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Thesis (M.Sc.(Food Science)--University of Pretoria, 2007. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes Bibliographical References. Also available via the Internet.

No description available.

False codling moth is a known pest of economic importance to many cultivated crops in South Africa and Africa south of the Sahara, and is particularly severe on citrus. If the fruit is infested just before harvest the chances of detecting signs of infestation are very low. As a result, the risk of packaging infested fruit and exporting them as healthy fruit is high. It is therefore a priority to develop a post-harvest technique for detection of False codling moth in citrus fruit at different levels of infestation in order to reduce phytosanitary risk. Compounds released and detected were indicative of infestation and were not insect produced but naturally produced fruit volatiles emitted at higher levels as a result of the insect within the fruit. Five major volatile compounds of interest were released by the infested oranges. These major volatile compounds include D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene, caryophyllene and naphthalene. Limonene was one of the most abundant volatile compounds released by the infested citrus fruit. Naphthalene, which is possibly produced due to larval feeding and development within the fruit maintained higher concentrations than controls throughout the infestation within the fruit. Naphthalene would be a good indicator of False codling moth infestation, however, not primarily for early infestation detection. A significantly higher concentration of D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene and naphthalene was detected using the SEP over the SPME technique. The application of an SPME procedure and the utilization of this method for detection of volatiles present in the headspace of intact infested fruit are evaluated and the possible volatile compounds diagnostic of Thaumatotibia leucotreta infestation of orange fruit and differences in volatile compound response in different orange varieties is discussed.

Five virus isolates RS 2, RS 25, RS 26, RS 28 and RS 29, were transmitted by juice-inoculation technique from sour and sweet cherry trees to cucumber. Four isolates were obtained from trees growing in the Kootenay cherry district of British Columbia. Another one was isolated from a tree growing in the coastal area of this province. Viruses known to occur in the source trees are Necrotic Ring Spot Virus, Sour Cherry Yellows Virus, Twisted Leaf Virus and Little Cherry Virus. The relationship and the complexity of the virus isolates was studied with herbaceous hosts, using a mechanical transmission technique. Pincherry (Prunus pennsylvanica L.) was inoculated by the same technique as a means for provisional identification of the virus isolates. The cucumber syndrome of isolate RS 25 was very mild, that of isolate RS 2 mild, that of isolate RS 29 was of medium severity and those of isolates RS 26 and RS 28 were very severe. Inoculates RS 2 and RS 29 varied greatly in symptom expression on cucumber, whereas the symptom expression of the other isolates was less variable. Isolate RS 29 was characterized by symptomless systemic infection of Nemesia sp.. var. Triumph. Isolates RS 26 and RS 28 both infected Petunia hybr., var. Blue Bee, without expressing symptoms, whereas the other isolates did not infect this species. Other host species too carried the isolates without expressing symptoms, whereas symptoms were produced on cucurbit hosts. Isolates RS 2, RS 26, RS 28 and RS 29 appeared to consist of more than one virus. Strains of a virus P occur in all isolates and isolate RS 25 itself is also a strain of this virus. All five strains of virus P express similar very mild symptoms on cucumber, whereas a characteristic severe savoying type of symptom is produced on squash (var. Table Queen). Species susceptible to virus P are cucumber, pincherry, squash, sweet pea, tobacco (under conditions of long day) and other species. Lathyrus odoratus L. and Lens culinaris Medic. are species useful in separating virus P from the other viruses occurring in isolates RS 2, RS 26, RS 28 and RS 29. It is possible that virus P is related to cucumber-mosaic virus as suggested by symptoms on squash and tobacco. In previous work by other investigators a strain of cucumber-mosaic virus was also isolated from Prunus hosts. On pincherry (P. pennsylvanica L.) isolate RS 28 caused acute symptoms of necrosis and shothole. The plants recovered but symptoms of mottling were systemic. Necrotic Ring Spot Virus caused similar symptoms on Prunus hosts and this virus and Sour Cherry Yellows Virus was present in the original source tree. The other isolates in pincherry all caused similar symptoms of mottling on the young leaves. A few necrotic lesions were produced also. On reisolation from pincherry virus P was obtained in case of isolates RS 2, RS 26 and RS 29. No virus was reisolated in the case of isolate RS 25. The complete parent isolate was reisolated in case of isolate RS 28. The results with pincherry suggest that virus P is responsible for the mild symptoms whereas virus P in conjunction with an additional virus as in isolate RS 28 incites the severe shock symptoms. The identification of the viruses present in the isolates can be carried out by scion inoculation of a set of suitable Prunus indicator hosts. / Land and Food Systems, Faculty of / Graduate

A new disease affecting potatoes was first detected in Mexico in 1993. Affected plants had aerial symptoms similar to those caused by potato purple top and psyllid yellows, but tubers had internal brown discoloration when sliced and dark stripes and streaks when processed to produce potato chips. The disease has been found in many potato production areas in Guatemala, Mexico, Honduras, New Zealand and the United States. The disease, termed Zebra Chip (ZC), has been associated with the presence of heavy infestations of the potato-tomato psyllid (Bactericera cockerelli). In 2009, a research group in New Zealand discovered that a new disease in tomato and pepper plants was caused by Candidatus Liberibacter solanacearum (Lso) and subsequently this same bacterium was associated with ZC in potato samples from Texas. The objectives of this study were: to assess the accumulation of Lso in various potato organs, to determine the effect of plant age on detection of Lso, symptom development and plant death, and (iii) to determine the effect of phosphorous acid on the development of ZC. Results from these studies showed significant differences in Lso populations between above and below ground tissues of the potato plant, with Lso populations in stolons and tubers being three to four times higher than those of leaf tissue and over seventy times greater than in stems. Time for detection of Lso by PCR in potato leaves of different ages at the time of inoculation ranged from 21 to 26 days after inoculation, symptoms development took 23 to 36 days. Plant death, took 24 to 47 days in plants of different age groups at the time of inoculation. In plants 15 weeks old at the time of inoculation, Lso was detected after 14 days in one plant out of 18; in plants 16 weeks old at the time of inoculation, Lso was detected after seven days in two plants out of 18. Phosphorous acid applications had no effect on the populations of Lso in potato tubers, onset of symptoms or plant death. All tubers showed ZC symptoms, making them unacceptable for the market. / North Dakota State University. Department of Plant Pathology

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Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries