Dynamics of cotton insect pests and natural enemies

Crop Pest Interactions :

Developed and validated Genotypic Resistance Ratio (GRR) technique to evaluate cotton breeding materials against bollworms that quantifies the combined plant resistance mechanisms to cotton insect pests including the tolerance trait of ?compensatory growth' in response to bollworm damage.

Loss assessment:

Avoidable losses due to sucking pests in cotton variety LRA 5166 and hybrid NHH 44 ranged between 15-22% and 5-18% respectively whereas due to bollworms ranged between 30-35% in hybrid and between 25-30% in variety. A linear relationship and significantly positive correlation was observed between bacterial blight intensity and losses in seed cotton yield. On susceptible cultivar a potential loss vary from 9.1 to 32.29% with an average loss of 18.07%.

Development of weather-based forewarning systems for crop pests and diseases:

  • Greater than 70% relative humidity during August-September months and un-seasonal excess rainfall during the season distributed on many rainy days and rainfall amount more than 50 mm during October results in outbreak of H.armigera. Maximum temperature greater than 33 0 C, morning relative humidity less than 70%, evening relative humidity more than 40% and minimum temperature less than 12 0 C during standard weeks of 40, 41, 43 onwards, 48 and 49, respectively led to the severity of P.gossypiella attack. Factors affecting disease onset and development were identified in order to develop prediction and forecasting models for bacterial blight. High disease intensity was favoured by maximum temperature of 29.4-34.9 0 C, minimum temperature of 21.7-24.2 0 C, Maximum relative humidity 81-93%, minimum relative humidity 55-87% and 1-6 rainy days.
  • An Expert System for Indian Cotton Insect Pest Management (ICOTIPM) for diagnosis of insect pests was developed to determine the population size or damage through sampling methods to use with ETL and select ETL based insecticidal control measures.

Variability among the pests :

Mitochondrial DNA studies revealed the presence of 18 haplotypes in Indian H.armigera. PCR RFLP with Rsa 1 was able to distinguish H.armigera from H.assulta in their morphological indistinguishable stages. The non-cotton strains of H.armigera preferred to feed on red gram and chickpea over cotton and in inter strain crosses the female moth influences the feeding preference of the progeny.

Host Resistance :

A total of 3000-5000 Gossypium hirsutum and G.arboreum lines have been screened against insect pests and diseases and many tolerant, resistant and immune lines were identified.

Xanthomonas axonopodis pv malvacearum(Xam) :

Fifteen races of Xam on the basis of differential host reaction have been recorded in India. Races 10 and 18 are most virulent and predominant. First molecular evidence of biotype variability within race 18 has been observed. Pathological evidence-At least ten biotypes evolved based upon growth curve analysis, rep-PCR, RAPD, plasmid profiles and RFLP analysis.

Ramularia areola:

Variability in R.areola was recorded on the basis of morphological or cultural characters host response to cross inoculation and polymorphism in RAPD-PCR profiles.

Resistance to insecticides:

Resistance to cry 1Ac has been recorded from any of the Indian populations of H.armigera or Earias sp.despite cultivation of Bt cotton for the last five years until 2007.

Characterization of new diseases:

  • Extensive investigations on new wilt disease of cotton showed that the malady was a physiological disorder that usually manifests when there is sudden downpour following a dry spell. Documentation of symptoms, factors affecting onset of the malady, ways of ameliorating the disorder were reported.
  • Late-season Phoma blight, a new disease of cotton was reported for the first time. Detailed symptoms of the disease with various characteristics features were documented.

Biochemical marker of disease resistance:

Critical biochemical markers for grey mildew resistance in diploid cotton were identified. The resistant cotton were characterized not only by their higher constitutive levels of Phenylalanine ammonia lyase and the phenolics catalyzed by the enzyme, but also their inherent rapid inducing ability when invaded by the pathogen.

Molecular basis of pathogenicity of Xam

  • Genes governing pigmentation, exopolysaccharide production and pathogenicity in Xanthomonas axonopodispv. Malvacearum (Xam) have been reported by us for the first time to be plasmid-borne.
  • Two plasmid-borne pathogenicity genes pthN and pthN2 were successfully cloned and characterized.pthN (3.6 kb) is completely sequenced and available in GenBank (AF016221).
  • The genes cloned from Xam strain are perhaps the first genes cloned as pathogenicity genes unlike all other members, which were cloned as avr genes. Cloning, characterization and sequencing of pathogenicity genes in a strain of Xam and delineation of its function lead to understanding of vital aspects of cotton- Xam interactions.

Races specific molecular marker of Xam:

RFLP marker, capable of identifying the most virulent race 18 strain of Xam has been developed.

PCR detection of CLCuV:

A pair of primer designed to detect CLCuV in infected cotton plants as well as symptom less host by amplification of a 0.7 kb coat protein gene of the virus has been developed. The PCR protocol is simple and can be accomplished within 1.44h.

Immunological detection of CLCuV:

Simple tissue imprint blotting protocol for detection of CLCuV infection is developed. The twig imprints of the infected and healthy plants can be observed by chromogenic detection using anti-CaLCuV (Cabbage leaf curl virus) antibody.

Documentation of CLCuV symptoms on cotton:

Six different symptoms types of cotton leaf curl virus disease viz., upward and downward curling of lamina, severe and mild curling, vein-thickening and enation, were documented based on a survey of disease in status of Punjab, Haryana and Rajasthan, where the disease is prevalent.

Characterisation of CLCuV strains:

Sequencing of viral genomes from six different symptomatic plants revealed wide variability in nucleotide sequences of DNA A and ß-DNA indicating possibilities of existence of different strains capable of inducing variable symptoms and disease severity.

