Potato Cyst Nematode Populations Research Articles

Evolving dynamics of insect frass fertilizer for sustainable nematode management and potato production.

Potato production faces major challenges from inadequate soil fertility, and nematode infestation, yet synthetic fertilizers and nematicides are costly and harmful to the environment. This study explored the potential of chitin-fortified black soldier fly-composted organic fertilizer (BSFCOF) as a multipurpose organic fertilizer amendment for enhancing potato yield and suppressing potato cyst nematodes (PCN). The BSFCOF was applied at a rate equivalent to 150 kg N ha-1 and fortified with chitin from black soldier fly pupal exuviae at inclusion rates equivalent to 0.5, 1, 2, 3, 4 and 5% chitin. Data were collected on potato growth characteristics, PCN population densities, and soil chemical properties for two growing cycles. Results showed that chitin fortified BSFCOF significantly improved potato growth parameters, chlorophyll concentration, marketable tuber yield and number of marketable tubers. The marketable tuber yield achieved using chitin-fortified BSFCOF was 70 - 362%, and 69 - 238% higher than the values achieved using unfertilized soil during the first and second growing cycles, respectively. Soil amendment with chitin-fortified BSFCOF significantly reduced the number of cysts per 200 g soil-1, number of eggs and J2 per cyst-1, eggs g-1 soil and reproduction rate by 32 - 87%, 9 - 92%, 31- 98% and 31 - 98%, respectively. The PCN suppression increased with chitin inclusion rates. There were significantly higher values for soil pH, ammonium nitrogen, nitrate nitrogen, available phosphorus, calcium, magnesium, potassium, and cation exchange capacity in soil amended with BSFCOF compared to unamended soil. This study demonstrates that BSFCOF fortified with 5% chitin is an effective soil enhancer with multiple benefits, including improved soil fertility, potato performance, and effective management of potato cyst nematodes.

Morpho-molecular characterization of golden potato cyst nematode population from Bauko, Mountain Province, Philippines

Morpho-molecular characterization of golden potato cyst nematode population from Bauko, Mountain Province, Philippines

Biodiversity and efficacy of fungal isolates associated with Kenyan populations of potato cyst nematode (Globodera spp.)

Potato Cyst Nematodes (PCN) (Globodera rostochiensis and G. pallida Woll.) are quarantine pests of potato (Solanum tuberosum L.) worldwide capable of causing significant yield loss and difficult to manage with conventional methods. The study explored the diversity of antagonistic fungi associated with PCN obtained from soil samples collected in Nyandarua and Nakuru Counties in Kenya and their effect on PCN egg viability and hatching was also evaluated. Twelve fungal isolates from five genera were isolated and characterized using morphological and molecular techniques. The twelve isolates were Trichoderma asperellum (4), T. hamatum, T. breve, T. atrobruneum, Amanita basiorubra, Setophoma terrestris (2), Penicillium chrysogenum and Clonostachys rosea. The most abundant isolate was Trichoderma spp. with 58 % occurrence. The effect of seven of the isolates on PCN eggs showed that T. breve and P. chrysogenum reduced egg viability by 41 % and 34 %, respectively while T. asperellum and T. breve reduced their hatching by 50 % on average. Trichoderma atrobrunneum, T. hamatum, and A. basiorubra also reduced the PCN egg viability by 27 % on average. These fungal isolates could provide a potential tool for PCN management in potato production systems for improved yields. However, further studies are warranted to validate these findings under greenhouse and field conditions. A more comprehensive bioprospecting survey for PCN associated antagonistic fungi needs to be extended to other potato growing regions to explore further cyst pathogens.

