Regulation of air humidity and effects on mineral levels and blossom-end rot incidence in pepper fruits

Abstract

Blossom-end rot (BER) is a physiological disorder common in tomato and pepper fruits, that is related to poor Ca translocation, connected to environmental conditions occurring in Mediterranean greenhouses in Spring and with a higher incidence in soilless culture. A study has been carried out in order to observe the effects of air humidity on the nutrients translocation, Ca, K, Mg, to the pepper fruit, cv. Atol, in growth chamber and hydroponic culture conditions. Treatments included 85 and 90 % air humidity during day and night respectively, (humid treatment), compared to a control representing standard Spring conditions in Mediterranean coast greenhouses with 55 % during the day and 90 % during the night, both cases with identical temperature levels, with a day maximum of 28degreesC and minimal of 18degreesC in the night. The calcium levels were significantly higher in the fruits developed under the humid conditions, with 40% more than the control in 25 to 35 days old fruits and 54.3% more in 35 to 45 days old fruits, both levels refered to the distal half part of the berry. The age of 25 to 35 days appears to be the stage with lowest Ca contents in fruit and consequently would be the most risky stage for BER. Similarly the K levels were also higher in the humid environment fruits whereas the Mg contents was quite stable in both treatments. The Ca contents in the distal half part of BER affected fruits was 56.3% lower than in the normal fruits. The higher Ca level in the distal part of the fruits could be related to the distribution of vascular bundles in the berries. There was a remarkable increase in the number of vascular bundles in fruits developed under humid conditions compared to the drier control, with 18.9% increase in the fruit basal half and 27.8% increase in the distal half part. Also a reduction in the number of bundles was observed in drier conditions compared to the same control in a previous experiment. Likewise leaf stomatal conductance, gs, in the humid environment arrived to be 5 to 8 times higher than in the control, with leaf to air vapour pressure differences (VPDL) between both environments of 0.92 to 1.78 kPa which resulted in leaf transpiration rates, E, 1.5 to 2.5 times higher in the humid conditions due to stomatic closure in the control plants.