Chitosan inhibited growth of Botrytis cinerea in liquid culture and suppressed grey mould on detached grapevine leaves and bunch rot in commercial winegrapes. Germination of B. cinerea was completely inhibited in malt extract broth containing chitosan at concentrations greater than 0AE125 g L )1. However, treated conidia were able to infect detached Chardonnay leaves and pathogenicity was not affected, even after incubation for 24 h in chitosan at 10 g L )1. When added after conidial germination, chitosan inhibited B. cinerea growth and induced morphological changes suggestive of possible curative activity. The effective concentration of chitosan that reduced mycelial growth by 50% (EC 50 ) was 0AE06 g L )1. As a foliar treatment, chitosan protected detached Chardonnay leaves against B. cinerea and reduced lesion diameter by up to 85% compared with untreated controls. Peroxidase and phenylalanine ammonia-lyase activities were also induced in treated leaves. In vineyard studies, Chardonnay winegrapes exhibited 7AE4% botrytis bunch rot severity at harvest in 2007 after treatment with an integrated programme that included chitosan sprays from bunch closure until 2 weeks preharvest, compared with 15AE5% in untreated controls and 5AE9% with fungicide treatment. In the following season, botrytis bunch rot severity was 44% in untreated Chardonnay at harvest and the integrated programme (21%) was less effective than fungicides (13AE8%). However, in Sauvignon blanc winegrapes, the integrated and the fungicide programme each reduced botrytis bunch rot severity to 4% and were significantly different from the untreated control (11AE5%). This study provides evidence that suppression of botrytis in winegrapes by chitosan involves direct and indirect modes of action.

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Methyl jasmonate (MeJA) can induce defence responses in plants to pathogen attack, but it can also have consequences for plant growth. The transient effects of exogenous MeJA treatment on the resistance of Monterey pine (Pinus radiata D. Don) seedlings to Diplodia pinea (Desm.) Kickx. and some physiological parameters affecting the impact of treatment on seedling growth were investigated. Following foliar application of 4.5 mmolÁL -1 MeJA, disease resistance was greatest 1-2 weeks after treatment and declined with time thereafter. Elevated disease resistance was accompanied by a reduction in seedling growth rate the second week following MeJA treatment. Thereafter, seedling growth rate recovered and exceeded that of the control seedlings 4-5 weeks after MeJA treatment. Within hours of MeJA treatment, reductions in both the capacity of photosystem II and transpiration rate were observed, resulting in a concomitant reduction in net CO2 uptake rate. The slight reduction in transpiration rate was also associated with an increase in needle water potential. Longer term measurements showed no effect of MeJA on photosynthetic rate, transpiration rate, chlorophyll content, or shoot water potential and thus could not account for the elevated growth rate observed 4-5 weeks after treatment. Résumé :Le méthyle jasmonate (MeJA) peut induire des réactions de défense contre les pathogènes qui s'attaquent aux plantes mais il peut aussi avoir des conséquences sur la croissance des plantes. Les effets passagers d'un traitement avec une source exogène de MeJA sur la résistance de semis de pin de Monterey (Pinus radiata D. Don) à Diplodia pinea (Desm.) Kichx. et certains paramètres physiologiques qui influencent l'impact du traitement sur la croissance ont été étu-diés. À la suite d'une application foliaire de 4,5 mmolÁL -1 de MeJA, la résistance à la maladie était la plus élevée une à 2 semaines après le traitement et a diminué progressivement par la suite. L'augmentation de la résistance à la maladie était accompagnée d'une réduction du taux de croissance des semis la deuxième semaine après le traitement avec le MeJA. Par la suite, le taux de croissance s'est rétabli et a dépassé celui des témoins 4-5 semaines après le traitement avec le MeJA. Dans les heures qui ont suivi l'application de MeJA, une réduction de la capacité du photosystème II et du taux de transpiration a été observée; ce qui a entraîné une réduction concomitante du taux d'absorption de CO 2 . La légère réduction du taux de transpiration était également associée à une augmentation du potentiel hydrique des aiguilles. À plus long terme, les mesures n'ont révélé aucun effet du MeJA sur le taux de photosynthèse, le taux de transpiration, le contenu en chlorophylle ou le potentiel hydrique des pousses et, par conséquent, le MeJA ne pouvait pas expliquer l'augmentation du taux de croissance observée 4-5 semaines après le traitement.[Traduit par la Rédaction]

Pseudomonas syringae pv. actinidiae (Psa) and Pseudomonas syringae pv. actinidifoliorum (Pfm) are closely related pathovars infecting kiwifruit, but Psa is considered one of the most important global pathogens, whereas Pfm is not. In this study of Actinidia deliciosa ‘Hayward’ responses to the two pathovars, the objective was to test whether differences in plant defense responses mounted against the two pathovars correlated with the contrasting severity of the symptoms caused by them. Results showed that Psa infections were always more severe than Pfm infections, and were associated with highly localized, differential expression of phytohormones and putative defense gene transcripts in stem tissue closest to the inoculation site. Phytohormone concentrations of jasmonic acid (JA), jasmonate isoleucine (JA-Ile), salicylic acid (SA) and abscisic acid were always greater in stem tissue than in leaves, and leaf phytohormones were not affected by pathogen inoculation. Pfm inoculation induced a threefold increase in SA in stems relative to Psa inoculation, and a smaller 1.6-fold induction of JA. Transcript expression showed no effect of inoculation in leaves, but Pfm inoculation resulted in the greatest elevation of the SA marker genes, PR1 and glucan endo-1,3-beta-glucosidase (β-1,3-glucosidase) (32- and 25-fold increases, respectively) in stem tissue surrounding the inoculation site. Pfm inoculation also produced a stronger response than Psa inoculation in localized stem tissue for the SA marker gene PR6, jasmonoyl-isoleucine-12-hydrolase (JIH1), which acts as a negative marker of the JA pathway, and APETALA2/Ethylene response factor 2 transcription factor (AP2 ERF2), which is involved in JA/SA crosstalk. WRKY40 transcription factor (a SA marker) was induced equally in stems by wounding (mock inoculation) and pathovar inoculation. Taken together, these results suggest that the host appears to mount a stronger, localized, SA-based defense response to Pfm than Psa.

Root drench application of Trichoderma atroviride isolates R32, R33, R40 and R84 promoted the growth of potted radiata pine seedlings. After 6 weeks, seedlings treated with R33 and R84 had thicker stems and greater stem and root biomass (p < 0.05) than untreated controls. Treatment with R32 increased seedling root biomass whilst R40 increased stem diameter. None of the isolates affected seedling height. One isolate, R33, induced systemic resistance to stem inoculation with Diplodia pinea and reduced dieback incidence by 20% compared with untreated controls. To our knowledge, this is the first report of systemic induced resistance by Trichoderma in a pine species. Furthermore, seedlings that were treated with R33 (root drench) plus foliar application of methyl jasmonate (MeJA) expressed elevated peroxidase activity in their stems 2 weeks later, compared with seedlings treated only with MeJA. Because R33 itself did not affect peroxidase activity, this may be indicative of treatment synergy or defence potentiation by R33. Curiously, R33 + MeJA induced terpenoids but suppressed phenylalanine ammonia-lyase activity suggesting possible trade-offs between phenolic and terpenoid defence pathways in the treated seedlings.