Phoma Medicaginis Var Research Articles

Techniques of Screening Peas for Resistance to Phoma medicaginis var. pinodella1

Footrot and foliar phases of the disease caused by Phoma medicaginis var. pinodella in peas (Pisum sativum L.) were studied. Major objectives were to develop repeatable inoculation procedures and to identify pea lines resistant to footrot and foliar infection. All tests were conducted under controlled environmental conditions. Fungal spore concentrations and plant age at inoculation were important for identifying differences in disease reactions among lines. Significant differences in reactions to footrot were obtained among lines when pea seeds were immersed for 5 min. in inoculum adjusted to 1 ✕ 104 spores/ml, planted in a sterile soil mixture, and scored 10 days later. Significant differences in resistance among pea lines to the foliar phase of the disease were obtained when 15‐day‐old pea seedlings were sprayed with inoculum containing 1 ✕ 105 spores/ml and scored 10 days later. Footrot scores ranged from 1.2 to 4.8, and foliar disease scores ranged from 2.1 to 4.9 when 96 pea genotypes were rated on a 1 to 5 scale (1 = symptomless and 5 = very severe disease). There was no significant correlation between footrot and foliar disease scores, indicating that different genetic factors may control reactions to the two phases of the disease.

Comparative Evaluation of Four Techniques for Screening Winter Peas for Resistance to Phoma medicaginis var. pinodella

Four techniques were evaluated for screening eight winter field pea lines [Pisum sativum subsp. arvense (L.) Poir] for resistance to foot rot and foliar infections caused by Phoma medicaginis var. pinodella (L. K. Jones) Boerema. The best differential follar symptoms in the greenhouse were obtained when 11-day-old seedlings were sprayed with a fine mist containing 1 ✕ 106 pycnidiospores/ ml of water, incubated for 10 days in a mist chamber and evaluated to determine the area of leaves and stems covered by lesions. The best differential foot rot symptoms in the greenhouse occurred when each seed was inoculated with 1 ml of a suspension containing 1 ✕ 106 spores as they were planted in fiats of sand, incubated for 14 days and evaluated on the basis of root lesion length. Differential foliar symptoms in the laboratory, occurred when excised leaflets were sprayed with a 2 ✕ 106 spores/ml suspension, incubated on moist filter paper in petri plates for four days, and evaluated on the percentage of leaf area covered by lesions. Differential foot rot symptoms were measured in the laboratory by imbibing pea seeds in a suspension of 2 ✕ 106 spores/ml in petri plates under continuous fluorescent light for three days and evaluated for the degree of inhibition of germination. Seven of the winter pea lines evaluated in the greenhouse and laboratory were also evaluated for the severity of foliar symptoms in the field during the spring of 1980. Results from the greenhouse and laboratory evaluations for resistance to foot rot symptoms were correlated with the resistance to foliar symptoms measured in the field (r = 0.95**, df = 5 and r = 0.78*, df = 5; respectively). Greenhouse and laboratory evaluations of resistance to foliar infection were not significantly correlated with foliar symptoms measured in the field (r = 0.69, df = 5 and r 0.60, df = 5; respectively). Both the laboratory and greenhouse foot rot screening techniques can be used to identify winter field pea lines with resistance to P. medicaginis under field conditions.

A standard technique for detecting seed-borne pathogens in peas, chemical control, and testing commercial seed in South Australia

A modified agar plate method was tested for its ability to detect Ascochyta pinodes, Macrophomina phaseolina, Phoma medicaginis var. Pinodella and Fusarium oxysporum on pea seed. It proved to be reliable. The characteristic colonies produced by the four pathogens from infected seeds on agar media are described. They were confirmed by microscopic examination. The method was used in a survey of 214 samples of commercial field pea seed from all parts of South Australia. Ninety per cent of samples had infection with A. pinodes with levels of infection ranging from 1-45%, making it the most important seed-borne pathogen. Seventy-two per cent of seed samples were infected with M. phaseolina with levels of infection ranging from 1-35%. Thirty-one and 24% of seed samples were infected with Phoma medicaginis and F. oxysporum, respectively. Only 10% of samples were free from infection. Two chemicals (benlate and thiram) were tested for in vitro control of these seed-borne pathogens. Complete control was achieved by thiram and benlate at both high and low dose rates.