Sequence of introduction determines the success of contrasting root symbionts and their host

Many crop species play host to a diverse range of soil-borne symbionts ranging from parasitic, such as potato cyst nematodes (PCN), to mutualistic, including arbuscular mycorrhizal fungi (AMF). Each of these organisms may establish symbiosis with the host prior to the arrival of another which may impact the fitness of all parties involved. We simulated a range of arrival time scenarios for both AMF and PCN and determined their consequences on potato host plants and subsequent symbionts to reflect the likely complexity of symbioses that occur in the field. Simulations were focussed on the first few weeks of plant growth to identify the importance of symbiont interactions during early plant development. Our data indicate that the order in which symbionts are introduced to crop roots is not only important for their own success, but also for that of the host and its additional symbionts. The presence of AMF increased the PCN population on the host, with earlier introduction of AMF increasing the magnitude of the effect. However, presence of AMF also increased the potato's tolerance to PCN, ameliorating the negative effects of the increased PCN burden. This tolerance was stronger the earlier the AMF were introduced and was sustained even when AMF were introduced after PCN. Overall, we show that the initial few weeks of crop emergence and growth may reflect a window of opportunity where the prosperity of the crop and its tolerance of parasites can potentially be influenced by coordinating application of AMF propagules. Additionally, these timings impact the success of below-ground plant parasites that can persist and impact crops for several years.

Arbuscular mycorrhizal fungal‐induced tolerance is determined by fungal identity and pathogen density

Societal Impact StatementPlant‐parasitic nematodes are a major concern for global food security, and many existing control options are being phased out due to adverse impacts on the environment. Here, we show that although application of arbuscular mycorrhizal fungi (AMF) increases host tolerance to these parasites, these benefits decrease as the parasite burden increases, limiting long‐term benefits. This effect was consistent between experiments in the glasshouse and in the field environment, demonstrating the relevance of research into usable technologies. Our findings have potential to aid decision making regarding application of AMF inocula for optimum results in agricultural systems.Summary Plant‐parasitic nematodes are a leading global threat to crop production and food security aims. Control strategies based on nematicides and fertilisers are increasingly undesirable due to economic and environmental impacts. Arbuscular mycorrhizal fungi (AMF) may induce host tolerance against pests such as the potato cyst nematode (PCN). Here, we determined the impact of PCN density on the tolerance induced by AMF‐host interactions. Additionally, we evaluated the effects of five AMF inocula on PCN fitness though glasshouse and field trials. Greater PCN densities reduce the increased tolerance that AMF may confer on their hosts. This may be due to reduced mycorrhizal colonisation of hosts under higher PCN infection and potentially a threshold at which the presence of PCN severely impacts fungal growth. When tested in the field, the outcomes of AMF inoculation on crop yields were still positive. Inoculation of soil in the field also increased PCN multiplication, suggesting that AMF‐induced tolerance may become reduced in the near future when the threshold PCN density is reached. Addition of AMF to agricultural soils may provide a short‐term benefit yet lead to a long‐term detriment by increasing PCN populations. The effects observed were driven by only one out of the five introduced AMF species, indicating that the remaining species were redundant for this application. This raises important considerations for future application of AMF inocula in agricultural systems and aids our understanding of how widely used ‘beneficial’ soil amendments impact the agricultural ecosystem.

Comparative genomics among cyst nematodes reveals distinct evolutionary histories among effector families and an irregular distribution of effector-associated promoter motifs.

Potato cyst nematodes (PCNs), an umbrella term used for two species, Globodera pallida and G. rostochiensis, belong worldwide to the most harmful pathogens of potato. Pathotype-specific host plant resistances are essential for PCN control. However, the poor delineation of G. pallida pathotypes has hampered the efficient use of available host plant resistances. Long-read sequencing technology allowed us to generate a new reference genome of G. pallida population D383 and, as compared to the current reference, the new genome assembly is 42 times less fragmented. For comparison of diversification patterns of six effector families between G. pallida and G. rostochiensis, an additional reference genome was generated for an outgroup, the beet cyst nematode Heterodera schachtii (IRS population). Large evolutionary contrasts in effector family topologies were observed. While VAPs (venom allergen-like proteins) diversified before the split between the three cyst nematode species, the families GLAND5 and GLAND13 only expanded in PCNs after their separation from the genus Heterodera. Although DNA motifs in the promoter regions thought to be involved in the orchestration of effector expression ("DOG boxes") were present in all three cyst nematode species, their presence is not a necessity for dorsal gland-produced effectors. Notably, DOG box dosage was only loosely correlated with the expression level of individual effector variants. Comparison of the G. pallida genome with those of two other cyst nematodes underlined the fundamental differences in evolutionary history between effector families. Resequencing of PCN populations with different virulence characteristics will allow for the linking of these characteristics to the composition of the effector repertoire as well as for the mapping of PCN diversification patterns resulting from extreme anthropogenic range expansion.

