Gaurav Kumar Taggar

Fluctuations in peroxidase and catalase activities of resistant and susceptible black gram (Vigna mungo (L.) Hepper) genotypes elicited by Bemisia tabaci (Gennadius) feeding

Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleryrodidae), is a serious pest of black gram, (Vigna mungo (L.) Hepper), an important legume pulse crop grown in north India. This research investigated the potential role of selected plant oxidative enzymes in resistance/susceptibility to whitefly in nine black gram genotypes. Oxidative enzyme activity was estimated spectrophotometrically from leaf samples collected at 30 and 50 d after sowing (DAS) from whitefly infested and uninfested plants. The enzymes showed different activity levels at different times after the infestation. The results indicated that in general, whitefly infestation increased the activities of peroxidase and decreased the catalase activity. Resistant genotypes NDU 5-7 and KU 99-20 recorded higher peroxidase and catalase activities at 30 and 50 DAS under whitefly-stress conditions as compared with non-stressed plants. The results suggest that the enhanced activities of the enzymes may contribute to bioprotection of black gram plants against B. tabaci infestation. The potential mechanisms to explain the correlation of resistance to whitefly in black gram genotypes with higher activities of oxidative enzymes are also discussed.

Role of catalase, H2O2 and phenolics in resistance of pigeonpea towards Helicoverpa armigera (Hubner)

Rapid generation of superoxide radicals and accumulation of H2O2 is a characteristic early response of plants following perception of insect herbivory signals. Induction of oxidative burst on account of herbivory triggers various defense mechanisms in plants. Response of superoxide and H2O2-metabolizing enzymes and secondary metabolites in nine pigeonpea genotypes to Helicoverpa armigera feeding was investigated. Out of nine, four genotypes were found to be moderately resistant, three were intermediate and two were moderately susceptible. In general, H. armigera infestation resulted in increase in superoxide dismutase activity, H2O2 and phenolics content and decrease in catalase (CAT) activity in leaves, developing seeds and pod wall of pigeonpea genotypes. Peroxidase activity was found only in leaves. Among genotypes, the increase in phenolic constituents was found greater in moderately resistant genotypes than in moderately susceptible genotypes; this might determine their contribution in providing resistance to genotypes against H. armigera infestation. The capability of moderately resistant genotypes to maintain relatively lower H2O2 content and higher CAT activity in pod wall and developing seeds also appeared to determine resistance of genotypes towards H. armigera. Expression of resistance to H. armigera was found to be associated with a negative correlation of H2O2-metabolizing enzymes and phenolics with pod damage as well as with negative association between CAT activity and H2O2 content. A positive correlation found between H2O2 content and pod damage suggested the accumulation of H2O2 in response to pod borer attack. In addition, correlation analysis also revealed a positive association between CAT, phenolic compounds and DPPH radical scavenging activity following pod borer attack; this indicated their contribution in resistance mechanisms against H. armigera herbivory.

Characterisation and inhibition studies of Helicoverpa armigera (Hübner) gut α-amylase

BACKGROUND The survival of a devastating pest, Helicoverpa armigera, is mainly dependent on the availability of α-amylase. Therefore, characterising H. armigera α-amylase and targeting it with effective inhibitors could aid in reducing its damaging effects. RESULTS H. armigera gut possessed four isozymes of α-amylase. The molecular weight of the major purified isozyme ranged from 79 to 81 kDa. The purified enzyme was identified to be α-amylase on the basis of products formed from starch. The optimum pH and temperature were 10.0 and 50 °C respectively. The activation energy was 5.7 kcal mol(-1) . The enzyme showed high activity with starch and amylopectin, whereas dextrins were poor substrates. The Michaelis constant Km with starch, amylose and amylopectin was 0.45, 1.23 and 0.11 mg mL(-1) respectively. ZnSO4 , FeSO4 , CuSO4 , citric acid, oxalic acid and salicylic acid were potent inhibitors. ZnSO4 , salicylic acid and pigeonpea α-amylase inhibitor (∼21.0 kDa) acted primarily as competitive inhibitors, FeSO4 and citric acid displayed mainly anticompetitive behaviour, while CuSO4 and oxalic acid behaved mainly as non-competitive inhibitors. CONCLUSIONS The identification of effective ecofriendly inhibitors could help in managing H. armigera infestation.

Induced resistance by oxidative shifts in pigeonpea (Cajanus cajan L.) following Helicoverpa armigera (Hübner) herbivory.

BACKGROUND Oxidative responses in leaves, developing seeds and the pod wall of nine pigeonpea genotypes were investigated against Helicoverpa armigera feeding. Out of nine genotypes, four were moderately resistant, three were intermediate and two were moderately susceptible genotypes. RESULTS A significant shift in the oxidative status of pigeonpea following herbivory was depicted by the upregulation of diamine oxidase (DAO), polyamine oxidase (PAO) and lipoxygenase 2 (LOX 2) activities. Polyphenol oxidase (PPO) activity was significantly higher in the infested pod wall and leaves of moderately resistant genotypes than in those of moderately susceptible genotypes. H. armigera infestation markedly enhanced phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) activities in wounded tissues. The decline in ascorbate peroxidase (APX) activity and ascorbate content was lower in moderately resistant genotypes than in moderately susceptible genotypes. A significant decrease in LOX 3 activity was also observed in the infested pod wall of moderately resistant and intermediate genotypes. A lower malondialdehyde (MDA) content and higher proline content of the infested pod wall and developing seeds was observed. Higher activities of PPO, PAL and proline content in leaves of uninfested moderately resistant genotypes could either be an unrelated observation or alternatively could help in identifying H. armigera-resistant genotypes. CONCLUSION The increase in activities of PPO, DAO, PAO, PAL and TAL and higher proline and lower MDA content upon herbivory suggested their integrated contribution in providing resistance to pigeonpea against H. armigera.

