Abstract
ABSTRACT The objective of this study was to develop a methodology for inoculum production and inoculation of Passalora sojina in soybean to assess the reaction to frogeye leaf spot. Thus, sporulation of fungal races was quantified in five substrates under two light regimes. The temperature and the leaf wetness period that resulted in greater infection efficiency were also determined. Petri dishes containing the culture media Oat Flour Agar (OFA), Tomato Juice (FTJ), V8 agar juice (V8), Infant Food (IF) and Potato Sucrose Agar (PSA) plus isolates of P. sojina races 23, 24 and 25 were subjected to 12-h photoperiod and 24-h continuous dark. Inoculated plants were incubated at temperatures of 15, 20, 25, 30 and 35 ºC and leaf wetness periods of 12, 24, 36, 48 and 72 hours. Experimental design was completely randomized with five replicates. There was interaction among isolate, culture medium and photoperiod. The highest sporulation (conidia/cm2) was obtained in the culture media FTJ (race 23) and V8 (races 24 and 25) under 12-h photoperiod. The optimum temperature for the disease development was 27oC under 72 hours of continuous leaf wetness.
Highlights
The objective of this study was to develop a methodology for inoculum production and inoculation of Passalora sojina in soybean to assess the reaction to frogeye leaf spot
Sporulation of Passalora sojina in different culture media and light regimes Regarding the number of conidia cm-2, there was significant interaction among the three factors
As to race 24, the highest value was obtained in V8, while the lowest means were found in Potato Sucrose Agar (PSA) and Oat Flour Agar (OFA), which were statistically similar
Summary
The objective of this study was to develop a methodology for inoculum production and inoculation of Passalora sojina in soybean to assess the reaction to frogeye leaf spot. Para isso foi quantificada a esporulação de raças do fungo em cinco substratos, sob dois regimes luminosos. Também foi determinada a temperatura e duração do período de molhamento foliar que resultasse na maior eficiência da infecção. Plantas inoculadas foram incubadas a temperaturas de [15, 20, 25, 30] e oC e períodos de molhamento foliar de [12, 24, 36, 48] e 72 h. O delineamento experimental foi inteiramente casualizado com cinco repetições. Foi obtida no meio de cultura STT (raça 23) e no meio V8 (raças 24 e 25), sob fotoperíodo de 12 h. A temperatura ótima para o desenvolvimento da doença foi de 27 oC com 72 horas de molhamento foliar contínuo
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