Tolerância de genótipos de citros ao estresse salino.

Abstract

This work was carried out aiming to evaluate the salt tolerance of citrus genotypes (varieties and hybrids) in the formation stage of seedlings under greenhouse conditions and in the initial growing under field conditions. Two experiments were conducted: one in a greenhouse located in the UFCG, Campina Grande Campus; and another in an experimental area of 'Tabuleiro' Farm located in the municipality of Pombal, State of Paraíba. In the greenhouse experiment, three factors were investigated: five levels of salinity of the irrigation water and twelve genotypes of citrus rootstocks grafted with two varieties - acid lime tree 'Tahiti [Citrus latifolia (Yu Tanaka) Tanaka] 'CNPMF 2001' selection, and grapefruit (C. Parididi) 'Star Ruby'. The statistical design was in randomized blocks with three replications and the experimental unit consisted of nine plants. The rootstocks were formed using polyethylene tubes (288 mL capacity), with their subsequent transplanting (150 days after sowing) to plastic bags (3400 mL capacity) with 12 cm diameter and 30 cm height. After grafting, the plant growth was evaluated and, after growth of grafts, the most promising six combinations (scion/rootstock) were selected, using as criteria the percentage of survival of the plants with increasing salinity. In the field experiment, the six selected combinations of scion/rootstocks were investigated under three different managements of water salinity: (1) Control management - plants were exposed to water with electrical conductivity (ECw) of 0.8 dS m"1 during the seedlings formation and in the field; (2) - plants irrigated with water with ECw of 0.8 dS m"1, during the seedlings formation, began to receive water with ECw of 2.4 dS m"1, at field conditions; (3) - plants were subjected to irrigated with water with ECw of 2.4 dS m"1, in the seedlings formation and in the field. Variables of growth and physiological parameters were evaluated under field conditions, at 60, 90 and 210 days after plant transplantation. The studied variables were subjected to the 'F' test comparing averages by Tukey's test or Scott-Knott. It was observed a greater growth in the formation stage of genotypes rootstocks G3 (TSKC x CTC25 - 010) and G4 (TSKFL x CTC13 - 025), followed by Gl (lime tree "Rangpur Santa Cruz"), G5 (Hybrid Trifoliate - 069) and G12 (lime tree 'Volkameriano'), and they, also, were less affected by increasing salinity. After grafting, especially with increasing salinity, the rates of survival involving combinations of rootstocks with G3 and G4 with the grapefruit or the lime tree 'Tahiti' were low; the best combinations were observed in G l , G5 and G12 with both treetop varieties, 'Tahiti' and 'Star Ruby'. Under field experiment, higher growth rates and better physiological behavior were observed in lime tree 'Rangpur' grafted with 'Star Ruby' or 'Tahiti' when irrigated with saline water.