Elsevier

Scientia Horticulturae

Volume 211, 1 November 2016, Pages 167-173
Scientia Horticulturae

Relationships between apple tree rootstock, crop-load, plant nutritional status and yield

https://doi.org/10.1016/j.scienta.2016.08.027Get rights and content

Highlights

  • Yield, fruit weight were crop-load, while metabolite changes were rootstock dependent.

  • Mineral sufficiency was dependent on both rootstock and crop-load.

  • Super-dwarfing P 22 rootstock resulted in the smallest yield and fruits.

Abstract

Impact of the choice of rootstock and crop-load on apple tree nutritional status and yield relationships between biochemical parameters were analysed. Apple cultivar ‘Ligol’ was grafted onto semi-dwarfing rootstock M.26; dwarfing rootstocks M.9, P 67 and B.396; and super-dwarfing rootstock P 22. Crop-load was adjusted to 60, 105 or 150 inflorescences per tree. Flower buds were removed at the pink bud stage. Super-dwarfing P 22 rootstock under intensive crop-load (150 inflorescences per tree) resulted in N deficiency in the leaves, which caused an accumulation of leaf sugars. Leaf elements were influenced by rootstock and crop-load. With the dwarfing rootstocks P 67 and B.396, a significantly larger leaf area and a decrease in photosynthetic pigment and leaf carbohydrate content were observed. Apple tree yield was directly correlated with the crop- load and the number of fruits, independent of the rootstock onto which they were grafted. Average fruit weight, independent of rootstock, was inversely related to crop- load. Generally, yield, fruit weight were crop-load, while metabolite changes were rootstock dependent. Mineral sufficiency was dependent on rootstock and crop-load. Super-dwarfing P 22 rootstock resulted in the smallest yield and fruits.

Introduction

Different genetic and technological tools, such as grafting to rootstocks and crop-load manipulation, can allow increases in yield, tolerance to abiotic stress or increased vigour. Seedling rootstocks and the fruiting clones grafted onto them within the same botanical genus or species have been investigated since the 19th Century. Recently, molecular aspects of rootstock-scion interactions, explaining connections between gene expression and the protein functions underpinning changes in physiology, have been examined (Harada, 2010). Few studies have focussed on the underlying vegetative and reproductive responses to different rootstocks and crop-loads by examining physiological and biochemical mechanisms (Wünsche et al., 2005). Understanding the relationships between the key physiological (growth, yield, fruit quality etc.), and physical (graft union repair, water usage and transport, hormones, nutrition) aspects mediated by the rootstock is important for the growth of high quality and commercially attractive fruit production (Koepke and Dhingra, 2013). The effects of rootstocks and crop-loads are some of the most important factors influencing yield and fruit quality in orchard management. Meland (2009) found the highest fruit weight, soluble solids contents and return bloom with the lowest crop-load in ‘Elstar’ apple trees. Increasing crop load resulted in a decrease in leaf area, dry mass per unit leaf area, and an increase in chlorophyll content in peach (Nii, 1997) but no difference in the ratio of chlorophyll a to b in pistachio trees (Vemmos, 1994) was observed. Moreover, crop-load, defined as number of fruits per light intercepting green area, is known to affect carbohydrate production and partitioning in apple. An increase in crop load conditioned an increased in chlorophyll concentration, and a decrease in leaf starch content (Wünsche et al., 2005); whereas soluble non-structural carbohydrates in leaves are affected by crop-load to a lesser extent (Klages et al., 2001). Relationships between sugar accumulation and leaf characteristics appear at the fruit development stage, when fruits become major sink organs and carbohydrates are typically transported from leaves to fruits (Nii, 1997). The apple tree is unique in metabolism and carbohydrate accumulation, because the primary products of photosynthesis are sorbitol, sucrose and starch (Teo et al., 2006). Moreover, almost all of the sorbitol and half of the sucrose is converted to fructose, so most of the total carbon flux goes through fructose (Li et al., 2012). Sucrose and hexoses are storage compounds, being the transport compounds for export from source leaves to sink tissues, but they may also control photosynthesis (Smith and Stitt, 2007). The relationships between plant leaf mineral status and carbohydrate metabolism are complex. Peuke (2010) described relationships between plant growth reduction or inhibition by mineral deficiency and increases in sugar concentrations in Ricinus communis. Deficiency in N leads to an accumulation of carbohydrates in Arabidopsis leaves (Remans et al., 2006). N deficient plants accumulated higher contents of sugars that led to reduced photosynthesis, probably due to feedback metabolite regulation (Martin et al., 2002). Hermans et al. (2006) suggested that starch and disaccharide metabolism related genes are significantly over-represented among the differentially regulated genes in the shoots of N deficient plants. P is the second most limiting mineral nutrient after N. Lemoine et al. (2013) described the relationships between the lack of leaf P, photosynthesis and reduced carbon assimilation. Low P resulted in the accumulation of sugar, starch and anthocyanin in Arabidopsis leaves (Zakhleniuk et al., 2001). A common phenomenon in Mg deficient plants is leaf carbohydrate accumulation. Hermans et al. (2005) stated that Mg deficiency affects sucrose loading by decreasing Mg-ATP and consequently H+-ATP activity. Generally, it can be stated that sucrose transport from the leaves is a necessary signal for responses to N and P starvation, but not for responses to K or Mg deficiency. Increased leaf sugar content, especially sucrose, is stress related (Lemoine et al., 2013, Peuke, 2010).

