Determination of Biocontrol Potentials of Endophytic Bacteria in Biological Control of Citrus Sour Rot Disease Caused by Geotrichum citri-aurantii

Abstract

Citrus fruits are susceptible to postharvest decays caused by various pathogenic fungal disease agents. Citrus sour rot, caused by Geotrichum citri-aurantii is one of the most important postharvest diseases of citrus fruits Although synthetic fungicides are commonly used to combat the disease, ineffectiveness of these applications as well as their harmful effects on human health and the environment have been reported in many studies recently. Biological control of postharvest diseases utilizing antagonistic bacteria has been explored in different host plant-pathogen interactions as a promising alternative to synthetic fungicides. In this study, biocontrol potentials of endophytic bacterial isolates, obtained from fruits, branch and leaves of healthy citrus trees, were investigated against Geotrichum citri-aurantii on petri plates (in vitro) and fruit tests (semi in vivo conditions). Among the 24 putative endophytic bacterial isolates isolated, sixteen different antagonist bacterial isolates were selected and assessed against mycelial growth inhibition of G. citri-aurantii in vitro studies. Among the bacterial isolates tested, Bacillus spp. isolates significantly inhibited mycelial growth of fungal agent by 59.5-78.6%. The highest mycelial growth inhibition was caused by B. subtilis CM8 (78.6%). Bacterial isolates of Acinetobacter johnsonii CT7, Erwinia herbicola CM5, Pseudomonas putida CL2, Pantoea agglomerans CM14, Acinetobacter lwoffii CP1 and Stenotrophomonas maltophilia CP3 failed to inhibit mycelial growth in dual culture assays. Antagonistic activities of bacterial isolates increased by the pre-incubation time before fungal inoculation. Bacterial isolates of Bacillus spp. caused considerably morphological changes such as vacuolation, shrivelling, swelling and lysis of hyphae close to inhibition zone. On artificially inoculated fruits, isolates of Bacillus spp. also found to suppressed disease incidence significantly by 56.7-83.3%. Due to strong antagonistic activities, isolates of Bacillus spp, tested in this study have the potential to be used as biofungicide for controlling post-harvest disease agent(s) of citrus fruits.

Keywords

• Citrus
• Sour rot
• Geotrichum citri-aurantii
• Antagonist
• Biological control
• Endophyte bacteria

Geotrichum citri-aurantii’nin Sebep Olduğu Turunçgil Ekşi Çürüklük Hastalığının Biyolojik Mücadelesinde Endofit Bakterilerin Biyokontrol Potansiyellerinin Belirlenmesi

Abstract

Turunçgil meyveleri, çeşitli fungal hastalık etmenleri tarafından neden olunan hasat sonrası hastalıklara karşı oldukça duyarlıdır. Geotrichum citri-aurantii'nin neden olduğu ekşi çürüklük, turunçgillerin en önemli hasat sonrası hastalıklarından biridir. Hastalıkla mücadelede genellikle sentetik fungisitler yaygın olarak kullanılsa da söz konusu uygulamaların son yıllarda etkisizliğinin yanı sıra insan sağlığı ve çevre üzerine olan zararlı etkileri birçok çalışmada bildirilmiştir. Hasat sonrası hastalıklara karşı antagonistik bakteri etmenlerinin kullanıldığı biyolojik mücadele, sentetik fungisitlere umut verici bir alternatif olduğu birçok farklı konukçu bitki patojen ilişkilerinin irdelendiği çalışmalarda araştırılmıştır. Bu çalışmada sağlıklı turunçgil ağaçlarının meyve, dal ve yapraklarından elde edilen endofitik bakteri izolatlarının biyokontrol potansiyelleri G. citri-aurantii'ye karşı petri denemeleri (in vitro) ve meyve testleri (yarı in vivo) ile araştırılmıştır. İzole edilen 24 aday bakteri izolatı arasından seçilen on altı farklı bakteri izolatı G. citri-aurantii'nin misel gelişiminin engellenmesi üzerine olan antagonistik potansiyeli in vitro çalışmalarda değerlendirilmiştir. Test edilen bakteriler arasında Bacillus spp. ait izolatlar fungal etmenin misel gelişimini % 59.5-78.6 oranında engellemiştir. En yüksek antagonistik etkinlik B. subtilis CM8 (% 78.6) izolatı tarafından neden olunmuştur. Acinetobacter johnsonii CT7, Erwinia herbicola CM5, Pseudomonas putida CL2, Pantoea agglomerans CM14, Acinetobacter lwoffii CP1 ve Stenotrophomonas maltophilia CP3 izolatları, ikili kültür denemelerinde misel gelişimini engellemede başarısız olmuştur. Bakteriyel izolatların antagonistik etkinlikleri, fungus inokulasyonundan önceki ön inkübasyon süresi ile artmıştır. Bacillus spp ait izolatlar engellenme bölgesine yakın noktalardaki hiflerde vakuolleşme, büzüşme, şişme ve erime gibi önemli morfolojik değişikliklere neden olmuştur. Yapay olarak enfekte edilen turunçgil meyveleri üzerinde hastalık çıkışı Bacillus spp. ait izolatlar tarafından % 56.7-83.3 gibi önemli oranlarda baskılanmıştır. Elde edilen sonuçlar, Bacillus spp. ait izolatların güçlü antagonistik aktivitelerinden dolayı, turunçgillerin hasat sonrası hastalık etmen(ler)i ile mücadelesinde biyofungisit olarak kullanılma potansiyeline sahip olduğunu göstermiştir.

Keywords

• Turunçgil
• Ekşi çürüklük
• Geotrichum citri-aurantii
• Antagonist
• Biyolojik mücadele
• Endofit bakteri

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