Persistence and frequency of application of an insecticide in relation to the rate of evolution of resistance

In an earlier paper, it was demonstrated that in order to delay the evolution of resistance, it is important to ensure that heterozygous carriers of resistance genes are killed so that the R gene is made effectively recessive. How this may be achieved is considered here, with (a) a persistent insecticide declining in effectiveness with time, and (b) a non-persistent insecticide (or fumigant). The relationship between the time taken for the dosage to decline to one-tenth (NGI) and the interval between insecticide applications (N12) was investigated. The optimal value of N12 was found to depend not only on the rate of decline but also on the shape of the degradation curve. Other important factors were (a) the dosage of insecticide applied (the initial effective dominance); (b) the initial frequency of the R gene; (c) the proportion of insects per generation that escaped exposure; and (d) whether selection occurred before or after mating. When considering non-persistent insecticides, it was necessary to distinguish between the short-lived deposit and the space spray, the latter being much less likely to lead to resistance.     

Identification of antifungal compounds from the seed oil ofAzadirachta Indica

Evaluation of the activity of the cold expeller neem oil(Azadirachta indica A. Juss.) and the fractions derived through solvent partitioning, againstDrechslera oryzae, Fusarium oxysporum andAlternaria tenuis showed that the active antifungal fraction is a mixture of tetranortriterpenoids. Further, testing the triterpenoidal mixture derived from the 90% methanol (MeOH) extract of neem oil against 13 phytopathogenic fungi revealed that various species were inhibited to different degrees. Direct preparative High Performance Liquid Chromatography (HPLC) of the active fractions and subsequent bioassay of the semi-pure fractions indicated that the active fractions contained major compounds such as 6-deacetylnimbin, azadiradione, nimbin, salannin and epoxyazadiradione. Pure azadiradione, nimbin, salannin and epoxy-azadiradione did not have appreciable activity. However, when these terpenoids were mixed and bioassayed, they showed antifungal activity, indicating possible additive/synergistic effects.     

Genetic variability of Channa punctatus populations using randomly amplified polymorphic DNA

Genetic variations between Channa punctatus populations collected from three rivers of south India were examined using randomly amplified polymorphic DNA (RAPD). Sixty samples from each population were collected. Genomic DNA was isolated from the blood samples. Out of the 20 primers tested, six primers were used for genetic variation studies. A total of 42 RAPD bands were amplified in C. punctatus by the six primers. The total number of bands observed ranged from 34 in the Quilon population to 37 in the Thirunelveli population. Among the three populations, the highest genetic identity (0.9231) was found between Thirunelveli and Quilon populations. The results of the present study demonstrated that Thirunelveli and Quilon populations are more related to each other than to the Coimbatore population.     

Cytogenetical studies of two amphidiploids in the genus Oryza

Results of cytogenetic studies of 2 amphidiploids, O. glaberrima-sativa and O. sativa-breviligulata, are reported for the first time in the genus Oryza. All the 3 species have 2n=24 chromosomes. They were produced by treating buds of F₁ stubbles with 0.1% colchicine solution.The gigas effect of polyploidy was observed in both the amphidiploids. While the F₁ hybrids were completely sterile polyploidy resulted in 75.0% pollen fertility in both, with 47.0% spikelet fertility in O. glaberrima-sativa and 12.7% in O. sativa-breviligulata. Meiosis in the 2 amphidiploids was generally similar. Quadrivalents ranging from 0 to 12 were observed with 2 modes at 6IV and 8IV. The average number of IVs in the C₂ and C₃ generations ranged from 6.2 to 7.8. Segregation of characters was observed in the C₂ and C₃ generations in O. glaberrima-sativa. The C₂ plants segregated for spikelet size and hairiness. Of the 4 C₃ progenies studied, one segregated in the ratio 3:1 for the presence of anthocyanin pigmentation and hairiness of spikelets.The occurrence of IVs in high frequency and the segregation for differences in characters of the original parents noted in O. glaberrima-sativa are similar to the results reported from autotetraploids of O. sativa. It is suggested that these results point out to the rather close structural similarity in the chromosome complements of the 3 species and provide experimental evidence to the theory that the 2 cultivated species O. sativa and O. glaberrima have evolved independently from a common species O. perennis.     

A New High-Temperature Superconductor: Bi2Sr3-x Cax Cu2O8+y

A new superconductor that displays onset behavior near 120 K has been identified as Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y), with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La(2)CuO(4) and YBa(2)Cu(3)O(7), but the copper-oxygen chains present in YBa(2)Cu(3)O(7) do not occur in Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y). The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca(2+) and Sr(2+) cations between the adjacent Cu-O sheets; Sr(2+) cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y) show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.     

Development and characterization of a fibroblastic‐like cell line from caudal fin of the red‐line torpedo,Puntius denisonii (Day) (Teleostei: Cyprinidae)

A fibroblastic‐like cell line was established from the ornamental fish, red‐line torpedo (Puntius denisonii). The red‐line torpedo fin (RTF) cell line is being maintained in Leibovitz's L‐15 medium supplemented with 10% fetal bovine serum (FBS) for over 1 year at 28 °C on a continuous basis in normal atmosphere. The growth rate of RTF cells increased as the FBS proportion increased from 5% to 20% at 28 °C with optimum growth at the concentrations of 10% FBS. The morphology of RTF cell was predominantly fibroblastic like. Propagation of these cell lines was serum dependent, with a low plating efficiency (<15%). Karyotyping analysis of RTF cells at the 25th passage indicated that the modal chromosome number was 2n=50. The cell line was cryopreserved in liquid nitrogen at ?196 °C and could be recovered from storage after 6 months with good cell viability. Polymerase chain reaction amplification of a fragment of two mitochondrial genes, 16S rRNA and CO1, confirmed the identity of these cell lines with those reported from this animal species, confirming that the cell lines originated from P. denisonii. The bacterial extracellular products from Vibrio cholerae MTCC3904 and Aeromonas hydrophila were found to be toxic to RTF. The cell lines were not susceptible to viral nervous necrosis virus, a marine fish virus.