The Impact of Management Strategies on the Development and Status of Potato Cyst Nematode Populations in Switzerland: An Overview from 1958 to Present.

Globodera rostochiensis and G. pallida are some of the most successful and highly specialized plant parasitic nematodes and among the most regulated quarantine pests globally. In Switzerland, they have been monitored by annual surveys since their first detection in Swiss soil in 1958. The dataset created was reviewed to produce an overview of the development and actual status of potato cyst nematodes (PCNs) in Switzerland. Positive fields represent 0.2% of all the samples analyzed, and their distribution is limited to central-west and western Switzerland, suggesting that new introduction of PCNs and the spread of the initial introduced PCN populations did not occur. In this way, the integrated management used in Switzerland appears to be effective. However, the increasing availability of potato varieties with resistance to G. rostochiensis and the limited availability of varieties with resistance to G. pallida, together with other biotic and abiotic factors, have promoted changes in the dominance of either species. Consequently, an extended monitoring program is of interest to Swiss farmers, to avoid favoring virulent traits that could be present in Swiss Globodera populations.

Genomic Reconstruction of the Introduction and Diversification of Golden Potato Cyst Nematode Populations in Indonesia.

Potato cyst nematodes (PCNs), the umbrella term for Globodera rostochiensis and G. pallida, coevolved with their Solanaceous hosts in the Andean Mountain region. From there, PCN proliferated worldwide to virtually all potato production areas. PCN is a major factor limiting the potato production in Indonesia. In our survey, only G. rostochiensis was found. Fourteen field populations were collected on Java and Sumatra, and unique variants were called by mapping resequencing data on a G. rostochiensis reference genome. A phylogenetic tree based on 1.4 million unique variants showed a genotypic separation between the outgroup, a Scottish Ro1 population, and all Indonesian populations. This separation was comparable in size with the genotypic distinction between the Javanese and the Sumatran PCN populations. Next, variants within PCN effector gene families SPRYSEC, 1106, 4D06, and venom allergen-like protein (VAL) that all interfere with the host innate immune system were compared. Distinct selective pressures acted on these effector families; while SPRYSECs (4,341 single-nucleotide polymorphisms [SNPs]/insertions or deletions of bases [indels]) behaved like neutral genes, the phylogenetic trees of 1106, 4D06, and VAL proteins (235, 790, and 150 SNPs/indels, respectively) showed deviating topologies. Our data suggest that PCN was introduced on Java not too long after the introduction of potato in the middle of the eighteenth century. Soon thereafter, the pathogen established on Sumatra and started to diversify independently. This scenario was corroborated by diversification patterns of the effector families 1106, 4D06, and VAL. Our data demonstrate how genome resequencing data from a nonindigenous pathogen can be used to reconstruct the introduction and diversification process.

Biodiversity and Efficacy of Fungal Isolates Associated with Kenyan Populations of Potato Cyst Nematode (Globodera Spp.)

Biodiversity and Efficacy of Fungal Isolates Associated with Kenyan Populations of Potato Cyst Nematode (Globodera Spp.)

