Reduction of postharvest anthracnose and enhancement of disease resistance in ripening mango fruit by nitric oxide treatment
2014
Hu, Meijiao | Yang, Dongping | Huber, Donald J. | Jiang, Yueming | Li, Min | Gao, Zhaoyin | Zhang, Zhengke
Nitric oxide (NO) acts as an important signal molecule with diverse physiological functions in plants. In this study we investigated the effects and possible mechanisms of exogenous NO on anthracnose caused by Colletotrichum gloeosporioides in mango fruit. ‘Guifei’ mango fruit were treated with NO donor (sodium nitroprusside of 0.1mM) at 25°C for 5min, inoculated with spore suspension of C. gloeosporioides after 24h of NO treatment, and stored at ambient temperature (25°C). NO treatment effectively suppressed lesion development on mango fruit inoculated with C. gloeosporioides, and lesion diameters at 2 through 8d in NO-treated fruit averaged 30% lower than those in control fruit. Additionally, NO treatment reduced natural anthracnose incidence and severity of mango fruit ripened at ambient temperature, and the values of both parameters from 4 to 10d of storage in NO-treated fruit averaged 40 and 45% lower, respectively, than those for control fruit. NO did not exhibit in vitro antifungal activity against C. gloeosporioides. NO treatment enhanced the activities of defense-related enzymes including phenylalanine ammonia-lyase (PAL), cinnamate-hydroxylase (C4H), 4-coumarate: CoA ligase (4CL), peroxidase (POD), β-1,3-glucanase (GLU) and chitinase (CHT). NO treatment also promoted the accumulation of total phenolics, flavonoids and lignin that might contribute to inhibition of the pathogen. In addition to antifungal efficacy, NO treatment delayed flesh softening, yellowing, and changes in soluble solids content (SSC) and titratable acidity (TA), and peaks of respiration rate and ethylene production during ripening. These results suggest that the resistance of NO-treated mango to anthracnose may be attributed to activation of defense responses as well as delay of ripening.
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