Effects of panicle development stage and temperature on rice panicle blast infection by Magnaporthe oryzae and visualization of its infection process

Abstract Panicle blast, caused by the fungus Magnaporthe oryzae (syn. Pyricularia oryzae ), directly contributes to yield loss in the field. The effects of panicle development stage and temperature on panicle blast were studied and the infection process of M . oryzae in panicles was visualized. Rice panicles at different development stages from three rice cultivars were inoculated with a conidial suspension in vitro. The rice cultivar Lijiangxintuanheigu was highly susceptible to panicle blast at 5 days postinoculation (dpi) when the pulvinus distance was 15–20 cm. Nanjing 9108 was moderately susceptible to panicle blast when the pulvinus distance was 8–10 cm, but Yliangyou 800 was resistant. The effect of temperature on panicle blast was determined under 22–35 °C temperature treatments. Inoculated panicles placed at temperatures of 28 and 30 °C showed the highest lesion grade based on lesion length at 5 dpi. The infection process of M . oryzae in rice panicles was observed by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). M . oryzae initially formed the appressorium to invade through the epidermis of rice panicles at 24 hours postinoculation (hpi). As the disease progressed, the invasive hyphae formed dense mycelial networks in the inner parenchyma cells at 60 hpi. Our results will contribute to the understanding of panicle development stage and temperature effects on panicle blast and improve resistance evaluation methods. Additionally, visualization of the infection process by CLSM and TEM are valuable methods to observe M . oryzae invasive hyphae inside rice panicle cells.