Harnessing Pseudomonas protegens to Control Bacterial Panicle Blight of Rice

Bacterial panicle blight of rice is a seedborne disease caused by the bacterium Burkholderia glumae. This disease has affected rice production worldwide and its effects are likely to become more devastating with the continuous increase in global temperatures, especially during the growing season. The bacterium can cause disease symptoms in different tissues and at different developmental stages. In reproductive stages, the bacterium interferes with grain development in the panicles and, as a result, directly affects rice yield. Currently, there are no methods to control the disease because chemical control is not effective and completely resistant cultivars are not available. Thus, a promising approach is the use of antagonistic microorganisms. In this work, we identified one strain of Pseudomonas protegens and one strain of B. cepacia with antimicrobial activity against B. glumae in vitro and in planta. We further characterized the antimicrobial activity of P. protegens and found that this activity is associated with bacterial secretions. Cell-free secretions from P. protegens inhibited the growth of B. glumae in vitro and also prevented B. glumae from causing disease in rice. Although the specific molecules associated with these activities have not been identified, these findings suggest that the secreted fractions from P. protegens could be harnessed as biopesticides to control bacterial panicle blight of rice.

Distribution of Xanthomonas hortorum pv. carotae Populations in Naturally Infested Carrot Seed Lots

Bacterial blight of carrot (Daucus carota subsp. sativus), caused by the plant-pathogenic bacterium Xanthomonas hortorum pv. carotae, is a common seedborne disease of carrot wherever the crop is grown. Carrot seed lots were evaluated to determine the variability and distribution of populations of X. hortorum pv. carotae among individual carrot seeds. Twenty-four carrot seed lots harvested between 2014 and 2016 were subjected to a bulk seed wash dilution-plate assay to obtain mean X. hortorum pv. carotae levels. Mean infestation levels resulting from the bulk seed wash assays among the 24 seed lots ranged from 1.2 × 107 and 9.6 × 108 CFU/g seed and averaged 3.6 × 108 CFU/g seed. Individual seeds from the same 24 lots were also tested with a scaled-down wash assay of individual seeds. Among the 1,380 seeds that were individually assayed, 475 X. hortorum pv. carotae-positive seeds were detected (34.4%). Rates of X. hortorum pv. carotae detection on individual seed in seed lots ranged from 0% (not detected) to 97.9%, and the mean and median X. hortorum pv. carotae population on an individual seed was 8.3 × 104 and 6.3 × 101 CFU/seed, respectively. Among individual seeds, X. hortorum pv. carotae populations ranged from 2 (the limit of detection of the assay) to 3.6 × 107 CFU/seed. CFU data for 23 of the 24 seed lots were nonnormal and the Log-Logistic (3P) distribution best described populations of X. hortorum pv. carotae recovered from individual carrot seeds. The influence and impact of nonnormal distributions of X. hortorum pv. carotae in commercial carrot seed lots on seed health tests, seedborne transmission, and bacterial blight epidemiology requires further study.

Molecular Characterization, Fitness, and Mycotoxin Production of Fusarium asiaticum Strains Resistant to Fludioxonil

Fludioxonil is used in seedborne disease management of various fungal pathogens, including Fusarium asiaticum, the predominant causal agent of Fusarium head blight in China. In this study, we screened resistant strains from a large number of F. asiaticum strains collected from 2012 to 2016 and found that 4 of 1,000 field strains were highly resistant to fludioxonil. The 50% effective concentration values of the resistant strains and induced mutants ranged from 80 to >400 μg/ml. Compared with field-sensitive strains, all field-collected and laboratory-induced resistant strains exhibited fitness defects in traits including mycelial growth, conidial production, pathogenicity, and sensitivity to osmotic conditions. In the presence of fludioxonil, significantly higher glycerol accumulation was found in sensitive strains but not in resistant individuals. The fludioxonil-resistant strains produced lower amounts of glycerol in liquid culture and lower amounts of trichothecene mycotoxins in rice culture and inoculated wheat spikelets than the fludioxonil-sensitive strains. Sequence analyses of the key genes of the two-component histidine kinase signaling pathway showed various amino acid substitutions in the Os1, Os4, and Os5 genes between field-sensitive and resistant strains or mutants. The results of this study suggest a potential risk of fludioxonil resistance development and a possible influence of resistance mutations on fitness parameters and toxin production in F. asiaticum.

