Potential for biological control of Heterodera schachtii by Pochonia chlamydosporia var. chlamydosporia on sugar beet

The biological control potential of an isolate of Pochonia chlamydosporia var. chlamydosporia against Heterodera schachtii was examined by assessing the percentage of females and cysts that became infected on water agar, the effect of culture filtrate on juvenile mobility, and the effects of the fungus on the final population of the nematode on sugar beet under greenhouse conditions. After 3 weeks at 20°C, 74 and 95% of the eggs within cysts and females, respectively, were colonised by the fungus on water agar. The full concentration of the fungal filtrate from cultures in malt extract broth killed only 12% of the juveniles after 24 h at 25°C. In the greenhouse experiment, adding 16,000 chlamydospores of the fungus per gram of soil as either colonised barley grains or spores reduced the final number of females on roots of sugar beet by 50 and 66%, respectively, after 3 months. The reproduction factor was reduced to ×2 in spore-treated soil compared with ×5 in the untreated control, and 18% of the eggs in spore-treated soil were colonised by fungal mycelium. Generally, P. chlamydosporia var. chlamydosporia was more efficient at reducing the nematode population when applied as spores without any substrate than when used as colonised barley grains.     

Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii

Sedentary plant‐parasitic cyst nematodes are obligate biotrophs that infect the roots of their host plant. Their parasitism is based on the modification of root cells to form a hypermetabolic syncytium from which the nematodes draw their nutrients. The aim of this study was to identify nematode susceptibility genes in Arabidopsis thaliana and to characterize their roles in supporting the parasitism of Heterodera schachtii. By selecting genes that were most strongly upregulated in response to cyst nematode infection, we identified HIPP27 (HEAVY METAL‐ASSOCIATED ISOPRENYLATED PLANT PROTEIN 27) as a host susceptibility factor required for beet cyst nematode infection and development. Detailed expression analysis revealed that HIPP27 is a cytoplasmic protein and that HIPP27 is strongly expressed in leaves, young roots and nematode‐induced syncytia. Loss‐of‐function Arabidopsis hipp27 mutants exhibited severely reduced susceptibility to H. schachtii and abnormal starch accumulation in syncytial and peridermal plastids. Our results suggest that HIPP27 is a susceptibility gene in Arabidopsis whose loss of function reduces plant susceptibility to cyst nematode infection without increasing the susceptibility to other pathogens or negatively affecting the plant phenotype.     

Isolation and characterization of microsatellite loci in the sugar beet cyst nematode Heterodera schachtii

We report the isolation of five microsatellites loci from the sugar beet cyst nematode (Heterodera schachtii). Multilocus genotypes were obtained on individual larvae freshly emerged from cysts. Allelic diversity ranged from four to 27 among the five loci. The primers were tested for cross‐species amplification in six other species of phytoparasitic nematodes of the Heterodera genus. Those molecular markers will be used to study the genetic structure of this obligatory parasite and how it is affected by the use of resistant plants.     

Impact of soil suppressiveness on various population densities of Heterodera schachtii

Infectivity of second‐stage juvenile (J2) populations of Heterodera schachtii was assayed with radish.The numbers of J2 in three‐day‐old seedlings were proportional to the numbers of J2 in two differently textured soils.In a microplot trial with a known H.schachtii‐supprcssivc soil, half of the plots contained untreated suppressive soil, the other half contained the same soil, but methyl iodide‐fumigated and therefore conducive.Both soils were infested with cysts introducing the equivalents of 0, 30, 60 or 120 H.schachtii eggs g‐¹ soil, kept moist for 2 months, and then planted to Swiss chard.The numbers of J2 in radish roots were proportional to the numbers of H.schachtii eggs introduced into the microplots, at a low level of detection in suppressive soil and at a high level in conducive soil.Growth of Swiss chard was not different at increasing infestation levels in suppressive soil, but growth was reduced in conducive soil proportionally to increasing nematode infestation level.     

