Symptoms and Signs
Coniella granati causes stem and crown cankers, resulting in decline and eventual death of young pomegranate shoots. Fruit decay may occur in the field and postharvest.
Infection turns the arils brown and juicy. Fruit membranes and the rind also turn brown. Black fungal pycnidia with characteristic large, elliptical, colorless, one-celled spores can develop on the surface of the arils, membranes, and surface of the rind (fruit skin). Pycnidia can also be found in the bark of trunks, killed shoots, and thorns, as well as on the surface of leaves. Dry infected fruit left in the orchard are called mummies.
Coniella rot is very different from Alternaria fruit rot, Aspergillus fruit rot, and gray mold.
| Symptoms | Coniella stem canker and fruit rot | Alternaria fruit rot (Alternaria alternata and other Alternaria spp.) | Aspergillus fruit rot (Aspergillus niger) | Gray mold (Botrytis cinerea) |
|---|---|---|---|---|
| Fruit symptoms | Decay of fruit rind and arils
Pycnidia on fruit |
Decay of fruit arils but typically not the rind (rind shrivels only in later stages of infection); arils decay: brown decay and black sporulation inside fruit | Decay of fruit rind; arils decay: brown decay and black sporulation inside and outside the fruit when decay lesions become external | Decay of fruit rind and arils; grayish mycelium Sporulates on decayed fruit |
| Trunk, shoot and leaf symptoms | Pycnidia on trunk, shoots, thorns, and leaves | No symptoms or signs on trunk, shoots, thorns, and leaves | No symptoms or signs on trunk, shoots, thorns, and leaves | Sporulates on dead shoots, thorns, and leaves |
Comments on the Disease
The pathogen is isolated frequently from pomegranates, but the disease is only sporadically found in Fresno, Madera, and Kern county orchards.
In orchards, the pathogen overwinters as pycnidia and mycelia in stem cankers and rotten fruit (mummies), pruned limbs on the ground, and desiccated leaves.
Fruit infection occurs through wounds (e.g., insect exit holes, bird pecks, thorn punctures, and natural cracking). Infections, however, can spread by contact from infected fruit to healthy fruit in packed boxes, similar to gray mold. The pathogen can also be isolated from symptomless bark of the trunk, branches, and shoots.
The optimum temperature for the pathogen's growth ranges from 25 to 30°C; the fungus grows slowly at 15°C, but does not grow at 35°C.
Losses from Coniella stem canker and fruit rot have not been estimated, since this is a new disease of pomegranate in California.
Management
Sanitation may reduce overwintering inoculum. Remove or burn pruned limbs and bury mummies.