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 al bedo 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 sh owing some degree of albedo breakdown as follows: sweet orange < Cleop atra mandarin < trifoliate orange < Carrizo citrange = Troyer citrange < rough lemon < Rangpur lime. Rootstock strongly influenced fruit siz e 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 incidenc e and severity of albedo breakdown in Bellamy navel orange. Smaller fr uit (<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 bre akdown was not positively related to crop load, and despite removal of the effect of crop load, season remained a strong influence on the ap pearance of albedo breakdown, indicating that seasonal factors, such a s summer temperatures, may also be important in the development of alb edo breakdown.