A new leaf blight disease of browntop millet (Brachiaria ramosa) was noticed during rainy season (Kharif) 2018 at small millet experimental field, University of Agricultural Sciences, Gandhi Krishi Vignana Kendra (GKVK), Bengaluru, India. To assess the disease severity, an intensive roving survey was conducted during the 2019 cropping season. Based on the morphological characterization, the causal agent of leaf blight disease was identified as Bipolaris spp. Further sequencing and combined gene analysis of ITS (internal transcribed spacer of rDNA), GAPDH (glyceraldehyde 3‐phosphate dehydrogenase) and LSU (large subunit) of all the nine isolates confirmed the pathogen as B. setariae. Pathogenicity study showed that all the isolates were pathogenic and caused leaf blight symptoms on browntop millet. The B. setariae isolates showed marked variability with respect to disease incidence on browntop millet (cv. Dundu korale) under artificial inoculation conditions. However, the host range was limited only to browntop millet and found non‐pathogenic to other six small millets examined. To our knowledge, this is the first completely described study on characterization of B. setariae causing leaf blight disease of browntop millet in India.

In vitro efficacy of seventeen new molecules of fungicides were evaluated against Bipolaris setariae causing leaf blight on browntop millet at University of Agricultural Sciences, GKVK, Bangalore in order to find out effective fungicide against B. setariae. Mancozeb, among the six contact fungicides recorded cent per cent inhibition over control at 500 and 1000 ppm with mean inhibition of 96.54 per cent. Among the six systemic fungicides tested at 50, 100 and 150 ppm, propiconazole exerted 100 per cent inhibition of mycelial growth followed by tebuconazole which accounted 100 per cent inhibition at 100 and 150 ppm with mean inhibition of 94.69 per cent and cymoxanil + mancozeb among the five combi-product fungicides tested (100, 250 and 500 ppm) exhibited maximum (79.01 %) mean inhibition of mycelial growth. Among all groups, tricyclazole was found to be least effective.

Browntop millet was newly included in the millet cropping system in India as one of the small millet. Incidence of leaf blight was observed to be severe in all millet growing regions of India and the causal organism was confirmed as B. setariae using molecular tools viz., ITS and GPDH genes. As the crop was newly included in the millet system, investigation was needed to carry out about disease causing agents their biology and culture conditions. In this study, an attempt was made to identify the ideal culturing and physiological requirements for culturing B. setariae. Results revealed that solid media such as Czapek Dox agar (CDA) and host leaf decoction agar with 2 per cent sucrose are ideal for better growth and abundant sporulation while, pH 6.0 to pH 7.0 were found to be ideal for radial mycelial growth and sporulation. These cultural and physiological conditions can be used for the future studies while working on the pathogen causing browntop millet leaf blight.

Twelve botanicals were evaluated against Bipolaris setariae causing leaf blight on brown top millet under in vitro conditions at ICAR-AICRP on small millets. University of Agricultural Sciences, GKVK, Bangalore by poison food technique at 10, 20 and 30 per cent (w/v). Among the 12 botanicals Agave showed maximum inhibition of mean mycelial growth (81.52 %) and sporulation and also agave showed cent percent inhibition at 30 per cent concentration followed by datura and eucalyptus which accounted 40.62 and 34.32 per cent mean mycelial growth inhibition. Whereas, Calotropis was unableto inhibit the fungal growth and sporulation as evidenced by 0 per cent inhibition of mycelial growth. Similarly, Pongamia (1.48 %), turmeric (1.77 %) and Gliricidia (9.46 %) extracts exhibited less inhibition of mycelial growth.

Browntop millet (Brachiaria ramosa (L.) Stapf), which is native to the United States, was recently introduced into India as one of the small millet crop. In September 2018, leaf blight symptoms were observed on cv. Dundu Korale on the adaxial side of the leaves in a field at Bangalore, India (13.0784oN, 77.5793oE). Initial lesions were brown with small yellow halo that ranged from 1 to 5 mm and eventually enlarged exhibiting light brown centers. Afterwards, spots coalesced and leaves were blighted. About 75% of the plants were infected in the field of 0.5 ha. Samples of symptomatic and asymptomatic leaves were collected, and nine isolates were recovered from culture on potato dextrose agar (PDA). Single conidial isolation was performed. Colonies were grey to olive green with regular margins at 7 days when cultured on PDA at 27 ± 1oC and 16 h light and 8 h dark cycles. Conidiophores were single or in clusters from 4.92 to 6.04 μm in width. Conidia were fusoid, cylindrical to slightly curved ranging from 38.50 to 130 μm in length and from 8.30 to 17 μm in width, with 4 to 10 distosepta (n =100). Hilum was flat to inconspicuous or slightly protruded. Based on the morphology, the pathogen was identified as a Bipolaris species according to the genus standard descriptions of Helminthosporium (Alcorn 1988). Misra and Prakash (1972) reported that Helminthosporium setariae causing leaf spot on browntop millet in India, but they did not provide any morphological or molecular evidence of identification. For molecular identification, the genomic DNA of isolate BTMH3 was extracted and the internal transcribed spacer region (ITS) and glyceraldehyde-3-phosphate dehydrogenase gene (GPD) were amplified using the pairs of primers ITS1/ITS4 (White et al. 1990) and GPD1/GPD2 (Berbee et al. 1999), respectively. BLAST analysis of ITS (MT750301; 562 matching base pairs) and GPD (MT896702; 562 matching base pairs) sequences showed 99.82% of identity with sequences of Bipolaris setariae (Sawada) Shoemaker type strain CBS 141.31 (ITS: EF452444 and GPD: EF513206). Pathogenicity was proved by spraying 10 healthy 20-day-old browntop millet plants with conidial suspension (106 conidia/ml). Control plants were sprayed with distilled water. Plants were covered with transparent polythene bags in a greenhouse at 28 ± 2oC and high relative humidity of 90%. Symptoms were observed at five days post inoculation. The pathogen was re-isolated from infected areas using the same protocol as before, whereas the control plants were symptomless. The re-isolated pathogen was confirmed as B. setariae based on morphological characters and PCR assay. To the best of our knowledge, this is the first report of leaf blight on browntop millet caused by B. setariae in the southern peninsular region of India. Disease specimen was deposited in Herbarium Cryptogamae Indiae Orientalis (HCIO), New Delhi, India with accession number 52209. Grain yield losses caused by leaf blight on browntop millet remain to be determined, however our findings indicate that cultivar cv. Dundu Korale is susceptible to B. setariae.