Host Plant Resistance Mechanisms Research Articles

Jasmonic Acid and Salicylic Acid improved resistance against Spodoptera frugiperda Infestation in maize by modulating growth and regulating redox homeostasis

Exploring host plant resistance and elevating plant defense mechanisms through the application of exogenous elicitors stands as a promising strategy for integrated pest management. The fall armyworm, a pernicious menace to grain crops in tropical and subtropical regions, stands as a formidable threat due to its capacity for devastation and a wide-ranging spectrum of host plants. There is no literature regarding artificially induced resistance in maize against fall armyworm (Spodoptera frugiperda) by exogenous application of phytohormones. The present investigation was performed to evaluate the role of jasmonic acid (JA) and salicylic acid (SA) on two maize hybrids namely FH-1046 and YH-1898 against fall armyworm. Results showed that plant height, biomass and lengths, fresh and dry weight of root shoot which decreased with armyworm infestation improved with phytohormonal application. JA treatment resulted in a higher increase in all attributes as compared to SA treatment. Improvement in relative water contents, photosynthetic pigments and pronounced levels of phenol and proline accumulation were observed in infested plants after JA treatment. Infested plants recovered from oxidative stress as JA application activated and increased the antioxidant enzyme activity of superoxide dismutase, peroxidase and polyphenol oxidase activity in both FH-1046 and YH-1898 . The oxidative stress reduction in infested plants after JA treatment was also evident from a fair decrease in MDA and H2O2 in both varieties. The SA and JA mediated genes expression was studied and it was found that in FH1046 maize cultivar, JA dependent genes, particularly marker genes PR1 and Lox5 were highly expressed along with TPS10 and BBT12. Whereas SPI, WRKY28, ICS and PAL were shown to be activated upon SA application. Evidently, both JA and SA elicited a robust defensive response within the maize plants against the voracious S. frugiperda, which in consequence exerted a discernible influence over the pest's developmental trajectory and physiological dynamics. A decrease in detoxification enzyme activity of the insects was observed after feeding on treated plants. Moreover, it was recorded that the survival and weight gain of FAW feeding on phytohormone treated maize plants also decelerated. In conclusion, FH-1046 was found to be more tolerant than YH-1898 against fall armyworm infestation and 1 mM JA was more effective than 1 mM SA for alleviation of fall armyworm stress. Therefore, it was inferred that phytohormones regulated redox homeostasis to circumvent oxidative damage and mediate essential metabolic events in maize under stress. To our current understanding, this study is the very first presentation of induced resistance in maize against S. frugiperda with the phytohormonal application (JA and SA).

Field evaluation of UASD Bt-cotton Event-78 based early segregating generations for cotton leaf hopper

UASD Bt cotton Event-78 based early segregating generations (F2 & F3) derived from three diverse crosses were evaluated for field incidence of cotton leaf hopper during kharif-2021 & 2022 at Agricultural Research Station, UAS, Dharwad. A total 600 F2 plants from the crosses viz., UASD Bt-78 х DHS-29, UASDBt-78 х Suvin and Suvin х UASD Bt-78 were screened of which 103,100 and 102 plants respective to the three crosses were found to be resistant. The segregation of F2 population for the jassid tolerance deciphered the implicit “Inhibitory epistasis” mechanism of host plant resistance. Further evaluation of F3 families of these crosses leads to identification of 103 resistant lines from all the three crosses, the mean leafhopper population ranges from 0.67- 2.67 leafhoppers / 3 leaves with the LHRI score of 1.

