ABSTRACT The growing demand for gladiolus, especially at peaks of consumption, requires efficient scheduled production and good quality of floral stems. The objective of this study was to understand how water deficit affects the growth and development of gladiolus and, consequently, the quality of the floral stems produced. Plant development, quantitative parameters of the floral stems, and dry mass partitioning were evaluated in two field experiments with four gladiolus cultivars, with and without irrigation. The development cycle was longer in the non-irrigated treatment, whereas its duration under no water deficit was similar to that predicted by PhenoGlad, which is a gladiolus phenology model. As PhenoGlad predicts gladiolus development only for scenarios without water deficit, the inclusion of a water-stress submodel in the model would allow its application to any water supply scenario and help decision makers and farmers to plan gladiolus production more accurately. Water deficit also reduced gladiolus growth and flower stem size, but did not affect dry mass partitioning. As the development and quality of the floral stems of gladiolus were negatively affected by water stress, irrigation is essential for producing high-quality gladiolus floral stems and enabling production planning for peaks of consumption.

RESUMO Objetivou-se neste estudo desenvolver um zoneamento de risco climático para a cultura do gladíolo nos cenários de mudança climática previstos para o final do século no Rio Grande do Sul, considerando a ocorrência de danos causados por altas e baixas temperaturas. O modelo PhenoGlad foi utilizado neste estudo para determinar os períodos recomendados para plantio ao longo do ano em todo o Rio Grande do Sul. O modelo foi rodado para datas de plantio diários (de 01 janeiro a 31 dezembro), para diferentes ciclos de desenvolvimento da cultura (Precoce, Intermediário I, Intermediário II e Tardio). Os cenários de mudança climática utilizados foram do CMIP5: RCP2.6, RCP4.5 e RCP8.5, representing optimist, intermediate and pessimist scenarios of greenhouse gases emission, respectively. As datas de plantio foram consideradas recomendadas quando danos na cultura por altas ou baixas temperaturas ocorreram em menos de 10% dos anos avaliados. Regiões mais quentes como Uruguaiana e Iraí apresentam o menor período recomendado para plantio ao longo do ano nos três cenários climáticos. Plantios entre agosto e dezembro não são recomendados devido a maior chance de danos por altas temperaturas. Regiões mais frias como Bom Jesus serão favorecidas nos cenários de mudança climática, pois haverá uma ampliação do período recomendado para plantio nas épocas do ano que atualmente sofrem danos por baixas temperaturas. Para atender à demanda de gladíolo durante os períodos mais quentes do ano, será necessário desenvolver técnicas para reduzir os danos por altas temperaturas na cultura, como cultivares mais tolerantes ou o uso de telas de sombreamento sobre a cultura.

ABSTRACT The objective of this study was to develop a climate risk zoning for damage to gladiolus due to low and high temperature under climate change scenarios projected by the end of the century in the Rio Grande do Sul State, Brazil. The PhenoGlad model was used in this study to determine the recommended periods for planting gladiolus throughout the year across the Rio Grande do Sul State. The model was run for daily planting dates (from 01 January to 31 December), for different gladiolus developmental cycles (Early, Intermediate I, Intermediate II and Late). The climate change scenarios were from CMIP5: RCP2.6, RCP4.5 and RCP8.5, representing optimistic, intermediate and pessimistic scenarios of greenhouse gases emission, respectively. Planting dates were considered recommended when crop damage, due to high or low temperatures, occurred in less than 10% of the years. Warmer regions like Uruguaiana and Iraí have the shortest recommended time for planting throughout the year in the three climate change scenarios. Plantings between August and December are predicted to be the most affected and are not recommended because of the higher chance of damage from high temperatures. Colder regions like Bom Jesus will be favored in climate change scenarios since there will be an extended recommended period for planting in the seasons of the year that currently suffer damage by low temperatures. To meet demands of gladiolus during the hottest period of the year, it will be necessary to develop techniques to reduce damage from high temperatures in the crop, such as more tolerant cultivars or the use of shading screens on the crop.