Bruno Tabarelli Scheidt

The state of Santa Catarina is the second-largest producer of rice seeds in Brazil. Research on phytopathogenicbacterias in this crop is scarce and the high frequency of panicle diseases leads to the hypothesis that seeds may be infected by bacteria. This research quantified the incidence of bacteria in the seeds, verified the bacteria viability during the storage period and characterized the associated bacteria. Seeds from the 2018/19 and 2019/20 seasons were analyzed. To check the incidence, the seeds were disinfected, plated on a nutrient agar + fungicide culture medium, and incubated for seven days at 27 °C. To assess viability, every 45 days, three cultivars stored in a processing unit were subjected to the same detection methodology. To characterize, prevalent colonies were isolated on semi-selective culture medium Pantoea genus-specific agar (PGSA), where the ones that showed growth were subjected to deoxyribonucleic acid (DNA) extraction and Polymerase Chain Reaction (PCR), DNA sequencing, and sequence comparison on GenBank. The hypersensitivity reaction (HR) in tobacco was performed using a bacterial suspension of each isolate. All seed samples had an average incidence of 83%. During storage, the seeds maintained stable bacterial viability, with an average incidence of 95% at the beginning of storage and 99% at the end of it. All isolates that grew in PGSA culture medium were identified by molecular characterization with 100% identity with two specimens of Pantoeaananatis and one of them induced RH in tobacco.

The fungus Microdochium albescens can interfere in the germination of seeds and in the death of rice seedlings; however, there is not technical indication for its control by seed treatment. This research evaluated the efficiency of fungicides in the treatment of pre-germinated and dryland rice seeds in the control of M. albescens. Seeds of the cultivars, Epagri 109, SCS116 Satoru, SCS121 CL and SCS122 Miura were treated with the following fungicides (g a.i./100 kg of seeds): fluazinam + thiophanate methyl (9.45 + 63), pyraclostrobin + thiophanate methyl (5 + 45), carboxin + thiram (60 + 60), metalaxyl-M + thiabendazole + fludioxonil (3 + 22.5 + 3.75), carbendazim + thiram (45 + 105), carbendazim (45). Seeds without fungicide treatment constituted the control. The treated seeds were sown in potato-sucrose-agar (PSA) culture medium and incubated at 25 ± 2 °C and photoperiod of 12 hours for 14 days. Treated seeds were also submitted to the germination test. Fluazinam + thiophanate methyl and metalaxyl-M + thiabendazole + fludioxonil showed greater control of M. albescens, not differing statistically between them, in the five cultivars and in the two cultivation systems. The tested fungicides provided seed germination above 90% in the four cultivars.

Microdochium oryzae infects leaves and sheaths, but seed infection is also important because it reduces seed germination and seedling vigor (⁹). Under room conditions, M. oryzae can survive for three to 18 months in stored rice seeds (¹⁰). All parts of the rice seed are infection sites for M. oryzae (⁶), but defining the precise location of the pathogen can help determine the effectiveness of seed treatments (³).

In southern Brazil, diseases known as brown spot (Bipolaris oryzae (Breda de Haan) Shoem) and scald (Microdochium albescens Thüm (Syn. Microdochium oryzae Hashioka & Yokogi; Gerlachia oryzae Hashioka & Yokogi) it has occurred with greater frequency (^{CELMER et al., 2007}; ^{LUDWIG et al., 2009}).

The purpose of this study was to analyze prior seed disinfestation of irrigated rice seeds with sodium hypochlorite and its effect on physiological quality. The experiment was conducted in the seed analysis laboratory of Santa Catarina State University (UDESC). Twenty-four (four per cultivar) seed lots of the cultivars SCSBRS Tio Taka, Epagri 109, SCS116 Satoru, SCS118 Marquês, SCS121 CL, and SCS122 Miura, produced in the Upper Itajaí Valley in the 2016/2017 season, were used in a completely randomized experimental design with four replications. Germination and vigor tests were performed with and without disinfestation seeds. For the germination test with disinfected seeds, there was a higher percentage of normal seedlings and a smaller number of abnormal seedlings and dead seeds. There was significant decrease in vigor without prior seed disinfestation. The fungi that infested the seeds caused an increase in the percentage of abnormal seedlings and dead seeds. Seed disinfestation prior to physiological test positively affects the results regarding the physiological quality of irrigated rice seeds.

