Fusarium temperatum as a New Species Causing Ear Rot on Maize in Poland

Diseases caused by Fusarium spp. are probably the most important factors affecting the yield and grain quality of maize (Zea mays L.) in Poland. While Fusarium stalk rot problems were reported to be stable in all regions, ear rot tends to increase. This tendency probably results from warmer climate and conservation tillage techniques combined with maize- and wheat-dominated rotation systems increasingly practiced in these regions. Maize kernel samples were harvested from trials conducted with hybrids moderately resistant and susceptible to ear rot in three locations in 2011 (12 samples) and in seven locations in 2012 (20 samples) from regions of Poland where maize for seed production is grown for many years. For each sample, 56 kernels (1,792 total) were subjected to the investigation of fungal colonization as following: surface-disinfected in alcohol (15 sec), rinsed with distilled water, dried, placed on the water agar in petri plates, incubated 7 to 12 days at 22°C, and sub-cultured using the single spore technique on SNA. Pure cultures were grown on SNA at 22°C for 10 days to produce macroconidia of uniform size and form, as well as on PDA (1). The presence of Fusarium spp. was determined based on the SCAR-PCR markers and the translation elongation factor (tef-1α) sequence analyses (4). All samples were contaminated by Fusarium spp. at level ranging from 17.3 to 40.5% of kernels (444 strains were isolated). F. verticillioides was the most frequent species. The frequencies of F. temperatum (a recently described species closely related to F. subglutinans [3]) ranged from 2.3 to 54.3%, F. subglutinans from 0 to 37.9%, F. verticillioides 41.0 to 90.0%, and F. proliferatum from 0 to 11.5% of the total Fusarium strain number. After extraction and purification, Fusarium mycotoxins were detected using HPLC method. The majority of maize kernel samples contained fumonisins B₁ to B₃. Zearalenone and deoxynivalenol were not detected or their levels were below limit detections. Aggressiveness of 10 representative isolates (3 each of F. temperatum, F. verticillioides, and F. subglutinans, and 1 F. proliferatum) was evaluated under field conditions after kernel inoculation. Susceptible and moderate resistant inbreed lines were used. The experimental design consisted of a factorial arrangement with two factors and three replicates (7 plants per replicate). To produce inoculum, isolates were grown on a liquid SNA medium. After 2 weeks, cultures were filtered through cheesecloth and conidial concentrations were adjusted to ~10⁶ spores ml^-1. Inoculation of each ear was conducted 10 to 12 days after silking time using 1.5 ml of spore suspension. Control plants were inoculated with distilled water. Visual evaluation of ear rot severity was scored during harvesting time as the percentage of the ear area covering by mycelium (2). Differences of aggressiveness between genotypes, Fusarium spp., and isolates were statistically significant; ear area covered by mycelium ranged from 3.57 to 26.95% for F. temperatum, from 10.10 to 41.39% for F. subglutinans, from 5.90 to 14.33% for F. verticillioides, and from 9.57 to 17.14% for F. proliferatum. To our knowledge, this is the first report of F. temperatum causing ear rot of maize in Poland. References: (1) J. F. Leslie et al. Page 388 in: The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, 2006. (2) L. M. Reid et al. Can. J. Plant Pathol. 19:185, 1997. (3) J. Scauflaire et al. Mycologia 103:586, 2011. (4) Ł. Stępień et al. J. Appl. Genet. 54:367, 2013.