Researsh On Pseudostellaria Heterophylla Resistance To Leaf Spot Mutants And Elicitors Screening

Pseudostellaria hererophylla, also called "hair shen" in Chinese, is a member of Caryophyllaceae(the pink family). As a traditional Chinese herb with tonic effects. leaf spot has evolved as a mainconstraint to the production of this crop. In China, the prevailing control means for leaf spot ofPseudostellaria hererophylla mainly involves use of agronomic practices and chemicals. This methodnot only has undesirable control effect, but also may cause chemical residues and environmentalconcerns. Unfortunately, thus far there is scanty report concerning disease resistance breeding of thevaluable crop, and no cultivars with leaf spot resistance are currently available. Conventional breedingschemes are therefore impeded by the lack of sources of resistance. There is an urgent need to findnovel ways to disease control.Based above, carried out Pseudostellaria heterophylla resistance to leaf spot mutants and Elicitorsscreening studies, shew the following results.1) Pseudostellaria hererophylla leaf spot pathogen identification: In the present study, thetaxonomic status of the causal pathogen of Pseudostellaria hererophylla leaf spot was clarified based onmicroscopy section observations, isolation and purification of the pathogen, and pathogenic test throughartificial inoculation. It was confirmed that the pathogen belonged to Phyllosticta, Sphaeropsidales,Coelamycetes, Deuteromycota.2) Pseudostellaria hererophylla resistance to leaf spot mutants screening: Calli were induced fromcultures of Pseudostellaria hererophylla and test-tube plantlets regenerated in vitro. Effects of crudetoxin of Phyllosticta sp. of different concentrations on in vitro plant regeneration were studied. Resultsshowed that the crude toxin inhibited callus subculture and differentiation as well as plant regeneration,with inhibition effects in proportional to the toxin concentrations used. For obtaining desired callusmutants, the preliminary selection pressure of crude toxin was set at15-20ml/L, and the survival ratewas12.3%-19.0%. More subcultures of calli in the presence of lower toxin concentrations increased tosome extent their ability to tolerate higher concentrations of the toxin in subsequent cultures, and the25ml/L toxin were also acceptable. The optimum toxin concentration was recorded at10-20ml/L forselectionin the process of the differentiation of the callus mutants, and the percentage of differentiationof adventitious buds ranged from40.0%-52.7%. Fifty to seventy milliliters per liter of crude toxin wereoptimal to the selection of regenerated plantlet mutants, and the percentage of death caused by wilt was44.5%-75.3%. Resistance in the mutant plants recovered from stressed cultures was identified. The M1plantlets exhibited higher resistance to leaf spot compared to the wild type check, Zheshen No.1(statistically different at0.01level). Callus mutants and regenerated plantlet mutants did not differsignificantly in the percentage of highly resistant plants obtained, but differed significantly inmoderately resistant plants obtained. M2plantlets were found to have an average disease index (DI) of21.7, and were identified as resistant, in contrast to the average DI of66.7in the susceptible controlcultivar, Zheshen No.1. The study demonstrated that resistance was retained through clonal propagation.3) Pseudostellaria hererophylla resistance to leaf spot Elicitors screening: Changes in enzymeactivity of PAL, POD and PPO in leaves of regenerated plants of Pseudostellaria hererophylla weremeasured by spectrophotometry essays following treatment with resistance inducers including sodiumselenite, potassium hydrogen phosphate, chitosan, oxalic acid, salicylic acid, and self-made crude toxinof leaf spot of Pseudostellaria hererophylla. All the3defense enzymes showed marked increase inactivity after induction treatment. For PAL, the inducers listed from the most desirable to the leastdesirable were oxalic acid, salicylic acid, chitosan, sodium selenite, potassium hydrogen phosphate,andcrude Phyllosticta sp. toxin; for POD, they were oxalic acid, chitosan, salicylic acid, sodium selenite,potassium hydrogen phosphate,and crude Phyllosticta sp. toxin; for PPO, the order was oxalic acid,chitosan, sodium selenite, salicylic acid, potassium hydrogen phosphate,and crude Phyllosticta sp. toxin.The regenerated plants treated with various inducers all showed significantly higher resistance than theuntreated control, as demonstrated by resistance identification using crude toxin of the leaf spotpathogen. Oxalic acid at concentrations of190mg/L and380mg/L was most effective in inducingresistance, with average DI of21.5and22.7respectively (average DI of the control was as high as89.8),which was much lower than the DI of any other treatment and the control (significance at0.01level).