To clarify the mode of action of soybean lecithin (SL), we studied the effect on morphology of Pyricularia oryzae by using the onion epidermal strip method. SL at 500ppm induced an abnormal structure at the surface of the conidium or the germ tube. From observation 24hr after inoculation. SL did not inhibit appressorial formation at 5ppm, but 500ppm or more SL inhibited 86.2% or more appressorial formation. 500ppm SL also induced a morphological abnormality in germ tube with its branching at the tip and consequently inhibited appressorial formation. Besides, SL inhibited 96% appressorial penetration at 5ppm. The inhibition of appressorial penetration is the most characteristic action of SL.
A monomeric cDNA copy of cucumber mosaic virus (CMV) satellite RNA which is non-necrogenic to tomato was introduced into nuclear DNA of tobacco plants with the aid of the binary vector system of Agrobacterium tumefaciens. In order to check the stability of the introduced genes, kanamycin resistance and expression of biologically active satellite RNA upon infection with CMV were assayed up to the fifth generation of the homozygous progeny obtained from a primary transformant. The inserted cDNA in the progeny of the fifth generation was sequenced after cloning of the sequence amplified with the polymerase chain reaction. Neither loss nor mutations of the inserted genes were detected.
Components of partial resistance to southern corn leaf blight caused by Bipolaris maydis race O were analyzed using young plants of six corn inbred lines (H95rhm, R2040, Mo17Ht, H95, H93, Pa91) and compared with the progression of the disease in the field. In the greenhouse seedling tests, the infection efficiency (IE) did not vary among the inbred lines. Lesion area (LA), sporulating lesion ratio (SLR) and degree of sporulation (SP) were differed significantly among them and the resistant lines showed low values of LA, SLR, and SP. The LA values of each line corresponded to the disease progression in the field. The inbred line, H93, showed a moderate resistance in the field but the lesions expanded rapidly in young plants. However, H93 showed a low ability of spore production which might account for the moderate resistance in the field. Estimation of spore production in addition to lesion expansion as components of partial resistance should be performed for the prediction of field resistance using young plants.
Induction of dicarboximide fungicide-resistance by pre-culturing in the filtrates of the field resistant strains (IHES-2 and CAES-4) of Botrytis cinerea was examined by two bioassay methods. In the protoplast bioassay method, the regeneration frequencies of the mycelial protoplasts of the sensitive strain (IPCR-1) pre-treated with IHES-2 and CAES-4 filtrates, respectively, were 2.7 and 2.4% on the medium containing the fungicide, which were about tenfold higher than that by pre-treatment with IPCR-1 filtrate. In another method, IPCR-1 conidia were shaking-cultured in IHES-2 and CAES-4 filtrates for 3 days, respectively, and each of the conidia was harvested as a mycelial ball like structure (MBS). The MBSs pre-cultured in these filtrates formed the colonies about three times as many as those with IPCR-1 filtrate. From the two different bioassays, the induction of dicarboximide fungicide-resistance with the filtrates of the resistant strains was confirmed. Especially, MBS bioassay method may be a useful one for bioassays of filamentous fungi, in which it is hard to statistically detect the effects of physiologically active substances because of the morphogenic changes in the growth cycle.