Red rot resistance in interspecific protoplast fusion product progeny of Porphyra yezoensis and P. tenuipedalis (Bangiales, Rhodophyta)

Nine primary regenerants were recovered by interspecific protoplast fusion of Porphyra yezoensis Ueda T‐14 (Py) (cultivated Porphyra) and Porphyra tenuipedalis Miura (Pt). This combination is difficult to achieve with conventional sexual hybridization, yet is important in that non‐cultivated P. tenuipedalis is partially resistant (PR) to red rot disease, caused by the microbial pathogen, Pythium porphyrae Takahashi et Sasaki. Out of the nine primary regenerants, two strains (Py‐Pt‐4 and Py‐Pt‐7) were like the parent, P. tenuipedalis, while the rest were like the other cultivated parent P. yezoensis T‐14 in their life cycle. Red rot resistance was assessed in parents and interspecific fusion product progeny (FPP) by exposing the foliose thalli to equivalent infection and measuring two parameters of the host‐pathogen interactions: supported fungal biomass and amount of disease produced. Intermediate resistance between P. yezoensis T‐14 (1.00) and P. tenuipedalis (0.13) was observed in two of the Py‐type FPP, Py‐Pt‐2F₂ (0.25) and Py‐Pt‐5F₂ (0.23). Stable inheritance of resistance was observed through two subsequent generations. The morphologic and reproductive characteristics of the regenerated foliose thalli, and nature of host‐pathogen interactions were used to further verify the hybrid origin of the FPP. Host‐pathogen interactions were followed using epi‐fluorescence and scanning electron microscopy (SEM). The zoospores encysted at higher rates on the susceptible cultivated parent (P. yezoensis T‐14) germinated immediately and the short germ tubes formed appres‐soria and penetrated the algal cells near the site of encystment. While on the PR parental (P. tenuipedalis) and partially resistant FPP (PRFPP) progeny (Py‐Pt‐2F₂ and Py‐Pt‐5F₂) the low rate of zoospore encystment was followed by cyst germination, but only a few of the germ tubes formed appressoria and penetrated the thallus surface. Long germ tubes (with no appressoria) were seen growing on the thallus surface without host penetration. The minimal rate of encystment concomitant with low rate of appressorium formation on the PR parent and PRFPP was observed as the major factor responsible for the partial resistance in these thalli.     

Influence of Temperature on Pythium Splendens — Induced Root Disease on Carambola,Averrhoa Carambola

A series of glasshouse and incubator studies were conducted to investigate the role played by Pythium splendens in a decline disorder of carambola, Averrhoa carambola. Plants, 4-6 months old, were grown in native calcareous soil either infested or not infested with the pathogen. Isolates recovered from atemoya, carambola and passion fruit grew optimally at 30 degrees C, and significantly (P < 0.05) increased root necrosis and reduced root, shoot and total biomass of carambola. Temperature had a profound impact on the latter relationships. Two or more times more necrosis developed at 10 and 15 degrees C than at 25 and 30 degrees C. Total biomass accumulations were over four times greater at 30 degrees C than at 10 degrees C, and were always lower in soil infested with P. splendens. When biomass totals from infested and noninfested soil were compared, relative values were lowest at 15 and 20 degrees C and were almost two times greater at 30 degrees C than at 20 degrees C. Root infection by P. splendens was greatest at 15 and 20 degrees C, far below the species' optimum for growth, and at 30 degrees C was over nine times lower than at 15 and 20 degrees C. This is the first detailed report of P. splendens as a pathogen of carambola.     

Selection of turmeric callus tolerant to culture filtrate of <Emphasis Type="Italic">Pythium Graminicolum</Emphasis> and regeneration of plants

Root rot disease tolerant clones of turmeric variety Suguna of Curcuma longa L. were isolated using continuous in vitro selection technique against pure culture filtrate of Pythium graminicolum. Large amount of profuse, compact, creamish white callus was obtained from in vivo vegetative bud when cultured on LSBM fortified with 2,4-D (3 mg l⁻¹) after 45 days of culture. Callus was challenged with pure culture filtrate of P. graminicolum to isolate viable callus within 30 days of culture, which was further subjected to pure culture filtrate treatment. After three cycles of treatment, four cell lines which are tolerant to culture filtrate was isolated through continuous in vitro selection and subcultured on regeneration medium LSBM fortified with BAP (4 mg l⁻¹) along with the control non-selected callus to obtain complete plantlets through discontinuous in vitro selection technique. Plants regenerated from tolerant and non-selected calli were screened for disease tolerance by adopting in vitro sick plot technique. The data obtained from this experiment revealed a ratio of 225:49 tolerant: susceptible in vitro clones retrieved from tolerant callus. However, plants regenerated from the CL1a₁ and non-selected calli were susceptible under in vitro sick plot technique. The root rot disease tolerant clones were hardened and established in soil with 90% survival frequency.     

