Partitioning of Dry Matter into Fruit Explains Cultivar Differences in Vigor in Young Olive (Olea europaea L.) Trees

Abstract

<jats:p>Low vigor and early and abundant production are desirable traits for modern tree crops. In olive, most cultivars are too vigorous and cannot be successfully constrained in the small volume allowed by the straddle harvester used in the so-called superhigh-density (SHD) orchards. Only few cultivars appear to have sufficiently low vigor to be suitable for this system. These cultivars combine low vigor with earlier and higher yield. This study investigated the hypothesis that differences in vigor between Arbequina, a low vigor and the most commonly used cultivar in SHD orchards, and Frantoio, a highly vigorous cultivar not suitable for such orchards, are related to their differences in early bearing and consequent differences in dry matter partitioning into fruit. Young trees of both cultivars were deflowered either in 2014, 2015, both years, or neither one, resulting in a range of cumulative yields over the 2 years. Tree trunk cross-sectional area (TCSA) was measured at the beginning of each year. This was closely related to total tree mass, as assessed at the beginning and at the end of the experiment. Cumulative yield, in terms of fruit dry matter, was also assessed. TCSA increased less in fruiting trees in both years. As expected, when not deflowered, ‘Frantoio’ was less productive and more vigorous than ‘Arbequina’. However, there was no difference in TCSA increment when both cultivars were completely deflowered. TCSA increments were closely inversely related to yield across all treatments and cultivars (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.90). The regressions improved further when data from 2015 only were used (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.99). The results represent the first quantitative report showing that differences in vigor among cultivars can be completely explained in terms of different dry matter partitioning into fruit, supporting the hypothesis that early bearing is a major cause, rather than merely a consequence, of lower vigor in young ‘Arbequina’ trees. These results provide new understanding on vigor differences across cultivars, which will be useful for breeding and selection of new genotypes.</jats:p>

Effects of cultivar, fruit presence and tree age on whole-plant dry matter partitioning in young olive trees

“…Increments in TCSA (and thus for whole-tree biomass) were lower for fruiting than non-fruiting treatments ( Figure 2 A and Figure 3 ), in line with previous findings in olive trees ( Fernández et al., 2015 ; Rosati et al., 2018a ). The TCSA of Arbequina NF was comparable to that of Frantoio NF up to the first three years of observation, confirming that the low vigor generally observed in Arbequina is due to its early and abundant fruiting (up to 159 g of fruit + flower dry matter per tree in the first and second year after transplanting Rosati et al., 2018a ; 2018b ). In the fourth year, however, the TCSA in Frantoio NF was significantly greater than that of Arbequina NF ( Figure 2 A).…”

“…Recently, it has been found that deflowering resulted in strong increments in vegetative growth also in young olive trees, and that this eliminated differences in vigor (i.e. vegetative growth) between plants of the cultivar Arbequina (low vigor) and those of the cultivar Frantoio (high vigor), suggesting that cultivar differences in vigor may be explained in terms of different dry matter partitioning towards fruit (Rosati et al, 2017(Rosati et al, , 2018a. This demonstrated that competition for resources plays a major role in determining tree growth in young olive trees, suggesting that tree growth is source limited (Rosati et al, 2018b).…”

SILVOLIVE, a Germplasm Collection of Wild Subspecies With High Genetic Variability as a Source of Rootstocks and Resistance Genes for Olive Breeding

“…The branching habit is one of the main factors affecting carbon partitioning between wood and leaves. Low-vigor and highbranching genotypes of the SILVOLIVE collection have a higher number of nodes and leaves (R 2 = 0.7), which means increased canopy density and may determine higher number of potential fruiting sites, becoming an important trait to be used to produce and export more assimilates toward fruits (Rosati et al, 2018). Otherwise, the hexaploid MAR1 and MAR3, together with most FRA and AMS genotypes show high apical growth with a low number of secondary stems.…”

“…Convincing evidence has been provided that these traits are genetically encoded by the root portion of the grafted plant, playing the rootstock genotype essential roles in shaping variation of these traits in the scion (Warschefsky et al, 2016). In addition, rootstocks can also affect the branching pattern of the scion (Costes et al, 2010) and promote early and more abundant bearing in young olive trees (Rosati et al, 2017(Rosati et al, , 2018. On the one hand, we have verified that all subspecies can be grafted with commercial olive varieties, including cuspidata, which has the maximum genetic distance with europaea ( Supplementary Table S9).…”

Sugar Metabolism in Stone Fruit: Source-Sink Relationships and Environmental and Agronomical Effects

“…Notwithstanding, in stone fruit trees, the presence of an elevated number of fruits alters the source-sink balance, by increasing assimilate accumulation into the fruits and/or by inducing an intensification of competition among them and between vegetative and reproductive growth (Morandi et al, 2008;Costa et al, 2018). This is also the case in olive (Rosati et al, 2017(Rosati et al, , 2018b. As a rule, high crop loads cause a decrease in tree growth (Intrigliolo and Castel, 2009), mainly during the last phases of fruit development (Intrigliolo et al, 2014).…”