Isolation and Characterization of a Novel Jumbo Phage from Leaf Litter Compost and Its Suppressive Effect on Rice Seedling Rot Diseases

Jumbo phages have DNA genomes larger than 200 kbp in large virions composed of an icosahedral head, tail, and other adsorption structures, and they are known to be abundant biological substances in nature. In this study, phages in leaf litter compost were screened for their potential to suppress rice seedling rot disease caused by the bacterium Burkholderia glumae, and a novel phage was identified in a filtrate-enriched suspension of leaf litter compost. The phage particles consisted of a rigid tailed icosahedral head and contained a DNA genome of 227,105 bp. The phage could lyse five strains of B. glumae and six strains of Burkholderia plantarii. The phage was named jumbo Burkholderia phage FLC6. Proteomic tree analysis revealed that phage FLC6 belongs to the same clade as two jumbo Ralstonia phages, namely RSF1 and RSL2, which are members of the genus Chiangmaivirus (family: Myoviridae; order: Caudovirales). Interestingly, FLC6 could also lyse two strains of Ralstonia pseudosolanacearum, the causal agent of bacterial wilt, suggesting that FLC6 has a broad host range that may make it especially advantageous as a bio-control agent for several bacterial diseases in economically important crops. The novel jumbo phage FLC6 may enable leaf litter compost to suppress several bacterial diseases and may itself be useful for controlling plant diseases in crop cultivation.

Multiple endogenous seed-born bacteria recovered rice growth disruption caused by Burkholderia glumae

Burkholderia glumae is a causal agent of bacterial grain and seedling rot in rice, and is a threat to stable global food supply. The virulence of B. glumae was suppressed when it was inoculated on budding seed rather than on non-budding seed. To clarify the phenomena, pathogen titer inside the rice plant was measured by serial dilution plating of lysates from budding rice seedlings. Surprisingly, morphologically different types of colonies were observed on the plates. These ‘contaminated’ rice seed-born bacteria (RSB) were identified by sequencing 16S rRNA genes as three strains of Pseudomonas putida (RSB1, RSB10, RSB15) and Stenotrophomonas maltophilia (RSB2). All bacteria and B. glumae were simultaneously inoculated onto rice seeds, and all three P. putida RSBs suppressed the growth disruption caused by B. glumae, whereas RSB2 had no effect. Thus, the virulence was synergistically suppressed when co-treated with RSBs. The effect could be dependent on the high biofilm formation ability of RSB2. By comprehensive microbiota analysis, endogenous rice flora were changed by RSBs treatment. These results suggest the possibility of novel pathogen control through pre-treatment with endogenous beneficial microorganisms. The method would contribute substantially to the implementation of sustainable agriculture stated in Sustainable Development Goals of United Nations.

Biocontrol of Rice Seedling Rot Disease Caused by Curvularia lunata and Helminthosporium oryzae by Epiphytic Yeasts from Plant Leaves

Seedling rot disease in rice leads to significant loss in the production of seedlings. This research was conducted to explore yeasts that could be used as biological control agents against rice seedling rot disease caused by Curvularia lunata and Helminthosporium oryzae. In total, 167 epiphytic yeast strains were evaluated, revealing that 13 of these yeast strains demonstrated antagonistic activities against fungal pathogens and either C. lunata DOAC 2313 or H. oryzae DOAC 2293. The volatile organic compounds (VOCs) and biofilm produced were possible antagonistic mechanisms in vitro for all the antagonistic yeast strains. Using nursery trays in a greenhouse, this study evaluated the control of rice seedling rot disease caused by these two fungal pathogens using antagonistic yeasts, identified in the present study and from our previous study. Torulaspora indica DMKU-RP31 and Wickerhamomyces anomalus YE-42 were found to completely control rice seedling rot disease caused by both of these fungal pathogens. Furthermore, W. anomalus DMKU-RP04 revealed 100% disease control when the disease was caused by H. oryzae. This is the first report on using antagonistic yeasts to control rice seedling rot disease caused by C. lunata and H. oryzae. These three antagonistic yeasts also showed promising potential for development as biocontrol agents against rice seedling rot disease caused by fungi.