Effects of beet cryptic virus infection on sugar beet in field trials

The effects of beet cryptic virus (BCV) infection on sugar beet crops were investigated in field trials in 1990. Two sugar beet breeding stock lines were screened for infection by BCV. Seed lots containing different proportions of seed infected with BCV1 & 2 were obtained by crossing the stock lines and used in field trials at five different sites. Five characteristics of the infected plants were assessed. BCV infection appeared to have no significant effects on the sugar beet crop at four locations which suffered from drought stress but significant effects were found at one site where the crop was grown on grade 1 land with good moisture retention properties. Root yield and sugar yield were reduced by up to 17% and 20%, respectively, by BCV infection.     

Sporamin-mediated resistance to beet cyst nematodes (Heterodera schachtii Schm.) is dependent on trypsin inhibitory activity in sugar beet (Beta vulgaris L.) hairy roots

Sporamin, a sweet potato tuberous storage protein, is a Kunitz-type trypsin inhibitor. Its capability of conferring insect-resistance on transgenic tobacco and cauliflower has been confirmed. To test its potential as an anti-feedant for the beet cyst nematode (Heterodera schachtii Schm.), the sporamin gene SpTI-1 was introduced into sugar beet (Beta vulgaris L.) by Agrobacterium rhizogenes-mediated transformation. Twelve different hairy root clones expressing sporamin were selected for studying nematode development. Of these, 8 hairy root clones were found to show significant efficiency in inhibiting the growth and development of the female nematodes whereas 4 root clones did not show any inhibitory effects even though the SpTI-1 gene was regularly expressed in all of the tested hairy roots as revealed by northern and western analyses. Inhibition of nematode development correlated with trypsin inhibitor activity but not with the amount of sporamin expressed in hairy roots. These data demonstrate that the trypsin inhibitor activity is the critical factor for inhibiting growth and development of cyst nematodes in sugar beet hairy roots expressing the sporamin gene. Hence, the sweet potato sporamin can be used as a new and effective anti-feedant for controlling cyst nematodes offering an alternative strategy for establishing nematode resistance in crops.     

Tolerance Limit of the Sugarbeet to Heterodera schachtii

Field and greenhouse experiments showed that yield losses of sugarbeet, Beta vulgaris, did not occur in soil infested with fewer than eight Heterodera schachtii eggs/g soil. However, larger population densities greatly reduced sugarbeet yield. In the field experiment, the yield in microplots inoculated with more than 64 eggs/g soil was less than 20% of yields in uninoculated microplots. Nevertheless, tolerance limits of 4 and 1.8 eggs/g soil, in greenhouse and field microplots, respectively, were derived by fitting the data with the equation y =m + (l - m)z^P-T. Maximum rates of multiplication of 55 and more than 300, and equilibrium densities of 340 and 130 eggs/g soil, were estimated in greenhouse and field microplot tests, respectively.     

Characterization of nematode resistance genes in the section Procumbentes genus Beta: response to two populations of Heterodera schachtii

Three species of the section Procumbentes genus Beta, nine monosomic additions, and five translocation lines were tested for resistance to two Heterodera schachtii populations. Nematode population 129-v (129-virulent) was selected for virulence to resistance gene(s) transferred from chromosome 1 of Beta procumbens to the diploid resistant sugar beet KWS-NR1. This population is considered to be a pathotype. The unselected sib population 129-av (129-avirulent) was reared continuously on fodder rape, Brassica napus cv Velox. Monosomic additions with chromosome 1 from the three species of the section Procumbentes were susceptible to population 129-v, regardless of the origin of the alien chromosome. Translocations with a gene(s) for resistance from chromosome 7 of B. procumbens and B. webbiana were also susceptible to the pathotype. However, a monosomic addition with chromosome 7 of B. webbiana was resistant to population 129-v. The three wild beets of the section Procumbentes, Beta procumbens, Beta webbiana and Beta patellaris, also were highly resistant to the two populations. The results indicate the existence of just two different major genes for resistance to H. schachtii in the entire Procumbentes section.     

Genetic localization of four genes for nematode (Heterodera schachtii Schm.) resistance in sugar beet (Beta vulgaris L.)

