Theses

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    The compilation and analysis of a descriptor list for cocoa (Theobroma cacao L.).
    (2012-06-22) Bekele, Frances Louise
    The usefulness of several cocoa descriptors was assessed in this study. Thirty-five quantitative descriptors were analyzed to determine whether, and to what extent, they differentiate between fifty-three accessions. The latter represent a range of diversity. All the descriptors were discriminative. However, the leaf descriptors were more influenced by environment than the reproductive ones and the fruit descriptors displayed the most variability within the populations studied. There were several correlations between these descriptors. For the purpose of quick identification of accessions, the most discriminative were retained and those correlated with them discarded. The resulting subset of descriptors includes pod weight and length, total bean weight, bean length and width; staminode, petal and sepal lengths, ovule number; total leaf length and leaf apical angle. Information on the diversity of the accessions was important for assessing the usefulness of these descriptors. Seven homogeneous groups of accessions were identified by clustering with sixty-eight mixed variables. The presence of diversity was demonstrated and the accessions could be differentiated according to their geographic origin. No subsets of descriptors provided a classification identical to that of the full complement. However, a subset of thirty-four mixed descriptors furnished a similar classification. It may be appropriate for quick classification in the International Cocoa Genebank, Trinidad. Subsets of descriptors may be useful for differentiating between distinct accessions. However, as large a group of descriptors, as is practicable, is recommended for the reliable determination of the relationships between the accessions.
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    The effect of extracts from Serjania paucidentata (D.C.) on feeding, growth and mortality of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera : Noctuidae).
    (2012-06-22) Peterkin, Dorothy Dianne
    Green plants have developed protective secondary compounds or allelochemicals from evolutionary association with phytophagous animals. These chemicals occur in a range of chemical groups and may be toxins, antifeedants or insect hormone analogues which can be used in novel approaches to insect pest management. The extract from a local plant Serjania paucidentata contains saponins and is toxic to Brine Shrimp (ED50 = 0.32 mg/ml). The properties of S. paucidentata were investigated on the Fall Armyworm, Spodoptera frugiperda. The effect produced by the aqueous methanolic fraction and the crude extract were the same. These had ED50’s of 3.27 mg/ml and 2.355 mg/ml respectively when incorporated into a defined diet. A concentration of 11.43 mg/g diet produced 100% mortality in 10 days. Reduced feeding, decreased growth rates and pupal weights, and increased developmental periods were produced in S. frugiperda at sub-lethal doses. Insects were deterred from feeding on corn leaf squares treated with 1% extract in choice tests. Toxicity and antifeedant properties are dosage dependent. Typical of unpurified plant extracts, S. paucidentata extracts exhibited multiple modes of action as a stomach poison, antifeedant and possible growth retardant. Phytochemicals from local plants are unexplored resources, which must be documented and utilized. There is much scope in this area for further study.
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    Population studies of the pigeonpea pod borer, Ancylostomia stercorea (Zeller) (Lepidoptera : pyralidae) and relations to its parasitoids and host plant, Cajanus cajan (L.) millsp.
    (2012-06-25) Khan, Ayub
    Six parasitoids were found to attack the egg and larval stages A. stercorea the braconids Apanteles etiellae isolatus, Bracon cajani, B. thurberiphagae and Phanerotoma bennetti, the bethylid, Goniozus punctulaticeps, and the ichneumonid, Eiphosoma annulatum. Pupal diapause in A. stercorea was demonstrated and control of this stage was an important component of an integrated programme for the pod borer. The population parameters, mean generation time (T = 42.15 days), intrinsic (rm = 0.108) and finite rate of increase (λ = 1.11), in fecundity (34.71 ± 0.23) eggs per female and net reproductive rate (R0 = 94.81) were estimated for A. stercorea. Analysis of temporal distribution of the eggs of A. stercorea over two years showed regular cyclical patterns coinciding with the flowering of the host plant. A. stercorea egg distribution was best described by Taylor’s Power Law (b = 1.26) and lwao’s Regression (β=1.41) both indicating aggregation. A sequential sample table based on the egg stage was constructed for use in the field. Life tables prepared for A .stercorea were analysed using conventional key factor analysis and the newer multiple decrement life table approach. Fourth (k4) and fifth instar mortality (k5) as well as adult mortality (k7) were identified as the key mortality factors. The multiple decrement approach revealed that an average of 33.9% mortality occurred in all stages. Life tables were also prepared for pigeonpea and similar anlyses conducted. Mean bud, flower and pod abscission during the entire season was (30.4 ± 4.4%); (59.5 ± 4.5%) and (10.1 ± 2.5%) respectively. The key factor was identified as k3 (pod I) mortality), whereas the regulating factor was k2 (flower mortality). Multiple decrement life table analysis revealed that natural factors alone accounted for the major mortality (67.56%) from bud to pod (V) stage during the entire season. Comparison of insecticides between pest and parasitoids showed that malathion, fenvalerate and decamethrin were good candidates for the protection of A. etiellae isolatus, B. cajani and B. thurberphagae while causing high mortality to A. stercorea.
