Pollen limitation and xenia effects in a cultivated mass-flowering tree, Macadamia integrifolia (Proteaceae).

BACKGROUND AND AIMS: Pollen limitation is most prevalent among bee-pollinated plants, self-incompatible plants and tropical plants. However, we have very little understanding of the extent to which pollen limitation affects fruit set in mass-flowering trees despite tree crops accounting for at least 600 million tons of the 9200 million tons of annual global food production. METHODS: We determined the extent of pollen limitation in a bee-pollinated, partially self-incompatible, subtropical tree by hand cross-pollinating the majority of flowers on mass-flowering macadamia (Macadamia integrifolia) trees that produce about 200 000-400 000 flowers. We measured tree yield and kernel quality and estimated final fruit set. We genotyped individual kernels by MassARRAY to determine levels of outcrossing in orchards and assess paternity effects on nut quality. KEY RESULTS: Macadamia trees were pollen-limited. Supplementary cross-pollination increased nut-in-shell yield, kernel yield and fruit set by as much as 97, 109 and 92 %, respectively. The extent of pollen limitation depended upon the proximity of experimental trees to trees of another cultivar because macadamia trees were highly outcrossing. Between 84 and 100 % of fruit arose from cross-pollination, even at 200 m (25 rows) from orchard blocks of another cultivar. Large variations in nut-in-shell mass, kernel mass, kernel recovery and kernel oil concentration were related to differences in fruit paternity, including between self-pollinated and cross-pollinated fruit, thus demonstrating pollen-parent effects on fruit quality (i.e. xenia). CONCLUSIONS: This study is the first to demonstrate pollen limitation in a mass-flowering tree. Improved pollination led to increased kernel yield of 0.31-0.59 tons ha-1, which equates currently to higher farm-gate income of approximately $US3720-$US7080 ha-1. The heavy reliance of macadamia flowers on cross-pollination and the strong xenia effects on kernel mass demonstrate the high value that pollination services can provide to food production.

The effects of tree spacing regime and tree species composition on mineral nutrient composition of cocoa beans and canarium nuts in 8-year-old cocoa plantations.

The selection of shade trees with appropriate spacing is important for minimising their impact on nutrient accumulation by understorey cash crops in agroforestry systems. Cocoa trees may be intercropped with overstorey legume or non-legume shade trees. A legume tree and/or a non-legume timber tree with edible kernels (Gliricidia sepium and Canarium indicum, respectively) are used as shade trees in cocoa plantations particularly in Papua New Guinea. This study explored the nutrient concentrations of cocoa beans in response to both tree-shade species and shade-tree spacing regime. The study also investigated the extent to which C. indicum tree spacing altered the nutrient concentrations of canarium kernels. G. sepium trees in the study had a final spacing of 12 m × 12 m while the spacing regimes of either 8 m × 8 m or 8 m × 16 m used for C. indicum. The calcium (Ca) concentrations of cocoa beans did not differ significantly between plants located next to G. sepium and plants located next to C. indicum. Cocoa beans next to C. indicum trees with spacing of 8 m × 16 m had higher potassium (K) concentrations than those next to G. sepium trees. However, phosphorus (P) concentrations of cocoa beans next to C. indicum trees with spacing of 8 m × 8 m or next to G. sepium trees were significantly higher than those next to C. indicum trees with spacing of 8 m × 16 m. The K concentrations in cocoa beans and soil were not correlated nor were the P concentrations in cocoa beans and soil. Correlations between nutrients in leaves and cocoa beans, or between leaves and canarium kernels, were not strong. Our results suggest that cocoa and canarium trees can be intercropped successfully, and that they do not compete for soil nutrients.

Effects of roasting on kernel peroxide value, free fatty acid, fatty acid composition and crude protein content.

Roasting nuts may alter their chemical composition leading to changes in their health benefits. However, the presence of testa may alleviate the negative effects of thermal treatments. Hence, this study aimed to explore the effects of roasting on kernel chemical quality and colour development of Canarium indicum and examine to what extent testa would protect kernels against damage from roasting. Roasting decreased peroxide value but increased free fatty acid, probably due to increased cell destruction and lack of enzyme inactivation, respectively. Protein content of kernels significantly decreased after roasting compared to raw kernels. However, testa-on kernels contained significantly higher protein content compared to testa-off kernels. Whilst colour development and mottling were observed in temperatures beyond 120°C, roasting did not alter fatty acid compositions of kernels. The mild roasting and presence of testa in kernels can be used to enhance health benefits of kernels.