Optimization Of Fermentation Conditions Of Bacillus Subtilis Strain Bs-0728and Its Biocontrol Effect Against Apple Replant Disease

Apple replant disease (ARD) also known as continuous cropping obstacle, is aworldwide problem in replanted apple orchards. Fungicides treatment and soil fumigantsare the most effective method for ARD, the high toxicity and environmental cost ofpre-plant fumigation has led to the phasing out of common soil fumigants. Thecharacteristics including propagated rapidly, easy to colonize, wide antibacterialspectrum, and strong stress resistance, Bacillus subtilis is a kind of ideal biocontrol agent.Biocontrol bacteria B. subtilis Bs-0728strain was isolated from apple replanted soil byour research group, which has antagonism effect against19kinds of ARD pathogens. Inorder to improve the amount of Bs-0728spores in the medium, single factor experimentsand orthogonal experiments were used to optimize the fermentation medium andconditions of Bacillus subtilis Bs-0728. The results showed that: the optimal liquidmedium formula was corn flour1%, peanut meal1%, NaH2PO30.4%+Na2HPO30.4%.The optimum culture conditions were: the initial pH was7.2-7.5，the concentration ofMn2+was200mg/L. Seven days under the condition of the optimal fermentation, thenumber of spores in fermentation broth was4.92×1014cfu/mL. The optimal solid culturemedium was: corn meal100g/kg, peanut meal50g/kg, CaCl28g/kg, the ratio ofmaterial water2:5, temperature28-30℃.Laboratory tests and field tests were used to study the inhibition effect of B. subtilisBs-0728on apple replant disease pathogen and the control effect on apple replant disease.Laboratory test results showed that Bs-0728had antagonism effect on apple replantdisease pathogens. Meanwhile, Bs-0728could promote the radicle elongation of Malusrobusta. The disease incidence rate of reduced from13.33%to6.67%. Two years potsexperiments results showed that Bs-0728strain had significant prevention and controleffect on replant disease. The height and root length of potted Malus seedlings treatedwith Bs-0728increased22.6%and19.5%seperately, dry weight increased96.2%. The diameter increased amount of field apple trees increased by66.1%. Colonizationdynamic test results show that Bs-0728strain can successfully colonize the rhizosphereof apple trees at least120days.