An isolate of <i>Botrytis cinerea</i> produced polygalacturonase (PG) activity when grown on a modified Czapek-Dox liquid medium containing 1% citrus pectin and 1&37 glucose. Activity was detected after 3 days of growth and reached a maximum of 0.7 units after 10 days. Four polygalacturonases were purified from this medium. The purification involved liquid-phase isoelectric focusing, ion exchange chromatography and concanavalin A-affinity chromatography. The mode of cleavage of polygalacturonic acid by PGs was studied by comparison of the rate of reduction in viscosity with corresponding increase in appearance of reducing groups. Two endo-PG isozymes (endo-PGI and endo-PGII) with pI values of 8.78 and 4.9 and two exo-PGs (exo-PGI and exo-PGII) with pI values of 4.9 and 3.5 were identified. Endo-PGI and endo-PGII both had apparent M<SUB>r</SUB> values of 30 kDa; exo-PGI and exo-PGII had M<SUB>r</SUB> values of 65 and 70 kDa respectively. Each protein consisted of a single polypeptide chain. Exo-PGI and exo-PGII were shown to be high mannose-containing glycoproteins by their affinity to concanavalin A. Treatment of exo-PGI and exo-PGII with endoglycosidase-H resulted in peptides with reduced M<SUB>r</SUB>s of 46 and 60 kDa respectively. The temperature maxima for endo-PGI, endo-PGII, exo-PGI and exo-PGII were 37, 34, 48 and 50<SUP>o</SUP> respectively, and all the isozymes showed optimal pH values between 4.0 and 5.0. The inducibility of PG activity by galacturonic acid was assessed. When the fungus was grown on a modified Czapek-Dox liquid medium containing galacturonic acid or glucose, there was no consistent increase with time in the total PG activity, relative to mycelial dry weight. However, preparative isoelectric focusing identified a peak of activity between pH 3.7 and 6.3 when the fungus was grown in the presence of galacturonic acid. This activity was attributed to the induction exo-PGs (exo-PGI and/or exo-PGII).

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No description available.

As all underground parts of a potato plant can be infected with <i>Colletotrichum coccodes </i>it was speculated that it may be possible to predict black dot development on harvested tubers by assessing stems and stolons for the presence of the disease in the growing crop. In a 3-year study stems and stolons were assessed for black dot in 123 potato crops and its incidence related to disease on the tubers at harvest. In cvs Estima and Maris Piper, if stems or stolons showed black dot symptoms as the onset of crop senescence then the disease was likely to be present on tubers at harvest. No relationship between black dot on stems and stolons in the growing crop and disease on tubers at harvest was found in the cv. Saxon. To explain these results a series of glasshouse and field experiments were performed to identify when symptoms of black dot developed on underground parts of a potato plant. Results showed that infection by <i>C. coccodes </i>could occur soon after these plant parts had formed. Visual symptoms did not appear on stems and stolons till just prior to foliage senescence and on tubers until after the start of foliage senescence. Further research considered whether a reduction in black dot symptoms on tubers is achievable through haulm destruction methods in the field. Results indicated that in a crop of cv. Maris Piper, where there was a high incidence of black dot, and no one technique gave a significant reduction in symptom developing on tubers. These inconclusive results are discussed.

No description available.

No description available.

No description available.

No description available.

The production of phytoalexins by the lucerne cultivars Dupuits (susceptible to Verticillium wilt) and Maris Kabul (resistant to Verticillium wilt) in response to substances (= elicitors) produced by pathogenic and non-pathogenic isolates of Verticillium albo-atrum was investigated. The elicitors are produced in culture filtrates from the log-phase and past log-phase stage of growth. They are also extractable from the mycelial walls. Certain similarities in the biological and chemical properties of the culture filtrate and cell wall elicitors suggest that the culture filtrate elicitor is derived from the mycelial wall. The elicitors were purified by gel-filtration and ion exchange chromatography. They were found to be thermostable and non-dialysable and proved sensitive to sodium periodate, protease and sodium hydroxide treatment which suggests that they are glycoproteins. Both elicitors contain mainly glucose, mannose, galacose and protein. The protein component is rich in aspartic + acid, glutamic acid, alanine, proline, glycine, threoaine and serine. Molecular weight of the culture filtrate elicitor was found to be ca. 4.5 x 104. When the culture filtrates from both pathogenic and nonpathogenic isolates were allowed to permeate cut shoots via the transpiration stream of either lucerne cultivar, phytoalexins were produced in the leaves but not in the stems. No difference in the reaction of the cultivars to this elicitor from either isolate was apparent, i.e. there was no evidence of strain or cultivar specific reaction. Specificity as reflected in the level of phytoalexin production is only exhibited when drops of spore suspension of the respective isolates are placed on the surface of excised leaves. Although the culture filtrate and cell wall elicitors had many similarities, some evidence for a differential activity in phytoalexin production in the two cultivars was obtained.

The pathogenicity of two isolates of the fungus <i>Verticillium albo-atrum</i> obtained either from lucerne (V1) or tomato(V2) towards four cultivars of lucerne (<i>Medicago sativa</i>.L), namely Maris Kabul, Europe, Vela, and Euver was investigated. The results confirmed that only the V1 isolate is capable of causing wilt disease in these four cultivars. A degree of resistance was observed, however, and of all cultivars Maris Kabul showed the highest degree of resistance. Following pathogenicity testing, production of the phytoalexin medicarpin, synthesis of which is preceeded by an increase in activity of the enzyme phenylalanine ammonia lyase (PAL) was also investigated. The results showed that both the pathogenic isolate (V1) and the non-pathogenic isolate (V2), can induce an increase in PAL activity but that the non-pathogenic isolate induced a greater accumulation of medicarpin in tissues of cv. Maris Kabul. The differential activity between V1 and V2 isolates was further studied using a elicitor produced from mycelial culture filtrate from each isolate of the fungus. It appeared that elicitor from the V1 isolate contains a 'suppressor' molecule that acts 'down stream' of the step in which the increase in PAL activity was induced. The elicitors were partially purified using a combination of Con-A Sepharose affinity and DEAE anion exchange chromatography, and characterized by SDS-gel electrophoresis and treatment with trypsin and periodate. The results indicated a degree of heterogeneity in the elicitors which appeared to be rich in glucose and/or mannose and protein. Treatment with trypsin and periodate confirmed that both elicitotrs are glycoprotein in nature and depend for their activity on carbohydrate moiety. Characterization with SDS-gel electrophoresis revealed that the molecular weights of both V1 and V2 elicitors from the culture filtrates is ca. 29,000. There is also present one minor component (M wt. ca. 45,000) in the V1 elicitor preparation, which may be responsible for the differential activity of the V1 and V2 elicitors.