Flower Colour Changes in Lantana camara

Lantana camara flowers undergo colour change subsequent to anthesis.In the colour variant selected for the present study, pink buds,yellow newly-opened flowers and ageing orange, scarlet and magentaflowers are found in the same inflorescence. The flower pigmentswere chemically analysed and identified as delphinidin monoglucosideand ß-carotene. Thrips are regular pollinators of Lantana under Delhi conditions.Pollination was identified as the trigger for rapid anthocyaninsynthesis. Even the presence of one pollen grain on the stigmaof a yellow flower was sufficient to cause colour change. Injectionof a suspension of pollen into flowers opened in vitro causedpigment changes. An extract of Lantana pollen was also ableto simulate the effect of pollination, suggesting the involvementof a pollen factor. The post-pollination shift in petal colourationis caused by the masking of carotenoids by differential amountsof anthocyanin. As thrips are attracted to only yellow flowers,chromatic changes play a role in conserving pollinator energy. Key words: Anthecology, Floral pigments, Lantana camara, Pollination     

Comparative developmental morphology of two populations of Ceratophyllum L. (Ceratophyllaceae) and their taxonomy

Developmental morphology of two natural populations of Ceratophyllum inhabiting the waters of Delhi has been investigated under natural conditions and in aseptic culture. Both the populations show an extreme degree of adaptability to hydrophily. The embryo is unusually highly developed and contains 12–14 whorls of leaves and a few lateral buds. The two populations differ significantly in colour and dichotomy of leaf; structure and position of male flowers; number, position and colour of horns on the fruit; stylar length and distribution of sexes. The latter two parameters are probably responsible for the reproductive isolation of the populations, despite their sympatric association. On account of these differences, the two populations are assigned to two distinct species C. demersum L. and C. echinatum Gray, respectively and their taxonomy is discussed; C. echinatum is a New World species not previously recorded from India.     

Induction of bacterial blight (Xanthomonas oryzae pv. oryzae) resistance in rice by treatment with acibenzolar-S-methyl

The role of the plant defence activator, acibenzolar‐S‐methyl (ASM), in inducing resistance in rice against bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) was studied. Application of ASM induced resistance in rice to infection by Xoo. When the pathogen was clip‐inoculated to the rice plants, it caused bacterial leaf blight symptoms in the untreated control. However, in the rice plants pretreated with ASM, infection was significantly reduced. Induced systemic resistance was found to persist for up to 3 days in the pretreated rice plants. Increased phenolic content and accumulation of pathogenesis‐related (PR) proteins, viz. chitinase, β‐1,3‐glucanase and thaumatin‐like protein (TLP; PR 5) were observed in rice plants pretreated with ASM followed by inoculation with Xoo. Immunoblot analysis using rice TLP and tobacco chitinase antiserum revealed rapid induction and over‐expression of 25 and 35 kDa TLP and chitinase, respectively, in rice in response to pretreatment with ASM followed by Xoo inoculation. Based on these experiments, it is evident that induction of disease resistance in rice was accelerated following treatment with ASM.     

Prospective role of insecticides of fungal origin: Review

Advances in the application of microbial‐based technology in insect pest management assist us to counter problems created by the application of chemical pesticides. These are mainly strong environmental effects, resistance development and high costs. Among the microbial pesticides, fungal pesticides are now preferred as they are target specific, ecofriendly, lacking in toxic residue and are economical. Being numerous with great diversification, entomopathogenic fungi therefore have great potential to control a large variety of insect pests. Fungi are applied directly in form of spores, mycelia or blastospores or by their metabolites (mycotoxins). Both approaches have very promising roles in insect pest management. However, there are three main obstacles in the development of fungal pesticides: (i) scant production of mycotoxins; (ii) carcinogenic mycotoxicosis in non‐target organisms; and (iii) slow effectiveness. Therefore, to eliminate these problems, attention has recently been paid to a synergistic approach to combating insecticide resistance. Next to synergism, genetic manipulation is also used to enhance the pathogenicity and virulence of fungal insecticides. However, the key risk associated with the release of recombinant microorganisms into the environment is that the novel organism may have unforeseen undesirable characteristics. Therefore, the introduction of synergists in pest control could have great benefit both economically and ecologically. An ideal synergistic approach is the mixing of more than two accelerating components together, i.e. tripartite or multiple synergism to enhance effectiveness. Thus, synergistic approaches have a bright future and require further research and financial support.     

Origin and Development of Secondary Capitula in Calendula officinalis L. in Response to Gibberellic Acid

Foliar application of gibberellic acid greatly enhanced theformation of secondary capitula. The proportion of primary capitulashowing this feature increased from 6% in the controls to 28,58, and 54% at 100, 250, and 500 parts 10^–6 GA₃, respectively.Secondary capitula were initiated either along the peripheryor in the centre of the receptacle or from both; their totalnumbers for 15 plants per treatment were 53, 215, 660, and 404in response to 0, 100, 250, and 500 parts 10^–6 GA₃, respectively.Secondary capitula were smaller and had fewer disc florets andfruits, particularly of the ‘wingless and small’type. Tertiary capitula, not observed in nature, formed on 2.72and 3.21% of the secondary capitula on plants sprayed with 250and 500 parts 10^–6 GA₃.The formation of a secondary inflorescencemeristem in treated plants in place of a floret primordium canbe detected histologically early in its development, and itspattern of development resembles that of the primary capitulum.     

Pollination biology and breeding system of Acacia senegal

Phenology, pollination biology and breeding system were investigated in three populations of Acacia senegal located in Delhi and Rajasthan. Flowers emit a mild fragrance and produce a minute quantity of nectar. The stigma is wet non-papillate, cup-shaped and generally accommodates one polyad with 16 pollen grains. The style is solid. The mass effect created by the brush type of blossoms attracts a wide variety of insects, of which the giant Asian honeybee, Apis dorsata , is the effective pollinator. Manual in vivo pollination studies have shown that the species is self-incompatible. Self-incompatibility appears to operate inside the embryo sac. Under natural conditions fruit set is as low as 0.36%. Insufficient pollination is the main cause of low fruit set. Manual xenogamous pollinations substantially improve fruit set to 30%