A Study On The Effects Of Water Stress During Florescence Of Macadamia

Six-year-old trees of three macadamia varieties: Kau (HAES344), Pahala (HAES788) and O.C. (Own Choice) were taken as the experimental materials. Effects of soil water stress at the flowering stage of macadamia on water status, POD and SOD activities, performance of flower development and its fertility, efficiency of photosynthesis, etc. were studied so as to find the way to increase fruit set and its economic performance by improving soil water status.Results showed that macadamia plants, treated with different water stress at the flowering stage, compared with control (no irrigation), had remarkable difference in pollen vigor and fertility, SOD and POD activities, fruit set and photosynthetic products (chlorophyll, sugar and starch). Under the condition of no irrigation, because of bad development of flowers, style and anthotaxy became short, growth of flower organ was restricted, quantity of pollen and its rate of germination decreased. Therefore, the pollination and fecundation was bad, a lot of fruit dropped, the rate of fruit set was low, the growth of young fruit was restricted, and the speed of fruit growth slowed down, and finally the yield decreased. Irrigation was favorable for the normal elongation of style and anthotaxy, as well as the increase of pollen germination rate, fruit set and fruit size. However, saturated irrigation was unfavorable for the stretch of style, germination of pollen, fruit set at the later stage and the growth of fruit. Plants with normal irrigation (Treatment N) had the best performances; whose pollen vigor and the rate of fruit set at the later stage were the highest, and the growth of flower style and young fruit fastest. Thus, irrigation is necessary for macadamia at its flowering stage. But the irrigation must be controlled; too much or too little water will be unfavorable for the growth and development of macadamia plants. In Xishuangbanna, the flowering, fruit set and fruit development of macadamia is at the stage of drought; irrigation of 60% field capacity at this stage can increase the pollination and fertility, and the fruit yield and quality.Different varieties had different reflects under the condition of water stress. As for the three varieties, the rate of pollen germination under the same water stress was: Kau > Pahala > O.C; but the response of pollen vigor of Kau and Pahala to water stress was sensitive, and that of O.C. on the contrary. Sensitivity of fruit set of Pahala to water stress was bigger than that of O.C, the speed of young fruit of Kau was slower than that of Pahala and O.C, which showed that Kau and Pahala at flowering stage need water even more.