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    Studies on the in vitro propagation of Highgate (Musa acuminata, AAA) with emphasis on production of mutants resistant to Fusarium oxysporum F.sp. Cubense.
    (2012-06-22) Bhagwat, Basdeo
    The use of conventional breeding techniques utilising Gros Michel as the female parent has to date failed to produce a commercially acceptable plant resistant to F.O. cubense. In the present study efforts were made to determine the level of 6 benzylaminopurine (6-BAP) which gave maximum shoot proliferation in vitro which could be treated with the mutagens gamma radiation, Sodium azide (NaN3), Diethyl sulphate (DES) and Ethyl methanesuiphonate (EMS); regenerate plantlets from treated propagules and screen these for tolerance to F.O. cubense race 1. Further, an in vitro method of screening for resistance was investigated. It was found that maximal shoot proliferation occurred between 3.0 and 4.0 mg 6-BAP/litre. Calloid initiation and calloid ‘bud’ proliferation were maximal between 15.0 and 20.0 mg 6-BAP/litre. The hormone concentration appeared to be the more important factor in calloid initiation than damaging of the apical meristem. Regeneration of shoots from calloid occurred most easily when buds were dissected out and cultured in MS medium supplemented with 0.0 to 2.0 mg 6-BAP/litre. The use of the growth regulators N6-(2-isopentyl) adeninc and Zeatin in combination with 3-indole-acetic acid and high phosphate also promoted satisfactory shoot regeneration/growth from calloid. For gamma radiation, meristems, shoots, and corms were treated with 0.2 to 5.0 kilorads (kR); with dose rates of 100.82, 177.37 and 256.8 rads/minute. For the chemical mutagens meristems were treated for 0.5 and 1.0 hour periods at the following concentrations: 0.0011 M, 0.0023 M and 0.0046 M for NaN3 0.01 M; 0.02 M and 0.025 M for DES; and 0.1 M, 0.2 M and 0.3 M for EMS. Gamma irradiation of corms and meristems produced the highest FE followed by DES, NaN3 and EMS. For all mutagens, except DES, a similar percentage of regenerated plantlets was selected for tolerance to the pathogen. For in-vitro screening for tolerance, the selection agents used were fusaric acid at 15, 25 and 35 mg/litre; culture filtrate at 50, 100, 200 and 500 mi/litre; and the live organism. A comparison of symptoms produced in Highgate, Robusta and Horse plantain revealed that differences were not large enough to allow a clear-cut classification of plants as tolerant or susceptible.
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    A study of the biology of Oebalus spp. on rice in Trinidad.
    (2012-06-22) De Chi, Lionel Wayne
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    The ecology of selected aquatic insects in the Maracas River.
    (2012-06-22) Maharaj, Lorraine Davina
    Seasonal fluctuations in the composition and abundance of the macroinvertebrate fauna of the Maracas River were examined between December 1987 and January 1989. Additionally, the life-cycle patterns of the Elmidae (Coleoptera) and Helicopsychidae (Trichoptera) inhabiting the stream were investigated. Eight replicate benthic samples were taken monthly along with measurements of depth, temperature, current velocity and dissolved oxygen. Monthly light trapping for adult aquatic insects was done each month between January 1988 and January 1989. Water chemistry analyses were conducted once during the dry and once during the wet season. Monthly rainfall data for the area were obtained from the Division of Water Resources. Benthic organisms from 15 orders and adults from 8 aquatic insect orders were collected. Abundances of most benthic groups increased to a maximum during the dry season, while peaks in emergence of adult aquatic insects occurred during the late dry/early wet season. The Bray-Curtis similarity terms analysis indicated high levels of similarity between dry and wet season samples and that seasonal differences were more the result of changes in the average abundance of each taxon, rather than changes in species composition. Cluster analysis and MDS ordination demonstrated that these changes in abundance were well correlated with rainfall and current velocity which may have influenced benthic numbers either as a result of increased scouring, or by depletion of food resources during the wet season. Life cycles of three species of Elmidae (Hexacylloepus smithi (Grouvelle), Macrelmis clypeata (Hinton) and Microcylloepus carinatus Hinton) and one helicopsychid (Helicopsyche margaritensis Botosaneanu) were studied. Six instar stages of H. smithi, M crinatus and H. margaritensis and eight stages of M. clypeata were identified. All four species were found to have two periods of first instar recruitment, one major period during the dry season and a second, smaller one during the wet season, suggesting bi-voltine life cycles. In all cases, maximum larval recruitment and abundance occurred during the dry season, possibly related to the increased availability of food material during this period.