INSIDEN PENYAKIT PADA KECAMBAH SENGON (Falcataria moluccana (Miq.) Berneby and J.W Grimes) DAN UJI PATOGENITAS

The Insidence of The Desease in Sengon Plant Sprouts and Patogenicity Tests Plant diseases commonly attack in nursery. The symptoms of attack are seed or seedling rot while in media or after weaning to bag. The aims of research were to describe the symptom of disease and identify the causing agent by postulate Koch examination. The research was conducted in laboratory and nursery as long as four months. Basic method were exploring the disease symptom and examining of disease by postulate Koch. Data was then analyzed descriptively. Results showed the disease symptom was damping off (Lodoh) characterizing, fell down, wilted and rot, performing flashed hot water (Lodoh). This attack categorized as post emergence damping-off level. The causing agent was identified as fungi Fusarium sp. It had three spore typically microconidia, macroconidia dan clamidospore.Key words: damping off, disease, moluccana, nursery, seedling. ABSTRAK Pada proses persemaian tanaman, insiden serangan penyakit sering terjadi. Salah satu gejala serangan yang timbul adalah pembusukan pada biji atau semai yang ditabur di media semai atau pasca penyapihan tanaman. Akibat serangan tersebut tingkat kematian tanaman dapat mencapai 80%. Tujuan dari penelitian ini adalah untuk menggambarkan gejala serangan penyakit dan mengidentifikasi penyebab primer dari penyakit tersebut melalui uji postulat Koch. Penelitian dilakukan di laboratorium dan persemaian selama 4 bulan. Metode dasar yang digunakan adalah eksplorasi untuk mengetahui gejala serangan penyakit dan eksperimen untuk pengujian postulat koch. Data dianalisis secara deskriptif. Hasil penelitian menunjukkan bahwa gejala yang ditunjukkan oleh semai sengon adalah akibat serangan penyakit lodoh (damping off) dengan cirri semai rebah, layu dan seperti tersiram air panas (lodoh). Serangan penyakit ini tergolong pada fase post emergence damping-off. Hasil identifikasi menunjukkan bahwa fungi penyebab penyakit ini adalah Fusarium sp. Fungi ini menghasilkan tiga jenis spora yaitu mikrokonidia, makrokonidia dan klamidospora.Kata kunci: lodoh, moluccana, penyakit, persemaian, semai.

Molecular diagnosis and intraspecific genetic variability of root pathogens of arid legumes in Western Rajasthan, India

The productivity of arid legumes remains stagnant over decades because of their susceptibility to root diseases. The information on molecular diagnosis and intraspecific genetic variability of root pathogens of arid legumes is limited. Besides dry root rot caused by Macrophomina phaseolina, 52 root samples were found infected with fungal pathogens. Irrespective of the geographical location from where the diseased samples were collected, all pathogen isolates clustered in RAPD dendrogram as per their respective genera. Phylogram based on multiple sequence alignment revealed that different genera (i.e. Fusarium, Neocosmospora and Syncephalastrum) separated from each other and species within the genera clustered together with their reference sequences with appreciable bootstrap values. Out of twenty representative isolates representing each cluster and all outgroups sequenced, eight were molecularly identified as Neocosmospora vasinfecta, five as Fusarium solani, two as Neocosmospora striata, two as Fusarium acutatum, one as Syncephalastrum monosporum, one as Fusarium oxysporum and one as Fusarium species. The root pathogens of the arid legumes were found neither restricted to a geographical location and nor were host specific in nature. Fusarium solani wilt in cowpea and seedling rot in mungbean, F. oxysporum wilt in mothbean, F. acutatum damping off in cowpea and cluster bean, Fusarium sp. seedling rot in cluster bean, Neocosmospora striata root rot in cowpea and wilt in cluster bean and Syncephalastrum monosporum root rot in cluster bean were molecularly identified as new fungal records as pathogens causing root diseases in arid legumes.