Histology of waxflower (Chamelaucium spp.) flower infection by Botrytis cinerea

Abstract

Botrytis cinerea infects waxflower (Chamelaucium spp.) flowers and can induce them to abscise from their petioles before disease becomes evident. Botrytis cinerea infection of flowers was studied on two waxflower cultivars by light and electron microscopy. Pot-grown waxflower flowers were harvested, inoculated with aqueous suspensions of B. cinerea conidia, incubated at 20-22°C and >95% RH and examined within 96 h post-inoculation (hpi). Conidial germination on petals started 4 hpi, penetration via germ tube tips was 6 hpi and protoappressoria were formed 8 hpi. Germination on petals approximately doubled every 4-6 h to 18 hpi. Conidial germination was ca. 50% at 22-24 hpi. Botrytis cinerea infected most waxflower flower organs, including petals, anthers and filaments, stigma and hypanthium, within 24 hpi. Hyaline and lobate appressoria were observed 36 hpi. Infection cushions on stamen bases were formed 36 hpi by saprophytic hyphae that originated from anthers. This infection process can give rise to tan-coloured symptoms typical of botrytis disease that radiate from this part of the flower. Subcuticular hyphae were present at high density near stamen bases and evidently resulted from multiple penetrations from single infection cushions. The subcuticular hyphae grew within the hypanthium and towards the centre of the floral tube. When flower abscission occurred, floral tube tissues close to the abscission zone remained uninfected. This observation infers possible transmission of a signal (e.g. ethylene) upon B. cinerea infection. Thus, B. cinerea causes flower abscission apparently as a defence response.

First Report of Botrytis cinerea Pers. on Salicornia bigelovii Torr. in North‐West México

“…Grey mould caused by the fungus B. cinerea usually occurs on the flower parts or in the early stages of maturation of the fruit; however, it is also common in the branches or stems or infected plants (Dinh et al. ). B. cinerea can remain quiescent for long periods of time.…”

“…Of the branches with symptoms of grey mould, different strains of B. cinerea were reisolated, which were identified according to their morphological features based on the taxonomic keys of Barnett and Hunter (1972) and Jarvis (1977), which coincide with the description for B. cinerea conidia presenting light brown, smooth, unicellular, ellipsoid-to ovoidform of 12 lm long 9 6.4 lm wide and visible sclerotia production, thus confirming that the causal agent of grey mould in S. bigelovii is B. cinerea. Grey mould caused by the fungus B. cinerea usually occurs on the flower parts or in the early stages of maturation of the fruit; however, it is also common in the branches or stems or infected plants (Dinh et al 2011…”

The influence of relative humidity on disease caused by Botrytis cinerea in non-harvested versus harvested waxflower flowers

“…However, this was not observed in the waxflower-Botrytis pathosystem. B. cinerea-associated floral abscission occurred within 2-4 days of infection (Dinh et al , 2008(Dinh et al , 2011. The data suggest that RH is a more important determinant than whether the sprigs are harvested or remain attached to the shrub in the field.…”

“…B. cinerea conidia are found on all waxflower flower parts in the field (Tomas et al 1995). On harvested waxflower flowers, B. cinerea produces various infection structures on flowers under at 20-22°C and >95% RH conditions (Dinh et al 2011). However, free water availability may be a limiting pre-requisite for preharvest conidial germination and disease development.…”

“…cinerea infection of non-harvested and harvested waxflower flowers has been studied (Dinh et al 2011) using a high B. cinerea inoculum level of 10 6 conidia/mL at 20-22°C and >95% RH. However, B. cinerea infection and associated abscission of waxflower flowers under natural environmental conditions in the greenhouse or field have not been investigated.…”