Characterisation of Breadfruit (Artocarpus altilis) Plants Growing on Lakoocha (A. lakoocha) Rootstocks

Abstract

Breadfruit (Artocarpus altilis) is a traditional fruit tree of 15–30 m tall in Oceania. The species is a staple crop for food security in the tropics. Tree loss from tropical windstorms, together with transition toward high-density planting has driven an interest in the dwarf phenotype of the species. Information on dwarfing rootstocks for breadfruit is currently limited. The aim of this study was to assess the performance of breadfruit growth with lakoocha (Artocarpus lakoocha) as rootstocks. We compared the phenotype of breadfruit trees on lakoocha rootstocks with those on self-graft and non-graft within 21 months after grafting. These led to the discovery of a rootstock-induced dwarf trait in breadfruit species. Breadfruit scions on lakoocha rootstocks displayed a reduction in tree height, stem thickness, and internode length, with fewer branches and leaves, resulting in about 32% of the standard height at the end of 21 months after grafting. These suggest lakoocha rootstocks have the potential to control breadfruit tree vigor. Non-structural carbohydrate analysis showed the composite trees exhibited lower hexose concentration in both scion stems and roots, but higher sucrose level in scion stems, and higher starch level in roots. The significance of these parameters in rootstock dwarfing is discussed.

Total Flavonoid Contents and the Expression of Flavonoid Biosynthetic Genes in Breadfruit (Artocarpus altilis) Scions Growing on Lakoocha (Artocarpus lakoocha) Rootstocks

“…There was no significant difference in scion height between self-grafts and non-grafts. These results were in agreement with previous findings for the period up to 21 months following grafting [ 2 ].…”

“…Breadfruit plants with lakoocha rootstocks were about one-third of the standard height by the end of 24 months following grafting ( Figure 1 and Figure S1 ), in agreement with previous findings showing the potential of lakoocha rootstocks in breadfruit dwarfing [ 2 ]. During the development of the dwarf phenotype, breadfruit scions displayed significant increases in total flavonoid content, together with an increase in the expression of the flavonoid biosynthetic gene, AaCHS ( Figure 1 ).…”

“…There was no significant difference in scion height between self-grafts and non-grafts. These results were in agreement with previous findings for the period up to 21 months following grafting [2]. Total flavonoid contents were measured in scion stems every 2 months in the period from 16 to 24 months after grafting.…”

“…However, the presence of size-controlling rootstock in the species is not known. In the same genus of Artocarpus , a small tropical tree species, lakoocha ( Artocarpus lakoocha ), was recently identified as a potential vigor-control rootstock conferring over a 65% reduction in breadfruit tree height when compared with those on self-graft and own-rooted standard breadfruit trees [ 2 ]. Importantly, the assessment also indicated that the rootstock-induced dwarf phenotype in breadfruit trees on lakoocha rootstocks was not associated with graft incompatibility [ 2 ].…”

“…In the same genus of Artocarpus , a small tropical tree species, lakoocha ( Artocarpus lakoocha ), was recently identified as a potential vigor-control rootstock conferring over a 65% reduction in breadfruit tree height when compared with those on self-graft and own-rooted standard breadfruit trees [ 2 ]. Importantly, the assessment also indicated that the rootstock-induced dwarf phenotype in breadfruit trees on lakoocha rootstocks was not associated with graft incompatibility [ 2 ]. The intriguing scion/rootstock communications whereby lakoocha rootstock imparts size-control over breadfruit scions have not yet been investigated.…”