Computational analysis of 16D10 effector peptides from root-knot nematodes and their interaction with Mi resistance (R) protein through molecular docking

Plant-parasitic nematodes, especially root-knot nematodes (RKNs), pose significant threats to global agriculture, affecting both the quantity and quality of crop yields. Central to the parasitism strategy of RKNs is the deployment of effector proteins, such as the 16D10 peptide, which interact with host plant resistance mechanisms. This study focuses on the computational analysis and molecular docking of 16D10 effector peptides derived from major RKN species (M. incognita, M. arenaria, M. hapla, M. javanica, and M. chitwoodi) to explore their interaction with the Mi resistance protein in tomatoes. Initial bioinformatics assessments included sequence retrieval, multiple sequence alignment, and phylogenetic analysis, utilizing tools such as CLUSTALW and the MEME Suite. Notably, our phylogenetic analysis revealed a close evolutionary relationship between M. incognita and M. chitwoodi, contrasting with other RKN species based on both DNA and protein data. Subsequent, in silico 3D modeling and docking studies, conducted using Chem-Sketch and MOE software, provided insights into the structural basis of the interaction between 16D10 peptides and the Mi protein. Our findings indicate that these interactions could play a crucial role in the modulation of plant defense mechanisms, potentially leading to effector-triggered susceptibility (ETS). This study not only enhances our understanding of nematode-host interactions but also aids in the development of novel strategies for managing RKN infections in economically important crops.

Update on the Basic Understanding of Fusarium graminearum Virulence Factors in Common Wheat Research.

Wheat is one of the most important food crops, both in China and worldwide. Wheat production is facing extreme stresses posed by different diseases, including Fusarium head blight (FHB), which has recently become an increasingly serious concerns. FHB is one of the most significant and destructive diseases affecting wheat crops all over the world. Recent advancements in genomic tools provide a new avenue for the study of virulence factors in relation to the host plants. The current review focuses on recent progress in the study of different strains of Fusarium infection. The presence of genome-wide repeat-induced point (RIP) mutations causes genomic mutations, eventually leading to host plant susceptibility against Fusarium invasion. Furthermore, effector proteins disrupt the host plant resistance mechanism. In this study, we proposed systematic modification of the host genome using modern biological tools to facilitate plant resistance against foreign invasion. We also suggested a number of scientific strategies, such as gene cloning, developing more powerful functional markers, and using haplotype marker-assisted selection, to further improve FHB resistance and associated breeding methods.

Comparison of Shoot Fly Resistance QTLs in Sorghum Introgression Lines Using SNP Genotyping

Shoot fly is a major pest in sorghum that causes significant annual yield loss. Use of pesticide to control this pest is an expensive and environmentally unsafe approach. Present study investigated the host plant resistance mechanism to develop shoot fly resistance (SFR) lines through transfer of shoot fly resistance QTLs (glossiness, trichome density, ovipositional non-preference) using SSR marker assisted backcrossing. Genomic regions for SFR showed four QTLs on SBI 01, SBI 07, SBI 05 and SBI 10 contributing up to 11.5%, 18.3%, 14% and 14.7% phenotypic variation. But QTLs on SBI 05 and SBI 10 for glossiness and trichome density are the major QTLs for which 10 SNPs have been designed. In earlier studies, three QTL regions associated with shoot fly resistance were successfully introgressed into elite cultivar SPV 1411 (Parbhani Moti) and a B line ICSB29004 using donors viz. J2658 (SBI01), J2614 (SBI10), and J2714 (SBI07) (which are derivatives of BTx 623). Phenotyping of introgression lines (ILs) led to the identification of resistant lines for each QTL region present on chromosome SBI-01, SBI-07 and SBI-10. Hence, in this study we have analysed the above developed ILs using single-nucleotide polymorphism (SNP) markers tightly linked to shoot fly resistant QTLs. The results showed that introgression lines with QTL present on chromosome SBI-10 were segregating for favorable alleles for leaf glossiness and for trichome density in homozygous condition. Other introgression lines with QTLs on chromosome SBI-01 and SBI-07 for component traits - oviposition non-preference, seedling vigor are segregated for glossiness trait also thus showing the transfer of non-targeted region, which in this case proved beneficial for SFR. This study showed that these SNPs can be used to analyze introgression lines and can be used as genomic markers for early generation selection of shoot fly resistance lines.

