Phenotypic Traits And Susceptibility To Diseases And Insect Pests Of Different Zanthoxylum Bungeanum Germplasm In Shaanxi Ecological Conditions

As an important ecological and economic tree species,Zanthoxylum bungeanum has a rich resource of germplasms.However,for the lack of consensus on the taxa,researchers and practitioners are often faced with difficulties in distinguishing and identifying specific varieties,which has hindered the further utilization of Zanthoxylum bungeanum resources.Shaanxi Province is one of the main planting areas of the red pepper in northern China.Due to the increase of Zanthoxylum bungeanum cultivation area and unreasonable management in recent decades,the occurrence of diseases and insect pests in Shaanxi Province is becoming more and more serious.Therefore,it is a major problem to clarify the harm and susceptibility of high-incidence venereal pests to Zanthoxylum bungeanum germplasm in the germplasm bank of Shaanxi Province,and it is necessary to find out the varieties suitable for popularizing and planting Zanthoxylum bungeanum germplasm in Shaanxi Province.In this study,482 Zanthoxylum bungeanum germplasms were selected from different sources to investigate their diversity of phenotypic traits and susceptibility to pests and diseases under the same ecological conditions in Shaanxi Province.The research offers a basic reference for Zanthoxylum bungeanum selection in Shaanxi,and provides superior parents with development potential for the breeding research on high-quality and pest-resistant Zanthoxylum bungeanum,thus contributing to both the theory and the practice of Zanthoxylum bungeanum resources utilization and germplasms protection.The main results are as follows:(1)Morphological study and quantitative classification were adopted to analyze character diversity of Zanthoxylum bungeanum germplasms from different sources.The genetic coefficients of variation and diversity indexes of 72 phenotypic characters were different accordingly,indicating that 482 germplasm materials had rich genetic diversities.In addition,a set of proxies for highly variable characters were established,such as leaf type,phenological period,prickly type,fruit type,skin hole type,skin pattern type,tree type,etc.,which could be used as key characters for the classification and identification of Zanthoxylum bungeanum germplasm resources.Besides,economic and agronomic traits with high genetic potential were identified,such as type with or without thorns,maturity stage,fruit hanging rate,fruit volume,fruit fresh weight,fruit volumetric weight,fruit density,etc.These traits are still calling for further improvement,which can be considered as indicators for the breeding research on high-quality Zanthoxylum bungeanum.(2)Relations between different traits were illustrated through correlation analysis,which revealed the interactions and restrictive relations among the traits.The results suggest that leaf character and tree type have direct effect on growth rate,phenological period,as well as the color and tightness of fruit.The productivity-related traits(pepper grain size,fruit volumetric weight,fruit weight,fruit volume,fruit lateral axis,fruit stalk,fruit hanging rate,etc.)are restricted by branch length.Type with or without thorns is positively correlated with growth location and tightness of fruit.A significant negative correlation between thorn density and fruit hanging rate is observed.There are many indexes affecting the fruit volume and pepper grain size,which demands a comprehensive consideration during the breeding of high-yield Zanthoxylum bungeanum.Altogether,these results build a basic understanding on the breeding of early-maturing,high-yield and thornless Zanthoxylum bungeanum.(3)Cluster analysis was introduced into this study,which divide the 482 Zanthoxylum bungeanum germplasm into 18 groups.The characteristics of different types and groups of Zanthoxylum bungeanum germplasm resources were preliminarily defined.Group No.18 is suitable for cultivating varieties with high fruit hanging rate and high yield potential.Group No.15 is applicable to the selection of heavyweight Zanthoxylum bungeanum.Group No.5can be used to breed large volume varieties,and relatively group Nos.1,4,6 and 9 are also acceptable alternatives.Group No.14 is available for choosing high granule density varieties.Several groups(group Nos.1,3,4,6,7,10,13,15 and 16)can help with the selection of thornless Zanthoxylum bungeanum.These results revealed the potential development value of each germplasm group from different perspectives,which manifests the inspiration that a proper selection among different advantageous germplasm groups of Zanthoxylum bungeanum can significantly improve its breeding efficiency.(4)In this study,a comprehensive evaluation model F was established to support the assessment on the overall performance of the Zanthoxylum bungeanum germplasm groups.According to the calculation,three germplasms(No.1,No.3,No.13)have excellent integrated traits with scores greater than 1.0.One germplasm(No.10)has a good comprehensive score over 0.8,and there are four varieties(No.4,No.15,No.6,and No.12)which own comprehensive scores ranging from 0.6 to 0.8.Compared to previous studies,this evaluation system adopts more indicators including tree type,tree potential,leaf type,prickle type,prickle density,prickle type,growth and development period,fruit tightness,fruit volume weight,pepper size,fruit hanging rate and other important agronomic and economic traits.For the further breeding research,this system also provides a practical reference on target trait setting and evaluation.(5)The critical diseases and insect pests(e.g.,root rot,Gummosis,rust,plaster disease,Aphis gossypii,Lycorma delicatula and Pochazia guttifera)of 18 Zanthoxylum bungeanum germplasm groups in Shaanxi were investigated.The occurrence patterns of these diseases and pests were summarized,whose hazard and host selectivity to different Zanthoxylum bungeanum cultivars were also clarified.The results reflect that under the same ecological conditions in Shaanxi Province,different germplasms have significant differences in the susceptibility to pests and diseases.Among the 18 Zanthoxylum bungeanum germplasm groups,12 were not susceptible to root rot,14 were not susceptible to Gummosis,13 were not susceptible to Zanthoxylum bungeanum rust,9 were not susceptible to plaster disease,14 were not susceptible to Aphis gossypii,9 did not suffer the targeted consumption by Lycorma delicatula,and Pochazia guttifera showed no directional selectivity to 7 of them.Particularly,the hazard symptom and occurrence patterns of Lycorma delicatula and Pochazia guttifera observed in Zanthoxylum bungeanum are reported for the first time.The results of this study clarify the susceptibility of different germplasms and present the key points of related disease control,thus providing reference to further research and practice on Zanthoxylum bungeanum resources utilization and germplasms protection in Shaanxi Province.