| Apple nursery plants are the basis of apple cultivation.The overall quality of apple nursery plants in China is low and the virus infection is serious,which has become one of the bottlenecks restricting the transformation and upgrading of apple industry.Shaanxi Province is the largest province of apple industry and apple nursery plants industry in China.In order to understand the quality of apple nursery plants and the situation of virus infection in Shaanxi Province,and to provide a focus for the research and development of high-quality virus-free nursery plants breeding technology,the quality and virus infection of apple nursery plants in Shaanxi Province were investigated comprehensively in this study.On this basis,efficient virus-free technology of main varieties and rootstocks was developed for Shaanxi Province.Provincial nursery stock industry transformation and upgrading to provide technical support.The results are as follows:The quality of 1050 samples of apple nursery plants from 7 main producing areas in Shaanxi Province was systematically investigated and compared with the national standards of apple nursery plants.The results showed that:(1)The quality of 3-year dwarfing interstock nursery plants are poor,the proportion of conventional nurseries meeting the standard of grade 1 nursery plants is 5.33%,and that of demonstration nurseries are only 29.17%.The quality of 3-year dwarfing rootstock nursery plants is significantly better than that of dwarfing interstock nursery plants,the proportion of grade 1 dwarfing interstock nursery plants in general nursery is 63.75%,and that of grade 1 in demonstration nursery is higher than 70%.(2)The average height of nursery plants is higher than 149 cm,and the proportion of grade 1 nursery plants is higher than 80%.The average diameter of dwarfing interstock and dwarfing rootstock nursery plants in general nursery is 9.57 mm and 13.08 mm,respectively,and the proportion of grade 1 nursery plants is 12.3% and 95.0%,while the average diameter of nursery plants in demonstration nursery is 11.45 mm and 15.9 mm,and the proportion of grade 1 nursery plants is 40.6% and 96.7%.The average number of lateral roots of dwarfing interstock and dwarfing rootstock nursery plants in general nursery were 4.52 and 6.6 respectively,and the proportion of grade 1 nursery plants required was 45% and 90%,while the average number of lateral roots in demonstration nursery was 5.45 and 6.81,respectively,and the proportion of grade 1 nursery plants required was 66.6% and 100%.(3)The proportion of rootstock length of dwarfing interstock nursery plants meeting national standards is higher than 47.0%,while that of dwarfing rootstock is lower than 10.0%;the proportion of the length of interstock meeting national standards in general nursery is 31.7%,63.1% in demonstration nursery;and the proportion of inclination and full buds in shaping zones meeting national standards is higher than 90%.There are 11 nurseries with branches,but the number of branches is less than 5 in most nurseries.In 2018,the number of branches in Qianyang demonstration nursery is obviously superior to that in other nurseries,with an average value of 17.8.The nursery density of different nurseries varies greatly,among which the lowest is Qianyang demonstration nursery,with a nursery density of 2200 plants per mu,while that in Fufeng general nursery is as high as 32000 plants per mu.Compare to the lowest density and the highest density,The average values of lateral root number,height and diameter of nursery were 2.5,19.1 cm and 6.49 mm,respectively.(4)Comprehensive analysis showed that the main factors limiting the quality of nursery plants were the number of lateral roots and the diameter of nursery plants.The key factors were the density of nursery plants and the management of fertilizer and water.In addition,the national standards should be revised and improved to reduce the length of rootstock and interstock and increase the require of branches.In 2017 and 2018 years,420 samples of apple nursery plants from 7 major apple nursery plants producing areas in Shaanxi Province were detected by RT-PCR for two consecutive years.The results showed that:(1)The infection rate of apple virus in Shaanxi Province is as high as 87%.Six kinds of virus: Apple stem groove virus(ASGV),Apple stem pox virus(ASPV),Apple chlorotic leaf spot virus(ACLSV),Apple scar skin viroid(ASSVd),Apple mosaic virus(ApMV)and apple dimple fruit viroid(ADFVd)all occur in Shaanxi nursery,and the infection rates are 78.86%,59.43%,46.29%,28.67%,52.15%,and 40.12% respectively,and accorded with the high compound infection rate(infection rate of more than one virus),about 60%.There was no significant difference in virus infection between general nursery and demonstration nursery.(2)The incidence of ApMV observed by naked eye was less than 2%,while the infection rate of ApMV detected by PCR was more than 15%.The lowest infection rate of ApMV was 15.38% in Tongchuan nursery,and the highest infection rate was 35.48% in Fufeng nursery.This indicated that some samples were infected with virus but did not develop.The infection rate of virus in Qianyang nursery was low.The incidence of ASGV was only 50%.The incidence of ASPV and ACLSV was less than 20%.No ASSVd,ApMV and AFCVd were detected in nursery.(3)The results of four apple orchards in Luochuan showed that the virus infection rate was 67.62% and the compound infection rate was 38.1%.The infection rates of ASGV,ADFVd and ACLSV were 49.52%,37.14% and 25.71% respectively.The incidence of ASPV,ASSVd and APMV was lower than 5%.The tissue culture nursery plants of four rootstocks `M26',`MAC9',`B9'and one variety `Gala' were used as materials.For ASGV,ASPV and ACLSV viruses,the virus was detoxified by heat treatment at 42 ?/ 34 ? combined with shoot tip culture.The results showed that:(1)After 40 days of heat treatment,the survival rates of `M26',`MAC9',`B9',`Gala'tissue cultured nursery plants were 96.0%,48.0%,32.0% and 76.0%,respectively.(2)Among the three viruses,ASGV was the most difficult to remove.The removal rates of ASGV in the four materials were 41.7%,33.3%,37.5% and 61.2%,respectively.ACLSV was easy to remove,and the removal rate was higher than 70%. |
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