Partial resistance to neck blast influenced by stage of panicle development and rice genotype

Summary Neck nodes of eight rice genotypes were inoculated with a virulent isolate of the blast pathogen at four slightly different, increasingly older stages of panicle development shortly after flowering. Resistance to infection as well as resistance to growth of the pathogen after infection was assessed. Significant differences between genotypes were found for both components of resistance. Resistance to growth of the pathogen sharply increased with aging of the neck node as was indicated by a large reduction of the length of the lesions on the culm, but resistance to infection did not change much. The lesion length was closely related to yield loss. A small delay in time of infection can lead to a large decrease in yield reduction. Meaningful comparison of partial resistance to neck blast between genotypes therefore requires infection at an identical stage of panicle development. In the field, where panicles are in different stages of development, selection of genotypes that do show the symptoms of neck blast together with relatively little yield loss in infected panicles is recommended.     

Fate of mucilage cell wall polysaccharides during coffee fermentation.

Effects of a 20-h fermentation on cell wall polysaccharides from the mucilage of pulped coffee beans were examined and compared to those of unfermented beans, on alcohol insoluble residues (AIRs), their hot-water-soluble crude pectic substances (PECTs), and their hot-water-insoluble residues (RESs). Yields and compositions were very similar: AIRs, which consisted of approximately 30% highly methylated pectic substances, approximately 9% cellulose, and approximately 15% neutral noncellulosic polysaccharides, exhibited no apparent degradation. However, PECTs from fermented beans were shown to have undergone a slight reduction of their intrinsic viscosity and weight-average molecular weight by capillary viscosimetry and high-performance size-exclusion chromatography. After fermentation, hot-water-insoluble pectic substances of RES exhibited partial de-esterification. Removal of coffee bean mucilage by natural fermentation seems to result from a restricted pectolysis, the mechanism of which remains to be elucidated.     

Survival of myxobacter strain 8 in natural soil in the presence and absence of host cells

Myxobacter strain 8 is one component of a sequence of three predatory bacteria that develop in soil when Micrococcus luteus host cells are added to the soil. The survival of strain 8 in the presence and absence of added host cells in natural soil not allowed to dry out was examined. Strain 8 vegetative cells died relatively rapidly in unamended soil. Death was faster and occurred to a greater extent in acidic than in neutral pH soil. However, in both cases death was accompanied by formation of sonication-resistant myxospores so that they comprised the ultimate population. These myxospores survived for prolonged periods in both acidic and neutral pH soils.Vegetative cells added in high numbers to soil did not multiply under any of the conditions tested. They did multiply, however, when they were added in low numbers to soil (including acidic soil) receiving sequential (additive) amendments of heart infusion broth or living M. luteus cells. This multiplication produced strain 8 cell numbers approximating those in the above experiments receiving high strain 8 cell number inoculations. Possibly, this represents a maximum vegetative cell number for soil.Germination of the myxospores in soil, followed by growth, seemed to require an approximately neutral pH and the presence of a proper host organism. Germination occurred with M. luteus as host, but not with Escherichia coli. A delayed germination occurred when sequential amendments of heart infusion broth, instead of M. luteus host cells, were made, but this could reflect a growth response by some indigenous components of the soil microflora that then served as host cells for germination.     

Otto Appel

Ohne Zusammenfassung

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Otto Appel

     

Biotypes of the citrus nematode (Tylenchulus semipenetrans Cobb) in Israel

Two biotypes of the citrus nematode, Tylenchulus semipenetrans Cobb, were identified among five populations occurring in different regions in Israel. These biotypes originated from Sour orange and Troyer citrange roots and differed in their ability to infestPoncirus trifoliata hybrids (particularly Troyer citrange). They appear to be close to two recognized biotypes known to be present in other countries and designated as the “Poncirus” and “Mediterranean” biotypes. The different infectivity of the two biotypes on Troyer citrange roots was maintained even after they were cultured for 6 months on Sour orange. Both biotypes readily reproduced on persimmon, but failed to infest olive and grapevine. Two newP. trifoliata x Poorman orange hybrids exhibited good resistance to both biotypes.     

Laboratory selection of resistance by the red flour beetle,tribolium castaneum (Herbst), to an atmosphere of low oxygen concentration

Adult populations of the red flour beetle,Tribolium castaneum (Herbst), were exposed for 40 generations to an atmosphere containing 99.5% N₂ and 0.5% O₂ at 95% RH, in order to select a strain resistant to the low oxygen concentration (LOC) atmosphere. Selection pressure was maintained at between 50% and 70% mortality. At the 40th generation comparison of sensitivity between the selected strain and the original non-selected strain indicated a resistance factor at the 50% mortality level (LT50) of x 5.2. However, throughout the selections, log-time against probit-mortality curves remained roughly parallel from generation to generation and the slope remained low. These findings indicate a multiplicity of genetic factors that at a high level of selection contribute together towards an adaptation of the insects to survival in the LOC atmosphere. Removal of selection pressure from a sub-population of the selected strain from the 13th to 21st generation revealed that resistance was partially retained with a decrease in resistance factor of 23%. Although the study revealed that the insects were able to develop a strain resistant to hypoxia, exposures were at 95% RH to minimize the desiccation effect. This does not reflect field situations, where ambient relative humidities are generally below 70%.     

The advantages and disadvantages of endoscopy

Endoscopy is generally a very safe and effective tool in the diagnosis and therapy of various gastrointestinal (GI) disorders, and must be used in conjunction with other diagnostic modalities. Endoscopy should not be a substitute for a complete work-up. There are many advantages of endoscopy, including minimal morbidity and mortality, and the sensitivity of this modality in the diagnosis of mucosal disorders of the GI tract. However, complications may occur, and there are limitations to endoscopy. This article will provide an overview of when to choose GI endoscopy and when other procedures might provide more information.