Effect of canopy manipulation on cane and fruit Botrytis in protected raspberry.

Botrytis cinerea causes disease on both the fruit and cane of raspberry. The incidence of latent and post-harvest fruit botrytis was examined in 19 commercial open-field and protected crops. Many samples showed a high incidence of infected fruit (>50%), even on protected crops sprayed with fungicides. Differences between open-field and protected crops, between sprayed and unsprayed crops and between two varieties (GLen Ample and Tulameen) were not statistically significant. The incidence of latent infection by B. cinerea in unripe fruit did not correlate with the incidence of botrytis fruit rot developing on ripe fruit. Experiments were conducted in two commercial crops to investigate whether the removal of Lateral Leaves and thinning of primocanes during the flowering and fruiting period could reduce the incidence of fruit and cane infection by B. cinereo. Canopy manipulation resulted in considerable decreases in humidity inside the canopy at one site, where the original cane density was very high, (20 canes/m) and not at the second site where cane density was lower (10 canes/m). Canopy thinning did not significantly reduce the incidence of fruit botrytis at either site but reduced the incidence of leaf and cane infection in the dense crop. Results suggest that a significant reduction of cane infection by canopy manipulation can be realised for situations where cane density and disease pressure are high. The present studies suggest that in dense canopies in a protected crop, cane Lesions are more likely to result from direct infection of canes by the pathogen, although the pathogen can readily invade wounds on canes, including de-leafing wounds.

Infection of raspberry leaves by Botrytis cinerea in relation to leaf and cane age.

Botrytis cinerea Pers, ex Fr. can cause diseases on both cane and fruit on raspberry. Previous observations in field crops led to formulation of the hypothesis that infection of canes arose from invasion by mycelium from the petioles of infected leaves and that only mature and old leaves are susceptible. Inoculation studies in protected crops were conducted to investigate infection of raspberry leaves and canes by B. cinerea with a particular emphasis on determining the timing of cane infection in relation to leaf infection. The results obtained in protected crops indicated that cane age rather than the leaf age per se influences the susceptibility of leaves; leaves on young canes were less susceptible to botrytis infection than those on old canes. On older canes, leaves of all ages, ranging from young expanding to old senescent, were equally susceptible. The overall incidence of cane infection from inoculation of leaves was very low; most of cane infection was likely to have resulted from the direct infection of canes and not through invasion via the petioles of infected leaves.

Epidemiology of mycotoxigenic fungi associated with Fusarium ear blight and apple blue mould: a review.

Research on the epidemiology of plant diseases is briefly reviewed, focusing on two diseases caused by mycotoxin-producing pathogens: Fusarium ear (or head) blight (FEB or FHB) of small grain cereals and apple blue mould (Penicillium expansum). Pathogen development during its key life cycles is discussed in relation to important environmental factors and host resistance. Current control methods are also reviewed, focusing on cultural and biological methods. The future challenge is to understand the relationships between disease severity, fungal biomass and the production of associated mycotoxins in order to minimize risks of both disease damage to crop yields and threat to human health posed by mycotoxins.

Modeling Infection of Strawberry Flowers by Botrytis cinerea Using Field Data.

ABSTRACT The incidence of strawberry flower infection by Botrytis cinerea was monitored in unsprayed field plots in three successive years together with meteorological data and numbers of conidia in the air. There were large differences in conidia numbers and weather conditions in the 3 years. Three sets of models were derived to relate inoculum and weather conditions to the incidence of flower infection; by inoculum only, by weather variables only, and by both inoculum and weather variables. All the models fitted the observed incidence satisfactorily. High inoculum led to more infection. Models using weather variables only gave more accurate predictions than models using inoculum only. Models using both weather variables and inoculum gave the best predictions, but the improvement over the models based on weather variables only was small. The relationship between incidence of flower infection and inoculum and weather variables was generally consistent between years. Of the weather variables examined, daytime vapor pressure deficit and nighttime temperature had the greatest effect in determining daily incidence of flower infection. Infection was favored by low day vapor pressure deficit and high night temperature. The accuracy and consistency of the weather-based models suggest they could be explored to assist in management of gray mold.

Possible role of volatile Fatty acids and abscisic Acid in the dormancy of oats.

