Crescimento das plantas, formação e partição de fotoassimilados e produção e qualidade de frutos de meloeiro cantaloupe cultivados sob diferentes níveis de salinidade

Abstract

Melon is a great relevance crop in Brazilian exports. It is produced almost entirely in the Northeast region due to favorable soil and climatic conditions to the detriment of other regions, there are some difficulties that affect its commercial production: the salinity of irrigation water and the low fruit quality. Thus, the objective of this study was to evaluate the plant biometry, gas exchanges, photoassimilate translocation, using the carbon-13 isotopic enrichment technique, fruit yield and quality of two cantaloupe melon hybrids, under saline conditions. Two experiments were carried out at the Experimental Station of Pacajus, Embrapa Agroindústria Tropical. The first experiment was carried out in a split-plot treatment design with 4 replicates. The primary factor was irrigation water saline levels: 0.5, 2.0, 3.5 and 5.0 dS.m-1, while the secondary factor was cantaloupe melon hybrids: Zielo and SV1044. In this first experiment the soil salinity evolution, the Na and Cl uptake, quantification of sugars in leaves, gas exchanges, phenological measures of growth, as well as fruit production and quality were evaluated. The variables were statistically evaluated by SISVAR software and the hybrid presented more tolerance to salinity was indicate. The second experiment was a factorial between water saline levels (ECw): 0.5 and 3.5 dS.m-1, and plant region: basal, middle and apical leaves of primary and secondary stem; with 4 replicates. Na, Cl, sugars concentrations, photoassimilates production and partion, fruit production and quality were analyzed. To characterize the behavior of photoassimilates produced and translocated, the isotopic enrichment with 13CO2 gas was used in basal and apical leaf of the primary stem and in apical leaf of the secondary stem in two weeks before last and in last week of the crop cycle. Six hours after enrichment with 13CO2, the plant was sectioned into leaves (a three leaves group from the basal, middle and apical region of the primary and/or secondary stem) and fruits to evaluate the isotopic value, and this might indicate whether the parties have received 13C assimilated from enriched leaves. The 13C natural value of diffent parts of the plant was used to determine whether there was enrichment. The increase in Na and Cl concentration in the soil profile caused accumulation of these ions in plants, impairing their growth, development, fruit production and quality through specific toxic effects and osmotic, as can be observed by the stomatal conductance and photosynthesis reduction of plants. The Zielo hybrid was tolerant until 2.18 dS.m-1 (ECe = 2.11 dS.m-1) of ECw and the SV1044 hybrid until 1.19 dS m-1 (ECe = 1.54 dS.m-1). Productivity losses per unit increase of ECw were 12.4 and 16.1%, respectively, indicating a lower negative impact of salinity on the Zielo hybrid. Plants under saline stress had a lower 13C discrimination when they were compared with plants without stress. In two weeks before last fruits are preferential sinks of basal and apical leaves that are vigorous and translocating quite photoassimilates independent of the salinity. However, in last week there is a translocation differentiation, so that in saline conditions leaves continue to contribute with photoassimilates to fruits, especially basal leaves, and basal and apical leaves of the plants irrigated with good quality water reduce or stop the contribution to the fruit, indicating a delay in photoassimilates metabolism of melon plants under saline stress.