Abstract: In Arabidopsis, non-expressor of pathogenesis related genes-1, NPR1 has been shown to be a positive regulator of
the salicylic acid controlled systemic acquired resistance pathway and modulates the cross talk between SA and JA
signaling. Transgenic plants expressing AtNPR1 constitutively exhibited resistance against pathogens as well as
herbivory. In the present study, tobacco transgenic plants expressing AtNPR1 were studied further for their
response to infection by the sedentary endoparasitic root knot nematode, Meloidogyne incognita. Transgenic plants
showed enhanced resistance against the root-knot nematode infection. Prominent differences in the shoot and
root weights of wild type and transgenic plants were observed post-inoculation with M. incognita. This was
associated with a decrease in the number of root galls and egg masses in transgenic plants compared to WT. The
transgenic plants also showed constitutive and induced expression of some PR protein genes, when challenged
with M. incognita.
Abstract: Nematodes by virtue of their trophic diversity occupy a central position in soil food webs and play an important role in providing vital ecosystem services. Acting directly as pests and indirectly as vectors of other plant pathogens and consumers of microflora and fauna, nematodes play a significant role in regulating plant growth, biological pest suppression and nutrient cycling in agroecosystems. Global warming resulting in elevated carbon dioxide (CO2) and temperature in the atmosphere influence parasitic nematodes directly by interfering with their developmental rate and survival strategies and indirectly by altering host physiology. It may also influence free-living (microbial feeding) nematodes due to changes in quality and availability of food under enriched CO2 conditions. Available information on effect of global warming on soil nematodes though limited, indicate that abundance of soil nematodes in general is either increased or unaffected by elevated CO2 levels while individual species and trophic groups differ considerably in their response to climate change. Herbivorous nematodes showed neutral or positive response to CO2 enrichment effects with some species showing the potential to build up rapidly and interfere with plant's response to global warming. Studies have also demonstrated that the geographical distribution range of plant and animal parasitic nematodes may expand with global warming spreading nematode problems to newer areas. These findings underline the importance of understanding the impact of climate change on soil nematodes and its implications to agricultural systems while developing mitigation and adaptation strategies to address impact of climate change on agriculture.
Abstract: Pests are the most important biotic constraints in crop production worldwide. Developing ecologically sound biorational plant protection strategies is important for achieving food security particularly in developing nations. Most plant protection methods currently in vogue rely on two approaches: (i) use of external factors such as hazardous chemical pesticides or relatively safer products like botanicals and biocontrol agents, or (ii) use of plant's internal factors such as resistant genes incorporated either through conventional breeding or genetic engineering. In contrast to these, induced resistance is a novel non-conventional approach that uses external factors to enhance the plant's internal defense machinery to combat the pathogens and pests. Induced resistance that exploits the plant's latent defense capabilities could be proposed as an ecologically sound biorational alternative to the use of hazardous chemical pesticides. Basic characteristics of two major types of induced resistance (Systemic acquired resistance (SAR) and induced systemic resistance (ISR)), mechanisms of induction, various types of inducers, field efficacy of ISR and SAR, advantages and ecological considerations in implementing induced resistance for plant protection are briefly discussed in the light of recent advances in research on induced resistance.
Abstract: Soil microbial community structure and crop yield was investigated in field tomato production systems that compared black polyethylene mulch to hairy vetch mulch and inorganic N to organic N. The following hypotheses were tested: (1) hairy vetch cover cropping increases crop yield and significantly affects soil microbial community structure when compared to the standard plastic mulch and synthetic fertilizer-based system; (2) within plastic mulch systems, organic amendments will increase crop yield and significantly affect soil microbial community structure when compared to synthetic fertilizer; (3) crop yields and microbial community structure will be similar in the hairy vetch cover cropping and the organic amended plasticulture systems. Treatments consisted of ammonium nitrate (control), hairy vetch cover crop, hairy vetch cover crop and poultry manure compost (10 Mg/ha), three levels of poultry manure compost (5, 10, and 20 Mg/ha), and two levels of poultry manure (2.5 and 5 Mg/ha). Black polyethylene mulch was used in all treatments without hairy vetch. Fatty acid analysis was used to characterize the total soil microbial community structure, while two substrate utilization assays were used to investigate the community structure of culturable bacteria and fungi. Crop yield was not significantly increased by hairy vetch cover cropping when compared to black polyethylene mulch, although microbial community structure was significantly affected by cover cropping. Under black polyethylene mulch, crop yields were significantly increased by the highest levels of compost and manure when compared to inorganic fertilizer, but there was no detectable effect on soil microbial community structure. When cover cropping was compared to organic amended plasticulture systems, crop yields were similar one year but dissimilar the next. However, hairy vetch cover cropping and organic amendments under black plastic mulch produced significantly different soil microbial community structure.
