A Dwarf Phenotype Identified in Breadfruit (Artocarpus altilis) Plants Growing on Marang (A. odoratissimus) Rootstocks

Abstract

Breadfruit (Artocarpus altilis) is a tropical fruit tree primarily grown as a staple crop for food security in Oceania. Significant wind damage has driven an interest in developing its dwarf phenotype. The presence of any dwarf breadfruit variety remains unknown. Little is known regarding the growth of the species on rootstocks. Here, we examined the phenotype of breadfruit plants growing on marang (Artocarpus odoratissimus) rootstocks within 18 months after grafting; we identified a rootstock-induced dwarf trait in the species. This dwarf phenotype was characterized by shorter stems, reduced stem thickness and fewer branches, with 73% shorter internode length, 51% fewer and 40% smaller leaves compared to standard size breadfruit plants. The height of breadfruit plants on marang rootstocks was reduced by 49% in 9 months, and 59% in 18 months after grafting. The results suggest marang rootstocks can be applied to breadfruit breeding program for tree vigor control. Further biochemical characterization showed plants on marang rootstocks displayed leaves without change of total chlorophyll content, but with lower total soluble sugars, and stems with reduced activity of plasma membrane H+-ATPase, a well-known primary proton pump essential for nutrient transport. The significance of the two parameters in rootstock dwarfing is discussed.

Expression of Gibberellin Metabolism Genes and Signalling Components in Dwarf Phenotype of Breadfruit (Artocarpus altilis) Plants Growing on Marang (Artocarpus odoratissimus) Rootstocks

“…Breadfruit plants growing on marang rootstocks were characterised by dwarf stature with~60% reduction in total plant height and~80% reduction in the length of internodes at the end of 24 months after grafting (Figure 1), consistent with the previous observation in the first 18-month period [6]. The phenotypes resemble the typical signs of GA deficiency [21,31].…”

“…There was no significant difference in both internode length and final plant height between the self-grafts and the non-graft ( Figure 1). The results were consistent with previous growth observation in the 18-month period after grafting [6].…”

“…In the current study, we focused on stem elongation as a key phenotype in breadfruit plants on marang rootstocks. However, the rootstock-induced dwarf traits in breadfruits involve other morphological and biochemical components [6] which are not examined in the current experiment. Future characterisation of the roles of GA and other hormones/factors in these dwarf traits is required for the unravelling of the molecular mechanism underlying rootstock-induced breadfruit dwarfing.…”

“…The species is an evergreen tree from 15 to 20 m. Breadfruits comprise fertile and sterile diploids and sterile triploids and has hundreds of cultivars [5], but there is currently no size-controlling rootstock within the species. Through interspecific grafting, a dwarf phenotype was recently identified in breadfruit plants growing on marang (Artocarpus odoratissimus) rootstocks [6]. Under the same genus of Artocarpus, marang is also a large tropical fruit tree to 25 m; no dwarf phenotype has been identified [7].…”

Unlocking the inherent potential of plant genetic resources: food security and climate adaptation strategy in Fiji and the Pacific

“…The morphological diversity of breadfruit cultivars in the Pacific provides a great opportunity to screen and develop dwarf varieties which are resistant to wind damage (Zhou et al 2014 ). Recently Zhou and Underhill ( 2019 ) identified a Marang root stock with traits of dwarfness in breadfruit. The foreground selection of root stocks with salinity and drought tolerance, and introgression with dwarf genes may be a viable approach to adapt breadfruit cultivars to climate change in the Pacific.…”