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Subject: search.filters.subject.Diseases and injuries

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    Studies on the effectiveness of various insecticides and drying in controlling granary weevil (Sitophilus granarius L.) in stored wheat seed : a thesis presented in partial fulfilment of the requirement for the degree of Master in Agricultural Science (Seed Technology) at Massey University, New Zealand
    (Massey University, 1986) Islam, Md. Nurul
    This study was designed to examine the effects of various insecticidal materials and of repeated seed drying during storage on the population dynamics and survival of Granary Wevil (Sitophilus granarious L.) in wheat. The study was conducted in three parts. The first experiment examined the immediate and longer term effectiveness of the contact insecticide malathion and the fumigant phosphine along with influence of repeated drying to safe moisture contents on granary weevil infestation. Wheat seed was stored for 165 days at 25 C and 80% R.H. Treatments were examined every 30 days to study the developrrent of Sitophilus granarius populations and associated damage to wheat seed and evaluation made of the effects of drying, malathion and phosphine on the established infestation and on seed quality. Granary weevils increased by about a factor of X 10 every 60 days and did extensive damage to chemically untreated seed. Repeated drying reduced the rate of increase but did not eliminate the insect population. Malathion dust added to infested seed severely checked insect development and when combined with drying destroyed the infestation completely. Malathion also displayed considerable residual effect and had no adverse effect on seed viability. Phosphine was found to be totally effective in eradicating an established population of granary weevils from seed without affecting seed quality. In a second experiment malathion was sprayed onto jute squares at 2.5% and at one half and one quarter of this rate. Treated squares were stored for 90 days at 20 C, ambient RH of 70 - 90% or 30 C, ambient RH of 60 - 80% and the residual toxicity of the deposit was assayed with live insects at intervals after treatment. Malathion was also applied at 2.5% concentration to the outside of grain filled sacks which were then placed individually into large plastic bags into which adult granary weevils were introduced at 7 day intervals. After 56 days storage, counts were made of live and dead insects inside the sacks to assess protective effect of the malathion treatment. On jute squares malathion was completely effective at all concentrations and at both storage temperatures (20 C and 30 C) immediately after application and also after 7 days. Thereafter, it lost its effectiveness slowly over the next 90 days storage. In whole sack treatment malathion was found to provide only immediate protection at both temperatures and was inadequate after only a few days. In the third experiment wheat seeds, uninfested and infested with Sitophilus granarius, were mixed with ground neem seed of each of two species of neem ( Azadirachta indica and Melia azaderach) at 1 g per 20 g wheat and were stored at 25 C and 80% R.H. Seeds were examined for live and dead insects and germination assessed after 90 days storage. Little or no direct mortality of adults was recorded but there was indirect evidence of suppression of egg laying particularly with Azadirachta indica. Neem seed powder did not affect the viability of the wheat seed. This study has clearly shown the short term residual effectiveness of malathion, the immediate eradicant action of phosphine and the poor performance of the natural insecticidal chemical in neem seed on granary weevil infestation in wheat. The results also show the maintenance of low seed moisture contents in wheat to be a practical method of reducing insect populations. The role of granary weevil in damaging seed was clearly seen by X-ray photography and by the extent of types of abnormal seedlings found in positional germination tests. In the absence of effective control Sitophilus granarius has the potential to devastate wheat seed quality in terms of both purity and germination in as little as 90 days.
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    Role of intermittent warming in reducing chilling injury in tomato : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand.
    (Massey University, 2012) Biswas, Palash
    Tomatoes (Solanum lycopersicum L.) are an important crop commercially and nutritionally. Tomatoes are often harvested at the mature-green stage and handled at low temperature to facilitate postharvest storage. However, long term storage at low temperature (below 13 °C) is challenging as mature-green tomatoes are susceptible to chilling injury (CI). Chilling injury, therefore, limits the advantage of using low temperature to maintain quality of fresh tomatoes during long term storage. Failure to develop red colour, uneven blotchy red colouration, excessive softening, and increased susceptibility to decay were found to be main CI symptoms. Different low temperature ranges affected tomatoes differentially. For a given storage duration, storage at 8 °C delayed but did not perturb red colour development, fruit held at 6 °C showed uneven blotchy red colouration and those at 2.5 °C showed a complete failure to develop red colouration and severe decay. It was suggested that there was a series of critical temperature thresholds at which different CI symptoms were induced. An increased rate of electrolyte leakage is often considered as an indicator of chilling damage to cell membranes. This can be confused with ripening-related increase in electrolyte leakage. This study indicated that electrolyte leakage in mature-green tomatoes increased with chilling either in stored discs or fresh discs cut from stored fruit independently of ripening during long term storage. Interruption of low temperature storage with one or more short periods of warm temperature for various periods of time (intermittent warming, IW) has been shown to reduce CI and improve keeping quality of several horticultural crops. While IW was effective in reducing CI, the responses were highly dependent on production conditions and cultivar and different symptoms of CI had independent responses to IW. The present study was undertaken to elucidate a basic mechanism (physiological response) by which IW reduces CI in tomato. IW stimulated ethylene production and reduced CI. It was suggested that IW-stimulated ethylene was required to reduce CI in tomato as also reported in some other climacteric fruit. However, blocking ethylene response of IW fruit by 1-methylcyclopropene (1-MCP) reduced chilling-induced decay indicating that reduction of CI symptoms by IW was not solely attributable to ethylene action. IW possibly has some metabolic benefit independent of ethylene. As adoption of IW in commercial situation is logistically challenging, one objective of the current study was to determine if intermittent ethylene (IE) supply during low temperature storage could be used as an alternative to IW for alleviating CI in tomato. Results suggested that IE supply was effective in reducing CI, although effectiveness was dependent on storage temperature and nature of CI symptoms. Additionally, treating tomatoes with 1-MCP in the absence of IW enhanced decay susceptibility, consistent with ethylene involvement in reducing decay during cool storage. While 1-MCP was found to reduce CI and extend storage life in many crops, our results indicated that 1-MCP may not be considered for commercial use in mature-green tomatoes before cool storage. Overall, the positive results of ethylene application may assist the tomato industry to store tomatoes for longer periods at chilling temperatures and hence enable sea freight of tomatoes to new markets. While ethylene showed promise as a tool to reduce CI and allow fruit to develop red colour after cool storage, further research is required to determine optimum concentration, time and frequency of application, and efficiency when applied at a range of temperatures in order to derive a successful treatment that may have significant commercial applications. Additionally, while the findings are positive for a possible industry application, the magnitude of the positive effect in reducing CI needs to be determined for other tomato cultivars and fruit from other growing locations. More importantly, if the recommendation of IE application is commercially adopted, in future it will be important to investigate the effect of IE on sensory perceptions of tomato quality.