Role of Nutrients in Plants, Its Deficiency and Management

Plants like all living beings need energy source. The energy needed by the plants are uptaken in the form of 17 essential elements. Among which Carbon, hydrogen, and oxygen are derived from surrounding. The remaining 14 essential necessary elements are supplied either from rhizosphere and soil organic matter or by important organic or inorganic fertilizers or value added soil amendments. Plants start showing nutrient deficiency when they do not get the necessary nutrients. More nutrient use can also show poor growth because of toxic chemicals in soil. So, required amount of use and the placement of nutrients is necessary. Soil and plant tissue tests have been developed to assess their’ nutrient content. By analysis, plant scientists determined the nutrient need of plant in a given soil. In addition to the levels of available nutrients, soil pH shows its role in nutrient availability and elemental toxicity in soil. In the majority, disease effect in crop plants has been reduced by fertilizer application. This is due to the host plant tolerance or resistance mechanisms involve these nutrients. When the plants were deficient, the application of nutrients significantly reduced disease.

Deciphering host plant resistance mechanisms of rice genotypes resistant against Brown Planthopper

Deciphering host plant resistance mechanisms of rice genotypes resistant against Brown Planthopper

Common resistance mechanisms are deployed by plants against sap-feeding herbivorous insects: insights from a meta-analysis and systematic review

Despite their abundance and economic importance, the mechanism of plant resistance to sap-feeding insects remains poorly understood. Here we deploy meta-analysis and data synthesis methods to evaluate the results from electrophysiological studies describing feeding behaviour experiments where resistance mechanisms were identified, focussing on studies describing host-plant resistance and non-host resistance mechanisms. Data were extracted from 108 studies, comprising 41 insect species across eight insect taxa and 12 host-plant families representing over 30 species. Results demonstrate that mechanisms deployed by resistant plants have common consequences on the feeding behaviour of diverse insect groups. We show that insects feeding on resistant plants take longer to establish a feeding site and have their feeding duration suppressed two-fold compared with insects feeding on susceptible plants. Our results reveal that traits contributing towards resistant phenotypes are conserved across plant families, deployed against taxonomically diverse insect groups, and that the underlying resistance mechanisms are conserved. These findings provide a new insight into plant–insect interaction and highlight the need for further mechanistic studies across diverse taxa.

Molecular assessment of selected rice genotypes to study their reaction to brown planthopper and underlying resistance mechanisms

Six promising rice genotypes (IET 23993, GSR 234, RNR 23079, Bobhu Kongbu, HHZ 25-DT-1-DT-1 with HHZ 25 SAL DT 1-DT-1) quality yield attributes were identified as moderately resistant to brown planthopper after preliminary studies based on Standard Seed box screening test (SSST). These six genotypes were further investigated to determine the kind of host plant resistance mechanism(s) operating in them along with two resistant checks viz., PTB33 and BM71 and one susceptible check i.e., TN1. IET 23993 was found to possess all three types of resistance mechanisms viz., antixenosis, antibiosis and tolerance while the genotype GSR 234 exhibited only two types of mechanisms i.e., antixenosis and tolerance. The other four genotypes viz., RNR 23079, HHZ 25-DT-1-DT-1, HHZ 25 SAL DT 1-DT-1, and Bobhu Kongbu exhibited moderate level of either antibiosis or antixenosis mechanisms. Molecular analysis using specific SSR markers could able to assess the reason for exhibition of all three types of resistance mechanisms was due to likely presence of five Bph resistance genes in IET 23993.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops.

Simple SummaryThe tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Maize streak virus research in Africa: an end or a crossroad.

