Induced resistance for plant disease control - Disease Control in Crops - page 76

postharvest inoculation with B. cinerea in 'Cote d'Azur' and 'Dukaat' fl owers (Darras
et al., 2006). Effi cacy of each compound was variable across different concentrations
and incubation temperatures. For example, in the fi rst year of the study, ASM (2.86 mM)
was most effective on 'Cote d'Azur' fl owers incubated at 5°C and reduced petal specking
by 45%, whereas in the second year, ASM (1.43 mM) was most effective on 'Dukaat'
fl owers (51% reduction) at 20°C. In general, MeJA was more effective and more consis-
tent than ASM and, when applied at 0.6 mM, reduced infection by up to 54% on 'Cote
d'Azur' and 63% on 'Dukaat' fl owers at 20°C.
When applied as postharvest treatments, ASM and MeJA have shown potential to offer
some protection against natural and artifi cial infections on 'Cote d'Azur' fl owers (Darras
et al., 2007). ASM spray application signifi cantly reduced natural infections at 5°C and
12°C, but not at 20°C, but was not effective against artifi cial inoculation at any tem-
perature. In contrast, MeJA was effective against both natural and artifi cial infections
when applied as a spray or as a pulse treatment, and tended to be more effective at the
higher incubation temperatures. This latter observation concurs with a previous fi ndings
that MeJA vapour (0.1 l MeJA/L) treatment reduced petal specking on 'Cote d'Azur'
fl owers when incubated at 20°C and at 12°C and but not at 5°C (Darras et al., 2005) .
Although ASM and MeJA show some promise for controlling petal specking in freesias,
it is unlikely that effi cacy is suffi cient to warrant their practical implementation at present.
The potentially synergistic effects of pre- and postharvest applications of ASM and MeJA
merits investigation.
Grey mould on roses, caused by B. cinerea, can signifi cantly reduce the ornamental
value of the cut fl owers. Postharvest treatment of six rose cultivars in a standard pulsing
solution supplemented with 0.2 mM MeJA induced systemic protection against B. cinerea
infection (Meir et al., 1998). MeJA neither caused phytotoxicity on leaves and petals, nor
impaired fl ower quality and longevity. More recently, this approach has been optimised
by combining the pulse treatment (0.35 mM MeJA) with spray application of 0.5 mM
MeJA (Meir et al., 2005). This method suppressed grey mould development following
both artifi cial and natural infections in eleven rose cultivars.
Fusarium wilt of cyclamen, caused by Fusarium oxysporum f. sp. cyclaminis, can be
a devastating disease and economically limiting to the production of quality cyclamen.
Treatment of 'Scarlet Red' seedlings with two applications of ASM (1050 mg l 1 ), at
7 days then again 1 day before inoculation, caused a dose-dependent suppression of
fusarium wilt (Elmer, 2006a). ASM treatment delayed the onset of symptoms by up to
3 weeks, with some plants remaining symptomless for the duration of the study. In the
absence of the pathogen, ASM caused a reduction in biomass, but not fl ower number or
quality. ASM has also been fi eld evaluated against fusarium corm rot ( Fusarium oxysporum
f. sp. gladioli ) in gladiolus (Elmer, 2006b). Corms were soaked in ASM (50 mg l 1 ) for
30 min before being sown in a fi eld site with a recent history of fusarium corm rot. ASM
reduced corm rot by 12%, compared with untreated controls, but this was not signifi cant
and was not as effective as chemical fungicides. Interestingly, despite relatively poor
disease suppression, ASM-treated corms produced 48% more marketable fl ower spikes
than untreated corms. Furthermore, there were interactions between ASM and fungicides.
For example, ASM and azoxystrobin alone were ineffective in reducing symptoms but,
when combined, they provided season-long suppression of corm rot. Twice-weekly foliar
applications of ASM demonstrated effi cacy against late blight on glasshouse petunias that
was as effective as fungicide controls (Becktell et al., 2005).