Pollen parent effects on macadamia yield

Macadamia integrifolia (Maiden and Betsche) and M. tetraphylla (L.A.S. Johnson)nfreely hybridise where their native Australian rainforest habitats coincide in northernnNew South Wales and southern Queensland. Macadamias (Proteaceae) are grownncommercially for their edible kernel. The current challenge is to identify highnyielding compatible pollen donor trees well suited to Australian conditions, tonenhance both productivity and quality in commercial macadamia orchards. Onenmeasure of inter-genotype compatibility is the comparison of fruit sets in response tonpollination using different pollen parents. A standardised pollination protocol wasnrequired to investigate both inter-genotype compatibilities between macadamiangenotypes, and the influences of pollen parents on fruit retention and fruit characters.nThese techniques involve a number of methodological assumptions which needed tonbe tested.The effect of the number of flowers pollinated on an inflorescence, the duration ofnpistil receptivity, and the relationship between Initial-Fruit-Set (IFS, the number ofnfruits retained two weeks post-pollination as a percentage of the number of flowersnpollinated) and mature fruit production have been investigated in Macadamia. Thesenresults show that the number of flowers pollinated, and the timing of pollinationninfluence both fruit set and the final number of fruit produced. The relationshipnbetween IFS and Final-Fruit-Set (FFS, proportion of fruits retained 32 weeks post-pollinationnas a proportion of the number of flowers pollinated) varied with thennumber of flowers pollinated per inflorescence, thus IFS cannot by itself be taken tonindicate successful fruit production. Therefore in order to use controlled pollinationsnto assess inter-genotype compatibility, standardisation of experimental pollinationntechniques and measures of reproductive success are required.Productivity of individual flowers was determined in three Macadamia genotypesnusing a 3 X 3 diallel and thinning racemes to leave 10, 25, 50, 75, 100 and 150nflowers, and using appropriate replication of racemes and trees. The pollinationneffects were investigated by measuring fruit set at fortnightly intervals from 2 until 16nweeks, and then at 4 weekly intervals until 34 weeks after pollination. As the numbernof flowers receiving cross and self-pollen were increased, IFS increased, howevernthese differences were not maintained after 12 weeks post-pollination. The effectivenpollination period of Macadamia pistils was investigated in 3 maternal genotypes,nusing a range of pollen sources including self. Replicate bagged racemes werenpollinated from anthesis at daily intervals until 14 days post anthesis. Receptivity wasnlow on the first two days post-anthesis, reached a maximum between days 3 and 7npost-anthesis and significantly declined thereafter. The effective pollination periodn(EPP) of pistils appeared to be genotype-specific, and varied with pollen sourcesntested. Fruit set occurred when pollinations were performed up to 12 days postanthesis,nafter the floral perianth had withered, discoloured and abscised. Abscissionnof emasculated, unpollinated flowers was genotype specific, but in all cases flowersnhad abscised by 13 days post-anthesis. The implications of these results for assessingninter-genotype compatibility within the Proteaceae are discussed.A 6 X 6 diallel cross was performed to determine the effect of pollen parent on fruitnretention, and mature nut characteristics between clonally propagated lines ofnmacadamia. Utilising an optimised pollination technique, this work demonstrated IFSnmeasured 14 days post-pollination, and FFS measured 32 weeks post-pollination,nvaried between 0.3 and 17.7%, and 0 and 2.2% of flowers pollinated respectively,nwhere parental combinations determined fruit abscission patterns. In 29 of 30 crossncombinations tested both IFS and FFS were greater than self-pollinated treatments.nAt FFS the only combination not responding to cross pollination, HV A4 X HV A16,nis known to have at least one shared parent. This result suggests cultivars selectednfrom the same breeding populations may exhibit reduced compatibility due to sharednalleles.Two peak periods of fruit abscission occurred, between anthesis and two weeks andnbetween four and seven weeks post-pollination. Small numbers of fruit werenobserved to abscise until 14 weeks post-pollination, when fruit set was equivalent to FFS. Fruit retention declined in a negative exponential relationship between IFS andnFFS, which varied depending on both maternal and paternal parent combinations.nPollen parent also had a significant influence on progeny weight, such that largernfruits were derived from those combinations producing the most fruit. Implicationsnfor natural and production systems will be discussed. n n