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The effect of nitric oxide (NO) on resistance of pitaya fruit against anthracnose caused by Colletotrichum gloeosporioides and its related mechanisms were investigated in this study. ‘Baiyulong’ pitaya fruit were immersed in 0.1 mM sodium nitroprusside (a NO donor) for 8 min, inoculated with spore suspension of C. gloeosporioides after 24 h of NO treatment, and then stored at 25 °C for up to 8 days. NO treatment markedly inhibited the lesion expansion on pathogen-inoculated pitaya fruit during storage. NO treatment also reduced the natural disease incidence and index of pitaya fruit stored at 25 °C. Furthermore, NO treatment increased the activities of defense-related enzymes including phenylalanine ammonia-lyase (PAL), CoA ligase (4CL), peroxidase (POD), polyphenol oxidase (PPO), chitinase (CHI) and β-1,3-glucanase (GLU), as well as elevated the contents of antifungal compounds including total phenolics, flavonoids and lignin. In addition, NO treatment reduced respiration rate and weight loss, while delayed the declines of firmness and soluble solids content (SSC). These results indicate that NO could effectively enhance the resistance of pitaya fruit to anthracnose, which might be ascribed to activation of defense responses and retardation of senescence.

With the development of bioinformatics, it is easy to obtain information and data about thousands of genes, but the determination of the functions of these genes depends on methods for rapid and effective functional identification. Virus-induced gene silencing (VIGS) is a mature method of gene functional identification developed over the last 20 years, which has been widely used in many research fields involving many species. Fruit quality formation is a complex biological process, which is closely related to ripening. Here, we review the progress and contribution of VIGS to our understanding of fruit biology and its advantages and disadvantages in determining gene function.

Melatonin (MLT) is a vital signaling molecule that regulates multiple physiological processes in higher plants. In the current study, the role of MLT in regulating chilling tolerance and its possible mechanisms in litchi fruit during storage at ambient temperatures after its removal from refrigeration was investigated. The results show that the application of MLT (400 &mu, M, dipping for 20 min) to &lsquo, Baitangying&rsquo, litchi fruit effectively delayed the development of chilling injury (CI) while inhibiting pericarp discoloration, as indicated by higher chromacity values (L*, a*, b*) and anthocyanin levels. MLT treatment suppressed the enhancements of the relative electrical conductivity (REC) and malondialdehyde (MDA) content, which might contribute to the maintenance of membrane integrity in litchi fruit. MLT treatment slowed the decline in cellular energy level, as evidenced by higher adenosine triphosphate (ATP) content and a higher energy charge (EC), which might be ascribed to the increased activities of enzymes associated with energy metabolism including H+-ATPase, Ca2+-ATPase, succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). In addition, MLT treatment resulted in enhanced proline accumulation, which was likely a consequence of the increased activities of ornithine-&delta, aminotransferase (OAT) and &Delta, 1-pyrroline-5-carboxylate synthase (P5CS) and the suppressed activity of proline dehydrogenase (PDH). These results suggest that the enhanced chilling tolerance of litchi fruit after MLT treatment might involve the regulation of energy and proline metabolism.

Litchis are tasty fruit with economic importance. However, the extreme susceptibility of harvested litchis to litchi downy blight caused by Peronophythora litchii leads to compromised quality. This study aimed to study the effects of melatonin on postharvest resistance to P. litchii in 'Feizixiao' litchis. Results showed that melatonin restricted lesion expansion in litchis after P. litchi inoculation. Melatonin enhanced the activities of phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and 4-hydroxycinnamate CoA ligase while promoting the accumulations of phenolics and flavonoids. Nicotinamide adenine dinucleotide phosphate content and glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase activities were higher in treated fruit than control fruit. Higher energy status along with elevated H+-ATPase, Ca2+-ATPase, succinate dehydrogenase and cytochrome C oxidase activities were observed in treated fruit. Ultrastructural observation showed reduced damage in mitochondria in treated fruit. The results suggest that melatonin induced resistance in litchis by modulating the phenylpropanoid and pentose phosphate pathways as well as energy metabolism. .