Study Of The Pathogen Of Begonia Anthracnose And Its Biological Control

The begonia is one of the most important ornamental plants in horticultural trade and is cultivated widely as a potted plant in China.In 2017,we received diseased begonia plants from a greenhouse in Taigu,Shanxi province of China.1.Anthracnose symptoms including large,sunken,brown lesions with numerous black acervuli were observed on begonia stems.Leaves were also infected.Foliar symptoms first appeared at the leaf margin.Infected leaves developed brown lesions with acervuli and the entire leaf could become blighted as the lesions coalesced.Severe infection usually resulted in the death of plants.2.Pure cultures were obtained and transferred to potato dextrose agar(PDA)at 25? for 10 days.Colonies grown on PDA were gray white at first,subsequently turning grayish to dark gray with smooth margins and sparse aerial mycelium.The average daily radial growth was 11.2 mm.Abundant acervuli with mucilaginous,salmon pink spore masses were observed in the cultures after 10 days of incubation.Conidia were hyaline,one-celled,falcate,with a prominent clear area in the center of highly granular cytoplasm,and measured 18.5 to 27.6 ?m×1.9 to 4.7 ?m(mean = 23 × 3.2 ?m).Setae were straight,dark brown,and septate.The isolates were identified as Colletotrichum truncatumon the basis of the cultural and morphological characteristics.3.Sequences of the internal transcribed spacer(ITS1/ITS4),glyceraldehyde-3-phosphate dehydrogenase(GAPDH)and ?-tubulin(TUB2)regions of 3 representative isolates were amplified and submitted in GenBank.Sequence analysis of the ITS-rDNA(GenBank No.MG009236,MG009237,MG009238),GAPDH(MG686558,MG686559,MG686560),?-tubulin(MG686561,MG686562,MG686563)obtained from the three representative isolates revealed 99 to 100%sequence identity with C.truncatum strains(KP748222,KP823799,KF697365)from GenBank.4.Pathogenicity tests were performed.After 5 days,initial symptoms of the disease were observed on leaves and stems of inoculated begonia and control plants did not show any symptoms of infection.C.truncatum was consistently reisolated from symptomatic tissue,thereby completing Koch's postulates.5.The effects of temperature,pH,carbon source and nitrogen source on the mycelial growth and conidia germination of C.truncatum were studied in this experiment.It was found that the optimum growth temperature for C.truncatum was 25-30 ?,and the optimum pH value was 7.A variety of carbon sources,such as monosaccharides and disaccharides,as well as organic nitrogen and inorganic nitrogen can be used by mycelium.The optimum carbon source was glucose.The optimum nitrogen source was sodium nitrate and glycine.The optimum temperature for conidia germination was 30-35 ?,the germination rate of conidia was the highest at 35 ?.6.The results of biological control study showed that the tested antagonistic bacteria Jk-2,D-9,D-29 and D-23 have certain inhibitory effect on C.truncatum,among which D-29 has the best antifungal activity.14 tested plant extracts could inhibit the mycelial growth of C.truncatum at the concentration of 2.0 mg·mL-1.The antimicrobial activity of clove?Acorus tatarinowii?Cnidium monnieri?radix?angelicae?pubescentis were over 80%.And the inhibitory effect of clove extract on mycelium growth reach 100%.Further study showed that the inhibitory activity of clove extract on mycelium growth of C.truncatum was positively correlated with the change of mass concentration.The inhibitory activity of the extract with 0.5 mg-mL-1 on mycelial growth was 87.88%.and its ECso value was 0.22 mg·mL-1.