Cryo-SEM study of the early symptoms of peteca in 'Lisbon' lemons

Early symptoms of the rind disorder peteca in 'Lisbon' lemons were investigated by cryo-SEM. The localized discoloration of the rind was associated with the albedo tissue. Oil glands showed varying amounts of oil contained within the oil gland cavity. In peteca-affected areas, rind oil was observed in the intercellular air spaces between the columns of epithelial cells forming the periphery of the gland and large amounts of oil accumulated in the albedo tissue. Ca levels were higher (ca. 23%) and B levels were lower (ca. 30%) in peteca-affected rind regions compared with unaffected rind regions of affected fruit. A considerable part of the Ca accumulated in the rind was in the form of Ca crystals, probably oxalate. The evidence for Ca oxalate deposition in rind tissue as a possible causal factor in peteca is reviewed.