Sub-cellular changes in the lytic compartment and the distribution of acid phosphatase and ribonuclease during infection of pea roots by Phoma medicaginis var. pinodella

Histochemical observations using light and electron microscopy revealed changes in the sub-cellular distribution of acid phosphatase activity in pea roots during infection by Phoma medicaginis var. pinodella . These experiments also showed particulate sites of enzyme activity in hyphae of the pathogen and observations were consistent with the view that some acid phosphatase may be secreted by the pathogen. Density-gradient ultracentrifugation of pea root homogenates on a Ficoll gradient resolved membrane-bound fractions which were characterized by electron microscopy, density determinations and biochemical assay for acid phosphatase and acid RNase activities. Infection of roots by Phoma resulted in specific transfer of molecular forms of these enzymes from their characteristic particulate sites to the supernatant-fluid fraction of cell homogenates. The results are discussed in relation to the nature and stability of the lytic compartment in healthy and diseased situations.

Purification and properties of a pectin-methyl trans-eliminase, a phospholipase and two aminopeptidases produced in culture by Phoma medicaginis var. pinodella

A pectin-methyl trans-eliminase produced in cultured by Phoma medicaginis var. pinodella was purified using ammonium sulphate fractionation, DEAE-cellulose ion-exchange chromatography, Sephadex G-100 gel-filtration and isoelectric focusing. A purification of 32·1-fold was achieved after gel-filtration and it was shown by gel electrophoresis that the enzyme was free from protein contaminants. An examination of the enzyme's properties revealed that it existed in two forms: as a monomer of mol. wt 29 500 and as a tetramer of mol. wt 118 000. Both forms possessed a pH optimum of 7·5, were activated by Ca2+ and combined during electrofocusing to show a pI value of 7·9.Using the same purification process, a phospholipase was obtained from a culture of the fungus and purified 6·4-fold after gel-filtration. Gel electrophoresis showed that it was free from protein contaminants after isoelectric focusing. The enzyme had a molecular weight of around 140 000 and a pI value of 5·5. Gas-liquid chromatography showed palmitic acid was produced by the degradation of dipalmitate derivatives of lecithin and lysolecithin suggesting that the phospholipase of P. medicaginis var. pinodella possessed B-type activity.The fungus also produced two aminopeptidases. One was purified 493·8-fold after gel-filtration and had a mol. wt of approximately 125 000. This enzyme exhibited a pH optimum of 7·0 and a temperature optimum of 35 °C; it was activated by Mn2+, threonine, glycine and sodium thioglycolate. The other enzyme was purified 287·5-fold after gel-filtration and exhibited a mol. wt of approximately 112 000. This enzyme possessed a pH optimum of 7·0 and a temperature optimum of 30 °C; it was activated by Co2+ and MoO42−. Both enzymes showed a pI value of 5·0.

Selection of pea lines for resistance to pathotypes of Ascochyta pinodes, A. pisi and Phoma medicaginis var. pinodella

The pathogenicity of 45 isolates of Ascochyta pinodes, Ascochyta pisi and Phoma medicaginis var. pinodella collected in South Australia has been examined on selected pea lines. Twenty-six isolates of A. pinodes were differentiated into 15 pathotypes, 15 isolates of A. pisi were differentiated into 13 pathotypes, and four isolates of P. medicaginis var. pinodella into one pathotype. Adequate sources of resistance were identified against all the pathotypes excepting pathotypes 1 of A. pinodes and A. pisi. The necessity to breed for broadly based resistance to Ascochyta species is discussed.

Decomposition of cellulose by three pea pathogens in pure culture

Ascochyta pisi (Lib.), Mycosphaerella pinodes (Berk. & Blox.) Vestergr., Phoma medicaginis var. pinodella (L. K. Jones) Boerema, which cause leafand pod spot, and foot rots of pea grow on filter paper as a sole carbon source in pure culture. Different isolates of the same pathogen utilized cellulose at different rates and decomposition was affected by the amount of nitrogen in the culture. These results have relevance to studies of the saprophytic survival of these organisms.

Mikrobielle umwandlung von gibberellinen—entacetylierung von O(3,13)-diacetylgibberellinsäure

The fungus Phoma medicaginis var. pinodella (L.K. Jones) Boerema has been shown to split off the O(3)-acetyl group of gibberellic acid acetates without affecting O(13)-acetyl 19,10-lactone, and methyl ester groups. Fungal deacetylation of O(3,13)-diacetylgibberellic acid (VII) yielded O(13)-acetylgibberellic acid (V), which has not previously been prepared.