El daño por helada en frutales se produce cuando la temperatura inferior a 0°C induce cristalización del hielo en el tejido vegetal. El polímero en base a polivinil alcohol (PVA) ha sido usado para inhibir la cristalización del hielo en condiciones de laboratorio. El objetivo de este trabajo fue evaluar la efectividad de un polímero en base a PVA para prevenir el daño por heladas en yemas florales del cerezo Prunus avium L. Se evaluaron los siguientes tratamientos: i) F1: PVA en dosis de 10 cm 3 L -1 ; ii) F2: (PVA + agente polisorbato) en dosis de 15 cm 3 L -1 ; iii) F3-15: (PVA + agente polisorbato + polivinilpirrolidona) en dosis de 15 cm 3 L -1 ; iv) F3-30: (PVA + agente polisorbato + polivinilpirrolidona) en dosis de 30 cm 3 L -1 . Como testigo se incluyó un agente anti-helada comercial (AAC) en dosis de 10 cm 3 L -1 y agua destilada. Los ensayos se condujeron bajo condiciones de campo (localidades, cultivares y aplicación de cianamida) y de laboratorio (micro-cámara). En los ensayos de campo se cuantificó el efecto del polímero en los siguientes parámetros de calidad de fruta: tamaño (mm), firmeza (g mm -1 ), sólidos solubles (°Brix) y color (escala CITFL). En los diferentes ensayos la formulación de polímero F3 fue la más efectiva en reducción de daño por heladas en yemas florales, cuya efectividad varió desde 40 a un 100%, sin causar efectos negativos en la calidad de la fruta. Estos resultados indican que el uso de polímero PVA es una herramienta promisoria para el control de daño por heladas en huertos de cereza.
Poly(vinyl alcohol) (PVA) displays ice recrystallization inhibition (IRI) properties as many antifreeze proteins found in cold tolerant organisms. The molecular architecture and composition (molecular weight and distribution of pendant OH and acetate groups) have been studied to improve the antifreezing properties of PVA, suggesting that the molecular architecture of PVA plays an important role in IRI activity. The present work deals with the preparation of PVA microparticles using an alkaline treatment. The effect of PVA molecular weight on the morphology and antifreezeing properties of PVA microparticles was investigated. The antifreezeing property of PVA microparticles on the susceptibility of flower bud tissues to freeze damage was also evaluated. The alkaline treatment of an aqueous PVA solution produced stable polymer chain aggregates with spherical shapes. The average size of the PVA microparticles increased significantly with the increasing molecular weight of the PVA macromolecule precursor. The PVA microparticles inhibited the growth of ice crystals and blocked ice growth at concentrations as low as 0.01 % w/v. The effect of impeding ice crystal growth by preventing the joining of adjacent ice crystals is attributed to the larger size of the PVA particles adsorbed on the ice surface compared to the aggregated PVA macromolecules in saline solution. The thermal hysteresis activity of PVA macromolecules and microparticles was not detected by differential scanning calorimetry analysis. The PVA microparticles reduced the incidence of freeze injuries in flower bud tissues by 55% and their application, considering the low toxicity of PVA, has a high potential for freeze protection in fruit crops.
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