Fungi on irrigated rice seeds produced in the pre-germinated system in the Alto Vale do Itajaí region, Santa Catarina state, Brazil

The aim of this research was to identify and quantify fungi infecting irrigated rice seeds produced in the 2015/16, 2016/17 and 2017/18 harvests in the pre-germinated system in the Alto Vale do Itajaí Region, Santa Catarina State, Brazil. A total of 479 lots of eight cultivars were analyzed. Seeds were disinfected and sown in potato-sucrose-agar culture medium with incubation for seven days at 25oC ± 2oC and photoperiod of 12 hours. The main fungus detected in the three crops season was Microdochium albescens with 54.9% of average incidence, followed by Alternaria padwikii (7.7%) and Bipolaris oryzae (3.3%).

Scheidt et al. SCSBRS Tio Taka (49), SCS118 Marquês (22), SCS117 CL (11) and Primoriso CL (10), from the AVI region, SC. Disease management in these crops followed the indications of the cooperative. For chemical control, a mixture of strobirulin + triazole + benzothiazole was sprayed at the stages of booting and flowering and / or grain formation (SOSBAI, 2018). In the cooperative the seeds were stored in polypropylene bags with humidity and room temperature. Seeds were collected and sent to the Plant Pathology Laboratory Santa Catarina State University (UDESC). Detection of fungi was done in PSA + A culture medium (Potato-Sucrose-Agar + Antibiotic = 200 mg L -1 streptomycin sulfate). Seeds were disinfected with sodium hypochlorite solution (1%) for two minutes and then washed with sterile water. For each lot, 200 seeds were analyzed, four replicates of 50, sown in acrylic Petri dishes and kept in growth chambers for seven days at 25 ºC and 12 hours photoperiod. For detection of P. oryzae the paper substrate incubation method (blotter test) was used. Six lots were randomly selected from each cultivar, totaling 48 lots. The seeds were arranged in a gerbox acrylic box containing two layers of moistened filter paper and incubated in a continuous light growth chamber at 27 ºC. The evaluation was performed at four and seven days. A completely randomized experimental design was used for both detection methods. Were considered infected in which it was possible to identify the colony and / or structures of the fungi, confirming the identification with microscope (BARNETT & HUNTER, 1998).
The main pathogenic fungus associated with seeds were M. albescens with 54.9% of the average incidence and 100% of the prevalence, respectively followed by A. padwikii (7.7% / 90.6%), B. oryzae (3.3% / 59.9%), Curvularia sp. (3.1% / 66.5%) and S. oryzae (2.7% / 49.4%) ( Table 1 and   Table 1 -Average incidence of fungi associated with seeds of irrigated rice cultivars produced in the Alto Vale do Itajaí Region, Santa Catarina State. Lages, 2019.    (Table 2). This pathogen causes scalding in rice leaves, a growing disease in crop in the AVI, SC. The fungus was reported in RS association with seeds ranging from 6 to 31% (average 18%) (FRANCO et al., 2001) and 1 to 33% (average 4.9%) (FARIAS et al., 2007), but with a lower incidence than that obtained in this study (range 43.1 to 72.3% and average 54.9%). This may be related to the detection method, reaction of rice genotypes and cropping systems. MALAVOLTA (2007), using filter paper method detected an average incidence of M. oryzae of 24.6 and 29.8%, respectively in 2003 and 2004, in rice genotype seeds in the of São Paulo (SP) state. PSA medium is more efficient in detecting M. albescens when compared to the filter paper method (GUTIÉRREZ et al. 2009). Analyzing genotypes, a higher incidence was observed in SCS116 Satoru (72.3% in 2015/16 crop) and lower in SCS122 Miura (43.1% in 2016/17 crop). These values are considered high for a possible obtaining of healthy seed for pathogen management, since there is no information on resistance reaction of cultivars for M. albescens in the states of SC and RS (SOSBAI, 2018).
The fungus A. padwickii, included in the group of grain spotters, obtained average incidence in the three harvests of 7.7% and prevalence of     (MATHUR et al., 1972). In Brazil, in SP in 2003and 2004, the average incidence of A. padwickii was 8.2% and 1.6%; respectively, in cultivation of genotypes in flood irrigated system (MALAVOLTA, 2007). In RS, FRANCO et al. (2001), detected values from 0.4% to 20.6%, but do not describe the Alternaria species. The fungus B. oryzae presented higher average incidence in cultivar SCS121 CL and SCSBRS Tio Taka (7.3%, 2015/16 crop), and lower average value in cultivar Primoriso CL (0.9%, 2017/18 crop). For this fungus, we highlighted a prevalence of 100% detected in the 2016/17 crop in the cultivar SCS122 Miura. In SP was detected an average incidence of 13.6%, higher than that found in this study (MALAVOLTA, 2007).
The fungus Curvularia sp. was detected with incidence and prevalence values similar to B. oryzae. It was not possible to identify the species of Curvularia since no morphological and molecular characterization was performed. The species C. eragrostidis (P. Henn) and C. lunata (Wakker) Boedijn, are detected in rice seeds (LIMA & FURTADO, 2007). Other fungi were detected with lower average incidence, such as: S. oryzae (2.7%), Nigrospora oryzae ( (Table 1). These are also reported in seeds in RS (FRANCO et al., 2001;FARIAS et al., 2007). The fungus P. oryzae was not detected by the tested. In RS P. oryzae was detected with low incidence (0.04%) in 350 seed samples (FRANCO et al., 2001), but later was not detected in 162 samples analyzed (FARIAS et al., 2007).
This was the first survey of fungi associated with irrigated rice seeds in the pre-germinated cultivation system carried out in Santa Catarina State, serving as a basis for future research related to the epidemiological importance of infected seeds.         In the table 2, where we read: