In Hawaii, the increase in inflorescence bud length of macadamia {Macadamia integrifolia Maiden and Betche) ‘Ikaika’ (Hawaii Agricultural Experiment Station No. 333) from bud emergence (the stage when the bud is first visible and 1-3 mm long) to anthesis followed a sigmoid curve. The flowering season was from early December, 1989 to end of May, 1990 and showed two peaks. Buds reaching anthesis between 12 February, 1990 and 28 March, 1990 were considered the first group, and those reaching anthesis between 23 April, 1990 and 21 May, 1990 were considered the second group. Total rainfall, average daily solar radiation, and average daily maximum temperature were found to be highly correlated with monthly survival rate. Crop load may be another factor affecting the monthly survival rate. No significant weather effect on the maximum raceme length was found.
The flower development of macadamia was divided into 5 stages: 1) bud emergence, 2) growth stage I which is a period of slow growth, 3) growth stage II which is a period of rapid growth, 4) mature stage which is the stage before anthesis when the raceme ceases increasing in length, and 5) anthesis. Total growing degree days (TGDD) with a base temperature of 12.5°C, the number of days with daily maximum temperature of at least 2 6 °C within the days to complete growth stage II or from growth stage II or mature stage to anthesis (D26Tmax), and total solar radiation (TSR) were found to be the three most important variables correlated to the days to complete growth stage II, growth stage II to anthesis, and mature stage to anthesis of inflorescence buds in groups one and two. With stepwise regression analysis, TGDD was always the most important parameter selected in the best two independent variable models in group one, whereas in group two, D26Tmax and TSR seemed to play more important roles.
Statistical models were constructed for two purposes: to describe and predict the time of peak flowering of macadamia ‘Ikaika’ (HAES 333) using weather data. The best statistical model constructed to describe the days from the starting date of the flowering season to the highest peak was Dsh = 249.15 + 0.12 (TGDDsh) - 5.81 (MAXTsh) - 6.26 (MINTsh) where Dsh is the time from the starting date to the highest peak (days), TGDDsh is the total growing degree days accumulated during the period from the startingdate to the highest peak, MAXTsh is the average daily maximum temperature from the starting date to the highest peak (°C), and MINTsh is the average daily minimum temperature from the starting date to the highest peak (°C ). The coefficient of multiple determination (r 2) was 0.99**. Validation of the model showed the model predicted the highest peak 4 days before it occurred in the field at location 1 (Mauna Loa Macadamia Nut Corporation in Keaau) and 4 days after it occurred in the field at location 2 (Mac Farms of Hawaii, Inc. in Honomalino).
Two statistical models were constructed to predict the days from the starting date of the flowering season to the first peak, one for each location. At location 1, the best model was Dsf1 = 118.61 - 0.11 (TG D D e sp I) + 0.000168 (TSO LARespI) where Dsf1 is the time from the starting date to the first peak at location 1 (days), TGDDesp1 is the total growing degree days accumulated during the 18 weeks after ending date to next starting date of flowering period at location 1, and TSOLAResp1 is the sum of solar radiation during the 18 weeks after ending date to next starting date of flowering period at location 1 (wh/m2). The R2 was 0.88**. Validation of the model showed the model predicted the first peak one day before it occurred in the field at location 1.
The best model at location 2 was Dsf2 = - 156.34 + 12.67 (MINTesp2) + 0.01 (TGDDesp2) where Dsf2 is the time from the starting date to the first peak at location 2 (days), MINTesp2 is the average daily minimum temperature during the 18 weeks after ending date to next starting date of flowering period at location 2 (°C), and TGDDesp2 is the total growing degree days accumulated during the 18 weeks after ending date to next starting date of flowering period at location 2. The r 2 was 0.88**. Validation of the model resulted In the precise prediction of 42 days