Pemetaan Sebaran Serangan Nematoda Sista Kentang (Globodera spp.) Pada Areal Sertifikasi Benih Kentang Kecamatan Pangalengan – Jawa Barat

The experiment was carried out, from September to November 2017 in the potato certification area of Kec. Pangalengan-West Java and Horticultural Plants Laboratory Center for Supervision and Certification of Seeds for Food Crops and Horticulture (BPSBTPH) West Java Province, Jl. Ciganitri II Bojongsoang-Bandung. The purpose of the experiment was to determine what factors affect the potato cyst nematode population and to determine the distribution of potato cyst nematode (Globodera spp.) in the potato seed certification area in Pangalengan District – West Java. The experimental design used was the field observation method in the potato seed certification area in Pangalengan District and areas suspected of being attacked by NSK, by measuring altitude, land slope, soil pH and rainfall data related to surface runoff and sampling. soil for laboratory analysis which will then be compared with field data for analysis using the ArcGIS 10.2 program. The experimental results show no correlation, showing the relationship between the variables has a small correlation value so that the degree of closeness of the relationship between the variables of altitude, land slope, soil pH, rainfall less influential. The distribution of potato cyst nematode attack (globodera spp.) in potato seed certification areas was found in Sukamanah, Margamukti, and Tribaktimulya villages in Pangalengan District - West Java.

A process-based, stage-structured model of potato cyst nematode population dynamics: Effects of temperature and resistance

Potato cyst nematodes (PCN) are responsible for large losses in potato yields in many of the world’s potato-growing regions. As soil temperatures increase due to climate change, there is potential for faster growth rates of PCN, allowing development of multiple generations in a growing season. We develop a process-based temperature-dependent model representing the life cycle of Globodera pallida, comprising juvenile, adult and cyst/diapause stages. To incorporate variability in the amount of time spent in each stage caused by genetic/environmental variation, the model is based on a mix of ordinary differential equations (ODEs) with sub-stages, and delay differential equations (DDEs). The effect of climate change is incorporated through the influence of soil temperature on the rate of development and survival in the hatching and juvenile stages. The level of the plant resistance to PCN is incorporated via the proportion of juveniles which become adults. After comparing the model with field data we run simulations to explore the effects of temperature and resistance on PCN populations. We find that with higher temperatures and longer growing seasons multiple generations of PCN can develop within a season, provided any required diapause period is short. Despite this, we show that growing resistant potatoes is a very effective control strategy and planting potatoes with even moderate levels of resistance can counter the effects of climate change.

Potato cyst nematode-infected soil as a source of egg and cyst parasitic fungi as potential biocontrol agents

Parasitic fungi are an important natural mortality factor of parasitic nematode populations in plants under environmental conditions. Indigenous parasitic fungi are challenging to develop as biological control agents for plant parasitic nematodes, including potato cyst nematode (PCN). Soils that suppress nematode populations are a challenging source of biological agents. This study aimed to explore PCN-infected soil as a source of egg and cyst parasitic fungi. Infected soils associated with healthy plants were compared with soils associated with PCN-infected plants to explore the presence and activity of putative fungal biological control agents. Parasitic fungi in nematode-infected soil were explored, heat treatment was performed to prove the biological ability of parasitic fungi in soil to suppress PCN population, and the biological activity of parasitic fungi was induced using a baiting technique. Results indicated that fungal activity in some PCN-infected areas of soil might suppress PCN population by parasitism of cysts or eggs. Heat treatment of soil eliminated the biological activity of these fungi against PCN cyst population. Baiting soil with PCN cysts promoted the parasitic activity of the fungi in the infected soil. These results indicate that nematode-infected soil is a source of parasitic fungi as candidate biological control agents.

Bacterial Microbiota Isolated from Cysts of Globodera rostochiensis (Nematoda: Heteroderidae).