DETEKSI PENYAKIT BACTERIAL FRUIT BLOTCH PADA MELON MENGGUNAKAN ELISA (DETECTION OF BACTERIAL FRUIT BLOTCH OF MELON USING ELISA)

Bacterial fruit blotch (BFB) caused by Acidovorax citrulli is a serious seedborne disease in Cucurbitaceae causing 90-100% yield losses. The aim of this study was to explore BFB symptom on melon and also to detect A. citrulli infection in commercial seed and symptomatic fruits from the field in Yogyakarta Special Region province and its surrounding using DAS-ELISA method. Samples include melon from Sleman, Bantul, Kulon Progo, Gunung Kidul, Magelang, Purworejo regencies while commercial seeds i.e. Action 434, Glamour and Mai 116 were collected. DASELISA detection method used reagent set from Agdia. Based on the field observation, this study found melon commercial fruit shares similar symptom with BFB, which showed discrete oily dark green spots, while the netting failed to develop over necrotic areas, resulting in smooth sunken spots. DAS-ELISA detection revealed that samples collected from Jetak village, district of Mungkid, Magelang and from Bligo village, district of Ngluwar, Magelang and in commercial seed Mai 116 were positively infected byA. citrulli.Keywords: Acidovorax citrulli, bacterial fruit blotch, ELISA, melonBacterial fruit blotch (BFB) merupakan penyakit penting pada famili Cucurbitaceae yang disebabkan oleh Acidovorax citrulli. Penyakit ini dilaporkan dapat menurunkan hasil mencapai 90-100%. Tujuan dari penelitian ini adalah untuk mengetahui gejala penyakit BFB pada melon dan deteksiA. citrulli pada benih komersial dan sampel buah bergejala dengan metode DAS-ELISA di DIY dan sekitarnya. Pengambilan sampel dilakukan di kabupaten Sleman, Bantul, Kulon Progo, Gunung Kidul, Purworejo dan Magelang. Selain dari lapangan, diuji pula benih melon komersial yaitu Action-434, Glamour dan Mai 116. Metode deteksi dengan ELISA menggunakanreagent set dari Agdia. Dari hasil pengamatan di lapangan ditemukan buah melon dengan gejala yang mirip dengan gejala BFB yaitu adanya becak berwarna hijau tua kebasahan pada permukaan buah, jaring tidak terbentuk sempurna dan pada bagian daging buah di bawah becak tadi membusuk. Hasil deteksi dengan DAS-ELISAmengindikasikan bahwa A. citrulli terdeteksi pada sampel yang berasal dari desa Bligo, kecamatan Ngluwar dan desa Jetak, kecamatan Mungkid, kabupaten Magelang, serta pada benih komersial MAI 116.Kata kunci: Acidovorax citrulli, bacterial fruit blotch, ELISA, melon

Adhesion and Fitness in the Bean Phyllosphere and Transmission to Seed of Xanthomonas fuscans subsp. fuscans

Deciphering the mechanisms enabling plant-pathogenic bacteria to disperse, colonize, and survive on their hosts provides the necessary basis to set up new control methods. We evaluated the role of bacterial attachment and biofilm formation in host colonization processes for Xanthomonas fuscans subsp. fuscans on its host. This bacterium is responsible for the common bacterial blight of bean (Phaseolus vulgaris), a seedborne disease. The five adhesin genes (pilA, fhab, xadA1, xadA2, and yapH) identified in X. fuscans subsp. fuscans CFBP4834-R strain were mutated. All mutants were altered in their abilities to adhere to polypropylene or seed. PilA was involved in adhesion and transmission to seed, and mutation of pilA led to lower pathogenicity on bean. YapH was required for adhesion to seed, leaves, and abiotic surfaces but not for in planta transmission to seed or aggressiveness on leaves. Transmission to seed through floral structures did not require any of the known adhesins. Conversely, all mutants tested, except in yapH, were altered in their vascular transmission to seed. In conclusion, we showed that adhesins are implicated in the various processes leading to host phyllosphere colonization and transmission to seed by plant-pathogenic bacteria.

Alternaria linicola. [Descriptions of Fungi and Bacteria].

A description is provided for Alternaria linicola. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Linum usitatissimum, L. grandiflorum. DISEASE: Damping off of flax seedlings. Seedlings develop a moist rot as a result of infection from the seed coat. The fungus starts by infecting the sepals and petals and is transferred to seed from the moribund flower parts. It may inhibit germination or retard debilitated seedlings. GEOGRAPHICAL DISTRIBUTION: Africa: Kenya, Tanzania. Europe: Denmark, France. UK. North America: Canada. TRANSMISSION: It is essentially a seedborne disease, but infection of the flowers must be due to airborne conidia.