http://ir.lib.ruh.ac.lk/handle/iruor/19199 2026-04-26T18:26:40Z http://ir.lib.ruh.ac.lk/handle/iruor/19423 Occurrence, distribution and control of papaya mealybug, Paracoccus marginatus (Hemiptera: Pseudococcidae), an invasive alien pest in Sri Lanka Galanihe, L.D.; Jayasundera, M.U.P.; Vithana, A.; Asselaarachchi, N.; Watson, G.W. A hitherto unrecorded species of mealybug was discovered in early 2008 in the western provincial districts Colombo and Gampaha in Sri Lanka, infesting a large number of plant species. Investigations were done to identify the pest and to study its host range, nature of damage and distribution, and to design and implement control measures. The pest was identified as papaya mealybug, Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae), an invasive alien species originating from Mexico and/or Central America. The mealybug found to heavily infest more than 40 plant species including papaw, the major host, and several horticultural and floricultural crops like Plumeria, manioc, bread fruit, Alstonia macrophylla and Jatropha spp. By 2009 the pest had spread to other parts of the country including the North Western, Saba ragamuwa, Southern, North Central, Central and Eastern provinces. As an immediate control measure, im idacloprid 200SL, thiamethoxam 25%WG and Mineral oil were recommended for the control of this pest until biological control agents could be introduced 2010-07-18T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/19422 Evaluation of the heat resistance of pathogenic Listeria monocytogenes in milk and milk products in Sri Lanka Jayamanne, V.S.; Samarajeewa, U. Listeria monocytogenes, which is a food-borne pathogen often isolated from milk and milk products, causes listeriosis in pregnant women, newborns, older adults and immuno-suppressed people. Listeria is said to be more resistant to heat treatments and the present study investigated the effects of current heat treatments on inactivation of Listeria in milk. Two isolates of L. monocytogenes, namely FSTLC2 and FSTLC55, were in troduced to sterilized milk at population levels of 102 and 107cfu/ml and were subjected to various tempera ture-time combinations. Listeria was enumerated using the FDA Listeria Enrichment Broth (LEB; Oxoid Ltd) and Modified Oxford Agar (MOX; Oxoid Ltd) medium. The Thermal Death Time (TDT) and Thermal Death Rate (TDR) curves were also constructed using thermal resistance data. The slope of the TDT curve (z) and the slope of the TDR curve (D; Decimal Reduction Time) were also determined using the statistical software package Minitab (release 8.21). It was observed that the normal pasteurization treatments of 62.8oC for 30 min (LTLT; Low Temperature Long Time) and 71.7oC for 15sec (HTST; High Temperature ShortTime) appear to be adequate to destroy a Listeria population of 102CFU/ml in milk, but not a population of 107 cfu/ml. A z value of 7.6oC and a D71.7 oCvalue of 2.9sec were observed for L. monocytogenes in milk. The current heat treatment techniques used in the dairy industry need to be reviewed and necessary modifications introduced to ensure a complete elimination of this pathogen. Moreover, the z and D71.7 oC values observed in the present study may be used in devising sound heat treatment techniques as well as suitable Hazard Analysis Critical Control Points (HACCP) systems in the dairy industry. 2010-07-26T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/19421 Evaluation of maize genotypes for resistance to aspergillus infection and aflatoxin production Rajapakse, R.G.A.S.; Karunarathna, K.M..; Premarathne, P.; Perera, R.N.I. Maize (Zea mays L) is one of the important food crops grown in Sri Lanka. Kernel infection of maize by Aspergillus flavus and subsequent aflatoxin production is a frequent and serious problem. Genetic resistance for A. flavus infection is the most economical and successful way of controlling infection and subsequent produc tion of aflatoxins. Therefore, a study was undertaken in two locations at Maha Illuppallama to evaluate inbred lines and hybrids for resistance to Aspergillus infection and aflatoxin production. Artificial inoculation in creased percentage kernel infection by Aspergillus compared to non-inoculated treatments. Percentage kernel infection by Aspergillus varied with genotypes and no significant relationship between percentage kernel in fection and aflatoxin levels was found. Aflatoxin production in some hybrids found to be zero when artificial ly inoculated with virulent isolates of A. flavus. Commercial hybrids, namely NK 40, Sampath and Pacific grown in Sri Lanka showed susceptibility to aflatoxin production. 2010-07-12T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/19420 Analysis of genetic variability, association and path analysis in the hybrids of sesame (sesamum indicum l) Sumathi, P.; Muralidharan, V. A field experiment was conducted with thirty hybrids produced by line x tester mating design from eleven sesame genotypes involving five branched and six monostem / shy branching types. Observations were recorded on days to 50% flowering, days to maturity, plant height, number of branches per plant, number of capsules per plant, capsule length, capsule breadth, number of seeds per plant, 100 seed weight, seed yield per plant and oil content. The traits, number of branches per plant, number of cap sules per plant and seed yield per plant showed high PCV and GCV estimates. There is scope for selec tion based on these characters, and the diverse genotypes can provide materials for a sound breeding programme. High heritability combined with high genetic advance (as per cent of mean) observed for plant height, number of branches, number of capsules and seed yield per plant showed that these char acters were controlled by additive gene effects and phenotypic selection for these characters would like ly to be effective. Seed yield per plant showed significantly positive correlation with plant height, num ber of branches per plant, number of capsules per plant, days to 50% flowering, days to maturity and 100 seed weight. Capsule breadth showed significantly negative association with seed yield per plant. 2010-07-06T00:00:00Z