‘Tropical Sunki’ mandarin and hybrid citrus rootstocks under ‘Pera’ sweet orange in cohesive soil and As climate without irrigation

Abstract

The search for alternative rootstocks to the 'Rangpur' lime tree is a challenge to the sustainability of citrus in the Tabuleiros Costeiros (Coastal Tablelands) of Northeastern Brazil. New varieties should meet high drought tolerance with water deficit, cohesive soils, resistance to citrus diseases and inducing high production of fruit. In this work, the performance of 'Pera' sweet orange was evaluated on 'Tropical Sunki' mandarin and 27 hybrid citrus rootstocks in Umbaúba, Sergipe. A local selection of the 'Rangpur' lime was the control. Planting was in 2013 at tree spacing of 6.0 × 3.0 m, without irrigation. Tree size, fruit yield and quality, tree survival rate and graft-compatibility were assessed until 2019. Experimental design was completely randomized blocks with 29 treatments, three replicates and four plants in the plot.Two selection indices were applied to the data to assist in decision making. The 'Tropical Sunki' mandarin induced similar cumulative fruit yield in relation to the 'Rangpur' lime, suggesting a good drought tolerance of the former rootstock. The TSKC × (LCR × TR) -073 induced slightly lower productivity, compensated by higher productive efficiency and higher concentration of soluble solids, whereas LCR × TR -001 and HTR -166 were highly efficient dwarfing rootstocks. The multiplicative and the rank sum indices showed high correlation, both classifying 'Tropical Sunki' mandarin, 'Santa Cruz Rangpur' lime, LVK × LCR -010 and -038, HTR -127, in addition to the three aforementioned hybrids, as superior to the local selection of 'Rangpur' lime.

Tree Growth and Production of Rainfed Valencia Sweet Orange Grafted onto Trifoliate Orange Hybrid Rootstocks under Aw Climate

“…Tropical Sunki mandarin. This is a putative nucellar embryo mutation of common Sunki mandarin that induced large tree size, high production and tree survival to sweet orange scions without irrigation under Aw and As climates in Brazil [15,19,20]. In this work, although the mean fruit production of Valencia sweet orange was relatively high, there was alternate bearing and low production efficiency, yet trees grafted on the Tropical Sunki induced the highest fruit number per cubic meter of bearing volume and excellent plant stand at the end of the experiment (Figure A2).…”

“…Because citrus cultivation is irrigated in most subtropical and Mediterranean regions, drought tolerance has been of less concern as a desirable trait in rootstock breeding programs, even though a higher water use efficiency has been increasingly relevant in the search of new rootstocks due to the escalating water scarcity worldwide derived from climate warming [12][13][14]. Furthermore, rainfed cultivation is usual in tropical conditions in Latin America, Africa and Asia, which has encouraged the creation and evaluation of new rootstocks in Brazil, mostly trifoliate orange hybrids and Sunki mandarin selections, that cope with seasonal water deficit and, in the case of São Paulo, should also be CSD-tolerant or resistant [15][16][17][18][19][20]. However, the etiology of CSD and other diseases such as blight is unknown, and reliable diagnosis tests are not available to date, making selection dependent on the observation of typical symptoms over time in endemic regions as compared to susceptible genotypes [8,9,21].…”