Due to their root system, trees on the super-dwarfing rootstock P 22 are more winter hardy than those on the dwarfing rootstock M.9, which is the most commonly used rootstock in western Europe (Foster et al., 2015). The dwarfing rootstocks P 67 and B.396 are good alternatives to the M.9 rootstock, due to their desirable characteristics of growth vigour, high yield and yield efficiency in areas where high winter hardiness is required (Kviklys et al., 2013). As roots absorb water containing dissolved minerals, it can be assumed that the rootstock will influence the ability to provide nutrients for the whole plant. Thus, nutrient sufficiency is also an important factor affecting fruit production. The relationships between different rootstocks and differences in leaf nutrient levels have been documented in peach (Tsipouridis and Thomidis, 2005), pear (North and Cook, 2008), apple (Kviklys et al., 2012, Tomala et al., 2008, Wünsche et al., 2005) and other woody plants. Kviklys et al. (2012) described the effect of eleven apple rootstocks on tree size (expressed as the tree cross sectional area), cumulative yield and yield efficiency, fruit weight and quality. Tomala et al. (2008) showed that fruits from trees on P 60 and B.396 rootstocks contained more soluble solids.

In this study, physiological insights into the influence of rootstock and/or crop-load on the relationships between some photosynthetic indices (chlorophyll, carotenoid content, leaf area), primary photosynthesis metabolites, leaf nutritional status and yield will be presented.

Section snippets

Growth conditions

A field experiment was carried out in an intensive orchard at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry in 2014 and 2015. Trees were planted in 2005 year in rows spaced 1.5 m apart with 4 m between the rows and trained as a slender spindle. The commercially important apple cultivar ‘Ligol' was grafted on the semi-dwarfing rootstock M.26, the dwarfing rootstocks M.9, P 67 and B.396 and the super-dwarfing rootstock P 22. Crop-load was adjusted to 60, 105

Results

The photosynthetic pigment data showed that a significant effect of crop-load was found only on chlorophyll a content in 2014 (Table 1). An increase in chlorophyll a (29.4%) and b (46.3%) was observed at a crop-load of 105 inflorescences per tree. In 2015, photosynthetic pigments were significantly affected by rootstock. Use of the P 67 rootstock resulted in a significant decrease in chlorophyll and carotenoid accumulation in 2015. Use of the B.396 rootstock resulted in a significant decrease

Discussion

The choice of rootstock is one of the key factors affecting plant welfare. The plasticity of the root system architecture is very important for the mineral self-sufficiency of orchard trees (Martínez-Ballesta et al., 2010) and affects generative development and yield. Rootstocks included in this trial belong to three different growth control groups: super-dwarf, dwarf and semi-dwarf. Accordingly, tree growth characteristics were related to the rootstock vigour. Stronger tree growth was recorded

Conclusions

The super-dwarfing P 22 rootstock with an intensive crop-load (150 inflorescences per tree) conditioned N deficiency in leaves, which caused an accumulation of leaf sugars and a significantly lower nitrogen balance index in July 2015. The dwarfing rootstocks P 67 and B.396 effected a significantly larger leaf area, and decreased photosynthetic pigments and leaf carbohydrates were observed. However, no significant differences in yield or fruit weight compared to the control dwarfing M.9

Acknowledgement

This research was funded by a grant (No. MIP-036/2014) from the Research Council of Lithuania.

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