Paulo Pazdiora

Mycotoxin and fungicide residues in wheat grains from fungicide-treated plants measured by a validated LC-MS method☆

Wheat (Triticum aestivum) is an annual crop, cultivated in the winter and spring and susceptible to several pathogens, especially fungi, which are managed with fungicides. It is also one of the most consumed cereals, and can be contaminated by mycotoxins and fungicides. The objective of this study was to validate an analytical method by LC-MS for simultaneous determination of mycotoxins and fungicide residues in wheat grains susceptible to fusarium head blight treated with fungicides, and to evaluate the relationship between fungicide application and mycotoxin production. All parameters of the validated analytical method were within AOAC and ANVISA limits. Deoxynivalenol was the prevalent mycotoxin in wheat grain and epoxiconazole was the fungicide residue found in the highest concentration. All fungicidal treatments induced an increase in AFB2 production when compared to the control (without application). AFB1 and deoxynivalenol, on the contrary, were reduced in all fungicide treatments compared to the control.

Silicon suppresses tan spot development on wheat infected by Pyrenophora tritici-repentis

Tan spot caused by Pyrenophora tritici-repentis is the main foliar diseases of wheat in Brazil. The effect of silicon (Si) on the components of resistance of a susceptible (Fundacep Horizonte) and a moderately resistant (Quartzo) wheat cultivar was studied in a controlled environment. Silicon was supplied as calcium silicate in the soil 30xa0days before sowing. At the booting stage, a conidial suspension of the fungus was sprayed onto the flag leaves of potted plants, which were incubated under moist conditions for 48xa0h. Afterwards, inoculated leaves were assessed for: incubation period (IP), infection efficiency (IE), area under lesion size curve (AULSC), lesion size (LS), severity (SEV) and area under severity curve (AUSC). Foliar Si concentrations were quantified at the end of the evaluations. Si supply to plants increased leaf Si concentration in 233% for Fundacep Horizonte (from 4.8 to 16.0xa0g kg−1 of dry matter) and 211% for Quartzo (from 5.3 to 16.5xa0g kg−1 of dry matter). In the Sixa0+xa0treatments, IP was longer by 24 and 17xa0h, IE declined by 53.5 and 65.5%, LS (at 264xa0h after inoculation) by 4.6xa0mm (from 9.5 to 4.9xa0mm) and 5.9xa0mm (from 8.2 to 2.3xa0mm), and SEV by 53% (from 54.4 to 18.8%) and 88% (from 47.7 to 5.5%) respectively, for the Fundacep Horizonte and Quartzo cultivars. The Si x cultivar interaction was not significant for AULSC and AUSC, and these variables were reduced by 55.8 and 80.8%, respectively, in plants supplied with Si. In conclusion, Si enhanced the resistance of wheat plants to tan spot development by affecting several resistance components, regardless of the resistance level of the cultivar. However, the greatest reduction in tan spot development by Si supply was observed when using a moderately resistant cultivar.

CONTROLE IN VITRO DE Bipolaris oryzae (Breda de Haan) COM EXTRATO DE Curcuma longa (Linnaeus) E SUA INTERFERÊNCIA NA FISIOLOGIA DAS SEMENTES DE ARROZ

This study was conducted to evaluate the use of Curcuma longa (Linnaeus) extract in the in vitro control of Bipolaris oryzae (Breda de Haan) and to characterize the effect of this extract on rice seed germination. A completely randomized arranged in a factorial experimental design was used: three isolates of B. oryzae from rice seed from different rice-growing regions of Rio Grande do Sul (Fronteira Oeste, Campanha, and Sul) were tested with three concentrations (20, 40, and 80 mg/mL) of C. longa plus a control treatment (0 mg/mL). Each reaction was repeated in quadruplicate. The effect of the extract upon the disease development was evaluated based on mycelial growth (PMG) and spore production; rice seed germination was evaluated using a germination test (Germitest®). The PMG results demonstrate that the treatments were effective in reducing PMG, with a stronger response observed as the concentration of the extract increased. An average inhibition of 84% of sporulation was observed for the tested strains compared with the control treatment. There were, however, no significant differences in terms of seed germination test with the different C. longa concentrations. Therefore, treatment of rice seeds with C. longa extract does not affect seed germination but positively inhibits mycelial growth and sporulation, affecting the in vitro sporulation of the different isolates of B. oryzae.

