Demarcating salinity tolerance in greenhouse rose production

Greenhouse rose production is likely the most intensive horticultural cropping system as the high productivity rates of this crop demand high water and nutrient inputs. Nitrogen (N) fertilization recommendations for roses, applied through liquid feeding, often result in annual N applications as high as 9000 kg Ha(-1). Our research indicates that such N application rates are in excess of crop demand, with leaching losses surpassing 50% of the applied N, and these can be contributing to undesirable salt levels- in the root zone. Roses have historically been categorized as salt-sensitive, an observation that contrasts with their high fertility management practices, the increasing utilization of poor-quality irrigation waters, and current pressures to recirculate greenhouse drainage effluents to minimize pollution. Some of our recent research results have shown that rose plants can in fact tolerate relatively high NaCl salinity levels (up to 30 mM) with minimal or insignificant impact on flower yield and quality. This response is significantly affected by rootstock selection, with Rosa manetti and R. x 'Natal Briar' being relatively more salt tolerant than R. odorata (i.e. R. indica 'Major'), R. multiflora 'Rum 91 and R. x 'Dr. Huey'. Sodium and CI accumulation in leaf tissue is affected by salt application levels and rootstock selection, with a remarkable Na exclusion being observed in plants grafted on R. manetti and R. x 'Dr. Huey'. An apparent positive effect of increasing leaf tissue CI concentrations (up to 0.45%) was also found in plants grafted on R. manetti.