Nitrate reductase and nitrite as additional components of defense system in pigeonpea (Cajanus cajan L.) against Helicoverpa armigera herbivory.

Amylase inhibitors serve as attractive candidates of defense mechanisms against insect attack. Therefore, the impediment of Helicoverpa armigera digestion can be the effective way of controlling this pest population. Nitrite was found to be a potent mixed non-competitive competitive inhibitor of partially purified α-amylase of H. armigera gut. This observation impelled us to determine the response of nitrite and nitrate reductase (NR) towards H. armigera infestation in nine pigeonpea genotypes (four moderately resistant, three intermediate and two moderately susceptible). The significant upregulation of NR in moderately resistant genotypes after pod borer infestation suggested NR as one of the factors that determine their resistance status against insect attack. The pod borer attack caused greater reduction of nitrate and significant accumulation of nitrite in moderately resistant genotypes. The activity of nitrite reductase (NiR) was also enhanced more in moderately resistant genotypes than moderately susceptible genotypes on account of H. armigera herbivory. Expression of resistance to H. armigera was further revealed when significant negative association between NR, NiR, nitrite and percent pod damage was observed. This is the first report that suggests nitrite to be a potent inhibitor of H. armigera α-amylase and also the involvement of nitrite and NR in providing resistance against H. armigera herbivory.

First report of flower chafer beetle, Oxycetonia versicolor, on pigeonpea and mungbean from Punjab, India

The occurrence of flower chafer beetle, Oxycetonia versicolor (Fabricius) (Scarabaeidae: Coleoptera) damaging the flowers of important grain legumes such as pigeonpea (Cajanus cajan (L.) Millsp.) and mungbean (Vigna radiata (L.) Wilczek) is reported for the first time from Punjab, India. Heavy infestation of these flower beetles at flowering may cause considerable damage to these crops. A mild to moderate level of infestation of 15–17 beetles per ten plants was recorded at the time of peak flowering period on both the grain legumes. Adult beetles devour the flowers and buds, thereby greatly reducing the number of pods that are set. Information on important taxonomic characters of the beetle is highlighted in this report. Careful monitoring and timely reporting on this chafer beetle is necessary to avoid any future outbreak.

Insect Biotypes and Host Plant Resistance

The green plants and herbivorous insects are engaged in a constant struggle for dominance. Humans usually intervene in this struggle by developing pest-resistant genotypes and other pest management tactics. Upon failure of a previously successful tactic to which the insect population has apparently adapted, the latter is often considered to be a novel or distinct entity and termed as a “biotype.” The success of host plant resistance (HPR) strategy is constantly challenged by the occurrence of resistance-breaking insect biotypes. In general, the term “biotype” usually designates an intraspecific group of organisms that are not morphologically distinguishable, but differ by a biological function. Variation among individuals within populations has always been the focus of population genetics. However, the term “biotype” includes the entities that are not consistent either within or between biotypes, and their underlying genetic composition and origins, while generally unknown, are likely heterogeneous within and variable between biotypes. Biotypes may differ in some biological parameters, including detoxification pathways, reproductive rate, dispersal, virus vectoriality, and capacity to damage plants, and are well defined by microsatellite polymerase chain reaction (PCR)-based DNA markers. Insect biotypes feeding on different species of host plants are particularly well documented. To slow down the process of biotype selection, crop cultivars with broad genetic bases are needed. The durability of host plant resistance can be enhanced by identifying a wide array of potential insect-resistant genes and ensuring their incorporation in commercially important cultivars.

Potential Protease Inhibitor Isoforms from Pigeonpea against Helicoverpa armigera Gut Proteases

Ten pigeon pea genotypes (four moderately resistant, three intermediate, two moderately susceptible and one unknown status) were evaluated for their efficacy against bovine trypsin and Helicoverpa armigera (H. armigera) gut proteases. The trypsin inhibitor content in pigeon pea genotypes varied from 147.75 (TIU/g) (AL 201) to 177.85 TIU/g (AL 1495). Sodium dodecyl-polyacrylamide gel electrophoresis (SDS-PAGE) of seed extracts revealed different proteins of molecular weight ranging from 15.6 kDa to 98.5 kDa. Using gelatin SDS-PAGE, six different trypsin inhibitors with bovine trypsin were identified and four of them with relative mobility (Rm) 0.39, 0.78, 0.84 and 0.93 were present in all the ten genotypes. Five H. armigera protease inhibitors (PIs) were detected using the gelatin SDS-PAGE. Four of them also inhibited the bovine trypsin. One (35.3 kDa) was specific only for H. armigera gut proteases. Two protease inhibitors (15.6 kDa and 20.1 kDa) were specific for bovine trypsin. However, it appears that it is the unspecific PI with Rm 0.39 (51.5 kDa) and 0.93 (16.6 kDa) which mainly determine the resistance towards H. armigera in pigeonpea.