Wheat leaf resistance to Pyrenophora tritici-repentis induced by silicon activation of phenylpropanoid metabolism

Tan spot caused by Pyrenophora tritici‐repentis is a disease present in all wheat‐producing countries and silicon (Si) treatment of wheat plants has been shown to increase plant resistance to tan spot. In this study, the effect of phenylpropanoid metabolism on resistance to tan spot was evaluated and some phenolic compounds that accumulated in response to P.xa0tritici‐repentis attack were identified. Furthermore, the effect of Si on phenylalanine ammonia‐lyase (PAL) activity and phenolic compound accumulation were determined inxa0situ. Antifungal activity of differentially accumulated phenolic compounds was also evaluated in inxa0vitro tests. Results showed that the increase in concentration of phenolic compounds was greatest at the onset of infection, and that some compounds showed fungitoxic effects including fungal tip swelling, granulation of germ tube and hyphae, and hyphal hyperbranching. Silicon‐induced reduction in both lesion size and tan spot disease progression were associated with activation of phenylpropanoid metabolism. PAL activity and accumulation of antifungal phenolic compounds were greater in pathogen‐inoculated plants supplied with Si. In these plants, fluorescence indicative of accumulation of phenolic compounds occurred early in epidermal cells and its intensity increased during the evaluation period, showing higher numbers of fluorescent cells around infected cells. Thus, the combined responses of cell fluorescence at sites of infection, increased PAL activity and accumulation of phenols indicate that Si strengthened wheat defence responses to infection by P.xa0tritici‐repentis, reducing the severity of tan spot.

First report of powdery mildew caused by Podosphaera xanthii on Lagenaria siceraria in Brazil

The bottle gourd (Lagenaria siceraria Mol.) is a plant in the Cucurbitaceae that is grown for its fruit which can either be harvested immature for consuming as a vegetable, or mature, dried and used for handcrafts as well as pipes and bottles. Powdery mildew on bottle gourd was observed on plants under field condition on three farms in the city of Capao do Leao (Rio Grande do Sul State – Brazil) during the spring/summer of 2016/2017. In the three areas, all bottle gourd plants were affected by powdery mildew, and foliar disease severity reached up to 50%. Powdery mildew symptoms characterized by circular white colonies on both leaf surfaces and on petioles were easily observed by the abundant production of mycelia, conidiophores, and conidia. On the oldest leaves, colonies coalesced, often covering the entire leaf surface causing chlorosis and eventual death. Mycelia was superficial with nipple-shaped to almost absent apressoria and producing erect conidiophores with three to six immature conidia produced...

First Report of Fruit Rot Caused by Diaporthe masirevicii on Physalis peruviana in Brazil

Physalis (Physalis peruviana L., Solanaceae) is a perennial bushy plant native to the Andes and grown throughout the world predominantly in Colombia and South Africa. The fruit have high nutritional and functional potential (Puente et al. 2011). Physalis fruit rot was observed in summer of 2013 on plants under field conditions in Capao do Leao, Rio Grande do Sul State, Brazil (31°4826.6S 52°3031.0W). The first symptoms observed on the fruit included water-soaked lesions followed by development of black dots (pycnidia), which over time covered the entire fruit surface causing a blackened appearance. Black pycnidia measuring 94.58 – 188.44 × 150.07 – 214.64 μm produced hyaline spores of both alpha conidia hyaline, cylindrical, rounded at the ends, containing one septum, and beta conidia, flexuous to hamate, hyaline, measuring 1.8 – 3.17 × 6.7 – 10.46 μm and 0.73 – 1.43 × 13.7 – 18.7 μm, respectively. On potato dextrose agar (PDA) incubated in photoperiod of 12 hours at 25±1°C colonies were grayish, cove...