Shuangshuang Tang

Improved control of anthracnose rot in loquat fruit by a combination treatment of Pichia membranifaciens with CaCl2

The beneficial effect of 2% CaCl(2) (w/v) on the antagonistic yeast Pichia membranifaciens for control of anthracnose rot caused by Colletotrichum acutatum in postharvest loquat fruit (Eriobotrya japonica L.) and the possible mechanisms involved were investigated. The results showed that treatment with P. membranifaciens at 1x10(8) CFU ml(-1) or 2% CaCl(2) alone both resulted in significantly smaller lesion diameter and lower disease incidence of anthracnose rot on loquat fruit wounds compared with the controls. The biocontrol activity of P. membranifaciens on the disease was enhanced by the addition of 2% CaCl(2), the combined treatment of P. membranifaciens with CaCl(2) resulted in a remarkably improved control of the disease in comparison with the treatment of P. membranifaciens or CaCl(2) alone. P. membranifaciens in combination with CaCl(2) induced higher activities of two defense-related enzymes chitinase and beta-1,3-glucanase in loquat fruit than applying the yeast or CaCl(2) alone. The in vitro experiment showed that the addition of 2% CaCl(2) in the suspensions of P. membranifaciens significantly inhibited spore germination and germ tube elongation of C. acutatum than the yeast or CaCl(2) alone. However, adding CaCl(2) did not significantly influence the population of P. membranifaciens in NYDB medium or fruit wounds. These results suggest that CaCl(2) could improve the biocontrol activity of P. membranifaciens on anthracnose rot in loquat fruit. It is postulated that the improved control of the disease is directly because of the higher inhibitory effect on pathogen growth and indirectly because of the enhanced disease resistance in loquat fruit by the combination treatment.

Effect of 1-methylcyclopropene treatment on chilling injury, fatty acid and cell wall polysaccharide composition in loquat fruit.

Loquat fruit was treated with 2.32 nmol L(-1) 1-methylcyclopropene (1-MCP) for 24 h at 20 degrees C, and then stored at 1 degrees C for 35 days to investigate the effect of 1-MCP treatment on chilling injury (CI) and fatty acid and cell wall polysaccharide composition. Loquat fruit developed CI, manifested as increased fruit firmness, internal browning and decreased extractable juice. These CI symptoms were reduced by 1-MCP treatment. 1-MCP-treated fruit exhibited higher levels of linoleic and linolenic acid and a higher unsaturated/saturated fatty acid ratio than control fruit during storage. The treatment also markedly delayed increase in alcohol insoluble residue, i.e. hemicellulose and cellulose. Meanwhile, the level of water- and CDTA-soluble pectins in treated fruit was higher than that in control. Our result suggested modifications of fatty acid and cell wall polysaccharide composition are associated with CI develpoment in loquat and 1-MCP treatment modulates the changes that seem to regulate the strength of cell wall and so to alleviate CI.

Biological control of post-harvest anthracnose rot of loquat fruit by Pichia membranefaciens

Summary The effect of Pichia membranefaciens on reducing post-harvest anthracnose rot caused by Colletotrichum acutatum in loquat fruit was investigated. Fruit were treated with different suspensions of P. membranefaciens before challenge with 1.0 105 spores ml–1 of C. acutatum, then incubated at 20°C for 6 d. The results showed that 1 108 colony-forming units (CFU) ml–1 of washed cell suspensions of the yeast provided better control of anthracnose rot than yeast in culture broth at the same concentration. Treatment with autoclaved cell cultures or culture filtrates did not prevent the incidence of disease. The concentration of a washed cell suspension of P. membranefaciens had a significant effect on the efficacy of controlling anthracnose rot in loquat fruit. At a concentration range from 1 106 to 1 109 CFU ml–1, the higher the concentration of the antagonist, the lower the incidence of the disease and the smaller the diameter of the lesions. In inoculated wounds of loquat fruit, populations of P. membranefaciens increased approx. 34-fold after 6 d of incubation at 20°C.Washed cell suspensions of P. membranefaciens also significantly inhibited spore germination and germ-tube growth of C. acutatum, in vitro. These results suggest that P. membranefaciens has potential as a biocontrol agent to reduce post-harvest decay caused by C. acutatum in loquat fruit.

The effects of 1-methylcyclopropene on chilling and cell wall metabolism in loquat fruit.

Summary Loquat (Eriobotrya japonica L.) fruit were pre-treated with 0 (control) or 50 nl l–1 1-methylcyclopropene (1-MCP) for 24 h at 20°C, then stored at 1°C for 35 d to investigate the relationship between chilling injury and cell wall metabolism. Chilling increased fruit firmness and browning, and decreased the extractable juice content, with fewer symptoms of chilling injury in treated fruit. 1-MCP inhibited the activities of phenylalanine ammonia-lyase, cinnamyl alcohol dehydrogenase, 4-coumarate:coenzyme-A ligase, peroxidase, polyphenol oxidase, and slowed lignification. Treated fruit had a higher polygalacturonase activity, higher contents of water-soluble pectins, and lower contents of water-insoluble pectins compared with values in control fruit. These results suggest that the reduction in chilling injury in loquat caused by 1-MCP was primarily due to inhibition of lignin accumulation, a higher PG:PME ratio, and enhanced solubilisation of pectin in the cell walls.