Studies on the effectiveness of artificial pollination and pollen xenia in macadamia nut Guire No. 1

【Objective】As the first new variety of macadamia nuts (Macadamia ternifolia F. Muell) independently selected and bred in Guangxi, Guire No. 1 is the macadamia variety with the largest cultivation area in Guangxi at present, accounting for about more than 65% of the total planting area. It was a self-incompatible variety. The study aimed to seek for the suitable pollinator variety for Guire No. 1 through artificial pollination.【Methods】4 varieties (695, O.C, JW and A16) were used as pollinator varieties for artificial pollination with Guire No. 1. The self-pollination and open pollination were set as controls. Three trees were used for each pollination combination in a block in 2021 and five trees were used for each pollination combination in a block in 2022, with three repeats. 10 bunches of inflorescences were used for pollination on each tree. The flowers were taken 24 h after pollination and counted forpollination efficiency according to pollen germination rate on the stigma. The fruit setting rates were investigated 14 days after pollination in 2021 and the final fruit setting rates were investigated in 2022. The yield for each combination was recorded after harvest. The fruit appearance traits and kernel quality were compared and comprehensively evaluated using principal component analysis.【Results】The fruit setting rates of artificial pollination of Guire No. 1with 695, JW and A16 were 28.86‰, 18.62‰ and 12.85‰ in 2021, and the fruit setting rate of self- pollination was 11.39‰, and the artificial pollination with the pollens of other varieties could significantly improve the fruit setting rate. The trial site experienced an inverted spring weather and the overall orchard yield was reduced by about 1/3 in 2022 compared with 2021. The yield of Guire No. 1 artificially pollinated with the pollens of different varieties was significantly higher than the yield of the bunches with open- pollination, and the yield of the bunches of flowers pollinated with 695 was up to 6.42 kg, which was comparable to the yield of 5-yearold Guire No. 1 under conventional climatic conditions. In terms of the fruit appearance, there was no significant difference in peel color, convex papillate on the top of the fruit, suture at the belly of the shell and fruit, and markings on the shell, but there was pollen xenia effect in the vertical, horizontal, single fruit weight and fruit shape index of the green peel and shell. In terms of fruit quality, there were pollen xenia effects in single kernel weight, kernel setting rate, crude protein, total sugar, mineral P, Fe, Ca elements, and palmitic acid, palmitic acid, 10-heptacenoic acid, linoleic acid in fatty acids. The correlation analysis revealed that the mineral Fe element was significantly and positively correlated with the monounsaturated fatty acid MUFA and extremely significantly and positively correlated with the polyunsaturated fatty acid PUFA, while on the contrary it was highly significantly and negatively correlated with the saturated fatty acid SFA. The results of the comprehensive evaluation by principal component analysis showed that 695 as pollen donor had the highest composite score of 0.720.【Conclusion】 The artificial pollination could significantly increase the yield of Guire No. 1 macadamia nut, and at the same time, it could mitigate the adverse effects of the detrimental climate to a certain extent. There were pollen xenia effects on some characteristics of the fruits of Guire No. 1 macadamia nut. Through the comprehensive evaluation of yield and fruit quality, it was concluded that 695 would be the most suitable pollination variety for Guire No. 1 in Guangxi province.