The economic importance of the maize streak virus disease to the African maize production dynamic is to be appreciated now more than ever due to the preponderant influence of a changing climate. Continued dependence on a single major-effect quantitative trait locus (QTL) called Msv1 on Chromosome 1 of Maize (Zea mays L.) is not guaranteed to ensure durable resistance to the causal pathogen. With over ten decades of research on the disease and its associated host plant resistance mechanisms, it is pertinent to consider future approaches to attaining durability by looking to the synergistic roles of moderate- and minor-effect QTLs located on other chromosomes so as to facilitate a secure farming system for sub-Saharan Africa. For this review, more than 40 publications relating to maize streak disease research were methodically analysed with about 30% making specific reference to conventional, molecular and transgenic approaches employed in introgressing, maintaining and improving streak resistance in maize. A meta-analysis of mapped QTLs conferring streak resistance was conducted in a bid to reveal any inter-dependence or co-localization of resistant loci and to aid decision-making for marker-assisted breeding. With the changing climatic conditions around the globe, man's preparedness in the event of an epidemic following any evolutionary process in the streak viral genome was determined as insufficient. Modern breeding approaches including gene pyramiding that could be considered in maize breeding programmes to ensure durability for streak resistance were proposed while improving maize for other abiotic stress tolerance, particularly drought.

Characterization of Current Fusarium oxysporum f. sp. vasinfectum Isolates from Cotton in the San Joaquin Valley of California and Lower Valley El Paso, Texas.

Fusarium oxysporum f. sp. vasinfectum race 4 is a causal agent of Fusarium wilt of cotton (Gossypium spp.). This study aimed to characterize the existing distribution and frequency of current field populations of F. oxysporum f. sp. vasinfectum race 4 genotypes in the San Joaquin Valley (SJV) of California and Lower Valley El Paso, TX and examine representative isolates for aggressiveness during different stages of seedling development. A survey was conducted from 2017 to 2019 across 13 locations in the SJV and one location in El Paso, TX during 2018. From the SJV, isolates identified as the F. oxysporum f. sp. vasinfectum race 4 T genotype were dispersed across the SJV, whereas isolates identified as the F. oxysporum f. sp. vasinfectum race 4 N genotype were most frequently isolated from cotton fields in the northern county of Merced. The F. oxysporum f. sp. vasinfectum race 4 isolates from the Texas location were identified as the MT genotype. A selection of representative isolates was evaluated using three inoculation assays (rolled-towel, F. oxysporum f. sp. vasinfectum-infested oat seed, and root-dip inoculation) to test the isolates' abilities to produce symptoms during seedling stages of cotton development. All isolates tested were capable of producing symptoms on cotton; however, isolate aggressiveness varied within and across inoculation assays. In all assays, higher levels of disease development were observed in the moderately susceptible Pima (Gossypium barbadense L.) cultivars (DP-340 or PHY-830) when compared with the moderately tolerant Upland (G. hirsutum L.) cultivar (FM-2334). However, no correlation was found among the different response variables for the rolled-towel assay when compared with the root-dip and infested oat seed assays. These results suggest that different genes are involved in the resistance response during the early seedling development stage measured in the rolled-towel assay compared with the later seedling development stages measured during the root-dip inoculation and infested oat seed assays, revealing the complexity of the Fusarium wilt disease and host-plant resistance mechanisms.

Characterization of Eggplant Genotypes for Different Resistance Mechanisms Against Leucinodes orbonalis.