The potato cyst nematode (PCN) Globodera rostochiensis is a plant parasite of potato classified into a group of quarantine organisms causing high economic losses worldwide. Due to the long persistence of the parasite in soil, cysts harbor numerous bacteria whose presence can lead to cyst death and population decline. The cysts of G. rostochiensis found in two potato fields were used as a source of bacteria. The universal procedure was applied to extract DNA from bacteria which was then sequenced with 16S primers. The aims of the study were to identify bacterial microbiota associated with the PCN populations and to infer their phylogenetic relationships based on the maximum likelihood and Bayesian phylogeny of the 16S sequences. In addition, the impact of the most significant climate and edaphic factors on bacterial diversity were evaluated. Regarding the higher taxonomy, our results indicate that the prevalent bacterial classes were Bacilli, Actinobacteria and Alphaproteobacteria. Phylogenetic analyses clustered Brevibacterium frigoritolerans within the family Bacillaceae, confirming its recent reclassification. Long-term climate factors, such as air temperature, insolation hours, humidity and precipitation, as well as the content of soil organic matter, affected the bacterial diversity. The ability of cyst nematodes to persist in soil for a long time qualifies them as a significant natural source to explore the soil bacterial microbiota.

Distribution, DNA barcoding and genetic diversity of potato cyst nematodes in Indonesia

Global trading of plant materials, in combination with agricultural practices, may facilitate the spreading of cyst nematodes to so far non-infected areas. Recently Potato Cyst Nematode (PCN) was recognized to be present in Indonesia and both diversity and distribution require further study. Assessment of PCN populations was done by collecting soil samples, determination of morphological characteristics in combination with ITS rDNA and COI mtDNA sequencing. Thirty-seven soil samples were collected from potato fields in the Indonesia archipelago. The results showed the presence of Globodera rostochiensis in 22 out of 37 sampling fields, namely North Sumatra (6 fields), Central Java (12 fields), East Java (3 fields), and -for the first time- in Sulawesi (North Sulawesi) (1 field). The highest observed density was found in Banjarnegara (Central Java), i.e., 872 cysts 100 ml soil−1. Globodera pallida was not recovered. Both ITS and COI characterisation of Indonesian PCN (G. rostochiensis) revealed the virtual absence of sequence variation as compared to most PCN from the rest of the world; the COI sequences were identical to the most common and mostly distributed haplotype around the world. Microsatellite genotyping indicated a higher genetic diversity for populations from East Java than for populations from North Sumatra, suggesting that cysts at the origin of populations in North Sumatra were coming from populations in East Java. These data on species identification, population density, genetic diversity, and distribution of potato cyst nematode over the Indonesian archipelago constitute the very basis for the design of environmentally-sound and effective PCN control strategies.

Prevalence and Spread of Potato Cyst Nematodes, <I>Globodera</I> spp. in Northern Hilly Areas of India

Potato cyst nematodes (PCNs), Globodera rostochiensis (Woll.) and G. pallida (Stone), are globally important pests of potato prevalent in the Nilgiri area of South India. PCNs were first intercepted from North India at Shimla, Himachal Pradesh (HP) in 2010. Subsequent surveys in the hilly areas of North India have revealed the occurrence of PCNs in several districts of HP, Uttarakhand and Jammu & Kashmir, despite domestic quarantine against this nematode. High populations of PCN were mainly encountered in the Potato Seed Multiplication Farms that supply seed potato to farmers. Here, a hypothesis on the dissemination of PCNs within India is proposed.

Potato Cyst Nematodes: A New Threat to Potato Production in East Africa.

