The foliar water relations in orange plants (Citrus sinensis L.) are affected by sooty mold

The following study was conducted to determine the impact of frequent foliar Cu applications on water relations of Huanglongbing (HLB)-affected Citrus sinensis cv. ‘Valencia’. HLB in Florida is putatively caused by Candidatus Liberibacter asiaticus that is vectored by the Asian citrus psyllid. The experiment was conducted in a psyllid-free greenhouse with trees grown in Immokalee fine sand soil with the trees well-maintained to promote health. Cu was applied to the foliage at 0×, 0.5×, 1×, and 2× the commercially recommended rates, which were 0, 46, 92, and 184 mM, respectively, with applications made 3× in both 2016 and 2017. Previous studies indicate that HLB causes roots to decline before the canopy develops symptoms, which increases the ratio between the evaporative surface area of the canopy to the uptake surface area of roots and increases the hydraulic strain within the tree. In the current study, overall growth was suppressed substantially by HLB and Cu treatments but the ratio between evaporative surface area (leaf surface area) and the uptake surface area of roots (feeder root surface area) was not affected by either treatment. Stem water potential (Ψxylem), which was used as a measure of plant water deficits and the hydraulic strain within the tree, was significantly 13% lower for HLB-affected trees than the non-HLB controls but were not affected by Cu treatments. All Ψxylem measurements were in a range typical of well-watered trees conditions. Stomatal conductance (ks) and root and soil resistances (Rr+s) were not affected by HLB and Cu. The results of this experiment suggest that tree leaf area and feeder roots are reduced when the trees are affected by HLB or are treated with foliar Cu applications such that plant water deficits are not significantly different over that of the controls.

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Gas Exchange, Water Relations and Ion Concentrations of Leaves of Salt Stressed 'Valencia' Orange, Citrus sinensis (L.) Osbeck

Functional Plant Biology ◽

10.1071/pp9870387 ◽

1987 ◽

Vol 14 (4) ◽

pp. 387 ◽

Cited By ~ 28

Author(s):

J Lloyd ◽

PE Kriedemann ◽

JP Syvertsen

Keyword(s):

Gas Exchange ◽

Water Relations ◽

Citrus Sinensis ◽

Sweet Orange ◽

Leaf Gas Exchange ◽

Co2 Assimilation ◽

Salt Treatment ◽

Soil Culture ◽

Co2 Compensation Point ◽

Valencia Orange

'Valencia' orange [Citrus sinensis (L.) Osbeck] scions grafted on sweet orange [C. sinensis (L.) Osbeck cv. Parramatta sweet orange] rootstock were grown in soil culture under controlled environmental conditions. Salt stress was imposed by adding NaCl to the nutrient solution in increments of 5 mol m-3 per day to a final concentration of 50 mol m-3. Leaf gas exchange, water relations and sodium, chloride and potassium concentrations were monitored until 89 days after commencement of salt treatment. Initial CO2 assimilation rates were relatively low (2.8-4.4 �mol CO2 m-2 s-1) and were stimulated by 72-86% when ambient oxygen partial pressure was reduced from 210 mbar to 21 mbar. After 14 days salt treatment, there was an increase in assimilation rate of approximately 20% associated with a decrease in osmotic potential (π) of 0.6 MPa. Reduction in � occurred without foliar ion accumulation. Assimilation rates gradually declined thereafter, averaging less than 1 �mol CO2m-2 s-1 at day 89. Lower CO2 assimilation rates were not a consequence of increased photorespiration as no change in the extent of oxygen inhibition of CO2 assimilation or CO2 compensation point occurred with salinisation. Stomatal conductance appeared less sensitive to salt treatment than intrinsic photosynthesis, resulting in higher intercellular partial pressures of CO2 in salt stressed leaves (291 cf. 259 pbar for controls at day 89). Water use efficiency was accordingly lower in salt affected leaves. Salinised leaves had consistently more negative osmotic potentials than control leaves; turgor potential was thus maintained at or above control levels for a given bulk-leaf water potential. Since leaf turgor was maintained via osmotic adjustment and uptake of sodium and chloride, lower assimilation rates were attributed to a toxic ion effect.

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