No abstract

Severity of storage rots in different sections of white yam tubers (Dioscorea rotundata Poir.) was investigated. Yam samples with rots were collected from a yam barn and from selected markets in Accra, Ghana, to identify the most predominant pathogens associated with the rots. Nine fungal spoilage microorganisms, including Aspergillus flavus, Aspergillus niger, Botryodiplodia theobromae, Fusarium culmorum, Fusarium oxysporium, Fusarium sp., Penicillium brevi-compactum, Penicillium sp. and Rhizopus stolonifer and a bacterium species Erwinia carotovora were identified. The mean incidence of occurrence of the organisms on rotten tissues ranged from 1.2% to 28.5%. Of the 10 microorganisms isolated, B. theobromae, F. oxysporium and R. stolonifer were the most frequently encountered spoilage microorganisms in the markets. E. carotovora, Fusarium solani and Penicillium sp. were relatively sparse (incidence not exceeding 3%) compared to the other yam spoilage microorganisms. The surface area and weight of necrotic tissue induced by the spoilage fungi in the various zones of the tubers over a 28-day storage period were assessed. All the spoilage microorganisms produced rots in the yams, although to different degrees. The severity of the rots increased in weight and area over the period when the tubers were in store but were normally not significantly different in the zones of tubers. There was, however, a linear progression of rots in the various zones of the yam tubers. Although there was generally no significant (P ! 0.05) difference in the severity of rots induced by the different microorganisms in the tubers, R. stolonifer commonly induced more rot in the zones of the tubers compared to B. theobromae and F. oxysporium.

The fungicides ethylenebis [dithiocarbamic acid] (nabam) and ethylenebis [dithiocarbamato] manganese (maneb) were dissolved in a modified Holtfreter's solution at concentrations of 0.1–5 ppm. Thirty to 60 yolk‐plug Xenopus laevis embryos were placed for 1–10 days in 200 ml of different concentrations of the fungicide solution. Treated and control (Holtfreter's only) embryos were fixed in Bouin's fluid or formalin for light microscopy, and in glutaraldehyde‐formaldehyde for electron microscopy. Gross morphological and histological observations were made. The first changes observed in experimental embryos was a slight growth retardation and a transient absence or reduction in melanogenesis in the eye and on the rest of the body. The tail was shortened and the notochord had a distinct waviness. Animals in higher concentrations were unable to swim as well as controls. Histological examination, both light and electron microscopic, showed a general decrease in melanin content of the melanosomes in the pigmented retina. The notochord was increased in diameter; in sagittal sections the foldings were obvious. These results indicate that minute doses of these commonly used fungicides are harmful to the normal development of amphibian embryos.

This chapter focuses on the benefits of the use of dynamic controlled atmosphere storage by using ultra-low oxygen levels and monitoring these by measuring physiological responses (respiration rate, chlorophyll fluorescence and fermentation) of the stored crop and controlling the storage atmosphere levels through a computer. The efficacy of various computer software for monitoring and controlling the storage atmosphere levels of the crop is also presented.