Sugar beet (Beta vulgaris L.) is highly susceptible to the beet cyst nematode (Heterodera schachtii Schm.). Three resistance genes originating from the wild beets B. procumbens (Hs1 ^pro-1) and B. webbiana (Hs1 ^web-1, Hs2 ^web-7) have been transferred to sugar beet via species hybridization. We describe the genetic localization of the nematode resistance genes in four different sugar beet lines using segregating F₂ populations and RFLP markers from our current sugar beet linkage map. The mapping studies yielded a surprising result. Although the four parental lines carrying the wild beet translocations were not related to each other, the four genes mapped to the same locus in sugar beet independent of the original translocation event. Close linkage (0–4.6 cM) was found with marker loci at one end of linkage group IV. In two populations, RFLP loci showed segregation distortion due to gametic selection. For the first time, the non-randomness of the translocation process promoting gene transfer from the wild beet to the sugar beet is demonstrated. The data suggest that the resistance genes were incorporated into the sugar beet chromosomes by non-allelic homologous recombination. The finding that the different resistance genes are allelic will have major implications on future attempts to breed sugar beet combining the different resistance genes.     

The effects of yellowing viruses on yield of sugar beet in field trials, 1985 and 1987

The separate effects of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) on yield of sugar-beet cultivars inoculated at different growth stages were assessed in field trials in 1985 and 1987. Early or mid-season inoculation decreased sugar yield by up to 47% for BYV, and up to 29% for BMYV. Infections after the end of July had no significant effect on yield. Both viruses caused significant increases in the juice impurities sodium, potassium and amino-nitrogen after infecting plants early in the season. Yield losses associated with infection were determined by the causative virus, the time of infection, and susceptibility of the sugar-beet cultivars.     

Relationships between EUF-N fractions,N uptake and quality of sugar beet in deep loess soils of Southern Lower Saxony

Summary In field experiments conducted in 1981 on deep loess soils a significant correlation was obtained between EUF-N content in the topsoil and N in sugar beet roots as well as in whole plants. A very close correlation was found to exist between EUF-N values in June 1981 and -amino N in sugar beet roots at harvest. Also other quality criteria such as the contents of sugar, K and Na in roots and yield parameters correlated with EUF-N contents in topsoils.The inorganic and organic EUF-N fractions changed during the vegetation period due to both N uptake by the crop and mineralization. Therefore it appears to be expedient to use both fractions when calculating N fertilizer requirements.The correlation between EUF-N (topsoil samples drawn in the year preceding sugar beet) and sugar yield increases obtained by N fertilization that was found in Austria¹² was confirmed in our experiments with soils from Southern Lower Saxony.     

Relationship between EUF-K contents,K uptake and sugar yield of sugar beet in deep loess soils

Summary In field experiments with varying K fertilization (1981 and 1982) changes in EUF-K contents were studied in deep loess soils of Southern Lower Saxony under sugar beet. A significant positive linear relationship was found between EUF-K contents at 20°C and 200 V (15 mA) of the topsoils and quantities of K absorbed by sugar beet in both years. The corresponding regression lines for 1981 and 1982 are almost parallel, the only difference being the yield level which was higher in 1982.The relationship between EUF-K contents at 20°C of topsoils and sugar yields showed the same parallelism for the two years. Not much increase in sugar yield was found at EUF-K contents over 12 mg/100 g soil at EUF-K 80°C/EUF-K 20°C ratios between 0.5 and 0.7. To attain a sugar yield of 10 t/ha an EUF-K 20°C value of at least 12 mg/100 g soil is required for these deep soils at the beginning of the K uptake period. This finding confirms experiences gained over an 8-year period at the Tulln Sugar Factory (Austria) with fertilizer recommendations based on EUF.     

Physical mapping and cloning of a translocation in sugar beet (Beta vulgaris L) carrying a gene for nematode (Heterodera schachtii) resistance from B. procumbens

Two diploid (2n=18) sugar beet (Beta vulgaris L.) lines which carry monogenic traits for nematode (Heterodera schachtii Schm.) resistance located on translocations from the wild beet species Beta procumbens were investigated. Short interspersed repetitive DNA elements exclusively hybridizing with wild beet DNA were found to be dispersed around the translocations. The banding pattern as revealed by genomic Southern hybridization was highly conserved among translocation lines of different origins indicating that the translocations are not affected by recombination events with sugar beet chromosomes. Physical mapping revealed that the entire translocation is represented by a single Sal I fragment 300 kb in size. A representative YAC (yeast artifical chromosome) library consisting of approximately 13,000 recombinant clones (2.2 genome equivalents) with insert sizes ranging between 50 and 450 kb and an average of 130kb has been constructed from the resistant line A906001. Three recombinant YACs were isolated from this library using the wild beet-specific repetitive elements as probes for screening. Colinearity between YAC inserts and donor DNA was confirmed by DNA fingerprinting utilizing these repetitive probes. The YACs were arranged into two contigs with a total size of 215 kb; these represent a minimum of 72% of the translocation.     

