engleski

First report of soybean fusarium wilt caused by Fusarium oxysporum in Croatia

Soybean (Glycine max [L.] Merr.) is the leading oilseed crop produced and consumed in the world, grown in at least 70 countries in 2013. Wilted soybean plants were observed in May 2014 in commercial fields at Osijek (Slavonia County). Ten symptomatic plants, from each of 14 soybean fields surveyed, were collected at the V3 growth stage (Licht 2014). Plants were wilted with symptoms of external and internal browning at the base of stems, interveinal chlorosis of leaves, and death of shoots. Roots were symptomless. Fourteen soybean fields were observed and Fusarium oxysporum Schlecht. emend. Snyder & Hansen was determined as the causal agent of disease in 11 of them. To isolate the causal agent, the discolored stem tissues selected from symptomatic plants were sterilized with 1% sodium hypochlorite and placed on potato dextrose agar (PDA). Single- spore cultures were used for morphology and molecular analyses. Colony growths were rapid and aerial mycelium was white with hints of purple. The undersurfaces of colonies were cream-colored. Macroconidia were abundant, hyaline, slightly sickle-shaped with a foot- shaped basal cell, and 3- to 5-septations. Microconidia were formed abundantly in false heads. They were generally oval and single- celled. Morphological identification was done according to The Fusarium Laboratory Manual (Leslie and Summerell 2006). Species identity was confirmed on two representative isolates, TFus1 and TF2, by sequencing a portion of the EF1-α gene using the degenerate primers EF1 and EF2 (O’Donnell et al. 1998). The sequence comparison revealed a 100% match with F. oxysporum sequences in GenBank (KP964863) for isolate TFus1 and a 99% homology with GenBank gene sequences (KP710616) for isolate TF2. Greenhouse inoculations were performed to confirm pathogenicity. Two isolates of F. oxysporum (TFus1: KX165288 and FT2: KX165289) were used for preparing inoculum. Sterilized mixtures of wheat and barley seeds (10 g of each) were inoculated with a spore suspension (106 conidia/ml) of selected isolates and incubated for 2 weeks at room temperature. Control inoculum was prepared by applying sterile distilled water only to seed. After 2 weeks, the inoculum (6 g per pot) was placed 3 to 4 cm below the surface of sterile soil in 50 × 20 × 15 cm pots. After 3 days, 30 soybean seeds (cv. Tisa) per treatment (3 replicates) were sown in the pots and maintained at 25/22°C, 14:8 h photoperiod, and 75% relative humidity in a growth chamber. Seven weeks after sowing, stem discoloration was observed on 82.8% (TFus1) and 100.0% (FT2) of soybean plants. Symptoms on infected plants were similar to those observed in the field and the fungus was successfully reisolated. No symptoms were observed on control plants. To our knowledge, this is the first report of F. oxysporum causing soybean wilting in Croatia. In humid and cold springs, the presence of this pathogen could cause economically significant reduction in soybean yield.

Fusarium oxysporum ; soybean

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