Preliminary Study On The Potential Of Different Loquat (Eriobotrya Japonica) Resources As Rootstocks

Loquat[Eriobotrya japonica?Thunb.?Lindl]is a mall evergreen tree and low-season fruit native to China.Its fruits are not only juicy and delicate,but also have highly nutritional and economic value.Over the years,loquat rootstock breeding is relatively backward,especially in dwarf tree shape,drought resistance and other aspects of no specific varieties.China is rich in loquat germplasm resources including many wild types and cultivated varieties.Loquat ploidy researches have made an important progress involved in diploid in vitro,triploid,tetraploid and aneuploid loquat.At present,the meaningful rootstock materials of loquat,such as dwarfing,drought tolerance etc.,were lack.In our study,we analyzed some traits of different types of loquat materials in order to provide a reference for searching the distinct loquat varieties as rootstocks.The key results of our research were summarized as follows:1.Identification and character observation of aneuploid strain H39.Based on karyotype analysis,an aneuploid strain H39 was identified as the natural offspring of a new triploid aneuploid cultivar‘Wuheguoyu'which its chromosome number is 39.H39 plant was characterized by compact tree shape,dwarf plant,small leaf shape index?leaf length/leaf width?,low net photosynthetic efficiency of leaves,and weak growth potential.The stomatal density of H39 leaves?228.15/mm²?was between diploid‘Ruantiaobaisha'?the female parent of‘Wuheguoyu'??260.77/mm²?and triploid‘Wuheguoyu'?199.12/mm²?.The size of the stomata was close to that of triploid‘Wuheguoyu',which is larger than that of diploid‘Ruantiaobaisha'.Compared with diploid and triploid,H39 had thinner leaves?thickness about 257.56?m?,underdeveloped palisade tissue?thickness about 76.92?m,only one cell layer?,and thicker sponge tissue?about 139.44?m?.The Thickness ratio of palisade tissue to spongy tissue was small?about 0.56?.The tightness of leaf tissue structure was low?about 29.90%?,and the percentage of palisade tissue to the mesophyll was small?about 35.63%?.What's more,the content of chl a,car content,chl t content,chl t+car content per unit leaf area,and chl a/b ratio were all lower.Functional leaf N,P and K elements were lower,Ca,Mg,Cu,Zn,Fe and Mn elements were higher.The content of ABA,ZT and GA₃/IAA in the young shoots of H39 plants was low.2.Performance of aneuploid H39 as an intermediate anvil.The diploid variety‘Huabai 1'was grafted with aneuploid H39,triploid‘Wuheguoyu'and‘Ruantiaobaisha'as the intermediate stocks,which were denoted as Huabai/Aneuploid and Huabai/Triploid and Huabai/Diploid.The results showed that the scion growth rate and net photosynthetic rate of Huabai/Aneuploid and Huabai/Triploid were similar,which were lower than that of Huabai/Diploid.The chla a content,car content,chl t content,and chl t+car content per leaf area of Huabai/Aneuploid and Huabai/Triploid were similar,which were lower than those of Huabai/Diploid.The contents of Ca,Mg,Cu,Mn in mature leaves of Huabai/Aneuploid were higher,while the contents of N,K,Mg,Cu,Zn,Fe,Mn in leaves of Huabai/Triploid were all lower than those in the other two groups in a varying degree.Additionally,the ABA content?July and September?,IAA content?July and September?and ZT content?June,September and September?in young shoots of Huabai/Aneuploid were lower than that of Huabai/Diploid.The content of ABA?June,July,September?and IAA?July,September?in young shoots of Huabai/Triploid was lower than that of Huabai/Diploid.3.Observation of seed and seedling traits of natural tetraploid offspring.To preliminarily analyzed the potential value of natural tetraploid loquat as rootstock,study observed the main characters of tetraploid loquat seeds and seedlings.The number of seeds of tetraploid strains?1.30².20?was small,the seeds were large,the quality of single seeds was large,and the shape of seeds was diverse?mostly semicircular,few circular,oval,triangular,etc.?.By chromosome counting,the proportion of tetraploid?B456?in tetraploid offspring reached 73.49%,mostly tetraploid.Besides,the seedlings obtained by sowing had various forms.The leaves were mostly obovate,the leaf apex was acute-shaped and the leaf was dark green.The first-rate seeds?seed length>15 mm,seed width>12 mm,seed thickness>9 mm?had a high seedling rate?for example,B431 had a first-rate seed seedling rate of 46.05%,while the second-level seeds have a seedling rate of only 9.68%?.The seed shape also affected the seedling rate to a certain extent.Compared with diploid,natural tetraploid loquat seed had obvious advantages in seedling growth,such as higher plant height,coarser ground diameter,longer root system,heavier fresh weight,and higher water content.4.Screening of drought-tolerant diploid strains.To obtain materials with strong tolerance to drought and provide a reference for the subsequent selection of rootstocks for loquat drought resistance,17 seedlings of loquat varieties?strains?were selected for drought treatment.In this study,the test was performed in August and September and the daytime temperature was above 32?during our treatment.And three materials with strong drought resistance were initially screened without water for 17 days which were‘Bingtangzhong'and‘Changlv No.5',‘Ninghaibai'.Their survival rate and survival rate after rehydration were both 100%,but the survival rate and survival rate after rehydration were both below 80%for the other materials.Among them,‘Ninghaibai'had a large drought tolerance limit,but the recovery time of plants after water stress was relatively long.While,‘Bingtangzhong'and‘Changlv No.5'recovered faster after rewatering,and‘Bingtangzhong'has the least drought damage.Our study confirmed that aneuploidy loquat grows slowly and photosynthetic efficiency is low.And it also can dwarf the tree shape to a certain extent as a rootstock,which may be related to its element content and hormone content.The offspring of tetraploid loquat are relatively similar and their seedlings are stronger.These characters prove that tetraploid loquat is a potential material used as rootstocks.Drought treatment screening has obtained more drought-tolerant materials such as‘Bingtangzhong',‘Changlv No.5,and‘Ninghaibai'.These results provide an important reference for the subsequent researches in order to search the distinct loquat varieties as rootstocks.