Host plant resistance mechanisms play an important role in developing cultivars with resistance to the target pests; information regarding morphological and biochemical factors contributing to the resistance is essential for developing pest-resistant cultivars. As a result, we investigated the contribution of various morphological and biochemical characters in forty-two eggplant genotypes against Leucinodes orbonalisGuenée, in Himachal Pradesh, India. Out of all the phenotypic parameters evaluated, pericarp thickness (r = 0.89) has significantly positive correlation with fruit infestation, whereas trichome density had significantly negative correlation (r = - 0.89). Analysis of the biochemical compounds in the eggplant genotypes revealed that total phenols (r = - 0.71), polyphenol oxidase (r = - 0.63), peroxidases (r = - 0.35), phenylalanine ammonium lyase (r = - 0.71) and solasodine (r = - 0.81) had significantly negative correlation with the per cent fruit infestation by L. orbonalis while the reducing sugars (r = 0.66) and non-reducing sugars (r = 0.62) showed a significantly positive correlation. Molecular characterization by random amplified polymorphic DNA (RAPD) primers also revealed the presence of high genetic diversity among different eggplant genotypes, where 17 polymorphic RAPD primers produced a total of 167 amplicons, among which 144 amplicons were polymorphic and 23 monomorphic bands. PCR-amplified DNA fragment size ranged from 100 to 2500 bp, mean polymorphism was 86.42% and the average PIC value was 0.444. Jaccards coefficient-based dendrogram grouped 40 eggplant genotypes into two major clusters. Results also revealed that the resistant genotypes accumulated higher levels of defensive biochemical enzymes such as phenols, PO, PPO, PAL and solasodine to confer insect resistance. Molecular characterization also revealed that genotypes in the present study were genetically diverse and could be used in future breeding and improvement programmes in this crop. Genotypes, IC411485 and IC090951, in particular, can be used as varied parents in breeding programmes to generate improved lines in terms of resistance to L. orbonalis.

Metabolomic Response of Tomatoes (Solanum lycopersicum L.) against Bacterial Wilt (Ralstonia solanacearum) Using 1H-NMR Spectroscopy.

Ralstonia solanacearum is the pathogen responsible for wilting, yield losses, and death in tomato plants. The use of resistant cultivars has been proven as the most appropriate solution to controlling this pathogen. Therefore, further study of host-plant resistance mechanisms in tomatoes is urgently needed. 1H-NMR (nuclear magnetic resonance) spectroscopy combined with multivariate data analysis has been used to identify the biochemical compounds that play a crucial role in the defense mechanisms of tomato against bacterial wilt. Eleven metabolites consisting of amino acids, sugars and organic acids were identified and presented at different concentrations in each cultivar. Leucine and valine were determined as distinguishable metabolites of resistant and susceptible cultivars. Permata and Hawaii 7996 as resistant cultivars had a significant decrease of valine after inoculation about 1.5–2 times compared to the susceptible cultivar (GM2). Meanwhile, the resistant cultivars had a higher level of leucine, about 1.3–1.5 times compared to the susceptible ones. Synthesis of leucine and valine are linked as a member of the pyruvate family. Therefore, the decrease in valine may be related to the higher need for leucine to form the leucine-rich receptor, which plays a role in the plant’s immune system against the bacterial wilt.

Mitigation of bacterial spot disease induced biotic stress in Capsicum annuum L. cultivars via antioxidant enzymes and isoforms

Bacterial spot, caused by a group of Xanthomonads (Xanthomonas spp.), is a devastating disease. It can adversely affect the Capsicum annum productivity. Scientists are working on the role of antioxidants to meet this challenge. However, research is lacking on the role of antioxidant enzymes and their isoforms in the non-compatible pathogen and host plant interaction and resistance mechanisms in capsicum varieties. The present study was conducted to ascertain the defensive role of antioxidant enzymes and their isoforms in chilli varieties Hybrid, Desi, Serrano, Padron, and Shehzadi against bacterial spot disease-induced Xanthomonas sp. The seedlings were inoculated with bacterial pathogen @ 107 CFU/mL, and samples were harvested after regular intervals of 24 h for 4 days followed by inoculation. Total plant proteins were extracted in phosphate buffer and quantified through Bradford assay. The crude protein extracts were analyzed through quantitative enzymatic assays in order to document activity levels of various antioxidant enzymes, including peroxidase (POD), Catalase (CAT), Ascorbate peroxidase (APX), and Superoxide dismutase (SOD). Moreover, the profiles appearance of these enzymes and their isoforms were determined using native polyacrylamide gel electrophoresis (PAGE) analysis. These enzymes exhibited maximum activity in Hybrid (HiR) cultivar followed by Desi (R), Serrano (S), Padron, and Shehzadi (HS). Both the number of isoforms and expression levels were higher in highly resistant cultivars compared to susceptible and highly susceptible cultivars. The induction of POD, CAT, and SOD occurs at the early stages of growth in resistant Capsicum cultivars. At the same time, APX seems to make the second line of antioxidant defense mechanisms. We found that modulating antioxidant enzymes and isoforms activity at the seedling stage was an important mechanism for mitigating plant growth inhibition in the resistant ones.

