Heat Application as Complete or Partial Substitute for Postharvest Fungicide Treatments of Grapefruit and Oroblanco Fruits

Heat treatments, such as curing (34-36 °C, 42-72 hr) or hot dips, are promising non-fungicide means to control postharvest decay of citrus fruits and to reduce their sensitivity to suboptimal storage temperatures. Combinations of heat treatments (either curing or hot dips) with any of the following: individual seal-packaging, packaging in ployrthylene-lined cartons, or waxing, controlled decay of oroblanco fruit without fungicide use similarly to standard packing-house treatments including TBZ application (2000 ppm) and waxing. Hot water treatment (2 min at 51-52°C) improved firmness and retention of green colour in oroblanco fruit, especially in combination with individual sal-packaging. Addition of growth regulators (gibberellic acid and 2,4-D) improved the effectiveness of hot dips, so that the decay incidence in this treatment did not differ significantly of that in fungicide-treated fruit. Combination o a hot water dip with TBZ drench (1000 ppm) was more effective than SOPP dip (0.35%, 35°C) + TBZ 1000 ppm in controlling grapefruit decay during pilot packing-house trails. The risk of phytotoxic damage affects the consistency of hot dip results. A hot water dip in a pilot-plant installation simulating the packing-house conveyor path, resulted in more damage than this dip in a stationary bath regime. The changes in the fruit surface caused by high temperature, in particular the repair of cuticular cracks, may exolain some of the physiological effects of hot water on citrus fruit, such as reduction of weight loss, inhibiting softening and alleviation of chilling injury.