Abstract: The effectiveness of four entomopathogenic nematodes (EPN) viz., Heterorhabditis indica (isolate
LN2), H. bacteriophora, Steinernema glaseri and S. riobrave against pupae and adult beetles of Holotrichia
serrata F., a serious pest of sugarcane was evaluated in the laboratory. All the EPN tested caused mortality
of the pupae. The lowest LD50 value was recorded for S. glaseri (113.3 IJs/pupa) followed by H. indica
(127.0 IJs/pupa). The lowest LT50 value was recorded for S. glaseri (24.9 h) followed by H. indica (27.3 h)
at 1000 IJs/pupa. In another experiment, H. indica and S. glaseri were pathogenic to adult beetles of H.
serrata. The mortality of adult beetles noticed after 24 h of inoculation and 100 per cent mortality was
recorded when the nematodes were dispensed either through soil application or by injection of IJs into
haemocoel of white grub. Steinernema glaseri introduced by injection method caused 100 per cent mortality
of beetles in 3 days followed by H. indica in four days.
Abstract: We studied variation in isozyme patterns of 8 metabolic enzymes in 5 species of Heterorhabditis (H. bacteriophora, H. indica, H. marelata, H. megidis, and H. zealandica) comprising 18 isolates. Isozyme banding patterns of all the 8 enzymes were species specific; however, 3 enzymes, i.e., arginine kinase, fumarate hydratase, and malate dehydrogenase, displayed distinct patterns among all the 18 isolates. Phylogenetic analysis of the isozyme patterns produced dendrograms depicting a high degree of genetic variation among Heterorhabditis species, with the average pairwise distance of 0.2000. Trees constructed using different phylogenetic methods showed a relatively close genetic relationship between H. megidis and H. zealandica and between H. bacteriophora and H. indica. Also, H. bacteriophora HP88 was the most distant species from H. megidis (UK isolate), H. marelatus (Oregon isolate), and H. zealandica (X1 isolate) with pairwise distance of 0.1957, 0.2228, and 0.2120, respectively. Phylogenetic analysis also revealed genetic variation among H. bacteriophora isolates with the average pairwise distance of 0.1507. GPS2 and GPS3 were the most closely related isolates with the average distance of only 0.0870, followed by GPS1 and GPS2 with average distance of 0.1087. In contrast, KMD19 and HP88, OH25, and HP88, and OH25 and Acows isolates were the most divergent populations with a pairwise distance of 0.2011 and 37 character differences. Pairwise distance analysis also revealed that genetic divergence among populations of H. bacteriophora is relatively independent of geographic distance. Overall, these results demonstrate strong subspecies structuring in H. bacteriophora.
Abstract: 1. The fungus Neotyphodium lolii forms a symbiotic relationship with
its grass host Lolium perenne (perennial ryegrass). The fungus benefits from access
to plant nutrients and photosynthate, whereas the plant benefits from acquired
chemical defence against herbivory.
2. This study examined the potential for endophyte-mediated plant defences to
influence interactions between fall armyworm Spodoptera frugiperda, and the
entomopathogenic nematode Steinernema carpocapsae and clarified biological
mechanisms underlying the observations made.
3. In laboratory and greenhouse experiments, S. frugiperda larvae were fed
endophytic or non-endophytic L. perenne then exposed to S. carpocapsae or
injected with the nematodesâ symbiotic bacteria Xenorhabdus nematophila.
4. In all instances, S. frugiperda larvae fed endophyte-infected grass suffered
significantly lower mortality than those fed non-endophytic plants. Although
larvae fed endophyte-infected grass often had significantly lower biomass than
those fed uninfected grass, these differences did not account for altered susceptibility
to S. carpocapsae.
5. Endophyte-mediated reductions in herbivore susceptibility to the nematode
pathogen represent a herbivore adaptation that effectively turns the tables on both
plant and natural enemy by reducing the virulence ofthe nematodesâ symbiotic
bacteria while expanding the temporal window ofherbivor y.
Key words. Antagonism, multi-trophic interactions, Neotyphodium endophyte,
Spodoptera frugiperda, Steinernema carpocapsae, Xenorhabdus nematophila.
