Rootstock, seasonal, and fruit size influences on the incidence and severity of albedo breakdown in Bellamy navel oranges

The effect of stock and fruit size on the incidence and severity of albedo breakdown in fruit from Bellamy navel orange trees grafted onto 7 rootstocks was studied over 3 seasons. The rootstocks could be rated, from lowest to highest, according to the proportion of scion fruit showing some degree of albedo breakdown as follows: sweet orange < Cleopatra mandarin < trifoliate orange < Carrizo citrange = Troyer citrange < rough lemon < Rangpur lime. Rootstock strongly influenced fruit size distribution, and expression of albedo breakdown varied according to fruit size, but no fruit size x rootstock interaction occurred. Also, generally rootstock did not interact with year to affect the incidence and severity of albedo breakdown in Bellamy navel orange. Smaller fruit (<62 mm in diameter) had a lower incidence of albedo breakdown and the symptoms were less severe than for larger fruit. Very large fruit (>79 mm) had a lower incidence than medium (62-70 mm) and large fruit (71-79 mm). The proportion of fruit exhibiting symptoms of albedo breakdown was not positively related to crop load, and despite removal of the effect of crop load, season remained a strong influence on the appearance of albedo breakdown, indicating that seasonal factors, such as summer temperatures, may also be important in the development of albedo breakdown.