Potato cyst nematodes (PCN), such as Globodera rostochiensis and Globodera pallida, are quarantine restricted pests of potato causing major yield and financial losses to farmers. G. rostochiensis was first reported from Kenya’s key potato growing area in 2015. We sought to determine the diversity, prevalence and distribution of PCN species across the country by conducting a country-wide survey between 2016 and 2018, which included a more focused, follow-up assessment in three key potato growing counties. A total of 1,348 soil samples were collected from 20 potato growing counties. Information regarding local potato farming practices, potato cultivar use, their diversity and availability was also recorded. PCN cysts were obtained from 968 samples (71.8%) in all the counties surveyed, with Nyandarua County recording the highest PCN field-incidence at 47.6%. The majority of PCN populations, 99.9%, were identified as G. rostochiensis, while G. pallida was recovered from just one field, in a mixed population with G. rostochiensis. Inconsistencies in PCR amplification efficiency was observed for G. rostochiensis using the recommended EPPO primers, compared with ITS primers AB28/TW81, indicating that this protocol cannot be entirely relied upon to effectively detect PCN. Egg density in Nyandarua County varied between 30.6 and 158.5 viable eggs/g soil, with an average egg viability of 78.9 ± 2.8% (min = 11.6%, max = 99.9%). The PCN-susceptible potato cultivar named Shangi was the most preferred and used by 65% of farmers due to its shorter dormancy and cooking time, while imported cultivars (Destiny, Jelly, Manitou, and Markies) with resistance to G. rostochiensis were used by 7.5% of farmers due to unavailability and/or limited access to seeds. Thus, most farmers preferred using their own farm-saved seeds as opposed to purchasing certified seeds. Establishing the distribution and prevalence of PCN and elucidating the local farming practices that could promote the spread of PCN is a necessary precursor to the implementation of any containment or management strategy in the country and ultimately across the region.

Morphological and molecular characterization of potato cyst nematode populations from The Nilgiris

Quarantine species of potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, were reported from Nilgiris during 1961. The studies were carried out at ICAR-CPRS, Muthorai, Ooty and ICAR-CPRI, Shimla during 2015–17. To investigate the distribution of PCN, soil samples were collected from potato growing areas of Nilgiris and were identified based on morphological criteria and ITS-1 region. Molecular characterization using ITS-1 region specific primers revealed the presence of pure population of G. rostochiensis in 50% of the samples, G. pallida in 10.7% of the samples, mixed population in 28.6% of the samples and absence of both the species in 10.7% of the samples. The phylogenetic analysis inferred by the sequence of the ITS-1 region confirmed 92–100% genetic similarities in Globodera spp. Seventeen isolates of G. rostochiensis showed 92–99% genetic similarity and rest four 92–100% similarities. Whereas, genetic similarity among the ten isolates of G. pallida was 96.1–99.4%. In the morphometric characters J2s of G. rostochiensis exhibited shorter body length (459.8 μm) than G. pallida (493.7 μm). G. rostochiensis and G. pallida had difference in mean stylet length (21.1 μm and 23.4 μm respectively), hyaline tail terminal length (28.3 μm and 24.2 μm respectively) and shape of stylet knob. Highest mean value of vulval basin-anus distance (65.3 μm), number of cuticular ridges between vulval basin-anus (18.4) and Granek’s ratio (4.0 μm) was recorded in G. rostochiensis than G. pallida. Therefore, the present study will help to take appropriate and region specific PCN management decisions according to species dominance in that area.

Management of Potato Cyst Nematodes Using Liquid Bioformulations of Pseudomonas fluorescens, Purpureocillium lilacinum and Trichoderma viride

The field efficacy of liquid formulations of Pseudomonas fluorescens, Purpureocillium lilacinum and Trichoderma viride was investigated against natural populations of potato cyst nematodes (PCNs) Globodera rostochiensis and Globodera pallida. Two field experiments were conducted using these biocontrol agents applied as seed treatment (ST) at 1 L t−1 of seed and soil drenching (SD) at 5 L ha−1. Their effect was compared with carbofuran 3 G at 1 kg a.i. ha−1. Results showed that all the tested biocontrol agents were capable to reduce PCN egg density or multiplication rate, root penetration and egg numbers cyst−1 at various levels. The biocontrol efficacy also varied according to their delivery method. P. fluorescens-ST was found causing the highest reduction of egg density (83.1–86.5%), multiplication rate (83.1–86.5%), root penetration (67.1–68.1%) and egg numbers cyst−1 (35.4–36.0%). Similar efficacy was observed in P. lilacinum-SD that reduced egg density by 80.9–85.0%, multiplication rate by 80.7–84.3%, root penetration by 62.0–64.4% and egg numbers cyst−1 by 44.3–49.3%. The potato plants from P. fluorescens-ST and P. lilacinum-SD plots were 31.1–49.5% taller than untreated plants which also resulted in 27.2–32.0% higher tuber yield in P. fluorescens-ST and 25.9–30.2% in P. lilacinum-SD plots. The root colonisation of introduced P. fluorescens was 8.6–13.1 times higher in ST than SD. The trend was vice versa in P. lilacinum that colonised 3.1–3.6 times better in SD method than as ST. Their efficacy was comparable to carbofuran application. It is concluded that P. fluorescens-ST at 1 L t−1 of seed and P. lilacinum-SD at 5 L ha−1 are highly effective for management of PCN under naturally infested field conditions.

