A study on the difference of 'Newhall' navel orange and its sport 'Longhuihong' navel orange

Abstract:【Objective】Selective breeding of bud mutation is one of the most important methods for citrus new variety selection. Navel orange is a variety derived from bud mutation of sweet orange (Citrus sinensis Osbeck) in Brazil. At present, the southern region of Jiangxi province is the biggest navel orange production area in China, and‘Newhall'navel orange (Citrus sineses Osbeck, abbr. NH) covers more than 80%of the total plantation of navel orange. A mutant tree named‘Longhuihong' (Citrus sineses Osbeck, abbr.LHH) was found at the Ganliang navel orange orchard of southern region of Jiangxi province in the year2000 followed a freezing injury (-6 to-9 ℃) in December 1999. LHH has many features diifferent from those of NH like leaf curvature, leaf vein herniation, cold-resistance, freezing-tolerance, less summer shoots and higher and more stable yield. Regional trials of southern region of Jiangxi province and Beibei district of Chongqing showed that LHH had better adaptability compared with NH. This study aimed to find the reasons of the difference between the NH and the LHH.【Methods】The growing characteristics oftrees, the chlorophyll content, the characteristic of photosynthetic gas exchange of leaves, nutrient elementcontent of leaves, fruit quality and yield were investigated for both NH and LHH grown in the same or-chard. Five trees were randomly selected for measuring the perimeter of height of tree, crown diameter, trunk diameter, leaf length and width. Chlorophyll was extracted by 95% ethanol for twenty-four hours, and then the absorbency of chlorophyll a and chlorophyll b were detected under 665 nm and 649 nm byspectrometer. The photosynthesis (P_n) , stomatal conductance (G_s) , intercellular CO₂ concentration (C_i) andtranspiration (T_r) of the leaves of spring shoots, summer shoots and autumn shoots were measured by porta-ble LI-6400 photosynthesis measurement system. The internal and external qualities of fruits collectedfrom the different directions of the tree were analyzed. Finally, nitrogen (N) , phosphorus (P) , kalium (K) , Calcium (Ca) , Magnesium (Mg) , ferrum (e) , ZIncum (Zn) , manganum (Mn) , copper (Cu) and borium (B) inthe leaves of spring shoots were detected.【Results】The differences of trunk circumference, crown heightand diameter of the trees between NH and LHH were not obvious. The thickness, length and width of theleaves of LHH in different seasons were significantly larger than those of NH. The chlorophyll contents ofthe leaves of LHH (2.63, 2.77 and 2.75 mg·g^-1) were significantly higher than those of NH (1.91, 2.17 and2.36 mg·g^-1) in different seasons, respectively. The photosynthesis, stomatal conductance, intercellular CO₂ concentration and transpiration of the spring shoot leaves of LHH were significantly higher than thoseof NH, respectively. The nutrient element contents of LHH leaves were significantly higher than those ofNH except for phosphorus and zinc. And the average weight, peel thickness, diameter, shape index fruits, the a/b value of chromatic aberration, and the ratio of total soluble solid to titration acid of LHH were sig-nificantly higher than those of NH, whereas the titration acid of LHH (0.54%) was significantly lower thanthat of NH (0.62%) . The yield of LHH (61.3 kg) was higher than that of NH (51.0 kg) , and most of the qual-ity indexes of LHH fruits were better than those of NH, especially the skin color and fruit size.【Conclusion】The yield and quality of fruits of LHH are significantly higher than those of NH, LHH should be ex-tended widely in the citrus area.