Striga spp. are noxious parasitic weeds that attack important crop species such as rice, maize and sorghum. Estimated yield losses can reach 1 billion US dollars annually. Striga belongs to the Orobanchaceae family, which contains approximately 90 genera of parasitic species. The degree of parasitism varied among species, from facultative parasites that can set seeds without host plants, to obligate holoparasites that cannot photosynthesize and thus completely depend on their hosts. The obligate parasites (e.g., Striga and Orobanche) germinate only when host plants are close by, via recognition of host-secreted strigolactones. The germinated parasitic plants develop an invasive haustorium on their roots. The haustoria penetrate host roots and establish vascular connections between hosts and parasites to absorb water and nutrients. Induction of haustorium is provoked by host-derived small compounds, named haustorium-inducing factors, including quinones and flavonoids. Diversity of germination stimulants and haustorium-inducing factors is likely to contribute to host recognition by parasitic plants. On the other hand, host plants respond to parasitic plants by activating plant immunity. This review focuses on the interaction between the parasites and their hosts.
北海道内のコムギほ場から1989年に1017菌株,1992年に1931菌株のコムギ眼紋病菌Oculimacula yallundaeおよびOculimacula acuformisを分離してその分布を調査した.O. acuformisの割合はそれぞれ52.3%および43.7%で,道北および道東地域に優占する傾向が認められるものの道内に広く分布していた.2カ年の調査に大きな差異は認められなかった.O. yallundaeおよびO. acuformisのDMI剤に対する感受性を調査した結果,EC50値でプロピコナゾールではそれぞれ0.16~0.32 ppmおよび1.0~4.5 ppm,プロクロラズではそれぞれ0.03~0.09 ppmおよび0.04~0.18 ppmで,O. acuformisのプロピコナゾールに対する感受性が低かった.2カ年とも両剤に対する感受性は同様の傾向であった.O. acuformisの割合が5.0~100%と異なるほ場でプロピコナゾール乳剤およびプロクロラズ乳剤に対する防除効果を調査した.プロピコナゾール乳剤はO. yallundaeが優占するほ場では効果が認められたのに対し,O. acuformisが優占するほ場では効果が認められなかった.一方,プロクロラズ乳剤はいずれのほ場においても安定した効果が認められた.
A severe postharvest rot of acerola fruits (cv. Kanmikei) was found in Okinawa Prefecture, Japan in 2017. A fungus frequently isolated from the diseased fruits was identified as Colletotrichum tropicale based on morphological, cultural characteristics and sequence similarity of ApMat and GS gene regions. The isolates reproduced the symptoms on acerola fruits after inoculation and were reisolated from the inoculated fruits. This is the first report of anthracnose on acerola fruit in Japan.