Abstract: Infectivity of twenty nine entomopathogenic nematode (EPN) isolates belonging to the families of Heterorhabditidae and Steinernematidae to sugarcane shoot borer Chilo infuscatellus Snellen was investigated at 18 and 27°C under laboratory conditions. Although all the EPN isolates tested caused mortality of shoot borer larvae, there were differences in the level of mortality. Among the EPN isolates tested at 27°C, 120 h after inoculation Heterorhabditis indica (LN2),H. bacteriophora (German isolate) and Steinernema glaseri (Australian isolate) caused 100 per cent mortality of shoot borer larvae. Average time taken to kill shoot borer larvae was least (22.8 h) in case ofH. indica (LN2) followed by S. glaseri (26.5 h) and H. bacteriophora (German isolate) (28.4 h). Mortality percentage for other isolates ranged from 39.9 to 86.6. At 18°C,S. glaseri (Australian isolate) andH. bacteriophora (German isolate) caused 100 per cent mortality 120 h after nematode inoculation; with an average time taken to kill shoot borer larvae of 41.2 and 42.6 h respectively. All the EPN isolates took less time to cause mortality of shoot borer larvae at 27 than at 18°C. The multiplication of EPN in shoot borer larvae infected at 27°C was comparatively more than those infected at 18°C.
Abstract: Genetic variability in stress tolerance (heat, desiccation,
and hypoxia) and fitness (virulence and reproduction
potential) among natural populations of Steinernema
carpocapsae was assessed by estimating phenotypic
differences. Significant differences were
observed in stress tolerance among populations. Populations
isolated from North Carolina showed significantly
more stress tolerance than those isolated from
Ohio. Significant differences were also observed in
populations isolated from the same locality. Survival
of infective juveniles after exposure to 40°C for 2 h
ranged from 37 to 82%. A threefold difference was observed
in infective juvenile survival following exposure
to osmotic desiccation or hypoxic condition. Several
populations tested were superior to the most
widely used strain (âAllâ strain) in stress tolerance
traits, with one population KMD33, being superior to
the âAllâ strain in all traits. Fitness as expressed by
virulence and reproductive potential differed significantly
among populations but showed less variability
than the stress tolerance traits. All populations tested
had a reproductive potential greater than or similar to
that of the âAllâ strain and most of them caused >60%
insect mortality of the wax moth larvae, Galleria mellonella.
The high genetic variability in stress tolerance
among natural populations suggests the feasibility
of using selection for genetic improvement of these
traits.
Abstract: 1.There is growing awareness that biological control carries risks as well as benefits, but
there are few data on below-ground effects of inundative insect pathogens. We addressed
this issue using entomopathogenic nematodes and the soil nematode community in a
turfgrass ecosystem as a model.
2. Application of Heterorhabditis bacteriophora strain GPS11, Heterorhabditis bacteriophora
strain HP88 and Heterorhabditis indica strain LN2 significantly reduced the abundance, species richness,
diversity and maturity of the nematode community by reducing the number of genera and
abundance of plant-parasitic, but not free-living, nematodes.
3. Our results are the first to indicate selective suppression of plant-parasitic nematodes
by entomopathogenic nematodes, H . bacteriophora and H. indica , with no adverse
effect on free-living nematodes.
4. In contrast to the entomopathogenic nematode treatments, trichlorfon (a commonly
used insecticide in turfgrass) reduced the number of genera, abundance and diversity of
the nematode community by adversely affecting both plant-parasitic and free-living
nematodes.
5. The reduction in abundance and diversity of plant-parasitic nematodes without
any adverse effect on free-living nematodes that play a role in nutrient cycling, can be
considered as a beneficial non-target effect of entomopathogenic nematodes. The
mechanisms causing such an effect need to be elucidated in future studies.
