ISSN 2756-388X
International Journal of Plant and Animal Sciences ISSN 2167-0437 Vol. 5 (1), pp. 140-147, January, 2017. © International Scholars Journals
Full Length Research Paper
Effects of stages of maturity on the susceptibility of tomato fruits to postharvest fungal pathogens
Birgen J. K
Department of Plant Sciences, Kenyatta University, P.O. Box 43844 - 00100, Nairobi, Kenya.
E-mail: [email protected] or [email protected].
Received 15 September, 2015; Revised 25 November, 2016; Accepted 27 November, 2016 and Published 10 January, 2017
Abstract
The tomato is popularly grown in Kenya as a fruit vegetable, and hence provides employment and income to rural communities. Besides, it is a source of minerals and vitamins and therefore improves the quality of stew and salads when it is one of the ingredients. However, adequate amounts of tomatoes of good quality are rarely available due to production constraints, notably lack of varieties that are resistant to pre- and postharvest rots, not prone to spoilage during postharvest handling, and do not have a “short shelf life”. Postharvest tomato rots are principally caused by fungi and bacteria. Other factors that determine the magnitude of postharvest losses include: the fruit maturity stage at harvest, the fruit cultivar and the postharvest pathogen identity. Hence, a project was designed to find out the effect of colour maturity stage at harvest on the susceptibility fruits of tomato cultivar Cal J to the postharvest fungal pathogens (Fusarium oxysporum f. sp. lycoperisici, Fusarium solani, Alternaria alternata and Geotrichum candidum). Tomato fruits, cultivar Cal J, were harvested at the green, yellow and red colour maturity stages and inoculated with the 4 fungi (Fusarium oxysporum f. sp. lycoperisici, Fusarium solani, Alternaria alternata and Geotrichum candidum) that were isolated from diseased fruits sampled from tomatoes sold in a Nairobi market. The pathogenicity of the fungi was assessed by comparing the lesion development and amount of damage caused on inoculated tomato fruits. The susceptibility of the tomato fruits to the fungi at different stages of maturity was determined by comparing lesion development and fruit damage on the mature green, yellow and red cultivar Cal J tomato fruits. The fungus G. candidum caused significantly (P≤0.05) highest damage with respect to lesion diameters and fruit damage (97.2%) compared to the other fungi: F. solani (82.4%), F. oxysporum f. sp. lycopersici (62.6%) and A. alternata (52.2%) on mature red fruits. The damage caused by A. alternata was significantly (P≤0.05) smallest. This is probably because G. candidum produces enzymes that effectively degrade the tomato tissues while those produced A. alternata are not as effective. Similarly, G. candidum caused significantly (P≤0.05) highest (97.2%) damage on the mature red fruits while the damage (20.5%) caused on the green fruits was significantly (P≤0.05) lowest. The trend prevailed for the other fungi. This could be due to higher concentration of biochemical defence mechanisms in green tomato fruits, which reduce as the tomato fruits ripen. Storage trails indicated that the “shelf-life” of the mature green Cal J tomato fruits was up to 3 times longer than that of the mature red ones, confirming that Cal J tomato fruits harvested at the green maturity stage have a significantly (P≤0.05) longer “shelf-life” than those harvested at the other maturity stages. The results, from the study, makes it necessary to advice farmers to: harvest tomatoes at the green maturity stage, avoid postharvest handling process that inflict damage; plant tomato varieties that withstand mechanical damage, and are resistant to postharvest infection; and prevent contact between tomato fruits with sources of fungal inoculums.
Keywords: Maturity stage, tomato fruits, cultivar cal j, postharvest fungi, “shelf-life”, pathogenicity, susceptibility.