Flooding and Phytophthora cinnamomi: Effects on photosynthesis and chlorophyll fluorescence in shoots of non-grafted Persea americana (Mill.) rootstocks differing in tolerance to Phytophthora root rot

Abstract

a b s t r a c tLosses in the production of avocado (Persea americana (Mill.)) are incurred due to Phytophthora root rot (PRR), a disease of the feeder roots that results in tree-dieback and eventual tree death. Avocado is also a flood-sensitive species and flooding exacerbates the effects of PRR. The avocado industry relies on the use of rootstocks tolerant to PRR to minimise losses. The present study compared the gas exchange and chlorophyll fluorescence responses of avocado rootstock plants of 'Dusa™', the current South African industry standard, with 'Duke 7', and the selections R0.12 and R0.06 which show reduced and superior tolerance to PRR, respectively. A decline in stomatal conductance (g s ) and net CO 2 assimilation (P N ) over the 30 day evaluation period were early responses to flooding. 'Dusa™', the more tolerant rootstock plants, demonstrated a better recovery in P N and g s in response to inoculation; however, both rootstocks performed poorly under flooded conditions. A decline in P N in infected 'Duke 7' plants appeared to be associated with stomatal limitations due to reduced stomatal conductance. The decline in P N and g s was not apparent in infected 'Dusa™' plants. Non-stomatal limitations to P N in rootstock plants exposed to flooding were also evident as indicated by increases in the ratio of internal to atmospheric CO 2 concentrations (C i /C a ). Impaired photosynthetic capacity in flooded rootstock plants was reflected by reduced photosystem II efficiency and photochemical quenching. In comparison to 'Dusa™', R0.12 rootstock plants showed reduced P N and g s following inoculation with Phytophthora cinnamomi whereas the more tolerant R0.06 rootstock plants revealed sustained photosynthetic activity. Interestingly R0.06 was the only rootstock able to maintain P N and g s in non-inoculated, flooded plants.

Physiological, Biochemical and Chlorophyll Fluorescence Parameters of Physalis Peruviana L. Seedlings Exposed to Different Short-Term Waterlogging Periods and Fusarium Wilt Infection

“…A lower qP has been reported under waterlogging conditions in avocado (Persea americana Mill.) plants inoculated with Phytophthora cinnamomi [94]. Similar results were also reported in this study, in which cape gooseberry plants inoculated with Foph under the different waterlogging periods showed a decrease in qP.…”

Rootstock affects the blend of biogenic volatile organic compounds emitted by ‘Hass’ avocado

“…Modern agricultural practice of grafting vegetal material and rootstock use has allowed cultivating in unfavorable conditions such as extreme temperatures, drought, salinity and flooding (Colla et al, 2010;Schwarz et al, 2010;Reeksting et al, 2014). Resistant and/or tolerant rootstocks to insect pests and pathogens increase the production, scion vigor, and organoleptic fruit quality (Warschefsky et al, 2016).…”

Mild water stress-induced priming enhance tolerance to Rosellinia necatrix in susceptible avocado rootstocks

“…The expression of thirteen defense-related genes on roots of 'Dusa' avocado rootstock subjected to mild-WS and severe-WS and one week after re-watering, was analysed by performing a real time quantitative qPCR (qRT-PCRs). This selection included induced genes indicated in previous studies with 'BG83' (tolerant to R. necatrix) and 'Dusa' (tolerant to P. cinnamomi) avocado rootstocks after infection with the soilborne pathogens R. necatrix [43] and P. cinnamomi, respectively [19, [48][49][50]. In addition to their implication in pathogen defense, some of the selected genes are also involved in salt, oxidative, osmotic and water stress responses (Table 2).…”