Agriculture Reference
In-Depth Information
elevation of these defence proteins in food products since Roux et al . (2006) found that
transcripts for PR-10 allergens signifi cantly increased in apples in response to Pro-Ca
treatment. The major allergen in apple, Mal Dd 1, is a member of the PR-10 group of
defence proteins (PĆ¼hringer et al ., 2000) and therefore it would be prudent to consider
the impact of inducing agents on levels of potential allergens in fruit. Timing of activator
applications will play an important role in determining their impact on PR accumulation
in fruits.
The integrated use of activators and fungicides may offer a practical option for control-
ling apple scab. Flusilazole was more effi cacious against V. inaequalis on apple seedlings
that were treated with the activator dichloroisonicotinic acid (INA) than on untreated
seedlings (Ortega et al ., 1998). The effi cacy of INA against apple scab was not affected by
the sensitivity of different pathogen strains to the triazole group of fungicides. Additive
benefi ts from combining plant activators and fungicides in the fi eld could enable a reduc-
tion in the number of fungicide applications, and possibly fungicide dose rate.
'Red Delicious' apples expressed enhanced resistance to postharvest blue mould
( Penicillium expansum ) after treatment with chitosan, harpin, or UV-C irradiation (de
Capdeville et al ., 2002). Freshly harvested fruit, or fruit stored in controlled-atmosphere
for 3 months, were treated either 24, 48 or 96 hours before wound inoculation with the
pathogen. UV-C was the most effective treatment and reduced lesion development by over
60% compared with control fruit. Treatments were more effective on fresh fruit than on
stored fruit and were most effective when applied 96 hours before inoculation. This latter
fi nding is not surprising, since a time delay is required for the onset of resistance. UV-C
has also been shown to directly inhibit microbial growth and a packhouse UV-C treat-
ment may be an attractive commercial option for postharvest fruit treatment. Preharvest
treatment of apple trees with harpin, before fruit inoculation, resulted in enhanced
resistance to blue mould infection on 'McIntosh', 'Empire' and 'Red Delicious' apples
(de Capdeville et al. , 2003). Higher concentrations of harpin resulted in greater control,
but, there was no difference in disease control between fruit treated with harpin either
four or eight days before inoculation. Salicylic acid (Yu & Zheng, 2006), gibberellic acid
(Yu & Zheng, 2007) and chitosan (Yu et al., 2007a) have been shown to augment the
effi cacy of the biocontrol yeast, Cryptococcus laurentii against postharvest blue mould in
apples. The treatment combinations were applied to wounded fruit at least 2 hours before
inoculation with P. expansum.
4.2.1.4
Pear
Pear fruits are susceptible to postharvest diseases including blue mould ( Penicillium
expansum Link) and black mould ( Alternaria alternata (Fr : Fr.) Keissl.). Several non-
fungicidal control options, including antagonistic biocontrol agents, heat treatment,
antimicrobial natural products and resistance activators, have been investigated for their
potential to control postharvest rots. Field applications of salicylic acid (SA) (Cao et al .,
2006) and ASM (Cao & Jiang, 2006) enhanced resistance to postharvest fungal infec-
tion in 'Yali' pears. In both trials, the pear trees were sprayed with the activator on three
occasions, at 30, 60 and 90 days after fl owering. Fruit were harvested at full commercial
maturity ( ca 120 days after fl owering) and then surface sterilised before wound-inoc-
ulation with P. expansum , for SA-treated fruit (Cao et al. , 2006), and P. expansum and
Search WWH ::




Custom Search