Abstract: Effects of live and dead (heat-killed) infective juveniles (IJs) of the entomopathogenic nematode Steinernema carpocapsae on nematodes associated with boxwood Buxus spp. were evaluated in field experiments during 1999 and 2000. Both living and dead IJs of S. carpocapsae were equally effective, causing more than 50%reduction in total populations of plant-parasitic nematodes relative to the control 15 and 30 days after treatment in both years. No significant differences were observed between reductions in populations of plant-parasitic nematodes following entomopathogenic nematode and chemical nematicide (ethoprop) treatments. In 2000, populations of Criconemella,Hoplolaimus, Longidorus, and Rotylenchus were significantly reduced in all treatments relative to the control 30 days after treatment. However, in 1999 these genera were unaffected by treatments even though total plant-parasitic nematode population was decreased. The population of Tylenchorynchus was significantly reduced in all treatments 30 days after treatment in 1999. Further, the population of Tylenchus was significantly reduced in ethoprop and dead S. carpocapsae treatments 15 days after treatment relative to the control whereas the population ofAphelenchoides was unaffected by these treatments in 1999. Live S. carpocapsae showed no significant effect on the population of both these genera either 15 or 30 days after treatment in 1999. No viable symbiotic bacteria were observed in the dead nematodes used in this study indicating that dead nematodes alone or dead nematodes in combination with dead symbiotic bacteria produced the suppressive effect. In contrast to the plant-parasitic nematodes, populations of non-stylet-bearing nematodes were not affected by the application of entomopathogenic nematodes. Although ethoprop reduced population of non-stylet-bearing nematodes relative to the untreated control 15 days after treatment in 2000, no significant differences were observed 30 days after treatment. These findings suggest that allelochemicals produced by dead or live nematodes and/or by their symbiotic bacteria may be selectively acting against plant-parasitic nematodes. Our results demonstrate that both live and dead infective juveniles of S. carpocapsae may provide a possible control strategy for plant-parasitic nematodes on boxwood.
Abstract: Biological pest control using entomopathogenic nematodes has been thought to be ecologically
safe and risk-free. However, there is little information on impact of these biological control agents
on non-target soil organisms, especially the soil nematodes. We evaluated the response of nematode
communities in turfgrass ecosystems to inundatory application of native (Heterorhabditis
bacteriophora strains HP88 and GPS11) and exotic (H. indica) species of entomopathogenic
nematodes in comparison to application of a chemical insecticide, Trichlorfon (Dylox 80). Application
of both native and exotic species of entomopathogenic nematodes resulted in a decrease in
the population of plant-parasitic nematodes but the population of free-living nematodes was unaffected.
In contrast, the application of chemical insecticide significantly decreased the population
of both plant-parasitic and free-living nematodes with greater reduction in the population of
free-living nematodes. These results show the beneficial (non-target) effect of the application of
entomopathogenic nematodes in turfgrass. The possible reasons for the differential response of soil
nematode communities to application of entomopathogenic nematodes (native and exotic species)
and chemical insecticides are discussed.
Abstract: The infectivity of an Indian isolate of Pasteuria penetrans (PMI-1) to isolates of the entomopathogenic nematodes Steinernema sp. and Heterorhabditis sp. was tested in aqueous suspensions. Spores of P. penetrans did not attach to any of the entomopathogenic nematodes even after 72 hours of exposure at 25 deg C, while in the case of Meloidogyne incognita, from which the bacterium was originally isolated, spore attachment was observed after 24 hours of exposure. These results indicate that P. penetrans, a parasite of phytonematodes, does not adversely affect entomopathogenic nematodes.
Abstract: Sugarcane byproducts (bagasse, trash and pressmud) were separately evaluated (against sorghum grains as control) as substrates for mass multiplication of the biocontrol agents Trichoderma viride ITCC 1433 (used against fungal pathogens of crops) and Paecilomyces lilacinus (used against nematodes). All the substrates tested supported the multiplication of both the fungal species and yielded suitable population densities for field application. Best multiplication of T. viride (3.1 X 108 cfu/g) occurred on bagasse, and that of P. lilacinum (2.18 X 108 cfu/g) occurred on pressmud; these populations were much higher than those on sorghum grains (5 X 106 and 1 X 106, respectively).
Abstract: Four sugar factory zones of Tamil Nadu, India: Nellikuppam, Pugalur, Pennadam and Periasevalai were surveyed to study the distribution of Hoplolaimus spp. which were the predominant nematodes occurring in all the zones surveyed. The absolute frequency of Hoplolaimus spp. ranged from 40-72 and the absolute density ranged from 120-360 nematodes/100 cc soil.
Abstract: Glomus fasciculatum at 500g/m2 inoculum and castor (Ricinus communis) oilseed cake at 200 and 400g/m2 were evaluated singly and in combination for the management of M. incognita on tomato. Integration of G. fasciculatum with castor cake resulted in a significant reduction in root galling and fecundity of M. incognita and an increase in root colonisation by endomycorrhiza
Abstract: All the species of nematode antagonistic fungi tested, exhibited phosphate solubilization activity. Compared with Aspergillus awamori, Paecilomyces lilacinus recorded 30% higher phosphate solubilization, while the other species recorded 20-40% less activity.
