Increased growth of young citrus trees under reduced radiation load in a semi-arid climate1

Abstract

This study investigated the effects of radiation heat-load reduction by shading on the growth and development of citrus trees in a warm subtropical region. The experiment was conducted from mid-June until late October when daily maximal air temperature averaged 29.3 degrees C. Two-year-old de-fruited Murcott tangor (Citrus reticulata BlancoxCitrus sinensis (L.) Osb.) trees were grown under 30% or 60% shade tunnels, or 60% flat shade (providing midday shade only), using highly reflective aluminized nets. Non-shaded trees were used as the control. Shading reduced direct more than diffuse radiation. Daily radiation was reduced by 35% for the 30% Tunnel and 60% Flat treatments, and by 55% for the 60% Tunnel. Two days of intensive measurement showed that shading increased average sunlit leaf conductance by 44% and photosynthesis by 29%. Shading did not significantly influence root and stem dry weight growth, but it increased the increment in leaf dry weight during the three month period by an average of 28% relative to the control, while final tree height in the 30% Tunnel treatment exceeded the control by 35%. Shoot to root and shoot mass ratios increased and root mass ratio decreased due to shading because of the increase in leaf dry weight. Shading increased starch concentration in leaves while the shadiest treatment, 60% Tunnel, decreased starch concentration in the roots. Carbon isotope ratio (delta(13)C) of exposed leaves that developed under shading was significantly reduced by 1.9 per thousand in the 60% Tunnel, indicating that shading increased CO(2) concentrations at the chloroplasts (C(c)), as would be expected from increased conductance. Substomatal CO(2) concentrations, C(i), computed from leaf net CO(2) assimilation rate and conductance values, also indicate that shading increases internal CO(2) concentrations. Based on tree dry mass, tree height, and total carbohydrates fractions, the 30% Tunnel and the 60% Flat were the optimal shade treatments.

Plant regeneration and stable transformation in the floricultural plant Cleome spinosa, a C3 plant closely related to the C4 plant C. gynandra

“…To overcome the problem of dormancy, several treatments including chilling, heating, soaking, washing, adding gibberellic acid GA 3 (Ekpong 2009), stratification, changing photoperiod, temperature, and storage time (Raboteaux and Anderson 2010) have been attempted in Cleome seeds. Seeds of C. gynandra from fresh intact pods were sown directly (without standard sterilization) onto sterile Petri dishes with wet filter papers, resulting in high rates (80-90%) of seed germination (Newell et al 2010). In this study, fresh collection of seeds from C. spinosa, standard sterilization, chilling, and photoperiod, as described in ''Materials and methods'', were crucial to achieving high rates of seed germination (more than 90% were regularly obtained) and low levels of contamination.…”

“…Since transformation of C. gynandra (a C 4 plant in the genus Cleome) has been reported recently (Newell et al 2010), our protocol will facilitate the functional comparison between C 3 plant C. spinosa and C 4 plant C. gynandra using transgenic approaches.…”

“…Among the six Cleome species carrying C 3 -type photosynthesis, only C. spinosa has market value as a floricultural plant. To facilitate the functional analysis of C 4 -type photosynthesis, an Agrobacterium-mediated transformation protocol was recently developed in the C 4 species C. gynandra (Newell et al 2010). More recently, comparative transcriptomics of two closely related C 3 -type C. spinosa and C 4 -type C. gynandra have been carried out to examine the differences in gene expression between C 3 and C 4 species in the genus Cleome (Bräutigam et al 2011a, b).…”

Identification of photoperception and light signal transduction pathways in citrus

“…Surprisingly, recent evidence has demonstrated that light is also the main factor triggering the transition between vegetative to reproductive developmental stages of trees in Equatorial regions (Borchert et al, 2005). The effects of light on developmental processes in citrus and other neotropical tree species have been described in several situations, although without approaching the molecular aspects of the metabolism (Steppe et al, 2006;Chen L-S et al, 2005;Raveh et al, 2003;Torné et al, 2001). Mutant studies employing transgenically generated plants have demonstrated variable extents of functional conservation in the genes responsible for developmental control between citrus and model species (Pena et al, 2001;Pillitteri et al, 2004).…”

Influence of Nonpermanent Netting on Foliar Spray Deposition, Insect Pest Prevalence, and Production of ‘Nadorcott’ Mandarin (Citrus reticulata)

“…The use of protective netting in fruit tree cultivation is an effective method of preventing yield loss that can result from high temperatures and irradiation, strong wind, and hail (Manja and Aoun, 2019;Mupambi et al, 2018;Raveh et al, 2003;Stamps, 2009;Wachsmann et al, 2014). Often, the use of protective netting also results in changes in the orchard microclimate that can alter tree physiology and improve tree performance and fruit development (Cohen et al, 2005;Manja and Aoun, 2019;Mupambi et al, 2018;P erez et al, 2006;Raveh et al, 2003;Stamps, 2009;Wachsmann et al, 2014;Zhou et al, 2018). Various different types of permanent protective netting structures and/ or different colors of shade netting have been tested to determine their effects on tree physiology and fruit development and quality (Manja and Aoun, 2019;Mupambi et al, 2018;Stamps, 2009;Wachsmann et al, 2014;Zhou et al, 2018).…”