First Report of Crown Rot Caused by Fusarium nygamai on Wheat in Kazakhstan.

Abstract

Fusarium crown rot impacts wheat, causing yield and quality losses in arid and semi-arid regions worldwide. During wheat disease surveys in July 2023, crown rot symptoms were observed (20% incidence) across Aktobe Agricultural Experimental Station experimental plots (50°17'02"N, 57°09'14"E), Aktobe, Kazakhstan, from which 20 symptomatic spring durum wheat (Triticum durum Desf.) plants were collected. Infected plants showed brown discoloration that extended from the crown to 2-3 cm up the stem bases, with lesions on the subcrown internode and primary roots. Severely affected plants showed stunted growth. The affected tissues were washed, surface sterilized with 1% NaClO for 2 min, rinsed three times with sterile distilled water, and placed on 1/5 strength PDA plates. After a 5-day incubation at 23°C in darkness, 38 colonies exhibiting Fusarium-like morphology were observed and single spore isolates were obtained from each colony on fresh PDA and SNA, following the protocol of Leslie and Summerell (2006). The partial TEF1 and RPB2 genes were amplified and sequenced using primers EF1/EF2 (O'Donnell et al. 1998) and 5f2/7cr (Reeb et al. 2004; Liu et al. 1999). BLASTn analysis against NCBI GenBank and Fusarium-ID databases revealed that the sequences of three isolates showed 100% nucleotide identity with Fusarium nygamai holotype strain NRRL 13488 (TEF1: AF160273; RPB2: EF470114). The TEF1 and RPB2 gene sequences from the isolate 986b were deposited in GenBank under Accession Nos. PQ366035 and PQ366036, respectively. All three isolates showed white to violet mycelium, with colonies developing a central greyish-orange or dark violet spore mass; macroconidia measured 30.75 ± 2.79 × 3.61 ± 0.48 μm (n=30) and were hyaline, 3-septate, slender, and falcate to almost straight; microconidia formed on SNA measured 11.45 ± 0.95 × 2.77 ± 0.52 μm (n=30) and were produced in short chains or false heads; chlamydospores were formed in 2-4 weeks, conforming to the description of F. nygamai by Leslie and Summerell (2006). The pathogenicity of three isolates was tested on a susceptible durum wheat variety, Kızıltan 91. Seeds were surface-sterilized in 1% NaClO, rinsed, and germinated on water-soaked filter paper for 3 days. Five uniform seedlings were planted in 9-cm pots containing a sterile peat-vermiculite-soil mixture (1:1:1, v/v/v), with three replicate pots per isolate. A 1-cm mycelial PDA disc was placed on each seed and covered with the substrate, while control seeds received sterile PDA discs. Pots were arranged in a completely randomized design and incubated at 23°C with a 12-hour photoperiod. Four weeks of post-inoculation, typical crown rot symptoms appeared on plants, and the pathogen was re-isolated. The identity of re-isolated fungi was confirmed through morphological examination and TEF1 gene sequencing, establishing causation and fulfilling Koch's postulates, while control plants remained healthy throughout the experiment with no fungal growth detected in their tissues upon similar isolation attempts. Fusarium nygamai has been reported on wheat in Iraq (Minati 2020) and Kyrgyzstan (Özer et al. 2023). This report of F. nygamai causing crown rot on wheat in Kazakhstan, expanding the documented range of Fusarium species in the region, as noted by Akhmetova et al. (2022) and Bozoğlu et al. (2022), which adds complexity to disease management efforts since different Fusarium species may require tailored control approaches.