers. After 3 to 4 days, the number of larvae in resistant roots decreased sharply until at 7 days fewer than 5 larvae/seedling and no nematode development could be found. In susceptible roots, larvae became sedentary and developed normally; egg production began as early as 18 days after penetration of the host.     

Preferred Temperature of Meloidogyne incognita

In laboratory thermal gradients, newly hatched infective juveniles of the plant-parasitic root-knot nematode Meloidogyne incognita migrated toward a preferred temperature that was several degrees above the temperature to which they were acclimated. After shifting egg masses to a new temperature, the preferred temperature was reset in less than a day. Possible functions of this type of thermotaxis are discussed, including the use of thermal gradients around plant roots to locate hosts and to maintain a relatively straight path while ranging in the absence of other cues (a collimating stimulus).     

13种植物源化合物对南方根结线虫的毒力比较

利用离体生物测定法比较了13种植物源化合物对南方根结线虫(Meloidogyne incognita Chitwood)的毒力,并探讨了紫外光照射对这些化合物杀虫活性的影响。结果表明,对苯二酚、DL-薄荷醇、丁子香酚和苦豆碱对南方根结线虫的毒杀活性最强,邻苯二酚等6种化合物的毒杀活性次之,野靛碱、毒扁豆碱和间苯二酚的毒力较低。紫外光照射可明显降低苦豆碱和柠檬酸对南方根结线虫的毒杀活性,而其他11种化合物的毒杀活性则基本不受紫外光照射的影响。     

Behavior of Tethered Meloidogyne incognita

The tethered-nematode technique was adapted for use with second-stage juveniles of Meloidogyne incognita. The data demonstrate that M. incognita exhibits the same patterns of behavior as adults of the free-living nematode, Caenorhabditis elegans. The principal differences are that M. incognita is slower and less regular in its behavior than C. elegans. The frequency of normal waves is about 0.2 Hz; that of reversal waves is about 0.06 Hz. Reversal bouts last about 1 minute. In response to a change in NaCl concentration, M. incognita modulates the probability of initiating a reversal bout in the same manner as C. elegans except that it responds more slowly and is repelled instead of attracted.     

Surface Coat of Meloidogyne incognita

The nematode surface coat is defined as an extracuticular component on the outermost layer of the nematode body wall, visualized only by electron microscopy. Surface coat proteins of Meloidogyne incognita race 3 infective juveniles were characterized by electrophoresis and Western blotting of extracts from radioiodine and biotin-labeled nematodes. Extraction of labeled nematodes with cetyltrimethylammonium bromide yielded a principal protein band larger than 250 kDa and, with water soluble biotin, several faint bands ranging from 31 kDa to 179 kDa. The pattern of labeling was similar for both labeling methods. Western blots of unlabeled proteins were probed with a panel of biotin-lectin conjugates, but only Concanavalin A bound to the principal band. Nematodes labeled with radioiodine and biotin released ¹²⁵I and biotin-labeled molecules into water after 20 hours incubation, indicating that surface coat proteins may be loosely attached to the nematode. Antiserum to the partially purified principal protein bound to the surface of live nematodes and to several proteins on Western blots. Differential patterns of antibody labeling were obtained on immuno-blots of extracts from M. incognita race 1, 2, and 3; Meloidogyne hapla race 2; and Meloidogyne arenaria cytological race B.     

Inheritance of heat-stable resistance to Meloidogyne incognita in Lycopersicon peruvianum and its relationship to the Mi gene

Summary The inheritance of heat-stable resistance to the root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, was studied in crosses between different accessions and clones of Lycopersicon peruvianum L. F₁, F₂ and BC₁ generations were evaluated for their index of resistance based on numbers of eggs and infective second-stage juveniles (J₂) per gram of root, and the segregation ratios were determined in experiments carried out at constant soil temperatures of 25 °C and 30 °C. L. peruvianum P.I. 270435 clones 3 MH and 2R2 and P.I. 126443 clone 1 MH, all heatstable resistant, were crossed with L. peruvianum P.I. 126440 clone 9 MH, which is susceptible at both 25 °C and 30 °C. All F₁ progeny were resistant at 25 °C and 30 °C; F₂ and BC₁ generations at 25 °C gave resistant: susceptible (RS) ratios of 151 and 31, respectively, which suggests that resistance is conditioned by two independently assorting genes. However, at 30 °C, RS ratios of 31 and 11 were observed for the F₂ and BC₁ generations, respectively. These results indicate that heat-stable resistance is conferred by a single dominant gene expressed at 30 °C, while the second resistance gene is heat unstable and not expressed at 30 °C. P.I. 270435 clones 2R2 and 3 MH and P.I. 126443 clone 1 MH were crossed with P.I. 128657 clone 3 R4 (source of gene Mi), which is resistant at 25 °C but susceptible at 30 °C. All of the F₁ progeny were resistant at 25 °C and 30 °C.TC₁ progeny of 270435-2 R2 x 128657-3 R4, 270435-3 MH x 128657-3 R4 and 126443-1 MH x 128657-3 R4 crossed with susceptible 126440-9 MH were all resistant at 25 °C and segregated in a 11 ratio at 30 °C. These results also suggest that the heat-stable resistance is monogenic and that it is non-allelic to gene Mi. The non-segregation of TC₁ progenies at 25 °C, suggests that the heat-unstable resistance factor in L. peruvianum P.I. 270435 clones 2 R2 and 3 MH and in P.I. 126443 clone 1 MH is allelic to or the same as gene Mi. We propose the symbol Mi-2 for the gene in P.I. 270435 that confers heat-stable resistance to M. incognita.     