Screening of sugarcane genotypes against Top Borer (Scirpophaga exerptalis Walker) infestation

Fourty sugarcane genotypes with different period of maturity were evaluated against top borer (Scirpophaga excerptalis Walker) infestation under natural field condition during 2018 and 2019 at National Sugarcane Research Program, Jeetpur, Nepal. The experiment was conducted in alpha-lattice design under natural condition of infestation using Co 0238 as susceptible check. Based on the incidence, 26 genotypes were categorized as less susceptible, eleven genotypes were found moderately susceptible to S. excerptalis. However, among less susceptible genotypes lowest incidence of 3.11 percent was recorded in genotype CoS 8432. Whereas, highest incidence of 25.24 percent was recorded in highly susceptible genotype, CoSe 98255BD 24. Most of the cane genotypes were found low to moderately susceptible, having 5 to 20% incidence of the pest. Whereas, some of the varieties, namely CoH 160 (21.22%), CoSe 95255 BD 24 (25.24%) and BO 150 (22.02%) were found highly susceptible. The mechanism responsible for host plant resistance against top borer is not studied in this experimentation. The study in these aspects is to be conducted to explore the mechanisms of host plant resistance for using these resistant genotypes for breeding purpose.

Morphophysiological and biochemical attributes influence intra-genotypic preference of shoot fly [Atherigona soccata (Rondani)] among sorghum genotypes.

Shoot fly [Atherigona soccata (Rondani)] is a destructive pest of sorghum at the seedling stage and causes huge losses to grain yield and green fodder. The host-plant resistance mechanism is the best approach to reduce the attack of insects in plants. The damage parameters, morphophysiological traits, and biochemical metabolites had been investigated in the leaves and stem of contrasting sorghum genotypes, viz., resistant (IS18551, ICSV705, ICSV700), moderately resistant (PSC-4), and susceptible (SWARNA and SL-44) at 15 and 21days after emergence (DAE) against shoot fly infestation. The resistant genotypes recorded lowest shoot fly oviposition and incidence (0.3-0.7 eggs plant-1 and 10-15%) than the susceptible genotypes (2.4-3.0 eggs plant-1 and 70-80%), respectively. The susceptible genotype SWARNA recorded 50% and 80% higher deadheart formation than the resistant genotype IS18551 at 15 and 21 DAE, respectively. Resistant genotypes exhibited higher trichome density at adaxial and abaxial part of leaf (118-145 and 106-131) with pink colored leaf sheath (scale 1.50-3.25), glossy leaves (scale1.00-1.25), and lower leaf surface wetness (scale1.25-2.00) compared with susceptible genotype with 49.3-73.3 and 25.3-64.0, scale 2.50-4.00, scale 2.75-3.50, and scale 3.25-4.25 for the respective parameters. Another defense response of sorghum toward the insect attack was modulation of plant metabolism. The infested genotypes responded to insect attack by upregulation of total soluble sugar, total phenol, prussic acid, and chlorophyll content by 1.2-2.1-fold, 1.5-2.0-fold, 1.2-1.3-fold, and 1.2-3.9-fold with more induction in susceptible genotypes at 21 DAE. On the whole, the present study indicates that morphophysiological and biochemical attributes contribute toward the resistance mechanism in sorghum against shoot fly infestation.

