Development and use of anchored‐SSRs to study DNA polymorphism in bread wheat (Triticum aestivum L.)

In bread wheat, 21 anchored simple sequence repeat (SSR) primer pairs detecting SSR length polymorphism and 42 anchored SSR primers detecting microsatellite‐anchored fragment length polymorphisms (MFLPs) are reported. Eight bread wheat genotypes were used for detecting polymorphism. The number of alleles in SSR analysis ranged from two to six, with a mean of 2.9 alleles per SSR. The number of polymorphic bands in MFLP ranged from two to 40, with a mean of 12.74 polymorphic bands/primer combination, the SSRs with CT/GA motifs giving the highest level of polymorphism (a mean of 18.37 bands). The average value of polymorphic information content (PIC) was 0.473 for SSRs and 0.061 for MFLP.     

Evaluation of Solanum xanthocarpum extract as a synergist for cypermethrin against larvae of the filarial vector Culex quinquefasciatus (Say)

Cypermethrin and crude extracts of Solanum xanthocarpum were both observed for their larvicidal activity against Culex quinquefasciatus. Petroleum ether extract with lethal concentration (LC)₅₀ and LC₉₀ of 41.28 and 111.16 p.p.m. after 24 h and LC₅₀ 38.48 and LC₉₀ 80.83 p.p.m. after 48 h, respectively, was found to be the most effective, followed by carbon tetrachloride and methanol extracts. LC₅₀ and LC₉₀ for cypermethrin were 0.0027 and 0.0097 p.p.m. after 24 h and 0.0013 and 0.0092 p.p.m. after 48 h of exposure, respectively. Combined formulations were evaluated for synergistic activity and a 1:1 ratio of cypermethrin and petroleum ether extract was observed to be more effective than 1:2 and 1:4 ratios. Combinations of S. xanthocarpum extracts and cypermethrin demonstrated higher larvicidal activity, indicating synergistic activity. These results demonstrate the need for further studies on the effectiveness and toxicity to humans and animals, particularly aquatic forms.     

Effects of sulphur dioxide preservation of flax straw on fibre components and microbial colonisation during dew-retting

The changes in flax straw structure when treated with sulphur dioxide (SO₂) and consequent effect on dew-retting of the treated straw were investigated. The active oxoanions released by sulfurous acid degraded phenolics bound to the polysaccharides and lipids leading to an increase in water-soluble carbohydrates and polyphenols. As a result, proportions of hemicellulose, nitrogen, sulphur, ash and caustic weight loss were higher in treated straw while lipid was reduced. The coarseness of treated fibre was possibly caused by in situ dryback of the hydrolysed polysaccharides. The deposition of salts containing high concentrations of sulphur, calcium and potassium in the vicinity of the fibre bundles and epidermal layer was observed and investigated. In a dew-retting trial comprising SO₂-treated and untreated samples, the SO₂ treatment delayed microbial colonisation and, consequently, retting by nearly 2 wk compared to the controls. The changes in pH, fungal population and polysaccharide degrading enzymes were monitored. The differences in fibre yield, fineness and strength are presented.     

Reproductive strategies of Strobilanthes kunthianus, an endemic, semelparous species in southern Western Ghats, India

Strobilanthes kunthianus (Acanthaceae) is a semelparous species with synchronized flowering and mast seeding once in 12 years. As semelparous plants have only one chance to reproduce, they are expected to develop effective strategies to prevent reproductive failure. The reproductive strategies of S. kunthianus were investigated by studying the floral traits, pollination biology, and breeding system that are critical for reproductive success. The species exhibits a series of floral traits: (1) gregarious flowering attracts a large number of Apis cerana indica , the major pollinator; (2) the stigma is sensitive to touch by the pollinator; in fresh flowers, the receptive surface faces the entry path of the incoming bee, facilitating pollen deposition; as an immediate response, the stigma curves backwards moving the receptive surface away from the path of the exiting bee, thus preventing autogamy and interference in pollen transfer; (3) flowers remain fresh for 2 days with receptive stigma and nectar and pollen reward. These traits render the species 100% pollination efficient to ensure a high seed set. As the species is self-compatible, the prevailing high degree of geitonogamous pollinations does not interfere with fruit set. The evolution of the adaptive floral traits has facilitated mast seeding in the species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 155–163.     

A convenient method for detecting sulphate-reducing bacteria

Sulphate-reducing bacterial cells, after addition of sodium hydroxide, showed a pink colour under a visible light microscope. This phenomenon is suggested as a test for sulphate-reducing bacteria.     