Efek Limbah Padat Minyak Kayu Putih terhadap Populasi Nematoda Sista Kuning dan Pertumbuhan Kentang

Potato cyst nematode (PCN) is a pest organism on potato being able to reduce the yield of potatoes. The damage caused by the pest on potato yield about 50-75 %, so need to control the PCN by using natural pesticides. Eucalyptus oil waste may be used as natural pesticides, because these oil can volatile with many active compounds. This study aims to assess the effect of provision of solid waste of eucalyptus oil against populations of PCN, growth and yield of potatoes. The research method was used a randomized completely block design. There were two factors, namely the storage age of the waste (age one year and 5-6 year) and dosage (100 g, 200 g and 400 g). The research variable was the population of nematodes in the soil, the plant height and potato yields. Provision of the waste was able to reduce the population of the cyst as much of 39.7%. Treatment with the waste was reduce the eggs of nematodes at 26.3%, so treatment of waste a year was able to reduce the average cyst by 42.7%. A dose of waste 400 g provided the results of the population PCN low (222.1 every 100 g of soil for cyst and 0.06 every 100 g soil to PCN juvenile 2) compared with another dose. Treatment with a dose of 400 grams was able to reduce the population of cyst by 26%. The smallness of the population of PCN influenced by several factors such as the chemical compounds contained in the waste eucalyptus oil of . The growth of higher plants which was highest at a dose of 400 g (17.06 cm) with the highest yield i.e. 12.34 g.

Molecular Assessment of the Introduction and Spread of Potato Cyst Nematode, Globodera rostochiensis, in Victoria, Australia.

Potato cyst nematodes (PCN) are damaging soilborne quarantine pests of potato in many parts of the world. There are two recognized species, Globodera pallida and G. rostochiensis, with only the latter species-the golden cyst nematode-present in Australia. PCN was first discovered in Australia in 1986 in Western Australia, where it was subsequently eradicated and area freedom for market access was reinstated. In Victoria, PCN was first detected in 1991 east of Melbourne. Since then, it has been found in a small number of localized regions to the south and east. Strict quarantine controls have been in place since each new detection. It has previously been speculated that there were multiple separate introductions of PCN into Victoria. Our study utilized a historic (years 2001 to 2014) PCN cyst reference collection to examine genetic variability of Victorian PCN populations to investigate potential historical origins and subsequent changes in the populations that might inform patterns of spread. DNA was extracted from single larvae dissected from eggs within cysts and screened using nine previously described polymorphic microsatellite markers in two multiplex polymerase chain reaction assays. Sequence variation of the internal transcribed spacer region of the DNA was also assessed and compared with previously published data. A hierarchical sampling strategy was used, comparing variability of larvae within cysts, within paddocks, and between local regions. This sampling revealed very little differentiation between Victorian populations, which share the same microsatellite allelic variation, with differences between local regions probably reflecting changes in allele frequencies over time. Our molecular assessment supports a probable single localized introduction into Victoria followed by limited spread to nearby areas. The Australian PCN examined appear genetically distinct from populations previously sampled worldwide; thus, any new exotic incursions, potentially bringing in additional PCN pathotypes, should be easily differentiated from existing established local PCN populations.