This study aimed to evaluate the absolute and relative growth rates in stem diameter of the rootstock and scion and the production components of grafted West Indian cherry plant under saline water irrigation and potassium fertilization.
The rootstock was obtained from seedlings of landraces of West Indian cherry provided by Embrapa Agroindustria Tropical, located in Pacajus-CE.
There was significant effect (p < 0.05) of salinity levels on the absolute and relative growth rates in stem diameter of rootstock ([AGR.sub.DR]/[RGR.sub.DR]) and scion ([AGR.sub.DS]/[RGR.sub.DS]) of West Indian cherry plants (Table 2).
The relative growth rate in diameter of West Indian cherry rootstock was significantly affected by the interaction between factors (KD x SL) and, according to the regression equations (Figure 1B), the data of plants irrigated with ECw of 0.8 and 3.8 dS [m.sup.-1] fitted to the quadratic model, whose maximum estimated values of [RGR.sub.DR] (0.004469 and 0.003300 mm m[m.sup.-1] [d.sup.-1]) were reached, respectively, at [K.sub.2]O doses of 125 and 95% of the recommendation of Musser.
Together with evaluation of chloroplastidic pigments, the cell membrane damages were evaluated under conditions of saline stress, to identify the percentage of damage in the leaf cell membranes of the West Indian cherry crop, based on the methodology used by Lima et al.
There was an increase in the internal concentration of C[O.sub.2] (Ci) in the West Indian cherry plants as a function of the increased salinity of the irrigation water (Figure 1A).
The observed reductions in the activity of gaseous exchange of the West Indian cherry can also be attributed to the effect of saline stress on stomatal activity.
The increase in salinity of irrigation water increased the percentage of damages in the leaf cells of the West Indian cherry plants, showing a 1.02% increase in cell damage for each unit increase in the salinity of the irrigation water, resulting in a 39% rise in cellular damage to plants cultivated under the highest ECw level (3.8 dS [m.sup.-1]) in relation to the plants submitted to the lowest level (0.6 dS [m.sup.-1]) saline water (Figure 2D).
The experiment used West Indian cherry seedlings, cultivar BRS 366-Jaburu, grafted onto locally developed rootstocks from the Embrapa Tropical Agroindustry, Pacajus, CE.
Gas exchanges were evaluated in the middle third of the crown of West Indian cherry plants during the transition from flowering to fruiting (at 180 days after transplanting), based on the following parameters: stomatal conductance (gs--mol [H.sub.2]O [m.sup.-2] [s.sup.-1]), C[O.sub.2] assimilation rate (A) ([micro]mol [m.sup.-2] [s.sup.-1]), transpiration (E) (mmol [H.sub.2]O [m.sup.-2] [s.sup.-1]) and internal C[O.sub.2] concentration (Ci) ([micro]mol [mol.sup.-1]) using a portable infrared gas analyzer (IRGA), model LCPro+ Portable Photosynthesis System*.
Irrigation water salinity of 3.8 dS [m.sup.-1] negatively affected gas exchanges in West Indian cherry, leading to accentuated reductions of the order of 47.58, 33.14, 41.03 and 56.75% in stomatal conductance, transpiration, C[O.sub.2] assimilation rate and instantaneous carboxylation efficiency, respectively, in comparison to the ECw level of 0.8 dS [m.sup.-1] (Figures 1A, B, C and E).
This result is an indication that non-stomatal factors act on the photosynthetic activity of West Indian cherry, such as low activity of the enzyme Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), probably due to the low availability of substrate (ATP and NADPH) for activation and regeneration of the enzyme, which come from the photochemical phase of photosynthesis, leading to reduction in C[O.sub.2] carboxylation and increase in its internal concentration (Hussain et al., 2012; Silva et al., 2015; Sa et al., 2017).
Given the above, this study aimed to evaluate the effect of water salinity and nitrogen/ phosphorus combination on chlorophyll a fluorescence during the initial growth of grafted west indian cherry plants.
West indian cherry growth was analyzed based on measurements of rootstock and scion diameter to obtain the absolute growth rate (AGR) and relative growth rate (RGR), for the period between 1 ([t.sub.1]) and 150 days ([t.sub.2]) after applying the salinity levels (DASL), and on the number of leaves (NL).
Initial fluorescence (Fo) of west indian cherry plants treated with the P/N proportions of 100:100% and 100:140% increased as water salinity increased, with sharp increment from the ECw levels of 1.06 and 0.96 dS [m.sup.-1], respectively (Figure 1A).