Warming Scenarios and Phytophthora cinnamomi Infection in Chestnut (Castanea sativa Mill.)

Abstract

The main threats to chestnut in Europe are climate change and emerging pathogens. Although many works have separately addressed the impacts on chestnut of elevated temperatures and Phytophthora cinnamomi Rands (Pc) infection, none have studied their combined effect. The objectives of this work were to describe the physiology, secondary metabolism and survival of 6-month-old C. sativa seedlings after plants were exposed to ambient temperature, high ambient temperature and heat wave events, and subsequent infection by Pc. Ten days after the warming scenarios, the biochemistry of plant leaves and roots was quantified and the recovery effect assessed. Plant growth and root biomass under high ambient temperature were significantly higher than in plants under ambient temperature and heat wave event. Seven secondary metabolite compounds in leaves and three in roots were altered significantly with temperature. Phenolic compounds typically decreased in response to increased temperature, whereas ellagic acid in roots was significantly more abundant in plants exposed to ambient and high ambient temperature than in plants subjected to heat waves. At recovery, leaf procyanidin and catechin remained downregulated in plants exposed to high ambient temperature. Mortality by Pc was fastest and highest in plants exposed to ambient temperature and lowest in plants under high ambient temperature. Changes in the secondary metabolite profile of plants in response to Pc were dependent on the warming scenarios plants were exposed to, with five compounds in leaves and three in roots showing a significant 'warming scenario' × 'Pc' interaction. The group of trees that best survived Pc infection was characterised by increased quercetin 3-O-glucuronide, 3-feruloylquinic acid, gallic acid ethyl ester and ellagic acid. To the best of our knowledge, this is the first study addressing the combined effects of global warming and Pc infection in chestnut.

Keywords: abiotic stress; biochemistry; climate change.

Figure 1

Plant growth (A) and fine root biomass (B) of six-month-old Castanea sativa seedlings exposed to ambient temperature (green), high ambient temperature (orange) and two heat waves (red). Vertical bars are standard errors, and different letters indicate significant differences between means (Tukey’s HSD tests at p < 0.05).

Figure 2

Photosynthetic rate values (P_n) (A), transpiration rates (E) (B) and stomatal conductance (g_s) (C) of Castanea sativa seedlings exposed to ambient temperature (green), high ambient temperature (orange) and two heat waves (red). Measurements were obtained 0 and 10 days after plants were exposed to treatments (non-infected plants) and 10 days after plants were exposed to treatments and Phytophthora cinnamomi (Pc) infection (Pc-infected plants). Vertical bars are standard errors, different letters indicate significant differences between means (p < 0.05), and asterisks indicate marginally significant differences (p < 0.10) (Tukey’s HSD tests).

Figure 3

PCA of phenolic compounds included in Table 2 of non-infected Castanea sativa seedlings exposed to ambient temperature (green circles), high ambient temperature (orange circles) and two heat waves (red circles).

Figure 4

Survival probabilities of Castanea sativa seedlings exposed to ambient temperature (green), high ambient temperature (orange) and heat waves (red) and infected at day 0 with Phytophthora cinnamomi. Global log-rank test was significant at p = 0.080. Different letters indicate significant differences between survival curves (p < 0.05) and arrows indicate the dates of phenol assessment.

Figure 5

Mean values of phenolic compounds ethyl gallate (A), hydroxybenzoic acid (B), 4-hydroxyphenylacetic acid (C), and coniferyl aldehyde (D) of Castanea sativa seedlings not infected or infected with Phytophthora cinnamomi (Pc). According to the linear mixed models shown in Table 4, the four compounds were significantly affected by Pc infection. Measurements were taken 10 days after inoculation. Vertical bars are standard errors, different letters indicate significant differences (p < 0.05), and the asterisk indicates a marginally significant difference (p < 0.10) (Tukey’s HSD tests).

Figure 6

Phenolic compounds of Castanea sativa plants that showed different changes in their content in response to Phytophthora cinnamomi infection and the scenario plants were exposed to before inoculation (significant Pc × scenario interactions in Table 4; p < 0.05). Phenolic content was obtained at day 10 after inoculation in plants previously exposed to ambient temperature (green lines), high ambient temperature (orange lines) and two heat waves (red lines).

Figure 7

PCA of phenolic compounds included in Table 4 of non-infected Castanea sativa seedlings exposed to ambient temperature (green circles), high ambient temperature (orange circles) and two heat waves (red circles) (non-infected plants) and Phytophthora cinnamomi-infected C. sativa seedlings previously exposed to ambient temperature (green triangles), high ambient temperature (orange triangles) and two heat waves (red triangles) (Pc-infected plants). The five compounds that most contributed to the PC1 and PC2 axes were leaf 3-feruloylquinic acid (81.3%), root 4-hydroxyphenylacetic acid (8.7%), root coniferyl aldehyde (3.9%), root hydroxybenzoic acid (3.6%) and leaf ellagic acid (0.9%).

Figure 8

Experimental design and sampling plan.