In vivo control of Mycosphaerella pinodes on pea leaves by a crude bulb extract of Eucomis autumnalis

We previously reported on the in vitro antifungal activity of a crude whole plant extract from Eucomis autumnalis against seven economically important plant pathogenic fungi. A crude extract of the bulb showed similar in vitro mycelial growth inhibition of the same plant pathogenic fungi as well as that of an eighth fungus, Mycosphaerella pinodes, the cause of black spot or Ascochyta blight, in peas. Subsequently, fourth internode leaves were removed from 4 wk old pea plants, placed on moist filter paper in Petri dishes and inoculated with an M. pinodes spore suspension before and after treatment with the extract. The control of Ascochyta blight by different concentrations of the crude E. autumnalis extract was followed in vivo by leaf symptoms over a 6 day period at 20°C in a growth cabinet. The crude extract prevented M. pinodes spore infection of the leaves when the leaves were inoculated with spores both before or after treatment with the extract, confirming complete inhibition of spore germination. The crude E. autumnalis extract showed no phytotoxic reaction on the leaves even at the highest concentration applied.     

Inheritance of black sigatoka disease resistance in plantain-banana (Musa spp.) hybrids

Black sigatoka (Mycosphaerella fijiensis Morelet), an airborne fungal leaf-spot disease, is a major constraint to plantain and banana (Musa spp.) production world-wide. Gaining further knowledge of the genetics of host-plant resistance will enhance the development of resistant cultivars, which is considered to be the most appropriate means to achieve stable production. Genetic analysis was conducted on 101 euploid (2x, 3x and 4x) progenies, obtained from crossing two susceptible triploid plantain cultivars with the resistant wild diploid banana Calcutta 4. Segregating progenies, and a susceptible reference plantain cultivar, were evaluated over 2 consecutive years. Three distinct levels of host response to black sigatoka were defined as follows: susceptible (< 8 leaves without spots), less susceptible (8–10) and partially resistant (> 10). Segregation ratios for resistance at the 2x level fitted a genetic model having one major recessive resistance allele (bs ₁) and two independent alleles with additive effects (bsr ₂ and bsr ₃). A similar model explains the results at the 4x level assuming that the favourable resistance alleles have a dosage effect when four copies of them are present in their respective loci (bs _i ⁴ ). The proposed model was further validated by segregation data of S ₁ progenies. Mechanisms of black sigatoka resistance are discussed in relation to the genetic model.     

The talc formulation of Streptomyces antagonist against Mycosphaerella foot rot in pea (Pisum sativum l.) seedlings

Pea is highly susceptible to pre-emergence damping off and foot rot after emergence caused by Mycosphaerella pinodes in western Algerian regions. Rhizosphere Actinomycetes which were antagonistic to the growth of this pathogen were isolated from chellif soils. An isolate of Streptomyces St7c5 provided superior seed protection. An increased in both germination and plant growth were recorded following treatment of seeds with Streptomyces formulated with inert or organic charge when compared to control. Application of the antagonist agent resulted in a significant reduction of Mycosphaerella foot rot to 5% compared with untreated seeds (25%). Hence, the talc formulation of Streptomyces agent can be recommended as one of the crop strategies for the management of foot rotting and blight caused by Mycosphaerella pinodes.     

The Colletotrichum graminicola striatin orthologue Str1 is necessary for anastomosis and is a virulence factor

Striatin family proteins are key regulators in signalling pathways in fungi and animals. These scaffold proteins contain four conserved domains: a caveolin‐binding domain, a coiled‐coil motif and a calmodulin‐binding domain at the N‐terminus, and a WD‐repeat domain at the C‐terminus. Fungal striatin orthologues are associated with sexual development, hyphal growth and plant pathogenesis. In Fusarium verticillioides, the striatin orthologue Fsr1 promotes virulence in the maize stalk. The relationship between fungal striatins and pathogenicity remains largely unexplored. In this study, we demonstrate that the Colletotrichum graminicola striatin orthologue Str1 is required for full stalk rot and leaf blight virulence in maize. Pathogenicity assays show that the striatin mutant strain (Δstr1) produces functional appressoria, but infection and colonization are attenuated. Additional phenotypes of the Δstr1 mutant include reduced radial growth and compromised hyphal fusion. In comparison with the wild‐type, Δstr1 also shows a defect in sexual development and produces fewer and shorter conidia. Together with the fact that F. verticillioides fsr1 can complement Δstr1, our results indicate that C. graminicola Str1 shares five phenotypes with striatin orthologues in other fungal species: hyphal growth, hyphal fusion, conidiation, sexual development and virulence. We propose that fungal striatins, like mammalian striatins, act as scaffolding molecules that cross‐link multiple signal transduction pathways.     

Effects of pod infection by Mycosphaerella pinodes on yield components of pea (Pisum sativum)

Yield reduction of pea (Pisum sativum) due to various types of infections by Mycosphaerella pinodes on pods was assessed. A range of disease severities was created on pods of pea plants grown in the glasshouse, by painting the pods with different concentrations of spore suspensions, at three different pod development stages: lag phase, the beginning of seed filling (BSF) and mid-filling of the seeds. Seed number at harvest was reduced only if the pods were infected before BSF, as shown previously for whole plant infections. Pod infections led to individual seed weight (ISW) losses from zero (for late infections, at mid-filling) to 20% (for earlier infections and severe disease). Infection during the lag phase affected ISW by reducing seed growth rate, whereas infection at BSF tended to reduce the duration of seed filling. There was a linear relationship between the area under the disease progress curve and the percentage decrease in ISW. This model should be complemented by the effect of leaves and stem infections, in order to predict ISW losses in diseased crop conditions, in which epidemics occur on all aerial parts of the pea plant.