ピーマン品種「東京ししとう」から分離されたTMV-Pに属する1分離株(P6)を,Holmesの方法に従って熱処理を繰返し,弱毒ウイルスPa18を作出した。弱毒株Pa18は,ピーマンに対し軽微な病徴を現わすだけで,かつ強毒株P6に対しほぼ完全な干渉効果を示した。この干渉効果はPa18株接種10日以後に有効となった。しかし,TMV-トマト系統(P12株),黄斑系統(PY株)およびトマト系統とトウガラシ系統の中間的な性質を有するP2株には干渉効果が完全ではなかった。弱毒株Pa18によるピーマンの病徴は長期間にわたって微弱であった。またPa18株を更に局部病斑法で分離してもピーマンの病徴が異なる分離株は現われず,本弱毒株の性質は安定していた。弱毒株Pa18は5科24種の植物に感染し,宿主範囲は強毒株と一致したが,Nicotiana megalosiphon, N. benthamianaおよびPhysalis floridanaを除いたいずれの植物もPa18株による病徴はきわめて軽微であった。圃場でのピーマンのモザイク病防除への利用を試みた結果,本弱毒株Pa18による防除効果は顕著であった。すなわち,強毒株P6接種区のピーマンの生育は無接種区よりも著しく劣ったが,弱毒株Pa18接種区は無接種区とほぼ同等であった。強毒株P6接種区の収量は無接種区よりも約36%減少したが,弱毒株Pa18接種区では無接種区とほぼ同等であった。Pa18とP6株重複接種区の収量は無接種区より約18%減少したが,強毒株P6接種区よりは21.6%も増加した。更に,強毒株P6による果実のモザイク症状は外観品質を低下させるが,弱毒株Pa18は強毒株P6による果実のモザイク症状の発現を著しく抑制した。以上のことから,本研究によって作出された弱毒株Pa18は,TMVトウガラシ系統によって起きるピーマンのモザイク病の防除に十分利用が可能で,実用性が高いと考えられた。
A crude self-inhibitor of Botrytis cinerea was successfully extracted from highly concentrated spore suspension by ethylacetate (EtOAc). The inhibitory spot was shown at Rf 0.5-0.6 by the following procedure: after development with EtOAc: cyclohexane=1:1 (v/v), the thin-layer chromatogram was covered with water agar, and cellophane membrane was laid on the solid water agar, and then spores were spread over cellophane membrane. The ED50 of the crude extract determined from a plot of the percent inhibition of germination against the logarithm of concentration was 642ppm. The inhibitory activity was not lost after heating for 10min at 121C. The substance was permeable through cellophane membrane.
Mycelial growth and virulence of the dicarboximide-resistant strains of Botrytis cinerea isolated from greenhouses were compared with those of the sensitive strains after 6 month preservation at 10, 20, and 25C. The resistant strains were significantly inferior to sensitive ones in both mycelial growth on PSA media and virulence to excised kidney bean leaves. Sclerotia of the resistant strains buried in soil during summer were inferior to those of sensitive ones in viability.
In this paper, the authors report a new finding that an isolate of Xanthomonas campestris pv. oryzae became unexpectedly avirulent to a rice variety Kinmaze and some others. This isolate is the variant derived from Q6809 belonging to bacterial group III of X. campestris pv. oryzae. It was originally virulent to rice varieties belonging to Kinmaze, Kogyoku and Rantai Emas group and to IR 8, but has lost its virulence to japonica type rice varieties including Kinmaze group through successive transfers on artificial media. The virulence pattern of the variant is quite different from that of any of the already known bacterial groups.
Damping-off disease of radish seedlings declined in the soil into which normal field isolate 1271 belonging to Rhizoctonia solani AG-4 was repeatedly (3 times or more) inoculated. Diseased isolates which show abnormally slow growth were isolated from this disease declined soil. By incubating normal and diseased isolates in pair, diseased agent(s) of diseased isolate could be transferred to isolate 1271 by hyphal anastomosis, but not to other isolates of AG-4 and AG-2-2. This shows transmission of diseased agent is isolate-specific. Diseased isolates produce acidific substances, particularly oxalic acid. In comparison with that of isolate 1271, pathogenicity of diseased isolates is extremely low, though it varies from high to low. Using as inocula mixtures of isolate 1271 and diseased isolates, damping-off disease of radish seedlings decreased when inoculum of isolate 1271 was low, and cross protection could be seen among isolates.