Effect of Essential Nutrients on Roots Growth and Lifespan of Huanglongbing Affected Citrus Trees

Abstract

Understanding citrus tree root development and dynamics are critical in determining crop best nutrient management practices. The role of calcium (Ca) and magnesium (Mg), manganese (Mn), Zinc (Zn), and boron (B) on huanglongbing (HLB) affected citrus trees' root growth and lifespan in Florida is not fully documented. Thus, the objective of this study was to determine the impact of foliar and ground-applied essential nutrients on seasonal fine root length density (FRLD; diameter (d) < 2 mm) and coarse roots (d > 2 mm), FRLD dynamics, root survival probability (lifespan), and root-zone soil pH of HLB-affected sweet orange trees. Results indicated that Ca treated trees budded on Cleopatra (Cleo) and Ca and Mg combined treatments on Swingle (Swc) rootstocks significantly increased seasonal FRLD of fine (< 2 mm) and coarse roots. The highest median root lifespan of Ca treated trees was 325 and 339 days for trees budded on Cleo and Swc rootstocks, respectively. In the second study, the coarse roots showed a significantly higher reaction to the nutrition applied than the fine roots. Meanwhile, the 2× (1× foliar and 1× ground-applied) treated trees showed a significantly higher median root lifespan compared to the other treatments. Thus, the current study unwraps future studies highlighting the combined soil and/or foliar application of the above nutrients to stimulate FRLD and improve root lifespan on HLB-affected sweet oranges with emphasis on root-zone soil pH.Plants 2020, 9, 483 2 of 20 to 2.02 cmcm -3 for trifoliate orange (Poncirus trifoliata). Although the citrus root system is estimated to account for more than 65% of above-ground dry mass [12,13] the root system of HLB-affected citrus trees is usually poorly developed and new root growth can also be inhibited [14]. Studies indicated that 30%-50% of roots of HLB-affected citrus trees are impaired before canopy symptoms appear and 70%-80% of root loss could be prevalent as citrus deprived of intensive cultural management to pacify abiotic and biotic stress [10,15]. The optimum distribution of the root system is mainly restricted by water and nutrients available in soil profiles [16,17]. However, it has been reported that HLB develops an imbalance of nutrient concentrations, which cause nutrient toxicity for some nutrients, including Cu or deficiency for others such as Ca, Mg, Mn, and Zn [18]. Therefore, nutrient supply is an imperative aspect of disease control because nutrients influence plant resistance, pathogen vigor, growth, and associated factors [19,20].Ground-applied fertilizers are subject to unfavorable soil processes such as precipitation as forms that are unavailable to plants, leaching, and runoff [21,22]. Therefore, split ground and foliar-applied fertilizer improve nutrient use efficiency and reduce both nutrient leaching and application cost [23][24][25]. Moreover, HLB-affected trees are limited in soil nutrient uptake because of the associated decline in FRLD [12,16,26]. The role of adding essential nutrients in improving citrus growth in general a...

The Effect of Foliar and Ground-Applied Essential Nutrients on Huanglongbing-Affected Mature Citrus Trees

“…Trees were fertigated with a micro-sprinkler Max−14 (Maxijet Inc., Dundee, FL, USA), Fill-in blue emitters were placed 15 cm from the tree trunk. The irrigation was assisted with a 172.4 kpa irrigation pump at a flow rate of 45 L h −1 [ 30 ]. Citrus SmartIrrigation app, which is available on iOS and Android interfaces, was used to determine daily irrigation duration to meet tree water requirement based on reference evapotranspiration (ET o ) calculated with Penman-Monteith and crop coefficient related to the meteorological data of the study site [ 12 , 30 ].…”

“…Some essential nutrients (e.g., Ca, Mg, Fe, Mn, Zn, and B) are less available for uptake by some crops under alkaline soil conditions [ 28 , 29 ]. Therefore, multiple annual fertilizer applications in association with scheduling fertigation, and products with incorporated elemental sulfur (S) that releases S to lower soil pH were utilized to enhance nutrient availability and minimize the nutrient leaching probability [ 28 , 30 ]. Manganese (Mn) deficiency is normally a worldwide problem predominantly manifested in the spring after a cold winter [ 2 , 31 ].…”

“…The physiological impact of Zn on the leaves and fruit have not been identified [ 13 , 18 , 30 , 32 ]. Phloem translocation of Zn is one of the important features that contribute to HLB-induced Zn deficiency in grapefruit and the concentration was too low in young and mature leaves, such that no clear Zn distribution was detected in the phloem tissues [ 4 , 32 ].…”

Manganese adsorption, availability, and uptake in citrus under microsprinkler irrigation

“…If the disease is widespread, citrus trees may live for only 5–8 yr and never produce usable fruit (Alvarez et al., 2016; Roistacher, 1996). More importantly, research done over the past 20 yr has shown that citrus fibrous roots are mostly within the 0‐ to 30‐cm soil depth (Atta, Morgan, Hamido, & Kadyampakeni, 2020; Kadyampakeni, Morgan, Schumann, & Nkedi‐Kizza, 2014; Morgan, Obreza, & Scholberg, 2007) and can be restored with modified micronutrient application rates.…”

Chemical inducers, nutrient management, guava intercropping and insecticides can reduce huanglongbing incidence and severity in Sweet orange

“…Research that demonstrated that citrus greening symptoms could be reduced by foliar applications of micronutrients, especially Mn, Zn, B, and Mg, and other physiologically active compounds, such as salicylic acid and phosphite (Pustika et al, 2008;Shen et al, 2013;Stansly et al, 2014). Combined soil and/ or foliar application of the above nutrients to stimulate FRLD and improve root lifespan on citrus greening affected Sweet oranges with emphasis on root-zone soil pH (Atta et al, 2020 (Boina et al, 2010;Tiwari et al, 2012) while few studies evaluated their efficacy in the field (Qureshi and Stanslay, 2007;Abbaszadeh et al, 2011;Rao and Shivankar, 2011). Three IGRs, pyriproxyfen (juvenile hormone mimic), buprofezin and diflubenzuron (both are chitin synthesis inhibitors), showed promising ovicidal and nymphicidal activities against ACP, as well as adverse effects on reproduction (both fecundity and egg viability) and morphology of adults emerging from treated older nymphs (Boina et al, 2010;Tiwari et al, 2012).…”