Generally, the ability of germination of aged conidia of Botrytis cinerea Pers. in distilled water is almost lost, when they were incubated at 20°C for more than 6 days. However, when mono-, oligo-, or polysaccharide was added to the suspension, aged conidia regained the ability of germination, appressorium formation, growth of germ tubes, and the infectivity. This recovery effect of sugars on conidia aged by incubation at 20°C for 40 days, was recognized in 10-2-10-3M solution, but not in 10-5M solution. The recovery effect of monosaccharide, e.g., glucose and fructose, on the germinability of conidia was remarkably increased in 10-2-10-3M solution, and the growth of germ tubes, appressorium formation and infectivity were also promoted as well as the germination. However, effect of mannose, galactose, and xylose was not recognized in 10-210-3M solution. Although arabinose stimulated the germination of aged conidia in 10-2M solution, the appressorium formation was not effected. In oligosaccharide solution aged conidia also regained the germinability, growth of germ tubes, appressorium formation and infectivity in descending order of sucrose, maltose, and lactose. In polysaccharide solution this effect was also recognized in descending order of dextrin, inulin, and starch, but they were less effective than in mono- and oligosaccharide solutions. Generally, the growth of germ tubes was more vigorous in 10-2M solution than in 10-3M solution, and the appressorim formation and infectivity were also promoted more in 10-3M solution than in 10-2 and 10-5M solutions.
Genic analysis for the blast resistance of rice plants was carried out in two varietal crosses given in the title. The reaction of a plant to a fungus isolate appeared to be conditioned by two or three genes quantitatively. From Sensho×H-79 were foud three independent genes, Rb1, Rb2 and Rb3, whose alleles contributed different degrees of susceptibility cumulatively when the virulence of an isolate and the resistance of a host plant to it were each estimated by an index. For all genotypes, the index-values to the used three isolates were assumed to indicate their degree of resistance. Genotypes were divided into two groups as to each isolate, resistant and susceptible, to correspond with the ratio of the former to the latter given in experimental datum. The recombination fractions between Rb1 and la+ were consistently found to be 0.09-0.10 in five data. The gene-for-gene hypothesis was thus extended to a system of quantitative relationships. The data from Imochishirazu×H-79 could also be interpreted in the same manner: Gene Rb4 and Rb5 were responsible for the reactions to one of the isolates, but not to the other two isolates. Rb4 was found to be linked with la, showing 0.23 of recombination fraction.
A new detection method for the pathogen of bacterial leaf blight of rice (Xanthomonas oryzae was devised and its accuracy was evaluated. The process of this method is as follows: using seedlings of susceptible variety (Jukkoku or Kinmaze) at 4.5-5.0 leafstage, the materials to be detected are inoculated on leaf blade of the seedling twice with a bundle of 100 needles (i.e., 200 needle prick inoculation). Younger leaves are more suitable for detection than older ones, and the test plant should be applied with nitrogenous fertilizer. Seven days after inoculation, bacterial exudation is to be observed from a section of about 1.5mm wide cut at an upper part of the inoculated point. The bacterial exudation indicates the presence and abundance of the pathogen. The lower limit of detection seems to lie at about 100 cells per ml. Bacterial exudation is observed in the case of inoculation with Pseudomonas glumae, P. setariae and Xanthomonas phaseoli respectively, only when they are inoculated at high bacterial density of more than 107 cells per ml. Therefore, these contaminants seem to be negligible under field conditions when the method is applied to detect X. oryzae from natural materials. The author proposes to name this method “bacterial exudation method”.
Spore production of Pyricularia oryzae was relatively abundant on rice straw decoction plus V-8 juice agar (R+V-8), rice straw decoction agar (R), yeast starch agar (Y) and V-8 juice agar (V-8), but it was poor on oat meal agar (O) and potato decoction agar (P), in 7 days culture at 27°C in darkness. The spore production of the fungus on these media in 7 days culture at 27°C was increased by a continuous exposure to 20 watt “white” fluorescent lamp (Matsushita) at 30cm distance from the lamp to mycelium. A large amount of spores was produced on R+V-8, R, and V-8 media. The increase in the rate of spore production, however, was markedly higher on P and O media, on which the spore production in darkness was poor, than those on the other media. The spore productions in three isolates of P. oryzae, namely H67-1, Ken 60-19 and Ken 53-33, on R+V-8 medium in 7 days culture at 27°C, were markedly increased when exposed to a continuous irradiation with 20 watt “black light blue” fluorescent lamp at 30cm distance from the lamp to mycelium. However, stimulative or inhibitory effect on spore production of three isolates of P. oryzae was not observed on the same medium in 7 days culture at 27°C when exposed to a continuous irradiation with 20 watt “pure red” “pure yellow” “pure green” and “pure blue” fluorescent lamps. The spore production of three isolates of P. oryzae on R+V-8 medium, were markedly increased when exposed to a continuous irradiation with 340mμ or 365mμ wave length light obtained, through glass filters. Stimulative or inhibitory effect of spore production on the same medium was not observed when exposed continuously to lights with 380mμ, 401mμ 422mμ, 432mμ and 450mμ wave length.
Various methods for testing blast resistance of rice varieties were compared by drawing a correlation diagram of each pair of the methods. In all the diagrams drawn, curvilinear regressions were observed. This indicates that the level of estimation of resistance is different between two methods compared, and that there are upper and lower limits of measurable range in all the methods. By injection method the resistance of varieties belonging to intermediate reaction classes was estimated to be more susceptible than by spraying method for inoculation. In spraying method, intermediate varieties were judged to be more resistant by the evaluation based on the type of predominant lesions than by the evaluation based on the type of the largest lesion. Intermediate varieties showed more resistant reaction by inoculation at the 4 week stage than at the 2 week stage of rice seedlings, and by inoculation with Ken 54-04 than with Ken 54-20. Interrelations among these phenomena were schematically shown in one figure (Fig. 11). A part of field resistance which cannot be detected in the greenhouse by the usual method for differentiating pathogenic races could be tested by the following methods: 1) lowering the measurable range of testing method by using a less aggressive fungus strain, 2) increasing the resistance of varieties by increasing plant age, or by growing plant under conditions similar to field conditions.