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Abamectin

Avermectins are macrocyclic lactones produced by Streptomyces avermitilis. Abamectin is a blend of B_1a and B_1b 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.     

Interaction of Meloidogyne javanica with Different Races of Meloidogyne incognita

The interspecific interactions of Meloidogyne javanica with races 1, 2, 3, and 4 of M. incognita on tomato were determined. Impacts of the interactions on fecundity and morphometrics of females were also examined. Mutually inhibitory interactions occurred between M. javanica and the races of M. incognita, but the negative interactions did not reflect in plant growth. Numbers of root galls, egg masses, mature females, total population, fecundity, and reproduction factor declined in concomitant treatments, but the morphometrics of the females remained unaltered. In general, mutual suppressive effects in all parameters were smaller for M. javanica than M. incognita, but some variations occurred among the races of M. incognita. Race 2 appeared to be more competitive than other races. The interaction between the species was not intense; therefore, the species coexist in mixed populations in agricultural fields.     

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Fluopyram

Fluopyram is a succinate dehydrogenase inhibitor (SDHI) fungicide that is being evaluated as a seed treatment and in-furrow spray at planting on row crops for management of fungal diseases and its effect on plant-parasitic nematodes. Currently, there are no data on nematode toxicity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of fluopyram. Nematode toxicity and recovery experiments were conducted in aqueous solutions of fluopyram, while root infection assays were conducted on tomato. Nematode paralysis was observed after 2 hr of exposure at 1.0 µg/ml fluopyram for both nematode species. Using an assay of nematode motility, 2-hr EC₅₀ values of 5.18 and 12.99 µg/ml fluopyram were calculated for M. incognita and R. reniformis, respectively. Nematode recovery in motility was greater than 50% for M. incognita and R. reniformis 24 hr after nematodes were rinsed and removed from a 1-hr treatment of 5.18 and 12.99 µg/ml fluopyram, respectively. Nematode infection of tomato roots was reduced and inversely proportional to 1-hr treatments with water solutions of fluopyram at low concentrations, which ranged from 1.3 to 5.2 µg/ml for M. incognita and 3.3 to 13.0 µg/ml for R. reniformis. Though fluopyram is nematistatic, low concentrations of the fungicide were effective at reducing the ability of both nematode species to infect tomato roots.     

Behavioral Responses of Meloidogyne incognita to Small Temperature Changes

Small, rapid temperature changes were generated by incandescent radiation, and behavioral responses of Meloidogyne incognita juveniles were recorded with high time resolution by computer tracking. Temperature changes away from the preferred temperature resulted in decreases in the rate of movement and increases in the rate of change of direction, whether the changes were toward warmer or cooler temperatures. These behavioral changes lasted about 30 seconds. Temperature changes toward the preferred temperature caused the response rates to change in the opposite directions, and the behavioral changes persisted for several minutes. These results demonstrate that nematodes can respond to a purely temporal thermal stimulus in a manner consistent with efficient indirect orientation or klinokinesis. The rate of temperature change was estimated to be of the order of 10⁻⁴ C/second, suggesting that the nematodes detected a change of about 0.001 C.     

Hatching Response of Meloidogyne incognita acrita to Electric Shock

The influence of electric shock on hatch of Meloidogyne incognita acrita from egg masses taken from roots of ''Acala SJ-I'' cotton (Gossypium hirsutum L.) was studied. Egg masses in tap water were individually placed between the tips of needle electrodes 1 mm apart and exposed to potentials of l, 10, 20, and 60 vdc/mm at 1, 1, 1, and 86 milliamperes dc, respectively, for periods of 2 and 60 seconds. Hatched larvae were counted at five-day intervals for 60 days. Of the eight treatment combinations used, six gave a greater egg hatch than the control. The largest hatch, 520 percent greater than the control, resulted from exposure to 1 vdc/mm for 60 seconds; 60 vdc/mm for 2 and 60 sec decreased egg hatch 11 and 94 percent of the untreated control. Hatched larvae from all treatments except the 60 vdc/mm, 60-second exposure were infective and reproduced on young cotton plants in a glasshouse.     

Evaluating resistance of some rootstocks to grape phylloxera with in vitro and excised root testing systems

Summary The life table of a local strain of grape phylloxera was determined to evaluate the resistance of the most commonly used rootstocks: Rul40, R99, and 3309C, and one local variety ‘Helwani’. The study was carried out by applying both in vitro dual culture and small root pieces testing systems. The results showed that there was a great variation in percentage mortality of immature stages, number of eggs laid, adult fertility, oviposition period, and developmental time between all tested rootstocks and the local variety, regardless of the applied testing systems. Based on the population prediction, Helwani would be a suitable host as it would be susceptible to the destructive insects in the field and the rootstocks would be resistant. However, Rul 40 rootstock was more susceptible than R99 and 3309C rootstocks.