Leafy mustard (Brassica juncea L.), a member of Brassicaceae, is widely cultivated as a leafy vegetable for its nutritionally rich tender foliage. During January 2025, approximately 25% of locally cultivated B. juncea plants grown in a farmer field at Khuzama, Kohima district, Nagaland, India (25.66°N, 94.10°E), exhibited distinct chlorotic patches on the adaxial leaf surface. Corresponding leaves bore white blister rust pustules (sori) on the abaxial surface. Severely affected leaves abscised, dried, and became unmarketable. Freshly infected leaves were collected, transported to the laboratory, and examined under a compound microscope (Leica DM 6000B, Wetzlar, Germany). Sporangiophores were short, hyaline, and clavate to cylindrical. The sporangia formed in a basipetal arrangement with short connectives, were hyaline, globose to oval in shape, and measured a mean diameter of 19.83 µm (14.51–21.62 µm, n = 100). Morphological characteristics matched descriptions of Albugo candida (Camele et al. 2011; Choi et al. 2014). For pathogenicity tests, sporangia were aseptically collected from single pustules by gentle scraping with a sterile blade, suspended in sterile deionized water, and incubated at 5 °C for 2 h to induce zoospore release (Zapata et al. 2014). Inoculation was performed on cotyledon (10-day-old) and true leaf (25-day-old) stages of B. juncea var. Varuna by placing 5 µl inoculum (1.5 × 10⁴ sporangia mL⁻¹) on the abaxial surface. Inoculated plants were kept in darkness for 48 h, followed by 12 h light/12 h dark cycles at 20 °C in a moist chamber with 80% relative humidity. Sterile water served as control. After 8–10 days, minute pustules developed and enlarged into typical white blister rust pustules, occasionally circular, on all inoculated leaves at both stages, resembling field symptoms and fulfilling Koch postulates. The disease incidence rate ranged from 88–100% (n=100 leaves), with a mean pustule diameter of 10 mm and an average of 33.13 pustules per spot. Control plants remained symptomless. Inoculum was maintained through multiple passages on B. juncea var. Varuna and obtained consistent rust symptoms. For molecular identification, genomic DNA was extracted from sporangia following Choi et al. (2006). PCR amplification and bidirectional sequencing targeted (i) the internal transcribed spacer region using oomycetes-specific primers DC6f/LR0r and (ii) mitochondrial marker cytochrome oxidase subunit II (COX2) using COX2f/COX2r pair (Choi et al. 2006). BLASTn analysis of curated sequences in the NCBI database showed 100% (ITS) and 99.62% (COX2) identity with reference isolates of A. candida (e.g., OQ970165, KJ700641). Based on morphological and molecular data, isolate AcNg was identified as Albugo candida (Pers.) Kunze. Sequences were deposited in GenBank under accession numbers PZ000595 (ITS) and PX991762 (COX2). Phylogenetic analysis of concatenated ITS and COX2 sequences clustered the isolate with reference isolates of A. candida. This report documents white blister rust of leafy mustard caused by A. candida in Nagaland and indicates risk to Brassica cultivation in North-East India.
Balamurugan et al. (2026) studied this question.