Reproduction in Wild Populations of the Threatened TreeMacadamia tetraphylla: Interpopulation Pollen Enriches Fecundity in a Declining Species

Abstract

Macadamia tetraphylla is a subtropical rain forest tree from fragmented lowlands in eastern Australia. Owing to habitat loss and fragmentation, this commercially important species is vulnerable to extinction. Breeding system and fecundity were investigated in nine populations incorporating three habitat types (moderately disturbed, highly disturbed, and intact) to determine if seed set, seed weight, and genetic diversity are compromised by disturbance. Breeding success was also tested using pollen donors from distant (30–100 km), local (2–3 km), neighbor (10–20 m), and near‐neighbor (< 10 m) sources. Macadamia tetraphylla is weakly self‐compatible but incapable of automatic self‐pollination. Across populations, seed to flower ratios were always < 0.1 percent in open‐pollinated trees and trees from moderately disturbed habitats had the highest fruit production. Outcross pollen produced more seed per raceme than open‐pollinated or self‐pollination treatments. Seed set and seed weights were positively influenced by pollen source with local pollen and distant pollen effecting more or heavier seeds. Germination rates and genetic diversity did not vary significantly in seedlings from different pollen sources. Results suggest a pollen source from at least a 2 km distance is an optimal outbreeding distance; however, many wild populations do not have conspecifics at optimal distances owing to habitat fragmentation. Highly disturbed populations are producing seed but the longevity of these sites is threatened by weed invasions. We conclude that small populations in degraded habitats that are at risk of being overlooked should not be ignored but should be a focus for restoration efforts as they are a valuable asset for the conservation of M. tetraphylla.

Characterization of accessions and species of Macadamia to stem infection by Phytophthora cinnamomi

“…All four Macadamia species usually occur in small populations in the native ecosystem and are at risk of extinction (Pisanu et al ., ). Unlike M. ternifolia and the cultivated species M. tetraphylla and M. integrifolia where large genetic diversity exists (Steiger et al ., ; Peace et al ., ), genetic diversity in M. jansenii is low and subpopulations show little genetic differentiation (Shapcott & Powell, ).…”

“…Although all accessions of M. tetraphylla and M. integrifolia used in commercial productions have been selected from the native environments in Australia, wild macadamia populations represent a significant resource for the macadamia industry as potential sources of resistance to biotic and abiotic stress, and for improving yield and breeding efficiencies. These wild accessions are vulnerable to extinction due to habitat loss and fragmentation (Pisanu et al ., ; Neal et al ., ; Powell et al ., ). In addition to these two major threats, a large number of native plant species are threatened by P. cinnamomi in Australia (Kueh et al ., ).…”

Cross- and self-fertilization of plants – Darwin's experiments and what we know now

“…Recent work on Macadamia tetraphylla L.A.S.Johnson (Pisanu, Gross & Flood, 2009), which is weakly self‐compatible, has indicated that the situation is perhaps even more complex than Darwin could have imagined. In experiments using trees from highly disturbed to intact habitats, and using pollen from donors located at distances from less than 10 m to up to 100 km distance, plants artificially pollinated using outcrossed pollen produced more seed per raceme than did open‐pollinated or self‐pollinated trees.…”

Genome assembly and annotation ofMacadamia tetraphylla

“…But up to now, the genome sequencing of M. tetraphylla has not yet been reported. As an important parent species of macadamia varieties in production 23 , the genome sequencing of M. tetraphylla will lay a good foundation for macadamia breeding. Table 1 and Fig.…”