Species of Avena differ markedly in their levels of pre- and post-harvest dormancy. These species offer the opportunity of determining if dormancy is related to the endogenous level of growth inhibitor. Germinability in two species of differing levels of dormancy, common oat Avena sativa L., and wild oat Avena fatua L. was assessed as were the contents of abscisic acid and volatile fatty acids of chain length C(6)-C(10). In A. sativa which did not possess postharvest dormancy there was no correlation between germination and inhibitor levels but in A. fatua the relationship between the content of fatty acid and dormancy was good. The loss of these fatty acids in dry storage by evaporation could explain after ripening.

Effect of Temperature on the Short Chain Fatty Acid-induced Inhibition of Lettuce Seed Germination.

In lettuce, Lactuca sativa short chain fatty acids (C(6) - C(9)) vary in their effectiveness as inhibitors of germination according to temperature; the higher the temperature, the greater the inhibition. A linear relationship exists between temperature and the dose causing half-maximal germination. Nonanoic (C(9)) acid is the most effective.When extrapolated to the abscissa, really zero concentration of acid, the regression lines intercept at 36.8 C +/- 2.6 C. It may be that at this temperature the whole membrane becomes fluid without acid being present but with acid there was complete fluidizing at lower temperatures the degree of fluidity being determined by the amount and type of acid present. This speculation distinguishes between the fluidizing of the bulk lipids and the character of the lipid layer that may be around certain key membrane proteins.

Changes in Leaf Proteins of Peas, Pisum sativum L., during Development on Deflorated Plants.

The soluble (sap) proteins of leaves of pea, Pisum sativum L. cvs. Alaska and Greenfeast, allowed to develop normally or deflowered, to prevent senescence, were separated by isoelectric focusing.There was a decline in certain proteins, with increases in others as the leaves aged but preventing senescence of the whole plant did not alter the pattern of change in leaf proteins. We concluded that whole plant senescence proceeds independently of leaf senescence.

Abscisic acid as an endogenous component in lettuce fruits, Lactuca sativa L. cv. Grand Rapids. Does it control thermodormancy?

Abscisic acid (ABA) has been unequivocally identified as an endogenous component of seeds of Grand Rapids lettuce. Both "free" and "bound" ABA levels were followed during imbibition at various temperatures but no clear role for ABA in the imposition of thermodormancy emerged. Furthermore it was apparent that different seed batches showed different ratios of "free" to "bound" ABA and patterns of changes. An unsuccessful attempt was made to identify "bound" ABA, presumed to be the glucosyl ester.

The involvement of indole acetic acid in the thermodormancy of lettuce fruits, Lactuca sativa cv. Grand Rapids.

At 20° C and at 30° C in darkness, concentrations of indole acetic acid (IAA) greater than 10(-7) M inhibited the germination of Grand Rapids lettuce at 24 h and 48 h after the beginning of imbibition. There was no marked, readily defined period of inhibition during germination that could be associated solely with an effect of IAA on suppressing radicle extension. Gibberellin A4+7, benzyladenine and red light were capable of reversing the effects of IAA. There was no consistent pattern of change in the low endogenous levels (less than 11 µg kg(-1)) of extractable IAA during the first 30 h after imbibition.

Correlative effects of fruits and leaves in senescence of pea plants.

Whole plant senescence was studied in peas (Pisum sativum L.) by defruiting, defoliating, and grafting. Fruit removal delays senescence. The delay in senescence is associated with the initiation of bud expansion at nodes near those producing pods. The apical meristem dies regardless of defruiting though later than normal phants.Graft unions are only made if the stock is defruited The pattern of senescence of unions indicates a non polar movement of senescence factors from fruits.Leaves seem not to be involved in whole plant senescence.

The influence of expanding leaves and the reproductive stem apex on apical dominance in Lolium multiflorum.

In vegetative plants of Lolium multiflorum removal of the two youngest emerging leaves resulted in increased expansion of basal tiller buds. A similar release of inhibition of tiller buds took place if the floriferous apex was removed. The surgical procedures did not affect the response. Under conditions of N-deficiency total tiller number was reduced but on removal of the apex the deficient plants showed an increased initial rate of tiller bud expansion. Apical dominance during the vegetative stage of growth in this grass was apparently due to the expanding leaves in the vegetative apex, but in the flowering plant the control was exerted by the inflorescence or the elongating stem.