8. Resultados y discusión
8.5 Conocimiento y Creencias Acerca de la Evaluación en la Alfabetización
Both treated and untreated tomatoes stored at 2.5 °C showed severe decay as fruit were stored for 35 d. For MG fruit, while no significant difference was apparent between treated and untreated fruit (Table 5.3); the problem seemed to be more aggravated in 1-MCP treated fruit (Figure 5.6). This was obvious for breaker tomatoes, where 1-MCP treated tomatoes showed higher decay severity than non-treated control fruit (p < 0.05; Table 5.3). On the other hand, when tomatoes were stored at 20 °C, the opposite trend was observed with 1-MCP reducing decay significantly (p < 0.05).
Table 5.3 Decay severity (0 - 4 scale) of mature-green (MG) and breaker (Brk)
tomatoes treated with (+) or without (-) 1-MCP and stored at 2.5 or 20 °C for 35 d. Fruit were evaluated at the end of chilling at 2.5 °C and at the end of 4 d post-chilling period at 20 °C. Treatments End of Chilling at 2.5 °C End of 4 d post-chilling at 20 °C MG2.5 °C 1-MCP (+) 1.33 a 3.27 a MG2.5 °C 1-MCP (-) 1.13 a 2.60 a LSD α = 0.05 0.86 0.72 Brk2.5 °C 1-MCP (+) 2.30 a 3.40 a Brk2.5 °C 1-MCP (-) 1.30 b 2.10 b LSD α = 0.05 0.89 0.86 MG20 °C 1-MCP (+) 1.00 b 1.33 b MG20 °C 1-MCP (-) 2.88 a 3.62 a LSD α = 0.05 0.95 0.91
Pairs in values in columns followed by a different letter are significantly different at α =
0.05.
Reduction of decay by 1-MCP was possibly a function of storage temperature. At 2.5 °C, MG or breaker fruit were unable to advance in maturity rendering fruit more sensitive to chilling and thus developing more decay than non-treated fruit. On the other hand, 1-MCP treated fruit stored at 20 °C were possibly less ripe physiologically than fruit without 1- MCP and thus showed less decay since during normal ripening susceptibility to decay increases as tomato ripens (Fallik et al., 1993; Prusky, 1996). Therefore, the difference in 1-MCP effect on decay is due to the fact that 1-MCP shows differential response to chilling-induced decay and normal ripening-associated decay.
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Mature-green and Breaker tomatoes stored at 2.5 °C
MG BRK
1-MCP (+) 1-MCP (+)
1-MCP (-) 1-MCP (-)
Mature-green tomatoes stored at 20 °C
MG MG
1-MCP (+) 1-MCP (-)
Figure 5.5 Visual appearance of mature-green (MG) and breaker (BRK) tomatoes
treated with (+) and without (-) 1-MCP and stored at 2.5 or 20 °C for 35 d and examined immediately on removal to non-chilling temperature (20 °C).
It was possible that fruit stored at different temperatures became susceptible to different microorganisms. Area of decay development was quite different between storage temperatures. More than 80% of fruit stored at 2.5 °C developed decay at the calyx end which was characterised by black sunken spots attributed to Alternaria while none of the fruit stored at 20 °C developed decay on the calyx end either treated with or without 1- MCP (Figure 5.5 and Figure 5.6). Fruit stored at 20 °C showed white patches of decay
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symptoms mostly on the surface of the fruit. These results confirm our previous observation in chapter 2 that entry of pathogens or area of decay development possibly depends on storage temperature and this could be due to the fact that different types of microorganisms attack fruit stored at different temperatures. Artés et al. (1993) speculated a close relationship between storage temperature and fungal rotting in lemon. They observed that lemons stored at 2 °C were mainly infected by Alternaria citri whereas those lemons stored at warmer temperature (20 °C) were rotten by Penicillium digitatum and P. italicum. In the present study, when fungi were isolated on potato dextrose agar and incubated for 72 h at 25 °C, light microscope has confirmed the presence of Alternaria, Fusarium in mature-green fruit and Alternaria and Penicillium in the breaker fruit stored at 2.5 °C. Some of the rot was developed by secondary fungi attack. Fruit stored at 20 °C were mostly infected with Phytophthora and Rhizopus.
