Abstract
Brazil is the largest producer of sweet orange and its juice in the world. Extensive cultivated area is located under an Aw climate in the North–Northwest of the state of São Paulo and the Triângulo of Minas Gerais state, being subjected to severe drought events. Although 56% of the orchards are irrigated in these regions, there is a need for drought tolerant rootstocks as an alternative to traditional genotypes such as Rangpur lime and Volkamer lemon, which are susceptible to the endemic citrus sudden death disease (CSD). In this sense, the tree size and production of Valencia sweet orange grafted onto 23 rootstock genotypes were evaluated over a ten-year period in rainfed cultivation at 7.0 m × 3.0 m spacing. Most evaluated types resulted from the cross of Poncirus trifoliata with Citrus, but two interspecific hybrids of Citrus (Sunki mandarin × Rangpur lime hybrids), the Barnes trifoliate orange and a tetraploid selection of Swingle citrumelo were also tested. Tropical Sunki mandarin was used as the reference control. Those hybrids coming from the cross of Sunki × Flying Dragon induced large tree sizes to Valencia sweet orange as well as the other citrandarins, Tropical Sunki mandarin and the Sunki mandarin × Rangpur lime hybrids, whereas only the tetraploid Swingle citrumelo behaved as a dwarfing rootstock, decreasing the canopy volume by 77% compared to that induced by the most vigorous citrandarin 535. The citrandarins 543 and 602 and the citrange C38 induced the highest mean fruit production, 67.2 kg·tree−1, but they also caused pronounced alternate bearing and only the hybrid 543 led to a high production efficiency consistently. Graft incompatibility symptoms were not observed over the evaluation period, and the canopy shape of Valencia sweet orange was also influenced by the rootstocks tested. Two citrandarins and one citrange were selected as the most promising alternative rootstocks for Valencia sweet orange grown under an Aw climate, even though productivity would likely benefit from supplementary irrigation.
Highlights
Brazil is the largest producer of sweet orange [Citrus × sinensis (L.) Osbeck] and its derived products in the world, corresponding to 21.7% of the 78.7 million tons harvested worldwide in 2019 [1]
From 2000 to 2020, the use of the Rangpur lime in nurseries in Sao Paulo dropped from 75% to 27% of grafted trees, whereas Swingle citrumelo and Sunki mandarin increased to 55% and 9%, respectively, and became the main commercial alternatives [10,11]
The most vigorous rootstock was the citrandarin 535 (53.53 m3), followed by the group comprised of the Tropical Sunki mandarin, IAC 1710, both Sunki × Rangpur hybrids and most of the Sunki × Flying Dragon hybrids, with an averaged mean of 41.70 m3
Summary
Brazil is the largest producer of sweet orange [Citrus × sinensis (L.) Osbeck] and its derived products in the world, corresponding to 21.7% of the 78.7 million tons harvested worldwide in 2019 [1]. From 2000 to 2020, the use of the Rangpur lime in nurseries in Sao Paulo dropped from 75% to 27% of grafted trees, whereas Swingle citrumelo and Sunki mandarin increased to 55% and 9%, respectively, and became the main commercial alternatives [10,11] All of these rootstock genotypes are more sensitive to drought compared to the CSD-susceptible types [9,10], which has increased the exposure of the citrus industry in the region to severe drought events regardless of the use of irrigation. In 2020–2021, it was estimated that the eradication of orchards increased almost two-fold and fruit drop grew in relation to the previous season mainly due to severe drought conditions that resulted in significant tree decline and death [3]
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