Effects of self- pollination style extracts on the crossing- compatibility among Macadamia varieties

Abstract:【Objective】This study aimed to clarify the crossing-compatibility among Macadamia varieties and provide a theoretical and practical basis for arranging pollination varieties.【Methods】Thirteen and ten Macadamia varieties were respectively used as female and male parent materials for a total of 115 crossing combinations. The male pollenes were cultured the media containing self-pollination style extracts of the female parents, and the pollen germination rate (PGR) and pollen tube length (PTL) were determined for each combination. The strength of crossing- compatibility of the crossing combination was divided into three categories (strong, medium and low) by a combined evaluation with their pollen germination rate, pollen tube length, index of influence degree ofmacadamiapollen germination (PG) and index of influence degree of Macadamia pollen tube growth (PTG).【Results】(1) The crossingcompatibility was low between the variety HY and the 12 tested female parents, indicating that these combinations were not suitable for the field experiments. (2) The crossing-compatibility between the variety A16 and the respective variety of A4, O.C, D, HAES951 and HAES816 was strong, indicating that these combinations could be used for further field hybridization test. (3) Among the 11 crossing combinations with the variety A4, the crossing-compatibility of the 9 combinations was strong, and the cross-ing-compatibility of the 2 combinations was medium, indicating that the variety A4 could be used as a male parent in cross breeding. (4) The variety HAES695, having a strong cross-compatibility with the female parent HY, and a moderate crossing- compatibility with the varieties of O.C and D4, could be used for cross breeding. It also might be incompatibile with the varieties HAES815 and HAES863. (5) The variety HAES816 had strong crossing-compatibility with the variety D4, O.C and HAES951, indicating that such a combination could also be used for cross breeding. (6) In general, the variety HAES863, which had the highest pollen germination rate and the fastest pollen tube growth under all 12 growth media, could be used as a male parent for all of the tested varieties. (7) The variety HAES820, with strong crossing-compatibility in 11 of the 12 crossing combinations, except for a medium crossing- compatibility with the variety HY, could be used as a male parent. (8) The variety HAES951 could be pollinated with the variety of HAES816, HAES863, D4 and HAES842 respectively, but not with the variety O.C. (9) The variety D could be matched with the variety HAES863 or HAES816 for a pollination test, and would be a good material for studying pollen tube polar growth of macadamia as it had a greater pollen germination rate and also a faster pollen tube length than any of the other male parents. (10) The variety O.C, with a greater pollen germination rate and a rapid pollen tube growth under all the growth media tested, could be used as a pollination tree for the 13 tested female parents. (11) Among the 115 crossing combinations, the interval of index of influence degree of Macadamia pollen germination (PG) was -1.31-0.87, and the interval of index of influence degree of Macadamia pollen tube growth (PTG) was -0.64-0.62. The larger values of the PG and PTG the varieties had, the weaker the crossing-compatibility between the varieties they had; the smaller values of the PG and PTG the varieties had, the stronger crossing-compatibility between the varieties they had. Macadamia was gametophytically self-incompatible, and the pollen germination was lightly affected by the self-pollination style extract from the female parents, so the growth of pollen tube was taken as an important indicator for determining the crossing-compatibility between the varieties, and the PG was taken as the auxiliary index. The PTG values would be analyzed firstly, when PTG＜0, we would not consider the PG values and the combination would be considered as strong crossing- compatibility; another stander was that if PTG＞0.4, the PG was also not necessary to consider and the combination was the same as the weak crossing-compatibility directly. When the PG and PTG were be comprehensively analyzed at the same time, we found that the crossing- compatibility between the macadamia varieties would be obtained more accurately. At the last, according to the pollen germination rate, pollen tube length, index of influence degree of the pollen germination and index of influence degree of the pollen tube growth, the crossing- compatibility of the 115 crossing combinations were divided into 3 types, that is, strong (PG≤0.5; PTG≤0.2), medium (0.5＜PG≤0.7; 0.2＜PTG＜0.4 ), and low (0.7≤PG＜1; 0.4≤PTG＜1).【Conclusion】The crossing-compatibility among macadamia varieties was divided into strong, medium and low category according to their values in the index of influence degree of the pollen germination (PG) and the index of influence degree of the pollen tube growth (PTG). Among the 115 combinations, 54 combinations had a strong crossing- compatibility. The variety HAES863, O.C and HAES820 could be used as a male parent in cross breeding and also a pollination tree for the 13 tested female varieties. The variety HAES863, D4, HAES951, HAES816 and HAES842 could be used as excellent female parent materials in cross breeding.