Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate

Abstract

The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

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

“…15% lower than the 'Rangpur' lime group), but still higher than the averages of Bahia and Sergipe (Table 1). This corroborates Costa et al (2020), who reported intermediate fruit yield of 'Valencia' sweet orange grafted onto TSKC × (LCR × TR) -073 and TSKC × CTQT1439 -004, and França et al (2016) for 'Tuxpan Valencia' bearing good crops on TSKC × (LCR × TR) -001.…”

“…Selection indices are frequently used in crop breeding programs, especially at initial stages, because several traits can be evaluated at once in a simple procedure to select superior genotypes (Crevelari et al 2018). Most evaluated variables presented CV% lower than 20% (Table 1), which is commonly reported in similar studies and adequate for using the proposed indices (Costa et al 2020;Crevelari et al 2018;Schinor et al 2013). There was a positive correlation between the rank sum (I MM ) and the multiplicative (I e ) indices (r = 0.77**), indicating high degree of accordance and, consequently, a more reliable selection of the superior rootstocks.…”

“…The hybrid LCR × TR -001 was a dwarfing rootstock that induced high tree survival rate and the highest production efficiency of relatively large fruits (Tables 3 and 4). This hybrid induced similar performance to the 'Valencia' sweet orange in the north of the state of São Paulo, where it was also drought-tolerant (Ramos et al 2015;Costa et al 2020). The rootstocks HTR -166 and -127 were other efficient dwarfing rootstocks that induced good size of fruits and high productivity.…”

“…also observed that 'Pera' sweet orange trees were decreased by other hybrid trifoliate rootstocks, whereas LVK × LCR -010 confirmed its high vigor in the Tabuleiros Costeiros. In the cerrado region (Aw climate, deep red Oxisol), LCR × TR -001 decreased the tree size of 'Valencia' sweet orange (Ramos et al 2015;Costa et al 2020). Since the fruit production efficiency is conversely related to the tree size, dwarfing rootstocks induced the most efficient canopies, notably HTR -166 and LCR × TR -001 (superior to 15 kg•m -3 ), as compared to more vigorous rootstocks (Table 1).…”

“…The 'Tropical Sunki' mandarin induced high productivity to other sweet orange varieties, such as 'Tuxpan Valencia' , 'Jaffa' , 'Pineapple' and 'Sincorá' , compared to drought-tolerant 'Rangpur' lime and 'Rough' lime rootstocks in similar rainfed conditions in northeastern Brazil (França et al 2016;Teodoro et al 2020;Carvalho et al 2019). Costa et al (2020) observed similar productivity of 'Valencia' sweet orange grafted on the 'Rangpur' lime and 'Tropical Sunki' mandarin without irrigation under tropical savannah climate, thus, taken together, these results reinforce the potential of the later rootstock for the citrus industry, including the most important Brazilian scion variety, the 'Pera' sweet orange (Cunha Sobrinho et al 2013;Fundecitrus 2020). Although the hybrid citrus rootstocks evaluated in this work lead to cumulative productivity lower than the 'Rangpur' lime, the standard rootstock for the region, two groups induced slightly inferior cumulative fruit yields (mean of 77.5 t•ha -1 ,…”