Tolerance to reniform nematode (Rotylenchulus reniformis) race A in pigeonpea (Cajanus cajan) genotypes

The reniform nematode (Rotylenchulus reniformis) is an important pathogen of pigeonpea (Cajanus cajan). Forty‐six medium maturity (mature in 151–200 days at Patancheru, India) pigeonpea genotypes were evaluated for resistance and tolerance to the reniform nematode in greenhouse and field tests, over the period 1990–97. Each genotype was screened for number of nematode egg masses on a 1 (no egg mass = highly resistant) to 9 (> 50 egg masses = highly susceptible) scale. Plant biomass production in carbofurantreated plots was compared with that in non‐treated plots in a field naturally infested with R. reniformis. Pigeonpea genotypes C 11, ICPL 87119 and ICPL 270 were used as nematode susceptible checks. Genotypes with good plant growth, both in nematode‐free and nematode‐infested plots, were identified as tolerant and evaluated for plant growth and yield for at least three years. All the tested genotypes were susceptible (7 and 9 egg mass score). Single‐plant‐selections, based on plant vigour and yield, were made from genotypes showing tolerance to nematode infection. The level of tolerance was enhanced by plant‐to‐progeny row selection for plant vigour and seed yield in a nematode‐sick field for at least three years. The most promising nematode tolerant genotypes produced significantly greater yield and biomass than the locally grown pigeonpea cultivars in fields naturally infested with R. reniformis at two locations. Pigeonpea landraces are considered to be the most likely sources of tolerance to the nematode. These reniform nematode tolerant lines represent new germplasm and they are available in the genebank of pigeonpea at ICRISAT bearing accession numbers ICP 16329, ICP 16330, ICP 16331, ICP 16332, and ICP 16333.     

Soil water regimes and water extraction patterns under two semi-arid shrub (Atriplex spp.) communities

Soil water regimes and water extraction patterns estimated over a period of two years are described for two plantation communities of semi-arid shrubs, Atriplex vesicaria Hew. ex Benth. and A. nummularia Lindl., growing on the same soil type under identical climatological conditions near Deniliquin, New South Wales. In spite of poor water flow properties of the soil, surface run-off was negligible.About 90% of the extractable water was stored in the top (45 cm) soil layer. Both species withstood exceedingly low water potentials, although A, vesicaria reduced soil water to a much lower water potential than did A. nummularia. Water potentials at depths below 60 cm were always – 15 bars and remained constant. Water extracted beyond –15 bars amounted to 41% more than the water available within conventionally accepted water potential limits (between –0.3 to – 15 bars). During Slimmer, the plant water potential of A. vesicaria fell to much lower values than that of A. nummularia. Relationships between relative leaf water content and plant water potential differed between the two species, and the suggestion is made that at low plant water potential, leaf targidity of A. vesicaria would be higher, and thus this species would have a higher tolerance to desiccation. On a yearly, half-yearly and even a quarterly basis, evapotranspiration (FT) of the two communities did not differ. Fortnightly FT rates were similar during winter but during early summer, the initial ET rate of A. vesicaria was higher than that of A. nummularia; A, nummularia can therefore conserve water for later use. These differences in water extraction patterns and evapotranspiration were associated with differential rooting characteristics and probably differential stomatal functioning. The relationships between fortnightly ET/FO (ratio of actual evapotranspiration to that from a Class A pan) and profile water content, for both communities, were linear but different.     

Evaluation of larvicidal potential of certain insect pathogenic fungi extracts against Anopheles stephensi and Culex quinquefasciatus

Fungal metabolites are attracting attention as potential microbial insecticides, and they are anticipated to overcome the problems of pesticide resistance and environmental pollution that are associated with the indiscriminate use of conventional synthetic insecticides. The relative bioefficacies of selected fungal pathogens, Aspergillus flavus, A. niger, A. parasiticus, Fusarium sporotrichoides and Penicillium verrucosum were observed against Anopheles stephensi and Culex quinquefasciatus larvae. A. flavus demonstrated the greatest bioefficacy with 50% lethal concentration (LC₅₀) values of 9.54 and 10.98 ppm against Anopheles stephensi and Culex quinquefasciatus larvae, respectively, after 24‐h exposure. The bioefficacy of A. flavus increased in both species with an exposure time of 48 h, with LC₅₀ values of 7.26 and 8.55 ppm, respectively.