Research on the pathogen and infection regularity of blueberry disease while in storage

Abstract:【Objective】The blueberry is a type of small fruit, succulent and highly susceptible to post-har-vest pathogen invasion, resulting in the fruit commodity rate being down, the shelf life being shortenedand also serious losses to the blueberry industry. To make clear the pathogen and infection regularity ofblueberry post-harvest disease while in storage and to formulate reasonable and effective post-harvest dis-ease control measures will have great significance in extending the shelf life of blueberries and promotingthe healthy development of the blueberry industry.【Methods】7 blueberry varieties were collected from thesouth of Liaoning province, and the fruit of each cultivar had the same ripeness,health and was disease-free. 50 experimental fruits selected from the 7 varieties were stored in a plastic perforated box, and the re-sults from testing were obtained after being repeated 3 times. After 6 days, to ensure the fruit achieved itsnatural incidence, we applied the conventional tissue isolation method on the edge of the fruit spot diseaseand observed its health at the junction of the excised 3 mm × 3 mm lesion size by applying 70% alcoholfor 30 s, and then a 0.1% Hg Cl2 solution after 10 s by immersion with sterile water and then washed threetimes and the lesions were seperated in a PDA culture medium at 25 ℃. Morphological identification wasbeen done according to the colony's color, shape and size of the different spores. Pathogenicity identifica-tion was carried out according to Koch's postulates. The healthy and full uniform size blueberry fruits after disinfection with 75% ethanol were placed in the bottom of a culture dish lined with filter paper, and then sprayed with different strains of spore suspension(concentration was about 2×105per m L) on the surfaces of the fruit which were cultured at 25 ℃ while spraying sterile water as a control. After 4-7 days,when we found that the hyphae had grown out at the pedicel or skin surface, we observed the isolation of the pathogens to see whether or not they were consistent with the ones isolated from the diseased fruit. We collected each of the 50 experimental fruits from the 7 blueberry varieties, whether stem or stemless, packing them in plastic perforated packaging boxes, each treatment being repeated three times, and stored at25 ℃. After every 4, 6, 8, 11, 13 d intervals, we surveyed each variety whether stem or stemless to determine their disease incidence and also the incidence of the pedicel and other parts of the fruits of each cultivar and then analyzed further with statistical software.【Results】The pathogens were isolated and identified from the diseased fruits of the 7 cultivars during storage. We obtained four types of pathogens which can cause blueberry decay. Morphology identification confirmed that they were Botrytis cinerea, Alternaria sp., Penicillium sp. and Trichothecium roseum. The isolation rates for these four types of fungi were81.85%, 77.23%, 62.43% and 17.19%, respectively. By inoculating their identification, we found that the four strains were all responsible for the blueberry post-harvest disease. Post-harvest disease incidence rates were significantly different among the different blueberry cultivars in storage whether being stem or stemless. The average incidence rate for the different varieties of fruits with stems was 2.95%, while the average incidence rate for the stemless fruits was up to 21.81%. The experimental results showed that the post-harvest disease incidence of stemless fruit was significantly higher than the fruits with stems; the average disease incidence rate of pedicle and other parts of the surface of the cultivars‘Reka'‘Berkeley'‘Spartan'‘N5'‘Bluebird'‘Bluecrop'and‘Northland'were 25.29% and 5.07%, 34.67% and 8.06%,18.24% and 4.34%, 8.67% and 1.33%, 11.16% and 6.63%, 29.11% and 8.00%, 23.51% and 5.50% respectively while in storage for 6 d. The experimental data showed that the pedicle was the main pathogenic site of blueberry post-harvest disease, and the other parts of the surface of the fruits were less serious than the pedicle. The disease incidence rates of‘Reka'‘Berkeley'‘Spartan'‘N5'‘Bluebird'‘Bluecrop'and‘Northland'in storage for 4, 6, 8, 11, and 13 d at room temperature indicated that the progress rate of blueberry post-harvest disease among the different cultivars had significant differences. When in storage for 4 d, the different cultivars had incidence rates of 8.63%-27.13%, the lowest incidence cultivar was‘N5'and the highest one was‘Reka'; when in storage for 11 d, the high incidence cultivars were‘Berkeley'‘Reka'and‘Bluecrop', with their incidence rates being 46.25%, 42.12% and 36.39% while the low incidence cultivars were‘N5'and‘Bluebird', with their incidence rates being 19.64% and 24.54% respectively; when in storage for 13 d,the high incidence cultivars were‘Berkeley'and‘Reka', the incidence rates being 46.25% and 45.27%, and the low incidence cultivars were‘N5', with the incidence rate only being 26.19%; from the analysis of the data of different blueberry varieties for the post-harvest diseases, the rapid progress rates for the post-harvest disease cultivars were‘Berkeley'and‘Reka',while the slowest progress rate cultivar was‘N5'. The moderate cultivars were‘Bluecrop'‘Northland'‘Spartan'and‘Bluebird'. Based on the different blueberry varieties after being in storage for 6 d when considering the total incidence rates for the post-harvest diseases, the survey results showed that the different varieties of incidence rates from low to high in order were‘N5'‘Bluebird'‘Spartan'‘Northland'‘Reka'‘Bluecrop'and‘Berkeley'. The incidence rates of‘Berkeley'and‘Reka'were 42.72% and37.11% respectively, and they exhibited the same significance levels; and the incidence rate of‘N5'was10.00%, significantly lower than that of‘Berkeley'and‘Bluecrop'; the incidence rates of‘Reka'‘North-land'‘Spartan'and‘Bluebird'were 30.37%, 29.01%, 22.58% and 17.79% respectively, and there were no significant differences at the level of 5%. Therefore, from the point of view of acquisition of the seven varieties of blueberries, the resistant cultivar was‘N5', the less resistant varieties were‘Berkeley'and‘Bluecrop', and the middle resistant varieties were‘Reka'‘Northland'‘Spartan'and‘Bluebird'.【Conclusion】The pathogens causing blueberry post-harvest diseases are Botrytis cinerea, Alternaria sp., Penicillium sp. and Trichothecium roseum in the south of Liaoning province. The Pedicle is the main location of the disease. The resistent cultivar for blueberry post-harvest diseases is‘N5', the moderate ones are‘Bluecrop'‘Reka'‘Northland'‘Spartan'and‘Bluebird', while the susceptible cultivar is‘Berkeley'.