ROLE OF TEMPERATURE AND ALTITUDE ON FLOWERING PERFORMANCES OF MACADAMIA NUT

The study aimed to observe the flowering of macadamia grown under different locations in northern Thailand. It is hoped that the success of macadamia growing would be an opium substitute crop as well as a reforestation tree in northern Thailand. Although introduced cultivars have adapted well and are grown widely from sea level to the top of mountains, the yield is still low compared to those reported in other countries. The role of microclimate as a factor influencing annual growth cycle should be clearly understood to further develop appropriate cultural practices. Fifteen uniform mature macadamia trees were selected from three sites with two types of microclimate characteristics; mountain ridge and valley at commercial plantations of Doi Tung Development Project in Chiang Rai, northern Thailand. Floral biology, fruiting and vegetative flushing characters were observed from limb at 1.5-2 m above ground level. Air temperature and light intensity, as microclimate parameters were recorded during 2007-2008. Mostly racemes and fruits set on two-year-old shoots. The fruiting shoots of trees located at mountain ridge had significantly shorter length than at the valley site. Seasonal new vegetative shoots at three sites flushed on the same period. Racemes of trees at mountain ridge bloomed earlier in late November; however, it was one month later for trees at valley site. Interestingly, the flower phenology at the valley site showed better performances with a shorter bloom period and higher floret numbers resulting in higher fruiting rate. Daily light intensity, minimum and average temperature of two microclimate types or three altitudes showed similar pattern. Nevertheless, maximum temperature during flowering at the valley site was lower. Thus, the amount of daily temperature interval occurring at lower level might cause the differences in flowering and yield performances. In addition, the flowering and fruit setting of rain-fed and irrigated sites were observed on ten mature trees at the ridge. It was found that trees in rain-fed site had two periods of flowering; the first in-season bloom was in January after annual nut harvesting started and the second bloom, a so-called off-season, was found later in October. The off-season bloom of macadamia trees grown in northern Thailand reflected their adaptability to Thai environment. Thus, it might be a good potential that is of benefit to further develop off-season macadamia nut production.