Dynamic changes and correlation analysis of nutrient contents in ‘Pawnee' pecan (Carya illinoinensis)

Abstract:【Objective】The pecan, Carya illinoinensis(Wangenh.) K. Koch, is the most economically important member of the Carya Nutt of Juglandaceae.‘Pawnee', originated from north American, has become the largest cultivar in both north American and China recently for its good fruit quality and disease resistance, but the dynamic changes in nutrients in‘Pawnee'have not been reported. Studies on dynamic changes in nutrients can help to understand the mechanism of nut quality formation, which is crucial for better use of this nut crop or breeding programs. Pecan has the serious problem of irregular bearing, which is most likely caused by unstable accumulation and transformation of nutrients. Analyzing the dynamic changes in nutrients in both the kernel and the leaf during nut development may obtain information of nutrient accumulation and transformation. In this study, dynamic changes in the nutrient contents both in the kernel and in the leaves and their correlations were examined in relation to quality formation and productivity in pecan‘Pawnee'.【Methods】Samples were collected from six healthy‘Pawnee'trees(8- 12 years old, planting space 5.0 m×7.0 m) with similar trunk diameter and tree vigor at the orchard of Nanjing Lvzhou Pecan Technology Co. Ltd.(latitude 31°14′-32°36′N; longitude 118°22′-119°14′E) located at Liuhe district, Nanjing, Jiangsu province, China. Fruit and leaf samples were collected every 10 daysfrom 95 d after full blossom during the fruiting period for two successive years. The contents of fat, solublesugars, proteins, fiber, moisture and mineral elements such as P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn and Se in‘Pawnee'were measured and their correlations were analyzed. Fat content was determined by Soxhlet ex-traction method with the extraction solvent of hexane; protein concentration was measured by the Kjeldahlmethod; soluble sugar content was analyzed by anthrone colorimetry; fiber content was measured by nitricacid-ethanol method; and moisture content was analyzed by oven drying method. The determinations ofmetal elements such as Mn, Zn, Mg, Fe, Ca, Cu, K and Na were carried out by atomic absorption spectrom-etry, while Se was determined by UV spectrophotometry and P by colorimetric method.【Results】The re-sults showed that fat content in the kernel followed an unimodal pattern and was very low in the earlystage of nut development, then increased rapidly and reached the highest value around 145 d after fullblossom, and then slightly decreased. The change patern of sugars in the leaf differed from that in the ker-nel. Suger content in the kernel rearched a relatively low level around 165 d after full blossom, while inthe leaf it rose to the highest level. Protein content in the kernel increased frist and then decreased rapid-ly, but it maintained a high level with little variation in the leaf. Fiber was high during the early nut devel-opment stage with the highest value around 95 d after full blossom and then decreased rapidly until itreached the lowest value around 145 d after full blossom, after which it increased slowly. Moisture contentwas at a high level during the early nut development stage then decreased rapidly and reached the lowestvalue around 155 d after full blossom. Dynamic changes in Mn, Zn, Mg, Fe, Ca, Cu and Se contents in pe-can kernel showed a similar pattern, reaching their highest values at 95 d after full blossom, then decreas-ing sharply, and maintaining relatively low values during the later stage of nut development. P content inthe kernel reached the highest value around 125 d after full blossom, while P content in the leaf reachedthe highest value around 105 d after full blossom. The average content of P in the kernel was about 2times that in the leaf. In both tissues, P content was high in the early stage of nut development and re-duced slowly with nut development. K content in the kernel was very low in the early stage of nut develop-ment, then increased rapidly and reached the highest value around 155 d after full blossom, and then de-creased slightly. Na content in the kernel declined slowly with nut development, while Na content in theleaf had minor fluctuations.【Conclusion】The contents of soluble sugars, proteins, fiber and moisture inthe kernel showed a significant decrease tendency, and the mineral elements changed drastically from day95 to day 125 in the kernel but displayed relatively smooth changes in the leaf. Variations in nutrients inpecan were greatest during 95-145 d, which was the key period for quality formation. There was a close re-lationship between nutrient changes in the kernel and leaf. K, Ca, Mg, Mn, Cu, Zn and Se had a close linkwith nutrient accumulation, and K element had a vital role in fat accumulation.