Overall, our results suggest that 1-MCP can reduce or induce decay depending on storage temperature. The association of 1-MCP and fruit decay has been reported previously with mixed results. Guillén et al. (2006) found that 1-MCP was highly effective in reducing decay in many tomato cultivars harvested at advanced maturity stages (breaker or ripe) and stored at 10 °C, while Su and Gubler (2012) supported this where they found reduced decay in mature-green tomatoes stored at 18 °C. At 18 °C, fruit were allowed to ripen and 1-MCP reduced ripening associated decay. However, Jing and Zi-Sheng (2011) indicated that 1-MCP resulted in higher decay (chilling-induced) in mature-green tomatoes stored at 3 °C for 14 d than untreated control. It seems that the effect of 1-MCP in reducing decay depends on whether decay is associated with ripening or chilling-induced. It is possible that 1-MCP treatment accelerates decay in chilled fruit but not in non-chilled fruit and perhaps this may explain previous contradictory results.
Nonetheless, if ripening delay by 1-MCP resulted in increased chilling sensitivity, breaker tomatoes should have lower decay severity than MG fruit. But, no visual differences in decay severity were found between these two maturities fruit during post-chilling period at 20 °C. Perhaps fruit were stored at 2.5 °C for too long, so both maturities were equally prone to chilling induced decay. It was possible that fruit stored at 2.5 °C reached irreversible phase of CI by 35 d. Previously, it was demonstrated that ‘Cedrico’ tomatoes
stored at 2.5 °C showed an increase in ion leakage after 2 weeks and fruit lost the capacity to develop red colour and increased decay severity after 4 weeks. Therefore, determining
119 the effect of 1-MCP in inducing chilling related decay development warrants further research with shorter storage periods and other chilling temperature ranges.
Mature-green and Breaker tomatoes stored at 2.5 °C
MG BRK
1-MCP (+) 1-MCP (+)
1-MCP (-) 1-MCP (-)
Mature-green tomatoes stored at 20 °C
MG MG
1-MCP (+) 1-MCP (-)
Figure 5.6 Visual appearance of mature-green (MG) and breaker (BRK) tomatoes
treated with (+) and without (-) 1-MCP and stored at 2.5 or 20 °C for 35 d and examined 4 d after removal to non-chilling temperature (20 °C).
5.4. Conclusion
Effect of 1-MCP in delaying ripening of fruit is well documented. This chapter demonstrated that 1-MCP delayed colour development and retained firmness in tomatoes
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during normal ripening, although this affect was influenced by fruit maturity at time of 1- MCP application. Application of 1-MCP can extend the storage life by inhibiting the advancement of ripening, although fruit eventually overcome the inhibition and resume ripening. Moreover, these results support the hypothesis that ethylene perception is required throughout ripening as shown by the effects on hue angle and fruit firmness. The effect of 1-MCP on tomato ripening differs during chilling from normal ripening. During normal ripening 1-MCP retained stiffness and reduced decay whereas during low temperature storage more rapid loss of stiffness and increased decay was observed. Since 1-MCP inhibits advancement of fruit ripening, fruit may become more susceptible to CI and hence show more dramatic symptoms of CI than non-treated fruit. However, fruit had already spent too long at 2.5 °C to avoid chilling-induced Alternaria and that could explain why no significant differences in decay severity were seen in mature-green fruit. Therefore, it is important to investigate the effect of 1-MCP influencing decay susceptibility employing a range of low temperatures and varied duration of storage. Moreover, use of different maturity tomatoes needs to be considered in future research. The effect of 1-MCP on postharvest decay in tomato is not consistent. Both increase or decrease decay incidence by 1-MCP has been reported in tomato. Although data are limited, results in this chapter provide an indication that 1-MCP enhances decay incidence in fruit stored at a temperature which causes chilling injury whereas it reduces decay when fruit are allowed to ripen normally. It is possible that in the former case, 1-MCP may have interfered with ethylene-induced resistance in ripening tomato fruit, while the later 1-MCP kept the fruit in the more resistant unripe condition. This provides one explanation of having mixed results of ethylene in influencing decay in tomato. Since 1-MCP can enhance chilling-induced decay, it is possible that ethylene may have positive results in reducing chilling-induced decay and thus will be discussed in next chapter. While 1-MCP shows promising results in extending postharvest storage life in many crops including tomatoes, our results and others (Jing and Zi-Sheng, 2011) indicated that application of 1-MCP may not be appropriate for commercial use in tomatoes before cool storage.