Research on chemical control of peach shoot blight and the association between phloem volatile compounds and resistance

HU Zhu; WANG Li; ZHAO Hongyue

doi:10.13925/j.cnki.gsxb.20250423

Abstract：[Objective]Prunus persica(L.)Batsch,a member of the Rosaceae family,is native to China and has a cultivation and evolutionary history spanning thousands of years.In recent years,peach shoot blight caused by Diaporthe amygdali has been one of the most prevalent fungal diseases in major peach-producing regions of southern China.This study aimed to screen out highly effective chemical fungi-cides for controlling peach shoot blight,and investigated the relationship between volatile compounds in the phloem of peach shoots and resistance to the disease,providing a scientific basis for integrated disease management strategies and resistance breeding programs.[Methods]The inhibitory effects of 15 fungicides against D.amygdali were evaluated in vitro using the mycelial growth rate method.The active ingredient information was as follows:difenoconazole,pyraclostrobin,propiconazole,boscalid,carbendazim,hymexazol,flusilazole,fludioxonil,hexaconazole,prochloraz,azoxystrobin,trifloxys-trobin,tebuconazole,lprodione,and dithianon.A series of concentrations were prepared for each fungi-cide.The effective medium concentration(EC50)values were calculated based on the correlation be-tween fungicide concentration and mycelial growth inhibition rate by DPS in this study.At the same time,healthy and disease-free one-year-old shoot phloem tissues were collected from 22 peach variet-ies,which exhibited varying levels of resistance to D.amygdali.After rapid freezing within the liquid nitrogen,the samples were transported to the laboratory for volatile compound analysis.Volatile com-pounds were extracted and analyzed using Headspace Solid-Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry(HS-SPME-GC-MS).The correlation between the relative content of each identified volatile compound and the resistance level of the corresponding variety was exam-ined.In addition,two typical peach cultivars(Fenghua Pantao,susceptible;and Hakuho,highly suscep-tible)were selected for inoculation with D.amygdali.Phloem tissue around necrotic spots was collected 7 days after inoculation,flash-frozen,and used for volatile compound analysis.Key volatile compounds significantly correlated with resistance(identified in the correlation analysis)were quantified in these tissues to observe pathogen-induced changes.[Results]The toxicity test of fungicides showed that pro-chloraz had the strongest inhibitory effect,with an EC50 value of 0.004 2 mg·L1.Difenoconazole,pyra-clostrobin,propiconazole,fludioxonil,flusilazole,hexaconazole,and tebuconazole also showed strong activity.Boscalid showed the weakest inhibitory effect,with an EC50 value of 49.025 2 mg·L-1.Analysis of volatile compounds content showed that volatile compounds were identified in 22 peach samples.A total of 121 volatile compounds were identified,falling into 12 distinct categories:30 terpenoids,22 es-ters,17 alcohols,16 ketones,13 aldehydes,5 alkanes,4 fatty acids,3 phenolics,3 furans,2 acids,1 lac-tone,and 5 other compounds.Among the samples,Richuan Baifeng and Reddomun had the highest number of volatile compounds,with 85 and 80,respectively.In contrast,the samples Baihua and Zhoux-ingshantao had the fewest,with 52 and 51 compounds,respectively.To identify volatile metabolites as-sociated with resistance to D.amygdali,we conducted a correlation analysis between the volatile sub-stance content and germplasm resistance to D.amygdali across 22 samples.Sixteen compounds were significantly and negatively correlated with resistance,and six were significantly and positively correlat-ed.Negatively correlated compounds included one acid,one aldehyde,two alkanes,two esters,one fat-ty acid,four ketones,one phenolic compound,and four terpenoids.The ester compound icosyl oleate had the strongest negative correlation,with a coefficient of-0.676 5(P＜0.01).Positively correlated compounds included one alcohol,two aldehydes,one ester,one ketone,and one terpenoid.Among these,the aldehyde 2-heptenal had the highest positive correlation,with a coefficient of 0.570 4(P＜0.01).The distribution of two volatile compounds(a:n-Hexadecane;b:1-Nonanol)with different resis-tance level to D.amygdali of 22 peach varieties was revealed.To further validate the relationship be-tween volatile compounds and shoot blight resistance,we selected two peach cultivars with different re-sistance levels and inoculated them with D.amygdali.After 7 days,lesion diameters reached 52.62 mm in Fenghua Pantao and 84.50 mm in Hakuho.Volatile compounds in the phloem tissue around the le-sions were analyzed in both samples.After inoculation,the content of the volatile compound 2-hep-tenal,positively correlated with resistance,rapidly increased in the susceptible germplasm Fenghua Pan-tao,in comparison to the highly susceptible germplasm Hakuho,suggesting that higher 2-heptenal lev-els may enhance resistance.Benzoic acid,negatively correlated with resistance,was induced in both germplasms,but the increase was smaller in susceptible peaches,suggesting that lower accumulation may reduce resistance.[Conclusion]Among the 15 fungicides,prochloraz exhibited the strongest inhib-itory effect,with an effective medium concentration value of 0.004 2 mg·L-1.Correlation analysis iden-tified 16 compounds that were significantly and negatively correlated with resistance,with the ester ico-syl oleate showing the strongest correlation(r=-0.676 5).Six compounds were significantly and posi-tively correlated,with 2-heptenal showing the highest correlation(r=0.570 4).This study layed an im-portant theoretical foundation for achieving sustainable comprehensive control of peach shoot blight.