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    Studies on a new bacterial disease and other diseases of anthurium in Trinidad.
    (2012-06-25) Dilbar, Assim
    A new bacterial disease was first seen on imported Anthurium andreanum Linden hybrids cultivated in Trinidad in October, 1989. Isolation and biochemical tests were conducted to identify this organism. Pathogenicity and inoculation studies were conducted on a Dutch hybrid. A survey was undertaken to investigate the occurrence of diseases on both the local and imported hybrids cultivated commercially in Trinidad and in particular to determine the distribution of this new bacterial disease. The organism identified was a Pseudomonas species, a non-fluorescent pseudomonad. Symptoms of bacterial leaf spot were characterized by angular, water-soaked lesions along the leaf margins, veins and spathes, developing into large dark- brown to black necrotic areas. Lesions were surrounded by bright, narrow, chlorotic halos on the leaves and dark brown or purple necrotic areas eventually becoming black on spathes. Systemically infected plants developed a general yellowing of the leaves which eventually resulted in death. This new bacterial disease was found on seven out of thirty-four farms investigated: two located at Gran Couva in the Caroni county and five (three at St. Augustine, one at Wallerfield and one at Carapo) located in the St. George east county. Typical symptoms were found only on imported Dutch and Hawaiian hybrids. Other diseases found only on imported hybrids were bacterial blight and bacterial wilt. Anthracnose was the most common of all diseases on the farms. Pseudocercospora leaf and flower eye spot disease was seen mainly on local hybrids and on one farm with Dutch and Hawaiian hybrids. Anthurium decline was found mainly on Dutch and Hawaiian hybrids.
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    Studies on the in vitro propagation of Mussaenda erythrophylla 'Rosea'.
    (2012-06-22) Brookner, Nadia
    Investigations to determine a suitable medium for the in vitro propagation of Mussaenda revealed that of the macro-element formulations of MS, Anderson and Heller, that of MS appeared to be the most suitable for the growth and multiplication of shoots. Compared with kinetin and 2iP, 6-BAP enhanced the elongation of Stage I buds and promoted shoot proliferation. 5.0 and 10.0 mg/l 6-BAP promoted the multiplication process, but better quality shoots resulted at concentrations of 1.0 - 2.5 mg/l. The presence of a cytokinin in Stage I may be inessential since shoots formed in primary medium containing GA3 produced an acceptable rate of proliferation in Stage II. Two temperature regimes of 27°C and 31°C were tested. The elongation of buds in Stage I was significantly increased at 31°C. There was no apparent effect of temperature on the multiplication process. Explants derived from nodal positions 1-4 were compared. Shoots produced in nodes at positions 2 and 3 were significantly longer than those in other positions. The rate of multiplication was significantly less in shoots derived from nodes at position 1. Attempts to elongate proliferated shoots were unsuccessful. Shoots did not produce roots in vitro. Rooting extra vitrum appeared to be more promising. The problem of vitreous shoot formation was encountered. The disorder was promoted in the presence of Heller’s macro-elements. MS macro-nutrients (full-strength) appeared to be more suitable since leaves thus produced were anatomically similar to those formed in vivo. The disorder was promoted when sucrose was increased from 30 g/l to 50 g/l, or when the concentration of NH4NO3 in MS salts was reduced to one-third. Vitrification was less of a problem when culture vessels were left untaped, but could be reduced in taped vessels by increasing the agar level from 0.8 - 1.1 per cent and incorporating a desiccant. Phioro-glucinol in culture medium could also reduce the advent of vitrescence.
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    Studies on the in-vitro propagation of Heliconia spp.
    (2012-06-25) Cockburn, Brian Victor
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    A study of the biology of Oebalus spp. on rice in Trinidad.
    (2012-06-25) De Chi, Lionel Wayne