Simultaneous infection by red rot and chytrid diseases in <Emphasis Type="Italic">Porphyra yezoensis</Emphasis>Ueda

This paper presents the results of a study on the diseases of Porphyra yezoensisUeda along the north coast of China, where red rot (Pythium porphyrae) and the chytrid Olpidiopsis sp. diseases were both found to be present. Infection by the mycelia of Pythium porphyraeand the thallus of Olpidiopsis sp. was studied in detail. At the early stage of infecton the mycelia of Pythium porphyraeand the fungus of chytrid can be found in host cells at the same time. In the middle and late stages of the complication, it mainly appears as red rot disease, toward the end appearing almost completely as red rot disease. The complication even can be found on the cells of fronds from the freeze-storage nori nets. However, the freeze-storage nets can help prevent spread of the infection and improve nori quality.     

Organic acids and water-soluble phenolics produced by Paxillus sp. 60/92 together show antifungal activity against Pythium vexans under acidic culture conditions

Ectomycorrhizal fungi can produce antifungal compounds in vitro as well as in symbiosis with the host plant that can reduce root diseases. The objective of this study was to isolate antifungal compounds from culture filtrate of Paxillus sp. 60/92, which can form mycorrhizas with Picea glehnii seedlings. Culture filtrate of Paxillus sp. 60/92 showed antifungal activity against Pythium vexans at pH 3–4 but not at pH 5–10, although sterile MMN-b liquid medium (pH 3–10) did not show antifungal activity. Upon separation of antifungal compounds in the culture filtrate, antifungal activity was detected in the organic acid and water-soluble phenolics fractions adjusted to pH 3. Although antifungal activity of individual fractions was lower than that of the culture filtrate, a mixture of these fractions showed antifungal activity similar to that of the culture filtrate. Furthermore, antifungal activity of oxalic acid, which is known to be produced by Paxillus involutus, was increased by mixing with the water-soluble phenolic fraction. Our findings indicate that Paxillus sp. 60/92 produces organic acids and water-soluble phenolics that together show antifungal activity at pH 3–4 against P. vexans.     

The role of thionins in rice defence against root pathogens

Thionins are antimicrobial peptides that are involved in plant defence. Here, we present an in‐depth analysis of the role of rice thionin genes in defence responses against two root pathogens: the root‐knot nematode Meloidogyne graminicola and the oomycete Pythium graminicola. The expression of rice thionin genes was observed to be differentially regulated by defence‐related hormones, whereas all analysed genes were consistently down‐regulated in M. graminicola‐induced galls, at least until 7 days post‐inoculation (dpi). Transgenic lines of Oryza sativa cv. Nipponbare overproducing OsTHI7 revealed decreased susceptibility to M. graminicola infection and P. graminicola colonization. Taken together, these results demonstrate the role of rice thionin genes in defence against two of the most damaging root pathogens attacking rice.     

An annotated checklist of Pythium species from Iran

The genus Pythium, with slightly over 280 described species has been classified traditionally with other filamentous, coenocytic, sporangia-producing fungi as “Phycomycetes”. However, with recent advances in chemical, ultrastructural and molecular studies Pythium spp. are now considered as “fungus-like organisms” or “pseudo-fungi” and are placed in the kingdom Chromista or kingdom Straminopila, distinct from the true fungi or the kingdom Fungi. Little is known about the biodiversity of Pythium in Iran. This paper attempts to assess the position of the genus Pythium and provides details of the historical development of the study of Pythium in Iran. The survey list contains 33 species, 4 species groups and 1 unknown species of Pythium.     

Alteration of the Unsaturated to Saturated Ratio of Fatty Acids in Bacterial Lipids by Alcohols

Silver-coated cloth (SCC) effectively controlled root rot that was caused by Pythium aphanidermatum in hydroponically grown cucumber plants. The presence of SCC in the hydroponic solution reduced the root rot from 100% to 10% 20 days after inoculation with zoospores of P. aphanidermatum. It was suggested that the inhibition of SCC was caused not only by the silver ion dissolved from SCC, but also by the metallic silver and silver compounds formed on the surface of the root.