Tolerância de genótipos de citros ao estresse hídrico na fase de formação de porta-enxerto.

Abstract

In Northeast Brazil. long and varied drought periods occur, and it is of great importance to identify promising genetic materiais for farming in these conditions. Knowing the rootstock functions and its importance to the success of citrus crops, including its influence on the tolerance of stress factors, a research was carried out aiming to evaluate the tolerance of citrus genotypes (varieties and hybrids) to water stress on rootstock formation. For this, an experiment was conducted in the nursery at UFCG, on two stages (A and B), in which the treatments consisted of combinations factor, water management (MH) and genotypes (GEN). On stage A, from 60 to 135 days after sowing (DAS), the treatments were: MHi - substrate moisture in the tubes, corresponding to a levei of 100% of the water content at field capacity (CC), and MH2 - substrate moisture in the tubes, corresponding to a levei of 50% water content CC. In the stage B, from 136 to 210 DAS, the MH] factor with the remained plants in the CC moisture, and in the MH2 the stress levei was intensified, and the plants remained in a moisture of 25% water content CC. The GEN factor consisted of 10 citrus rootstock genotypes, 'varieties and hybrids'. of the Citrus Genetic Improvement Program. The experimental design was randomized blocks with a 2 x 10 factorial, and three replications; the plot consisted of 15 plants, cultivated individually in plastic tubes of 288 mL of volume capacity. The stress intensity was monitored daily by weighing the tubes, to measure the water loss. When 50% of the plant leaves began to dry and/or fali in more than half of the tubes, the stress evaluation was completed individually by genotype. During the experiment, growth and physiological variables were evaluated. In the final collection, biomass evaluations were performed, and according to the total biomass analysis the genotypes were classified into moderately tolerant, moderately sensitive, and sensitive to water stress. The data were evaluated by variance analysis and test 'F' (p<0.05) and analysis by comparison of averages by Scott-Knott test for genotype factor, to 5 % probability. Water stress provided changes on leaf gas exchange, on growth and biomass production of rootstocks citrus genotypes. The genotypes 'LCRSC, 'TSKFL x CTC25-010', 'CTSW 'LCRC and 'LVK' did not survive to water stress of 25% moisture corresponding to field capacity; and rootstocks 'TSKC x TRENG-256', 'TSKC x (TR x LCR)-059', 'TSKFL x CTTR-017', 'TSKC x TRENG-264' and 'TSKFL x LRM-007', are most promising for farming in scarce water availability.