Evaluation of alkali tolerance of 8 hybrid rootstock progenies of Ziyang Xiangcheng and Trifoliate Orange

Abstract: 【Objective】The alkali-resistance of eight F1 generation lines (ZZ1, ZZ6, ZZ7, ZZ31, ZZ42, ZZ60, ZZ65, ZZ948) of hybrid rootstocks of Ziyang Xiangcheng (Citrus junos Sieb. ex Tanaka) × Trifo-liate Orange (Poncirus trifoliata Raf.) in an alkaline orchard with pH 8.22 were tested in this study in order to accumulate data for the selection of new excellent rootstocks with the advantages of Ziyang Xiangcheng and Trifoliate Orange. Alkali stress has become an important factor restricting the develop-ment of fruit industry, leading to iron deficiency and chlorosis of fruits and the decline of fruit quality and yield in citrus fruit trees. Thus, it is necessary to breed new rootstocks.【Methods】We transplanted the biennial nucellar seedlings of these 8 rootstocks to the orchard with alkaline soil in 2016. At the same time, the seedlings of Ziyang Xiangcheng and Trifoliate Orange with same age were planted to-gether in the test orchard as control varieties. We measured the plant height and stem thickness, investi-gated the yellowing index of the seedling lines, analyzed the difference of leaf photosynthetic pigment and nutrient element contents of the seedling lines and plants of the control in 2018. The weight of core index was calculated by Analytic Hierarchy Process (AHP), and the comprehensive score was calculat-ed by Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS).Then the tolerance of the seedling lines to alkali were evaluated using AHP-TOPSIS.【Results】The seedling lines showed dif-ferent growth vigor, ranging from 68.52 cm to 228.23 cm. Among them, ZZ6 was the shortest, about 1/2 of the height of Trifoliate Orange; ZZ65 was the tallest, about 1.6 times of the height of Ziyang Xiangcheng. The seedling lines could be divided into three types according to the height, dwarfing type: ZZ6, ZZ7, ZZ948; moderate type: ZZ1, ZZ42, ZZ60; tall type: ZZ31, ZZ65. The stem thickness was re-lated to the plant height. The stem thickness of ZZ31 and ZZ65 was significantly bigger than those of the other seedling lines. According to the statistical results of the yellowing index of the seedling lines,ZZ6 was the lowest; ZZ7, ZZ31and ZZ948 were low; ZZ1 was medium; ZZ42 and ZZ60 were high;ZZ65 was the highest and its chlorination degree was next to that of Trifoliate Orange. There were sig-nificant differences in photosynthetic pigment contents among the seedling lines, ZZ6, ZZ31 and ZZ948 were significantly higher than those of the other seedling lines. The contents of chlorophyll a, chlorophyll b and chlorophyll a + b of ZZ6 were the highest, next to Ziyang orange. ZZ42, ZZ60 and ZZ65 with higher yellowing index had lower contents of chlorophyll a, chlorophyll b and chlorophyll a+b in leaves. The contents of chlorophyll a, chlorophyll b and chlorophyll a+b in leaves decreased with the increase of the yellowing index of the seedling lines. The element determination results showed that the ferrous Fe content of the seedling lines in leaves from high to low was Ziyang Xiangcheng, ZZ6, ZZ31, ZZ948, ZZ7, ZZ1, ZZ60, ZZ42, ZZ65, Trifoliate Orange. We could conclude that the ferrous Fe content in the leaves was negatively correlated with the yellowing index of rootstock, the P content in the leaves was positively correlated with the yellowing index of the seedling lines, while the total Feand other elements in the leaves had no significant correlation with the yellowing index of the seedling lines. In other words, the leaf chlorosis of the seedling lines was closely correlated with the low ferrous Fe and the high P content in the leaves. We used AHP to calculate the weight of chlorophyll a+b, yellow-ing index, ferrous Fe and P content in leaves (0.562 2, 0.096 1, 0.288 9, 0.052 8 respectively). After-wards, we performed a comprehensive evaluation of the alkali resistance of the seedling lines using the AHP-TOPSIS method. The order of the resistance was Ziyang Xiangcheng > ZZ6 > ZZ31 > ZZ948 >ZZ7 > ZZ1 > ZZ60 > ZZ42 > ZZ65 > Trifoliate Orange. The alkali resistance of ZZ6, ZZ31 and ZZ948 could be considered as strong ZZ7 and ZZ1 moderate ZZ60 and ZZ42 weak and ZZ65 very weak. The alkali resistance of the seedling lines was distributed in range of the Ziyang Xiangcheng and the Trifoli-ate Orange. Three seedling lines with strong alkali resistance were selected for further evaluation.【Conclusion】In this study, three rootstocks (ZZ6, ZZ31 and ZZ948) with strong alkaline tolerance were screened out, among which ZZ6 was a dwarf alkali tolerant rootstock.