Muscadine Grapes: Evaluation of Genotypes and Field Fungicide Applications on Postharvest Storage Attributes

A major limiting factor in muscadine grape (Vitis rotundifolia Michx.) commercialization is deterioration during storage.  Research on table grapes has shown that field fungicide applications increase storability, but little is known of its affect on muscadines.  The effect of field applications of fungicides on composition attributes during postharvest storage was evaluated on five muscadine cultivars (Nesbitt, Southern Jewel, Summit, Supreme, and Tara) and five breeding selections from the University of Arkansas Fruit Breeding Program (based at the Fruit Research Station, Clarksville, AR).  There were two field treatments (no fungicide and fungicide). For the fungicide treatment, alternating applications of two fungicides were applied at 14-day intervals during berry maturation.  Fruit was harvested and composition attributes including berry volume, titratable acidity (TA), pH, soluble solids (%), color (L, chroma, and hue), firmness (force to penetrate berry skins), storage weight loss (%), and decay (%) were evaluated weekly for a 4 weeks.  The initial berry volume among genotypes ranged from 86.3 to 193.5 cm³, TA ranged from 3.9 to 4.9 g/L, pH ranged from 3.3 to 3.9, soluble solids ranged from 16.9% to 26.8%, firmness ranged from 7.9 to 10.6 N, L ranged from 26.8 to 95.1, chroma ranged from 2.1 to 14.9, and hue ranged from 7.5 to 311.6. ‘Supreme’ and AM 01 had the highest soluble solids and ‘Southern Jewel’ the lowest.  ‘Supreme’ had the highest firmness value. Berry volume, TA, pH, soluble solids, and color of muscadines did not change during storage.  However, weight loss and firmness of muscadines decreased while decay increased during storage regardless of fungicide treatment. Soluble solids was positively correlated to pH (r = 0.63), pH was positively correlated to TA (r = 0.96). Decay and weight loss were positively correlated (r= 0.88) and firmness was negatively correlated to weight loss and decay (r > –0.46).  Firmness was lower for muscadines in the no fungicide treatment compared to fungicide-treated vines, the effect of fungicide treatments varied among genotypes.  Differences may have been minimal due to the unusually dry summer in 2012.  Due to less decay, less weight loss, and greater firmness during storage, AM 27, ‘Southern Jewel’, and ‘Supreme’ had the highest potential for postharvest storage, while AM 01, AM 15, and ‘Tara’ had the least potential. Although field fungicide applications did not affect all postharvest attributes, differences among genotypes and fungicide treatments did occur during the four weeks of storage.