Population genetic structure of the sugar beet cyst nematode Heterodera schachtii: a gonochoristic and amphimictic species with highly inbred but weakly differentiated populations

The sugar beet cyst nematode Heterodera schachtii is a soil-dwelling phytoparasitic nematode that feeds on beet roots. It is an important pest in most sugar beet growing areas, and better knowledge of its genetic variability is an important step to preserve the durability of resistant sugar beet varieties. The population genetic structure of this species in northern France was studied using five microsatellite markers. A hierarchical sampling design was used to investigate spatial structuring at the scale of the region, the field and the plant. Multilocus genotypes were obtained for single individual second-stage larvae, using only one individual per cyst in order to avoid the analysis of closely allied individuals (larvae from the same cyst share at least the same mother). A consistent trend of heterozygote deficit at all loci was observed at all spatial scales. Heterozygote deficit at the level of individual plants argues against its generation through a Wahlund effect. Inbreeding could be due to very limited active dispersal of larvae in the soil, favouring mating between siblings, such as larvae emerging from the same cyst. Such behaviour could have important consequences for the evolution of virulence in increasing the production of homozygous virulent individuals. Moreover, an analysis of molecular variance (amova) reveals that only 1.6% of the genetic variability is observed among regions, 3.7% among fields of the same region and 94.6% within fields. The very low level of genetic differentiation among fields is also indicated by low values of FST (相似文献   

Characterization of 15 microsatellite loci and genetic analysis of Heterodera schachtii (Nematoda: Heteroderidae) in South Korea

Heterodera schachtii, the sugar beet cyst nematode, is a major pest of agricultural crops worldwide. We report the development of fifteen polymorphic microsatellite markers and assess the genetic diversity and structure of three populations following a recent invasion of a previously unaffected region. Populations had low levels of heterozygosity, likely indicative of population structure, history, and inbreeding. Genetic diversity analysis suggested that the current infestation in South Korea may have come either from a single source population of mixed ancestry, or from multiple sources, indicating that implementing adequate prevention measures is still an unmet challenge. Much more work is needed on this species to identify global patterns of spread, and the microsatellite loci we develop here should be useful in many regions for modeling range expansion, studying the evolution of resistance, and increasing the effectiveness of pest management strategies.     

Morphological and morphometrical analysis of Heterodera spp. populations in Jordan

Phenotypic diversity of five Jordanian populations of cyst nematodes, Heterodera spp. collected from five regions from Jordan (Ar-Ramtha, Madaba, Dana, Al-Karak, and Jerash) was investigated. Soil samples were collected from one representative field in each region. Morphological and morphometrical characteristics revealed that Heterodera latipons is dominated in cereal fields at Ar-Ramtha, Madaba, Dana and Al-Karak regions and Heterodera schachtii in Jerash. Cysts populations from all cereal fields had bifenestrate vulval cone and a strong underbridge. Wherever, cysts of the cabbage population had ambifenestrate vulval cone with long vulval slit. The bullae were absent in Ar-Ramtha, Madaba and Dana populations, but present in Al-Karak and Jerash. Based on 12 morphometrical characters, the first three functions in canonical discriminant analysis accounted 99.3% of the total variation. Distance from dorsal gland duct opening to stylet base, underbridge length, a = L/W (body length/midbody width) and length of hyaline tail tip had strong and significant contributions in the first function. While the second function was strongly influenced by length of hyaline tail, fenestral length, fenestral width and tail length. However, the third canonical discriminate function was found to be influenced by stylet length, fenestral length, a = L/W (body length/midbody width) and underbridge width. The graphical representation of the distribution of the samples showed that the first canonical discriminant function clearly separated H. schachtii from Jerash from other populations. Whereas, H. latipons collected from Madaba and Dana were clearly separated in the second function. The results indicated that differences at morphological and morphometrical levels revealed diverse populations of Heterodera spp. in Jordan.