Mechanisms of Soybean Host-Plant Resistance Against Megacopta cribraria (Hemiptera: Plataspidae)

A number of soybean varieties traditionally bred for resistance to various soybean arthropod pests have been identified as resistant to Megacopta cribraria (F.) (Hemiptera: Plataspidae). However, the mechanisms of host-plant resistance (HPR) in this system are not understood. The goal of this study was to identify the mechanisms of resistance by examining the role of plant volatile organic compounds (VOCs) and free amino acids (FAAs) among 16 soybean varieties. Choice and no-choice cage experiments identified several soybean varieties that demonstrated antixenosis as well as antibiosis. However, resistance varied over time in certain soybean varieties, such as N02-7002 and PI567352B. Mean nymph number from choice experiments had positive correlations with the FAAs asparagine, tryptophan, alanine, phenylanaline, and serine; negative correlation with leucine and threonine. Four plant volatiles, hexanal, 2-pentylfuran, beta-cyclocitral, and cis-9-hexadecenal, were positively correlated with subsequent nymph development, whereas n-hexadecenoic acid was negatively correlated with nymph number only, in adult choice cage experiments. This study contributes to understanding the mechanisms of HPR through associations with plant VOCs and FAAs in relation to M. cribraria development and provides useful knowledge for developing soybean varieties for M. cribraria management.

Bio-chemicals triggering host preference mechanism against tomato fruit borer, Helicoverpa armigera (H�bner)

Mechanism of host plant resistance in tomato varieties was evaluated and compared against tomato fruit borer, Helicoverpa armigera (Hubner) attack in the Solan district known to be ‘Tomato bowl of Himachal Pradesh’. Eight varieties utilized for the experiment included three self pollinating indeterminate varieties developed by selection (Solan Lalima, Solan Vajar, Palam Pink) and four hybrids (Naveen 2000+, Heem Sohna, Red Gold, Rakshita Yash Tomato). In order to locate the sources for resistance in tomato foliage various macro and micro- nutrients were extracted from these varieties and chemical composition of tomato fruits viz., content of total phenols, titrable acidity, reducing sugars and total sugars were also estimated to compare for varying levels of resistance to Helicoverpa armigera . The content of phenol and sugars in tomato fruits was found to be negatively correlated with fruit infestation with values of correlation coefficient (r = - 0.895) and (r = - 0.650), respectively, indicating that susceptible varieties were low in phenols as well as in sugars. Nitrogen (r = 0.660), potassium (r = 0.679), magnesium (r = 0.698), iron (r = 0.547) and manganese (r = 0.546) content were found to be optimistically correlated with per cent fruit infestation while, phosphorous (r = - 0.857) and zinc (r = - 0.801) content did not favor the fruit borer attack. This observed resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as important components of integrated pest management compatible with other approaches like biological control, cultural control as well as chemical control.

The Probing Behavior Component of Disease Transmission in Insect-Transmitted Bacterial Plant Pathogens.

Insects can be effective vectors of plant diseases and this may result in billions of dollars in lost agricultural productivity. New, emerging or introduced diseases will continue to cause extensive damage in afflicted areas. Understanding how the vector acquires the pathogen and inoculates new hosts is critical in developing effective management strategies. Management may be an insecticide applied to kill the vector or a host plant resistance mechanism to make the host plant less suitable for the vector. In either case, the tactic must act before the insect performs the key behavior(s) resulting in either acquisition or transmission. This requires knowledge of the timing of behaviors the insect uses to probe the plant and commence ingestion. These behaviors are visualized using electropenetrography (EPG), wherein the plant and insect become part of an electrical circuit. With the tools to define specific steps in the probing process, we can understand the timing of acquisition and inoculation. With that understanding comes the potential for more relevant testing of management strategies, through insecticides or host plant resistance. The primary example will be Candidatus Liberibacter asiaticus transmitted by Diaphorina citri Kuwayama in the citrus agroecosystem, with additional examples used as appropriate.