First Report of Common Root Rot on Triticale Caused by Bipolaris sorokiniana in Kazakhstan

Abstract

Triticale (×Triticosecale Wittmack) is a man-made crop obtained from the crossing of wheat (Triticum sp.) × rye (Secale cereale L.), and is adapted to harsh conditions. It is mainly cultivated as a feed grain for livestock in Kazakhstan. In 2019, a survey in three triticale fields in Almaty province revealed a pathogen on underground portions of the plant, which caused stunting and subcrown internode necrosis of the infected roots. To identify the causal agent(s), sections of necrotic tissues (3-5 mm) were superficially disinfected in 1% NaOCl solution for 2 min, rinsed with sterile distilled water, and placed on 1/5 strength potato dextrose agar (PDA) amended with 0.01% streptomycin. After five days of incubation period at 20°C in the dark, fungal colonies of similar morphological features were observed and purified to separate PDA plates using the single-spore isolation technique. Dematiaceous (darkly pigmented) mitosporic fungal growth was noted after five days. Conidia were mostly straight or slightly curved, dark olivaceous brown, 4 to 9 distoseptate and mostly tapering towards the ends, with an average dimension of 17.3 to 23.3 × 51.3 to 84.7 μm (n = 100). These features were consistent with those of Bipolaris sorokiniana (Sacc.) Shoemaker (teleomorph = Cochliobolus sativus) described by Manamgoda et al. (2014). The pathogen was also characterized by sequencing of the internal transcribed spacer regions and intervening 5.8S gene of the nuclear rDNA (ITS) and partial glyceraldehyde-3-phosphate dehydrogenase gene (GPDH) of three isolates using primer pairs ITS1/ITS4 (White et al. 1990) and gpd1/gpd1 (Berbee et al. 1999), respectively. Sequences were deposited in GenBank with accession numbers MT254730-32 and MT262922-24, for ITS and GPDH, respectively. A BLAST query of the sequences matched B. sorokiniana with 100% identity (GenBank accession nos. JN943406, and LT715781 for ITS and GPDH, respectively). To prove pathogenicity, sterilized mixture substrate of vermiculite, sand, and soil (1:1:1, v/v/v) was inoculated with a conidial suspension of each isolate to obtain an inoculum density of 250 conidia per gram. Control seeds were sown in uninoculated mixture substrate. Five seeds of a susceptible triticale variety (Balausa) were sown into a plastic pot (15 cm height, 9 cm diam.), and filled with the inoculated soil. Inoculated pots were maintained in a growth chamber with a 12 h photoperiod at 24°C for 7 weeks. Common root rot symptoms were observed on the inoculated plants, while no symptoms were observed on the control plants. The experiment was repeated two times, and pathogenicity tests employed with three pots for each isolate and control. Koch’s postulates were fulfilled by reisolating and identifying the pathogen based on the morphology described above. To our knowledge, this is the first report of common root rot caused by B. sorokiniana on triticale in Kazakhstan. The pathogen was reported to cause diseases mostly on Poaceae hosts as well as non-Poaceae including such as Allium sp., Helianthus annuus, Cicer arietinum, Medicago sativa, Phaseolus vulgaris, etc. (Farr and Rossman 2013). Further investigation is needed to understand its potential distribution and impact on triticale cultivation in the country.