Effects of exogenous B supply on growth, B accumulation and distribution of two navel orange cultivars

Abstract

To investigate the effects of boron (B) on growth, B concentration and distribution of two navel orange cultivars, 'Newhall' (Citrus sinensis Osbeck) and 'Skagg's Bonanza' (Citrus sinensis Osbeck) grafted on the rootstock trifoliate orange [Poncirus trifoliata (L.) Raf.], B at five levels was exogenously supplied to 1-year-old grafted plants of both cultivars under greenhouse conditions. Plants were grown in sand:perlite (1:1, v/v) medium and were irrigated every 2 days with half-strength Hoagland's No. 2 nutrient solutions containing different B, 0.01, 0.05, 0.10, 0.25 and 2.50 mg l -1 (0.25 and 2.50 mg l -1 were considered as control and excess B treatment, respectively, and the other three B levels were considered as low B treatments). After treatments for 183 days, leaves (from basal, middle, upper parts of the shoots), stem of scion, stem of rootstock and root were separately sampled. Our results showed that plant growth (plant height, root volume and dry weights of various parts) was inhibited in response to low or excess B supplies in both cultivars. It was found that B concentrations in the upper leaves of both cultivars were substantially higher than those in the basal leaves when low concentrations (B0.05 mg l -1 ) of exogenous B were applied, suggesting that B was preferentially translocated to the upper-younger leaves to support their growth. Analysis of B distribution in different parts indicated that translocation of B from the root to the scion's shoots (stems and leaves of scion) may be restricted upon exposure to low B conditions. When B was inadequately supplied, growth of 'Skagg's Bonanza' was better than 'Newhall', implying that the former cultivar was more tolerant to low B status, which may be due to the higher efficiency of B translocation from the root to the scion's shoots. However, when the plants were treated with excess B (2.50 mg l -1 ), both cultivars showed a similar degree of B toxicity. The probability of scion-rootstock interactions in relation to the differential responses of growth and different efficiency of B translocation involved in the two orange cultivars following the long-term low B stress were discussed.

cDNA-AFLP analysis reveals the adaptive responses of citrus to long-term boron-toxicity

“…The present work, like that of the previous workers [8,13,15], indicates that the major of B in B-toxic citrus plants was accumulated in the leaves (Figure 2A and B). As shown in Figure 2B, B concentration was not lower in C. sinensis than in C. grandis leaves regardless of B concentration in the nutrient solution, indicating that C. sinensis leaves may tolerate higher level of B.…”

Transcription profiles of boron-deficiency-responsive genes in citrus rootstock root by suppression subtractive hybridization and cDNA microarray

“…Although citrus plants are not classified as the most sensitive species to B-deficiency, the occurrence of B-deficiency has been reported in the major citrus producing countries of the world, such as Spain, United States, Brazil, and China (Shorrocks, 1997 ; Sheng et al, 2008 , 2009 ). In eastern and southern china where is the major area of navel orange production, the soil B levels are low (hot water extraction B < 0.25 mg Kg −1 ) (Sheng et al, 2008 ). Soil fertilization with B is one approach to grow citrus plants undertaken to prevent B-deficiency in the field (Schon and Blevins, 1990 ).…”

Distribution of boron and its forms in young “Newhall” navel orange (Citrus sinensisOsb.) plants grafted on two rootstocks in response to deficient and excessive boron

“…and ''Skagg's Bonanza'' (Citrus sinensis Osb.) navel orange (Sheng et al 2009) and melon (Cucumis melo L.) (Edelstein et al 2005). Boron concentration in new leaves was much higher than mature leaves, regardless of rootstocks or B treatments ( Table 2), indicating that B might be preferentially transported to new leaves of ''Newhall'' navel orange (Citrus sinensis Osb.).…”