As podridões de colmo do milho são responsáveis por significativas reduções em rendimento de grãos. O objetivo deste estudo foi avaliar a relação existente entre a incidência de podridões de colmo e o ciclo de seis híbridos de milho. O experimento foi conduzido a campo, semeados no mês de outubro nas safras 2012/2013 e 2013/2014 utilizando-se 70.000 sementes ha-1 dos híbridos comerciais P32R22 YHR e AG9045 VT PRO (superprecoces) e P30F53 Hx, DKB250 VT PRO2, AS1656 VT PRO2 e AG8025 VT PRO (precoces). O delineamento utilizado foi de blocos casualizados com quatro repetições avaliando-se, em cada parcela cinco metros lineares. A incidência de podridões foi determinada pela presença de descoloração e menor resistência do colmo. Espigas provenientes de plantas sadias e doentes foram trilhadas separadamente para determinação do dano percentual. Danos ocasionados por podridões de colmo, em função da severidade da doença podem ser variáveis em função dos híbridos, mesmo com características semelhantes de ciclo. Os fungos detectados nos colmos foram Stenocarpella sp., Colletotrichum graminicola, Fusarium graminearum e F. verticillioides. Todos os híbridos avaliados expressaram sintomas de podridão de colmo demonstrando não haver resistência, mas sim, apenas diferentes graus de suscetibilidade entre os materiais testados. O híbrido AG8025 VT PRO demonstrou ser o menos suscetível a podridões de colmo. Os híbridos superprecoces P32R22 YHR e AG9045 VT PRO apresentaram maior incidência do que híbridos de ciclos precoces, indicando que a maior precocidade está associada à maior suscetibilidade a podridões de colmo.

M. phaseolina is a cosmopolitan pathogen with a wide range of hosts and over 500 different species, including economic crops, such as bean (P. vulgaris L.), maize (Zea mays L.), soybean (Glycine max (L.) Merrill), sorghum (Sorghum bicolor (L.) Moench, peanut (Arachis hypogaea L.), sunflower (Helianthus annuus L.) and cotton (Gossypium hirsutum L.) (⁷, ¹¹, ¹³, ¹⁸).

The objective of this study was to analyze the effects of nitrogen rates and sowing dates on the severity of white spot disease (WSD) in first season maize hybrids, and their correlation with relative chlorophyll content, thousand grain weight and yield. The experiment was set in a randomized block design with treatments arranged in split-split plots. Two hybrids were tested in the main plots: AG9025 PRO3 (super early) and 30F53 VYH (early). Two sowing dates were evaluated in the split plots: preferential (9/20/2016) and late (12/05/2016). Four nitrogen rates were applied in the split-split plots. Nitrogen rates were top-dressed at the V4, V8 and V12 vegetative stages. The relative chlorophyll content reading was performed at VT stage. The quantification of WSD severity was made at R6, using diagrammatic scale. The AG9025 PRO3 hybrid showed higher average WSD severity (17.7%) than the 30F53 VYH (9.3%). The preferential sowing date showed lower severity (2.2%) compared to the late sowing date (31.4%). There was a significant positive correlation between the disease severity and the relative chlorophyll content, thousand grain weight and grain yield, except for the 30F53 VYH hybrid on the late sowing date. The hybrid AG9025 PRO3 showed increase in WSD severity when the highest nitrogen rates were applied, on both sowing dates. The effect of N rates on WSD was not significant for the 30F53 VYH hybrid. The late sowing time generates greater disease severity. The AG9025 PRO3 hybrid is more susceptible and the severity of its white spot is increased with the increment in N doses. There is a positive correlation between the relative chlorophyll content, disease severity, yield and thousand grain weight.

Na cultura, a cercosporiose é a principal doença, por reduzir a área foliar sadia com reflexo na produtividade de raizes (⁸). Sua ocorrência generalizada pode causar redução na produtividade de 15% a 45%, em condições de alta umidade relativa do ar, maior que 90%, e temperatura entre 22 e 26^o C (⁴). Os sintomas foliares são manchas circulares com bordos de cor purpúrea e centro claro e, à medida que aumentam em diâmetro, tornam-se com tonalidade acinzentada, porém com a necrose o tecido lesionado se desprende e a folha torna-se perfurada. O aumento do número de lesões e o aumento da área, juntamente com o acúmulo de fitotoxinas, induzem à completa senescência da folha e uma redução significativa da área foliar, e sua conseqüente produção. As folhas mais velhas são mais suscetíveis ao desenvolvimento da doença (¹⁰).

Fungi Alternaria padwickii (Ganguly), Bipolaris oryzae (Haan’s Breda), Cercospora janseana (Racib.), Fusarium moniliforme (Sheldon), Microdochium albescens (Thüm.) syn. Microdochium oryzae; Gerlachia oryzae (Hashioka & Yokogi), Pyricularia oryzae (Cav.) and Sarocladium oryzae (Saw) some of the main pathogens associated with rice seed (^{MEW & GONZALES, 2002}; SOSBAI, 2018). Infected seeds may affect physiological quality and constitute an important agent of pathogen dissemination (^{OU, 1972}).