Insecticide Resistance Detection Kits:

Eleven kits to detect resistance to pyrethroids, Endosulfan and methomyl were developed which include 4 SCAR markers, 3 ELISA kits, 2 dot-blot

Development of detection Kits

Bt detection kits:

Six kits namely: Bt-Express, Bt-Quant, Bt-Detect, Bt-Zygosity, Bt-Express-II and Bt-Elisa II have been developed and commercialized. A Bt referral lab was opened by Government of India in the Institute. And 2 immunochromatographic dip-sticks. The immunochromatographic kits were distributed to immunochromatographic kits were distributed to entomologists of State Agricultural Universities for field validation. Resistant strains selected with cry1Ac exhibited a broad-spectrum resistance, to a variable degree, to almost all the Cry1 toxins tested but showed an unchanged susceptibility pattern to cry2Ab. A near isogenic cry1Ac-line exhibited some amount of cross-resistance to cry2Ab. Joint toxic action studies indicated that none of the Cry1 toxin combinations displayed any significant synergism.

Kits to detect quality of spurious insecticides formulations:

Eight kits, which include ELISA as well as dipstick to test the quality and residue of pyrethroids and Endosulfan, have been developed.

PCR Detection of Fusarium oxysporum f.sp.Vasinfectum:

PCR method was used for detection of Fusarium oxysporum f.sp.vasinfectum from cotton seed. This method can be used in quarantine testing of seed material.

PCR Detection of bacterial blight pathogen Commercialization of Xanthomonas axonopodis

Pv. malvacearum detection kit:

A ready-to-use PCR kit for detection of strains of Xanthomonas axonopodis pv. malvacearum has been approved by the Institute for patent filing. PCR-mix was able to support amplification of 0.4kb diagnostic fragment without any loss in efficiency even after 12 months when stored at -20 0 C.The kit was successfully validated at seven research labs of ICAR Institutes and SAU's. The kit is routinely used to detect the pathogen strains and also to differentiate it from morphologically alike yellow colored non-Xanthomonads that are consistently associated with cotton and encountered in cultures as contaminants. An application has been filed for patenting of the invention.

Biological control

  • The mass multiplication protocols for HNPV, Crysoperla carnea and Trichogramma were standardized. Further the institute facilitated and supported the establishment of biocontrol factories in Vidarbh region of Maharashtra.
  • Full-fledged world class in sectary set up for the first time where rearing of bollworms has been successfully carried out for more than 20 generations. The in sectary maintains up to 53 cultures of Helicoverpa and 20 cultures of spotted bollworms.
  • Near isogenic lines of Helicoverpa with reference to specific insecticide groups such as Endosulfan, methomyl, Quinalphos, cry 1 Ac etc. are being maintained. Insecticide susceptible reference strains of Helicoverpa are being maintained.
  • Farmers friendly Bt production technology popularly known as Bt bucket was developed which was subsequently converted to Bt drum.
  • Out of 148 bacterial isolates 5 were found to be very inhibitor of Xam in vitro. Eight potential isolates of Pseudomonas fluoresces and one isolate of Bacillus firmus isolated were found to be effective against Xam. 9 selected isolates provided high levels of antagonism against Xam in vitro.
  • Of the 16 indigenous isolates of Entomopathogenic nematodes belonging to Steinernema and Heterorhabditis spp.collected and evaluated against H.armigera, five were found to be effective against H.armigera at 10-15 infective juveniles per insect larva, under laboratory conditions. Two photorphabdus isolates symbiont of entomophogenic nematodes were recorded to be antagonistic towards sucking insect pests of cotton.

Development of management strategies for Stem Weevil (Pempherulus affinis Faust)

  • Several management strategies were developed to control the stem weevil incidence:
  • Reduced cropping intensity and high seed rate.
  • Destroying affected and dried plants and earthing upto prevent oviposition.
  • Application of Neemcake (150 Kgs/ha) +Carbofuran(1.0 Kg a.i/ha) at 15-20 days after sowing (DAS) and stem drenching with Neem seed extract 5% from 45 DAS,4 times at weekly interval or drenching with Chlorpyriphos 0.1%,4 times at weekly interval from 45 DAS.

Biochemical mechanism of resistance to bollworms

  • Squares of Bollworm tolerant genotypes possessed lesser protein,sugars and higher levels of secondary metabolites like condensed tannin, gossypol and phenolics as compared to susceptible cultivars.

Developmental biochemistry of cotton pest/disease interaction

  • Seed dressing insecticides imidacloprid and Chlothianidine helped in better metabolic status of cotton seedling due to enhanced peroxides, acid and alkaline phosphates activities.
  • Carbosulfan and Thiomethoxam helped in enhancement of Nitrate Reductase activity and soluble protein content.
  • Variation seen in Polyphenol oxidase, Superoxide dismutase and Catalase enzymes during interaction of cotton genotypes with isolates of grey mildew is useful in diagnostic tool development.

Integrated Pest Management (IPM)

  • Established nucleus and cluster villages for promotion and implementation of IPM practices.
  • Implementation of two pest management approaches viz., IPM with biocontrol options including ETL based insecticidal sprays and need based chemical sprays were undertaken in addition to IPM on Bt cotton.
  • Created awareness on field scouting and need based chemical interventions through weekly visits and through on farm days.
  • Created off season management practices and refined the package for seasonal cotton pest management.

Insecticide Resistance Management (IRM)

  • Strategies were implemented in an area of about 200,000 ha in fields of 132000 farmers of 1682 villages in 30 districts of 10 cotton growing states over a period of 6 years during 2001-2007.The overall benefit due to the project implementation was estimated at Rs.130 crores, accured from Rs.80 crores due to yield increase and Rs.50 crores from reduced insecticide usage.

Information compiled, Page designed and developed by M. Sabesh, CICR