In vitro Antagonistic Potential, Plant Growth-promoting Activity and Indole-3-acetic Acid Producing Trait of Bacterial Isolates from Button Mushroom (Agaricus bisporus) Spent Substrate

Spent mushroom substrate (SMS) is widely used as a fertilizer and to control plant diseases. The microorganisms surviving in SMS play a crucial role in plant growth promotion and biocontrol activity. In this study, an effort was made to isolate and characterize the bacterial species present in the SMS of Agaricus bisporus and to study their antagonistic potential, plant growth-promoting ability and indole-3-acetic acid (IAA) producing trait. Six different bacterial isolates exhibiting morphological variabilities were obtained from the SMS by serial dilution technique. On the basis of 16S rRNA gene sequences, these isolates were identified as Staphylococcus epidermidis (Sh1 and Sh3), S. aureus (Sh2), Bacillus albus (Sh4), Delftia lacustris (Sh6) and Comamonas aquatica (Sh7). These bacterial strains were assayed for their antagonism against Pythium aphanidermatum, a phytopathogenic oomycete. The results of in vitro dual culture assay revealed that all the 6 bacterial isolates showed low levels of suppression of P. aphanidermatum and recorded less than 5 mm inhibition zone. Among the bacterial isolates, S. epidermidis Sh3 recorded the maximum inhibition zone of 4.2 ± 0.5 mm. Plant growth promotion test using roll paper towel method revealed that C. aquatica Sh7, B. albus Sh4, D. lacustris Sh6 and S. epidermidis Sh3 caused a significant increase in seedling vigour of cucumber compared to control. The seeds treated with the bacterial isolate C. aquatica Sh7 showed the maximum seedling vigor (2018 ± 255). Assessment of in vitro production of IAA by the bacterial isolates revealed that the bacterial isolates highly varied (ranging from 0.28 to 9.25 mg L-1) in their potential for production of IAA. The maximum amount of IAA was produced by C. aquatica Sh7 (9.25 ± 0.02 mg L-1). Further studies are required to assess the possibility of using the IAA-producing bacterial isolates identified in this study or their metabolites to promote plant growth or to enhance growth and yield of mushrooms. KeywoRds: Button mushroom; spent compost; IAA production; Agaricus bisporus; antagonistic activity; plant growth promotion. تاــتابنلل ةــضرملما تاــيرطفلا ةــحفاكم في اــضيأو دماــسك عــساو لكــشب موشرــلما رــطف جاــتنإ دــعب )تــسوبمك( كلهتــسلما دماــسلا مدختــسي :ةصلاخ:صلختــسلما فــ يصوتو لزــعب اــ نمق ةــساردلا هذــه في .يــجولويبلا ةــحفاكلما طاــشنو تاــ بنلا وــنم زــ يزعت في مًاــساح ارًود دماــسلا اذــه في شــ يعت يــ تلا ةــ قيقدلا ةــ يحلا تاــ نئاكلا بــعلت وـنم طيــشنتو تاــ يرطفلا ضــعب وــنم طـيبثت ىــع اــهتردق اــضيأ ةــساردلو Agaricus bisporus رــطف جاـتنإ في مدختــسي يذــ لا تــسوبمكلا اذــه في ةدوــجولما اــ ييرتكبلا يــ سلستلا فــ يفختلا ةــ ينقت مادختــ سإب اــ هيلع لوــ صحلا مــ ت ةــ فلتخم ةــ يرهاظ تاــ فص تاذ اــ ييرتكبلا نــ م تلازــ ع تــ س .كيتيــ سلأا ضــ مح -3 لودــ نلإا جاــ تنإو تاــ تابنلا ىــ ع )S1٦( كــ يلكوينوبيرلا ضــ مح ىــ ع ةدوــ جولما تاموــ سوبيرلا ةدــ حو لــ سلست في يــ نيجلا فــ ينصتلا مادختــ سإب اــ ييرتكبلا فــ ينصت مــ ت .تــ سوبمكلا زــ يكرت ىوــ تحم في و Delftia lacustris )Sh٦(و Bacillus albus )S4h(Hو S.aureus )Sh2( و Staphylococcus epidermidis )Sh 3 و 1Sh( اــهنإ ترـهظأ . Pythium aphanidermatumضرـملما بذاكـلا رـطفلا وـنم طـيبثت ىــع اـهتبرجت مـت ةـييرتكبلا تلالاـسلا هذـه .Comamonas aquatica )sh٧( ةقطنم تلجـسو ةضفخنم طـيبثت تايوتـسم ةتـسلا ةـييرتكبلا تلازـعلا عـيمج عـم P. aphanidermatum ستيـسيموأ نـم لك عـضو دـعب برـتخلما في تـيرجأ يـتلا جـئاتنلا تلجـس ،ةـييرتكبلا تلازـعلا نـب نـم . مـم ٥ نـم لـقأ طـيبثت B. و C. aquatica sh٧ نأ ةــ يقرولا لــ يدانلما تاــ فافل ةــ قيرط مادختــ ساب تاــ بنلا وــ نم راــ بتخإ فــ شك . مــ م ٠,٥ ± 4,2 طــ يبثت ةــ قطنم ىــ قأ S. epidermidis Sh3 ةـجلاعلما روذـبلا ترـهظأ . دهاـشلاب ةـنراقم راـيخلا تارداـب تاـبنإ ةوـق في ةيرـبك ةـيونعم ةداـيز في وببـست epidermidis Sh 3 . و D. lacustris Sh٦ و albus Sh4