In fluorescent pseudomonads, the Gac/Rsm signal transduction pathway controls secondary metabolism to suppress of fungal root pathogens via the expression of regulatory small RNAs (sRNAs). Because of its high cost, this pathway needs to be turned off in response to environmental stress. However, little is known about its underlying molecular mechanisms. In this study, it has been demonstrated that Lon protease negatively regulated the Gac/Rsm cascade in Pseudomonas protegens. It has also been shown that the alarmone ppGpp (guanosine tetraphosphate) appears to be essential for sustaining epiphytic fitness and biocontrol activity of P. protegens.
Since April 2014, a severe canker disease has been observed on trunks, branches, shoots, leaves and flower buds of kiwifruit (Actinidia chinensis and A. deliciosa) in several kiwifruit-producing areas of Japan. In some cases, symptoms such as shoot die-back, and bleeding cankers on the trunk with red-rusty exudation are more severe than those of any other canker disease ever confirmed in Japan. Twenty-two strains of the causal bacterium, isolated from Ehime, Fukuoka, Saga, and Wakayama Prefectures, and demonstrated by inoculation and reisolation to be pathogenic on A. chinensis, were gram-negative, aerobic rods with one to two polar flagella, and formed opaque, pale-yellowish, circular colonies. On the basis of biochemical and physiological characterization, PCR assays targeting ITS, hopZ3 and hopO1-2, and a multilocus sequence analysis (MLSA) using the concatenated sequences of seven housekeeping genes (acnB, cts, gapA, gyrB, pfk, pgi and rpoD), we identified the pathogen as Pseudomonas syringae pv. actinidiae (Psa). The results of the MLSA, additional PCR tests on argK, cfl, acnB, hopH1 and hopZ5, and biochemical and physiological characterization using API 20NE clearly showed that this pathogen corresponds to biovar 3 (=Psa3), one of four known biovars (biovars 1, 2, 3 and 5) of Psa. In addition, because Psa biovar 3 strains are known to carry integrative conjugative elements (ICEs) in their chromosomes, we used PCR tests to investigate whether or not biovar 3 strains used in this study possess ICEs. Of 22 strains, 14 possessed Pac_ICE1, and the other 8, derived from Fukuoka and Saga Prefectures, had no homologs of Pac_ICE1, Pac_ICE2, or Pac_ICE3. This study is the first to show that biovar 3, divided into two groups based on the presence of Pac_ICE, is present in Japan in addition to biovars 1 and 5.
It is vital that those who grow plants are able to effectively address the problems caused by plant diseases. Although growers and the increasing number of agricultural companies in Japan face various problems related to plant diseases, few studies have examined how they actually deal with such challenges and what kind of support they need. In July of 2007, we distributed questionnaires to 114 firms involved in growing and maintaining plants and to 224 farmers. We found that 94% of the firms and 93% of the farmers had encountered difficulties related to plant diseases. The results revealed a serious need for services related to the diagnosis, control, and prevention of plant diseases, especially among businesses. More than 60% of the business respondents spent more than one million yen to control plant diseases each year. Most respondents had positive results when they consulted an outside expert or professional body about dealing with plant diseases. However, only about 50% of firms had consulted an outside source, significantly lower than the proportion of farmers. In Japan, public institutions, such as agricultural extension centers, have provided support related to plant diseases for many years, but this support is directed primarily at farmers. The results of this survey indicate high demand for a new support system to help businesses address plant diseases more effectively.
Pathogenicity, morphological and genetic aspects of fungi isolated from seven gramineous plants with blast disease in the southern Tohoku region were studied. Spores had the typical form of Pyricularia. Most isolates did not form lesions on rice, but all were pathogenic to the host of origin. On the basis of toxin production and a phylogenetic tree based on the rDNA-ITS sequence of the isolates, the fungi isolated from plants in the grass genera Lolium, Erichloa, Panicum and Setaria were identified as Pyricularia oryzae, but are unlikely to serve as inoculum to cause rice blast disease.
A simple paper-disc method was developed to prepare DNA from a large number of samples of Pyricularia oryzae for polymerase chain reaction (PCR)-based analyses such as simple-sequence repeat analysis was developed by testing variables such as culture period, drying the culture, buffer volume and centrifugation for extracting DNA, and stability after storage. Mycelium from a single-spore isolate in the center of a plate of oatmeal–0.5% w/v sucrose–1.6% (w/v) agar is allowed to grow onto paper discs (ø 6 mm) on the plates. After 7 days at 26°C, the mycelium-permeated discs are dried in a dessicator, placed in 200 µl Tris-EDTA buffer (10 mM Tris·HCl, 1 mM EDTA, pH 8.0) in a microtube, and vortexed for ca. 2 s. After the preparation is centrifuged at 21,500×g for 30 min at 4°C, 1 µl of the supernatant with the fungal DNA can be used as the template to detect genomic and mitochondrial genes using PCR or the preparation can be stably stored at 4°C for 8 weeks.