Effect of photosensitisers on growth and morphology of Phytophthora citrophthora coupled with leaf bioassays in pear seedlings

The phytopathogenic oomycetes of the genus Phytophthora cause devastating economic losses worldwide.<br />Naphthodianthrone compounds, present in plant extracts of buckwheat and Saint John’s wort act as photosensitiser<br />agents and exhibit antimicrobial activity against a number of pathogens. In this study, we investigated the potential<br />inhibitory effects of fagopyrin and hypericin on Phytophthora citrophthora (R.E. Sm. &amp; E.H. Sm.) Leonian 1906, the<br />main causal agent of rot diseases in deciduous trees. Fagopyrin had the highest inhibitory effect in the colony growth<br />at a concentration of 2% of a stock solution (3 mg/mL), inducing clubbed hyphae with round tips. Notably, hypericin<br />also inhibited the radial colony growth and increased the hyphal branching at the subapical region, while also promoting<br />the formation of enlarged cells with irregular shapes growing collectively as biofilm-like structures. In terms of the<br />mycelial dry weight, although both photosensitisers had considerable inhibitory effects, the fagopyrin treatment was<br />most effective. Leaf bioassays showed that under dark conditions the photosensitiser pre-treated zoospores formed a<br />dense, but aberrant, mycelial growth with penetration defects. In contrast, when the zoospore production was performed<br />under light conditions, the zoospores failed to cause necrotic lesions and penetration events implying that their<br />virulence was impaired. These findings shed light on the biological effects of fagopyrin and hypericin in the regulation<br />of the mycelial growth, morphology and pathogenicity of P. citrophthora.

Efikasi Asap Cair dari Kayu Bengkirai terhadap Phytophthora citrophthora

Bengkirai is one of kind of woods usually used for furnitures and produces lots of woodcuts. This woodcut become the raw material for liquid smoke. The efficacy of liquid smoke produced from bengkirai wood against Phytophthora citrophthora was evaluated. The aim of this research was to evaluate antimicrobial properties of liquid smoke from bengkirai wood against P. citrophthora. Three kinds of liquid smoke were used in three temperatures i.e., 350, 400 and 450ºC. Efficacy of liquid smoke from bengkirai wood for antimicrobial used PDA medium. Simple linear regression was used to measured the effect of liquid smoke concentration to inhibition of P. citrophthora growth. The relationship between the concentration of liquid smoke (X) and inhibition of fungal growth, P. citrophthora (Y) at 350, 400, and 450ºC were Y = 24.51 + 5.27X (r2 = 0.98), Y = 54.31 + 5.53X (r2 = 0,92), and Y = 51.32 + 16.87X (r2 = 0.80). The results showed that the concentration of liquid smoke was significantly different for inhibition of P. citrophthora growth. The higher the concentration the higher the inhibition of microbial growth. The highest inhibition was on liquid smoke of bengkirai wood with temperature pyrolysis of 450ºC and concentration of liquid smoke of 1% with average value of 100%. IntisariBengkirai merupakan bahan baku pembuatan furniture yang banyak menghasilkan limbah potongan kayu. Limbah potongan kayu ini dapat dijadikan sebagai sumber pembuatan asap cair. Penelitian tentang efikasi asap cair dari kayu bengkirai terhadap Phytophthora citrophthora telah dilakukan. Penelitian ini bertujuan untuk mengevaluasi sifat antimikrobia asap cair kayu bengkirai dalam menghambat pertumbuhan P. citrophthora secara in vitro. Tiga jenis asap cair kayu bengkirai hasil pirolisis pada suhu 350, 400, dan 450ºC. Medium PDA digunakan untuk efikasi asap cair kayu bengkirai terhadap pertumbuhan P. citrophthora. Analisis regresi linier sederhana digunakan untuk mengevaluasi pengaruh konsentrasi terhadap daya hambat pertumbuhan P. citrophthora. Konsentrasi asap cair kayu bengkirai yang digunakan adalah 0; 0,5; 1,0; 1,5 dan 2,0 %, v/v. Hasil penelitian menunjukkan bahwa hubungan antara konsentrasi asap cair (X) dan daya hambat pertumbuhan P. citrophthora (Y) pada suhu pirolisis asap cair 350, 400, dan 450ºC berturut-turut adalah Y = 24,51 + 5,27X (r2 = 0,98), Y = 54,31 + 5,53X (r2 = 0,92), dan Y = 51,32 + 16,87X (r2 = 0,80). Makin tinggi konsentrasi asap cair kayu bengkirai makin tinggi daya hambat terhadap pertumbuhan P. citrophthora. Daya hambat pertumbuhan P. citrophthora tertinggi (100 %) pada perlakuan asap cair kayu bengkirai yang diproduksi pada suhu pirolisis 450ºC dan konsentrasi 1 %.

Baseline Sensitivities of New Fungicides and Their Toxicity to Selected Life Stages of Phytophthora Species from Citrus in California

Phytophthora citrophthora, P. syringae, P. nicotianae, and P. hibernalis are important pathogens of citrus in California but few chemical treatments are currently available. In vitro toxicities of four new fungicides to isolates of Phytophthora spp. from California were determined. Mean effective concentration values to inhibit mycelial growth by 50% for ethaboxam, fluopicolide, mandipropamid, oxathiapiprolin, and mefenoxam were 0.068, 0.04, 0.004, 0.0003, and 0.039 µg/ml, respectively, for 62 isolates of P. citrophthora; 0.005, 0.045, 0.003, 0.0001, and 0.008 µg/ml, respectively, for 71 isolates of P. syringae; 0.016, 0.057, 0.005, 0.0005, and 0.183 µg/ml, respectively, for 31 isolates of P. nicotianae; and 0.030, 0.018, 0.005, <0.0003, and ≤0.001 µg/ml, respectively, for two isolates of P. hibernalis. Mean values for ≥90% inhibition of sporangia formation of four isolates of P. citrophthora were 0.1, 0.28, 0.026, 0.005, and 55 µg/ml for ethaboxam, fluopicolide, mandipropamid, oxathiapiprolin, and mefenoxam, respectively. Zoospore cyst germination of P. citrophthora was most inhibited by oxathiapiprolin and mandipropamid. Chlamydospore formation of P. nicotianae was most sensitive to oxathiapiprolin, with a mean ≥90% reduction (EC>90) of 0.002 µg/ml, moderately sensitive to mandipropamid (EC>90 = 0.2 µg/ml) and mefenoxam (EC>90 = 0.6 µg/ml), and least sensitive to ethaboxam and fluopicolide (EC>90 = 1 µg/ml). Oospore formation of P. nicotianae was inhibited by ≥90% using oxathiapiprolin at 0.0004 µg/ml, mandipropamid at 0.02 µg/ml, ethaboxam at 0.1 µg/ml, or fluopicolide at 0.4 µg/ml, whereas 62% inhibition was obtained by mefenoxam at 40 µg/ml.