D. citriの侵入をうけたウンシュウミカン(Citrus unshiu)葉の表皮細胞は接種1日後には顆粒化し,2日後には褐変した。つづいてその周囲の細胞の顆粒化,褐変が起こり,接種7日後には3∼5層の細胞を半径として,最初に褐変した表皮細胞を中心に半球形状に褐変した。その後,褐変細胞群に隣接した細胞が分裂し,2細胞となった。細胞分裂はくり返され,10∼12層の細胞から成るカルスが形成された。さらに褐変細胞群とカルス組織との間に周皮が形成された。このため,病原菌の侵入をうけた部位は健全組織から遮断された。黒点病斑はこれらの組織から構成されたものの総称である。したがって,カンキツの自己防衛のために形成されるものと推察された。さらにスターメラノーズ(銅の薬害)および傷害跡も褐変細胞群,カルスおよび周皮から構成されており,両者はともに黒点病斑形成と同様の過程で形成されることが明らかにされた。以上のことから,カンキツは病原菌の侵入,薬剤の浸透,機械的傷害などに対して自己防衛反応を引き起こし,防衛組織を形成すると考えられる。
In order to eliminate the grapevine leaf roll virus (GLRV) from grape cultivar, Zenkoji (socalled Ryugan), some experiments on the heat treatment and meristem tip culture were conducted and new plants were successfully obtained. These plants were indexed for GLRV by the observation of symptoms appeared on them and also indicator cultivar, Pinot noir, plants green-grafted with candidate plants. The results indicated that the elimination ratio in meristem tip culture (80.4%) was higher than that in heat treatment (27.3%).
Radish residue infested with radish-yellows fusarium was piled up for 20 days to examine for inactivating effect on the pathogen. No Fusarium oxysporum was detected in the tissue samples collected from the lower parts of the pile without plastic-film cover, from the parts where temperature rose up more than 50C, and from almost all parts of the pile covered with plastic-film even though temperature ranged from 15 to 35C. These results suggest that F. oxysporum is well inactivated under the conditions of anaerobic fermentation.
Solar heating of out-door field soil with plastic-film mulching produced significant raise of soil temperature. Maximum temperature in the mulched soil were 45.2-47.0C and 37.9-39.9C at the depth of 5 and 20cm, respectively. Fusarium oxysporum was not detected at all from the mulched soil at the depth of 5cm, and approximately 60% decrease of F. oxysporum population was noted from that at the depth of 10 to 15cm. Disease incidence in the mulched field was significantly reduced, especially in lightly infested soil and in more insolated summer. Effect of combined treatment of plastic-film mulching with application of calcium cyanamide on the disease incidence was almost similar to that of mulching only.
Since 1973, a new disease of maskmelon caused by Rhizopus sp. occured in Shizuoka prefecture. The fungus of Rhizopus disease attacks on fruits of maskmelon were arrived at a market. Rhizopus sp. isolates obtained with high frequency from affected fruits. The symptoms appeared on the peduncle of muskmelon fruits at the begining of the disease development. The symptom on peduncle are covered with black mycelia. Soon after, the disease fruits softened and rotted circularly at the peduncle. The fungus was similar to Rhizopus stolonifer because of the agreements in their morphological and pathogenical properties to the description by Inui and Zycha. From these results, the causal fungus was identified as Rhizopus stolonifer (Eherenberg Ex Fr.) Lind (syn. Rhizopus nigricans Ehr.).